STMicroelectronics 的 L6599 规格书

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Not for new design

This is information on a product still in production but not recommended for new designs.

February 2009 Rev 3 1/36

L6599

High-voltage resonant controller

Features

■50 % duty cycle, variable frequency control of

resonant half-bridge

■High-accuracy oscillator

■Up to 500 kHz operating frequency

■Two-level OCP: frequency-shift and latched

shutdown

■Interface with PFC controller

■Latched disable input

■Burst-mode operation at light load

■Input for power-ON/OFF sequencing or

brownout protection

■Non-linear soft-start for monotonic output

voltage rise

■600 V-rail compatible high-side gate driver with

integrated bootstrap diode and high dV/dt

immunity

■-300/800 mA high-side and low-side gate

drivers with UVLO pull-down

■DIP-16, SO-16N packages

Applications

■LCD and PDP TV

■Desktop PC, entry-level server

■Telecom SMPS

■AC-DC adapter, open frame SMPS

Table 1. Order code

Order codes Package Packaging

L6599D SO-16N Tube

L6599DTR SO-16N Tape and reel

L6599N DIP-16 Tube

DIP-16 SO-16N

www.st.com

Figure 1. Block diagram

STANDBY

DI S

ISEN_DIS

GND

Ifmin

ISEN

0.8V

1.5V

PFC_STOP

Vcc

VBOOT

OUT

CBOOT

LC TAN

CIRCUIT

H.V.

LV G

DETECTION

HVG

SYNCHRONOUS

BOOTSTRAP DIODE

HVG

DRIVER

LVG DRIVER

Css

DISABLE

DIS

LINE

DEAD

TIME

LEVEL

SHIFTER

RFmin

1.85V S Q

UVLO

Q S

RUVLO

CONTROL

LOGIC

-LI NE_O K

1.25V

µA

DIS

ISEN_DIS

17V

6.3V

VCO

1.25V

STANDBY

STBY 5

DRIVING

LOGIC

DELAY

Contents L6599

2/36

Contents

1 Device description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2 Pin settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2.1 Connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2.2 Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

3 Typical system block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

4 Electrical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

4.1 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

4.2 Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

5 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

6 Typical electrical performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

7 Application information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

7.1 Oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

7.2 Operation at no load or very light load . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

7.3 Soft-start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

7.4 Current sense, OCP and OLP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

7.5 Latched shutdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

7.6 Line sensing function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

7.7 Bootstrap section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

7.8 Application example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

8 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

9 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

L6599 Device description

3/36

1 Device description

The L6599 is a double-ended controller specific for the resonant half-bridge topology. It

provides 50 % complementary duty cycle: the high-side switch and the low-side switch are

driven ON\OFF 180° out-of-phase for exactly the same time.

Output voltage regulation is obtained by modulating the operating frequency. A fixed dead-

time inserted between the turn-OFF of one switch and the turn-ON of the other one

guarantees soft-switching and enables high-frequency operation.

To drive the high-side switch with the bootstrap approach, the IC incorporates a high-voltage

floating structure able to withstand more than 600 V with a synchronous-driven high-voltage

DMOS that replaces the external fast-recovery bootstrap diode.

The IC enables the designer to set the operating frequency range of the converter by means

of an externally programmable oscillator.

At start-up, to prevent uncontrolled inrush current, the switching frequency starts from a

programmable maximum value and progressively decays until it reaches the steady-state

value determined by the control loop. This frequency shift is non linear to minimize output

voltage overshoots; its duration is programmable as well.

The IC can be forced to enter a controlled burst-mode operation at light load, so as to keep

converter's input consumption to a minimum.

IC's functions include a not-latched active-low disable input with current hysteresis useful for

power sequencing or for brownout protection, a current sense input for OCP with frequency

shift and delayed shutdown with automatic restart.

A higher level OCP latches off the IC if the first-level protection is not sufficient to control the

primary current. Their combination offers complete protection against overload and short

circuits. An additional latched disable input (DIS) allows easy implementation of OTP and/or

OVP.

An interface with the PFC controller is provided that enables to switch off the pre-regulator

during fault conditions, such as OCP shutdown and DIS high, or during burst-mode

operation.

_|:|:|:|__|__|:|:|_ V EEEEEEEE

Pin settings L6599

4/36

2 Pin settings

2.1 Connection

Figure 2. Pin connection (top view)

2.2 Functions

GND

Css

DELAY

STBY

ISEN

LINE

LVG

VBOOT

HVG

N.C.

Vcc

PFC_STOP

OUT

DIS

RFmin

Table 2. Pin functions

N. Name Function

Soft start. This pin connects an external capacitor to GND and a resistor to RFmin (pin 4)

that set both the maximum oscillator frequency and the time constant for the frequency shift

that occurs as the chip starts up (soft-start). An internal switch discharges this capacitor

every time the chip turns OFF (VCC < UVLO, LINE < 1.25 V or > 6 V, DIS > 1.85 V, ISEN >

1.5 V, DELAY > 3.5 V) to make sure it will be soft-started next, and when the voltage on the

current sense pin (ISEN) exceeds 0.8V, as long as it stays above 0.75 V.

2DELAY

Delayed shutdown upon overcurrent. A capacitor and a resistor are connected from this pin

to GND to set both the maximum duration of an overcurrent condition before the IC stops

switching and the delay after which the IC restarts switching. Every time the voltage on the

ISEN pin exceeds 0.8 V the capacitor is charged by an internal 150µA current generator and

is slowly discharged by the external resistor. If the voltage on the pin reaches 2 V, the soft

start capacitor is completely discharged so that the switching frequency is pushed to its

maximum value and the 150 µA is kept always on. As the voltage on the pin exceeds 3.5 V

the IC stops switching and the internal generator is turned OFF, so that the voltage on the

pin will decay because of the external resistor. The IC will be soft-restarted as the voltage

drops below 0.3V. In this way, under short circuit conditions, the converter will work

intermittently with very low input average power.

3CF

Timing capacitor. A capacitor connected from this pin to GND is charged and discharged by

internal current generators programmed by the external network connected to pin 4 (RFmin)

and determines the switching frequency of the converter.

L6599 Pin settings

5/36

N. Name Function

4RFmin

Minimum oscillator frequency setting. This pin provides a precise 2 V reference and a

resistor connected from this pin to GND defines a current that is used to set the minimum

oscillator frequency. To close the feedback loop that regulates the converter output voltage

by modulating the oscillator frequency, the phototransistor of an optocoupler will be

connected to this pin through a resistor. The value of this resistor will set the maximum

operating frequency. An R-C series connected from this pin to GND sets frequency shift at

start-up to prevent excessive energy inrush (soft-start).

5STBY

Burst-mode operation threshold. The pin senses some voltage related to the feedback

control, which is compared to an internal reference (1.25 V). If the voltage on the pin is lower

than the reference, the IC enters an idle state and its quiescent current is reduced. The chip

restarts switching as the voltage exceeds the reference by 50 mV. Soft-start is not invoked.

This function realizes burst-mode operation when the load falls below a level that can be

programmed by properly choosing the resistor connecting the optocoupler to pin RFmin (see

block diagram). Tie the pin to RFmin if burst-mode is not used.

6 ISEN

Current sense input. The pin senses the primary current though a sense resistor or a

capacitive divider for lossless sensing. This input is not intended for a cycle-by-cycle control;

hence the voltage signal must be filtered to get average current information. As the voltage

exceeds a 0.8 V threshold (with 50 mV hysteresis), the soft-start capacitor connected to pin

1 is internally discharged: the frequency increases hence limiting the power throughput.

Under output short circuit, this normally results in a nearly constant peak primary current.

This condition is allowed for a maximum time set at pin 2. If the current keeps on building up

despite this frequency increase, a second comparator referenced at 1.5 V latches the device

off and brings its consumption almost to a “before start-up” level. The information is latched

and it is necessary to recycle the supply voltage of the IC to enable it to restart: the latch is

removed as the voltage on the Vcc pin goes below the UVLO threshold. Tie the pin to GND if

the function is not used.

7LINE

Line sensing input. The pin is to be connected to the high-voltage input bus with a resistor

divider to perform either AC or DC (in systems with PFC) brownout protection. A voltage

below 1.25 V shuts down (not latched) the IC, lowers its consumption and discharges the

soft-start capacitor. IC’s operation is re-enabled (soft-started) as the voltage exceeds 1.25 V.

The comparator is provided with current hysteresis: an internal 15 µA current generator is

ON as long as the voltage applied at the pin is below 1.25 V and is OFF if this value is

exceeded. Bypass the pin with a capacitor to GND to reduce noise pick-up. The voltage on

the pin is top-limited by an internal zener. Activating the zener causes the IC to shut down

(not latched). Bias the pin between 1.25 and 6 V if the function is not used.

8DIS

Latched device shutdown. Internally the pin connects a comparator that, when the voltage

on the pin exceeds 1.85 V, shuts the IC down and brings its consumption almost to a “before

start-up” level. The information is latched and it is necessary to recycle the supply voltage of

the IC to enable it to restart: the latch is removed as the voltage on the VCC pin goes below

the UVLO threshold. Tie the pin to GND if the function is not used.

9PFC_STOP

Open-drain ON/OFF control of PFC controller. This pin, normally open, is intended for

stopping the PFC controller, for protection purpose or during burst-mode operation. It goes

low when the IC is shut down by DIS > 1.85 V, ISEN > 1.5 V, LINE > 6 V and STBY < 1.25 V.

The pin is pulled low also when the voltage on pin DELAY exceeds 2V and goes back open

as the voltage falls below 0.3V. During UVLO, it is open. Leave the pin unconnected if not

used.

10 GND

Chip ground. Current return for both the low-side gate-drive current and the bias current of

the IC. All of the ground connections of the bias components should be tied to a track going

to this pin and kept separate from any pulsed current return.

Table 2. Pin functions (continued)

Pic bREREéUL/XTOR (OPLY \ONAL) REéOQMTHALﬁmeGE E. Resonam HEIwStumed om case of PFC: anuma‘uus Uperalmn‘for 551er % L6551/2/3 A ﬂ ; f L6599 PFCCaW he turned Dﬂ aihgm \oadto ea;e comphance Wm snag/sauna regmauons

Typical system block diagram L6599

6/36

3 Typical system block diagram

Figure 3. Typical system block diagram

N. Name Function

11 LVG

Low-side gate-drive output. The driver is capable of 0.3 A min. source and 0.8 A min. sink

peak current to drive the lower MOSFET of the half-bridge leg. The pin is actively pulled to

GND during UVLO.

12 VCC

Supply Voltage of both the signal part of the IC and the low-side gate driver. Sometimes a

small bypass capacitor (0.1 µF typ.) to GND might be useful to get a clean bias voltage for

the signal part of the IC.

13 N.C. High-voltage spacer. The pin is not internally connected to isolate the high-voltage pin and

ease compliance with safety regulations (creepage distance) on the PCB.

14 OUT High-side gate-drive floating ground. Current return for the high-side gate-drive current.

Layout carefully the connection of this pin to avoid too large spikes below ground.

15 HVG

High-side floating gate-drive output. The driver is capable of 0.3 A min. source and 0.8A min.

sink peak current to drive the upper MOSFET of the half-bridge leg. A resistor internally

connected to pin 14 (OUT) ensures that the pin is not floating during UVLO.

16 VBOOT

High-side gate-drive floating supply Voltage. The bootstrap capacitor connected between

this pin and pin 14 (OUT) is fed by an internal synchronous bootstrap diode driven in-phase

with the low-side gate-drive. This patented structure replaces the normally used external

diode.

Table 2. Pin functions (continued)

L6599 Electrical data

7/36

4 Electrical data

4.1 Maximum ratings

Note: ESD immunity for pins 14, 15 and 16 is guaranteed up to 900 V

4.2 Thermal data

Table 3. Absolute maximum ratings

Symbol Pin Parameter Value Unit

VBOOT 16 Floating supply voltage -1 to 618 V

VOUT 14 Floating ground voltage -3 to VBOOT -18 V

dVOUT /dt 14 Floating ground max. slew rate 50 V/ns

VCC 12 IC Supply voltage (ICC ≤ 25 mA) Self-limited V

VPFC_STOP 9 Maximum voltage (pin open) -0.3 to VCC V

IPFC_STOP 9 Maximum sink current (pin low) Self-limited A

VLINEmax 7 Maximum pin voltage (Ipin ≤ 1 mA) Self-limited V

IRFmin 4 Maximum source current 2 mA

1 to 6, 8 Analog inputs and outputs -0.3 to 5 V

Table 4. Thermal data

Symbol Description Value Unit

RthJA

Max. thermal resistance junction to ambient (DIP16) 80 °C/W

Max. thermal resistance junction to ambient (SO16) 120

TSTG Storage temperature range -55 to 150 °C

TJJunction operating temperature range -40 to 150 °C

PTOT

Recommended max. power dissipation @TA = 70 °C (DIP16) 1

Recommended max. power dissipation @TA = 50 °C (SO16) 0.83

Electrical characteristics L6599

8/36

5 Electrical characteristics

TJ = 0 to 105 °C, VCC = 15 V, VBOOT = 15 V, CHVG = CLVG = 1 nF; CF = 470 pF;

RRFmin = 12 kΩ; unless otherwise specified.

Table 5. Electrical characteristics

Symbol Parameter Test condition Min Typ Max Unit

IC supply voltage

VCC Operating range After device turn-on 8.85 16 V

VCC(ON) Turn-ON threshold Voltage rising 10 10.7 11.4 V

VCC(OFF) Turn-OFF threshold Voltage falling 7.45 8.15 8.85 V

Hys Hysteresis 2.55 V

VZVCC clamp voltage Iclamp = 10 mA 16 17 17.9 V

Supply current

Istart-up Start-up current Before device turn-ON

VCC = VCC(ON) - 0.2 V 200 250 µA

IqQuiescent current Device ON, VSTBY = 1 V 1.5 2 mA

Iop Operating current Device ON,

VSTBY = VRFmin 3.5 5 mA

IqResidual consumption

VDIS > 1.85 V or VDELAY

> 3.5 V or VLINE < 1.25 V

or VLINE = Vclamp

300 400 µA

High-side floating gate-drive supply

ILKBOOT

VBOOT pin leakage

current VBOOT = 580 V 5 µA

ILKOUT OUT pin leakage current VOUT = 562 V 5 µA

rDS(on) Synchronous bootstrap

diode ON-resistance VLVG = High 150 Ω

Overcurrent comparator

IISEN Input bias current VISEN = 0 to VISENdis -1 µA

tLEB Leading edge blanking After VHVG and VLVG

low-to-high transition 250 ns

VISENx Frequency shift

threshold Voltage rising (1) 0.76 0.8 0.84 V

Hysteresis Voltage falling 50 mV

VISENdis Latch OFF threshold Voltage rising (1) 1.44 1.5 1.56 V

td(H-L) Delay to output 300 400 ns

L6599 Electrical characteristics

9/36

Symbol Parameter Test condition Min Typ Max Unit

Line sensing

Vth Threshold voltage Voltage rising or falling

(1) 1.2 1.25 1.3 V

IHyst Current hysteresis VCC > 5 V, VLINE = 0.3 V 12 15 18 µA

Vclamp Clamp level ILINE = 1mA 6 8 V

DIS function

IDIS Input bias current VDIS = 0 to Vth -1 µA

Vth Disable threshold Voltage rising (1) 1.77 1.85 1.93 V

Oscillator

D Output duty cycle Both HVG and LVG 48 50 52 %

fosc Oscillation frequency

58.2 60 61.8

kHz

RRFmin= 2.7 kΩ240 250 260

Maximum

recommended 500 kHz

TDDead-time Between HVG and LVG 0.2 0.3 0.4 µs

VCFp Peak value 3.9 V

VCFv Valley value 0.9 V

VREF Voltage reference at

pin 4 (1) 1.92 2 2.08 V

KMCurrent mirroring ratio 1 A/A

RFMIN Timing resistor range 1 100 kΩ

PFC_STOP function

Ileak

High level leakage

current

VPFC_STOP = VCC,

VDIS = 0 V 1 µA

VLLow saturation level IPFC_STOP =1mA,

VDIS = 2 V 0.2 V

Soft-start function

Ileak Open-state current V(Css) = 2 V 0.5 µA

R Discharge resistance

VISEN > VISENx 120 Ω

Standby function

IDIS Input bias current VDIS = 0 to Vth -1 µA

Vth Disable threshold Voltage falling (1) 1.2 1.25 1.3 V

Hys Hysteresis Voltage rising 50 mV

Table 5. Electrical characteristics (continued)

Electrical characteristics L6599

10/36

Symbol Parameter Test condition Min Typ Max Unit

Delayed shutdown function

Ileak Open-state current V(DELAY) = 0 0.5 µA

ICHARGE Charge current VDELAY = 1 V,

VISEN = 0.85 V 100 150 200 µA

Vth1Threshold for forced

operation at max.

frequency

Voltage rising (1) 1.92 2 2.08 V

Vth2Shutdown threshold Voltage rising (1) 3.3 3.5 3.7 V

Vth3Restart threshold Voltage falling (1) 0.25 0.3 0.35 V

Low - side gate driver (voltages referred to GND)

VLVG L Output low voltage Isink = 200 mA 1.5 V

VLVG H Output high voltage Isource = 5 mA 12.8 13.3 V

Isourcepk Peak source current -0.3 A

Isinkpk Peak sink current 0.8 A

tfFall time 30 ns

trRise time 60 ns

UVLO saturation VCC = 0 to VCC(ON),

Isink = 2 mA 1.1 V

High-side gate driver (voltages referred to OUT)

VHVGL Output low voltage Isink = 200 mA 1.5 V

VHVGH Output high voltage Isource = 5 mA 12.8 13.3 V

Isourcepk Peak source current -0.3 A

Isinkpk Peak sink current 0.8 A

tfFall time 30 ns

trRise time 60 ns

HVG-OUT pull-down 25 kΩ

1. Values traking each other

Table 5. Electrical characteristics (continued)

Pln 12 Ice [mA] Pin 12 [mA] 50 5 1o Dperaﬁng©50 km 5 2 Quiescent 1 u 5 ‘ 0 1 0 5 o 05 o 3 o 01 CWG=CLvn=1nF 0 2 a 005 u 0 1 0 5 1o 15 20 -20 o 20 40 so so 100 120 Vcc [V] TI ["5] Pin 12 [v1 Pin 12M 15 11 175 \ 17 \ 165 15 rm 0 20 40 6D 50 100120 U ['C] Tum-on IO 5 m 95 8 ~20 o 20 40 an EU TII'C] 100 120

L6599 Typical electrical performance

11/36

6 Typical electrical performance

Figure 4. Device consumption vs supply

voltage

Figure 5. IC consumption vs

junction temperature

Figure 6. VCC clamp voltage vs

junction temperature

Figure 7. UVLO thresholds vs

junction temperature

Pin3 Pins11&15 1 05 1 15 1 1 1 Nurmahzedk: fsw @251 Normahzedtofsw (325°C SOkszsw<250khz><><250khz vu="15v" 1="" 1="" 7="" vcc="15V" 1,025="" 105="" 1="" '="" 1="" 0,975="" n="" 95="" 095="" 09="" .20="" o="" 20="" 40="" 50="" so="" 100="" 120="" -20="" 0="" 20="" 40="" so="" so="" 100="" 120="" tj[”c]="" tj'[°ci="" plnzoslexl="" pinj="" [vi="" 1,000="" cf:="" mpf="" vcc="" 5v="" 500="" mar="" f:=""><><250khz \="" .="" l70pf="" vac—15v="" w\§\="" 200="" 1.0nf\="" 1cd="" 21="" f="" \="" n="" \="" so="" 20="" 10="" 51="" 2="" 3="" 5="" 1o="" 20="" rlen="" [kn]="" 1']="" [“cl="">

Typical electrical performance L6599

12/36

Figure 8. Oscillator frequency vs junction

temperature

Figure 9. Dead-time vs

junction temperature

Figure 10. Oscillator frequency vs

timing components

Figure 11. Oscillator ramp vs

junction temperature

PinA M 2 DE 205 204 202 198 196 ‘94 192 -20 a 20 An 50 30100120 T] ['C] Pin53&4 1015 Narmahzed w W @ 25*0 1.01 5DkHz<><25dkhz v:r.="15\/" 1="" nos="" 0="" 995="" 0.99="" a="" 955="" 0.93="" 0975="" -20="" n="" 20="" 4d="" 60="" so="" me="" 120="" 71="" ['cl="" pin="" 1="" [ual="" 200="" 150="" 160="" me="" 120="" 100="" 720="" o="" 20="" a0="" 50="" so="" 100="" 120="" 11="" [‘cl="" fin="" 2="" [v]="" :55="" a‘waﬁ="" on="" resxan="">20 0 20 4o 60 so 100 ‘20 TIFCI

L6599 Typical electrical performance

13/36

Figure 12. Reference voltage vs

junction temperature

Figure 13. Current mirroring ratio vs junction

temperature

Figure 14. OCP delay source current vs

junction temperature

Figure 15. OCP delay thresholds vs junction

temperature

PIn5M Pin6[V] 14 1e 1 V” 5v Latch-elf 1.35 / ,//“"' 13:51am 12 13 1 125 CSSIW 0.5 _ 1 ’/ Stop T Cssu‘aen 12 0.5 -20 o 20 40 so so 100 120 720 0 20 40 so so 100 120 UPC] UPC] pin 7 IV] Pm 7 [WA] 13 17 15 ‘ \ 15 14 13 o 12 -20 u 20 no so so 100 120 -20 u 20 40 so an 100 120 'nl'cl m‘cl

Typical electrical performance L6599

14/36

Figure 16. Standby thresholds vs junction

temperature

Figure 17. Current sense thresholds vs

junction temperature

Figure 18. Line thresholds vs

junction temperature

Figure 19. Line source current vs junction

temperature

Figure 20. Latched disable threshold vs

junction temperature

fsw a) 1': o E E :1 an Va bl quencymode Pin Pinmax

L6599 Application information

15/36

7 Application information

The L6599 is an advanced double-ended controller specific for resonant half-bridge

topology. In these converters the switches (MOSFETs) of the half-bridge leg are alternately

switched on and OFF (180° out-of-phase) for exactly the same time. This is commonly

referred to as operation at "50 % duty cycle", although the real duty cycle, that is the ratio of

the ON-time of either switch to the switching period, is actually less than 50 %. The reason

is that there is an internally fixed dead-time TD, inserted between the turn-OFF of either

MOSFET and the turn-ON of the other one, where both MOSFETs are OFF. This dead- time

is essential in order for the converter to work correctly: it will ensure soft-switching and

enable high-frequency operation with high efficiency and low EMI emissions.

To perform converter's output voltage regulation the device is able to operate in different

modes (Figure 21), depending on the load conditions:

1. Variable frequency at heavy and medium/light load. A relaxation oscillator (see

"Oscillator" section for more details) generates a symmetrical triangular waveform,

which MOSFETs' switching is locked to. The frequency of this waveform is related to a

current that will be modulated by the feedback circuitry. As a result, the tank circuit

driven by the half-bridge will be stimulated at a frequency dictated by the feedback loop

to keep the output voltage regulated, thus exploiting its frequency-dependent transfer

characteristics.

2. Burst-mode control with no or very light load. When the load falls below a value, the

converter will enter a controlled intermittent operation, where a series of a few

switching cycles at a nearly fixed frequency are spaced out by long idle periods where

both MOSFETs are in OFF-state. A further load decrease will be translated into longer

idle periods and then in a reduction of the average switching frequency. When the

converter is completely unloaded, the average switching frequency can go down even

to few hundred Hz, thus minimizing magnetizing current losses as well as all frequency-

related losses and making it easier to comply with energy saving recommendations.

Figure 21. Multi-mode operation

16/36 W. I The foHowing approximake relaxionships he frequency respectively:

Application information L6599

16/36

7.1 Oscillator

The oscillator is programmed externally by means of a capacitor (CF), connected from pin 3

(CF) to ground, that will be alternately charged and discharged by the current defined with

the network connected to pin 4 (RFmin). The pin provides an accurate 2 V reference with

about 2 mA source capability and the higher the current sourced by the pin is, the higher the

oscillator frequency will be. The block diagram of Figure 22 shows a simplified internal

circuit that explains the operation.

The network that loads the RFmin pin generally comprises three branches:

1. A resistor RFmin connected between the pin and ground that determines the minimum

operating frequency;

2. A resistor RFmax connected between the pin and the collector of the (emitter-grounded)

phototransistor that transfers the feedback signal from the secondary side back to the

primary side; while in operation, the phototransistor will modulate the current through

this branch - hence modulating the oscillator frequency - to perform output voltage

regulation; the value of RFmax determines the maximum frequency the half-bridge will

be operated at when the phototransistor is fully saturated;

3. An R-C series circuit (CSS + RSS) connected between the pin and ground that enables

to set up a frequency shift at start-up (see Chapter 7.3: Soft-start). Note that the

contribution of this branch is zero during steady-state operation.

Figure 22. Oscillator's internal block diagram

The following approximate relationships hold for the minimum and the maximum oscillator

frequency respectively:

L6599

2 V

4RFmin

3 CF

1 V

4 V

2·KM·IR

KM·IR

RFmin RFmax

RSS

CSS

KM·IR

0.9V

3.9V

fmin

3CFRF

min

⋅⋅

-------------------------------------=

fmax

3CF RF

min RFmax

()⋅⋅

-----------------------------------------------------------------=

as 4.;

L6599 Application information

17/36

After fixing CF in the hundred pF or in the nF (consistently with the maximum source

capability of the RFmin pin and trading this off against the total consumption of the device),

the value of RFmin and RFmax will be selected so that the oscillator frequency is able to

cover the entire range needed for regulation, from the minimum value fmin (at minimum input

voltage and maximum load) to the maximum value fmax (at maximum input voltage and

minimum load):

A different selection criterion will be given for RFmax in case burst-mode operation at no-load

will be used (see "Operation at no load or very light load" section).

Figure 23. Oscillator waveforms and their relationship with gate-driving signals

In Figure 23 the timing relationship between the oscillator waveform and the gate-drive

signals, as well as the swinging node of the half-bridge leg (HB) is shown. Note that the low-

side gate-drive is turned on while the oscillator's triangle is ramping up and the high-side

gate-drive is turned on while the triangle is ramping down. In this way, at start-up, or as the

IC resumes switching during burst-mode operation, the low-side MOSFET will be switched

on first to charge the bootstrap capacitor. As a result, the bootstrap capacitor will always be

charged and ready to supply the high-side floating driver.

RFmin

3CFf

min

⋅⋅

------------------------------=

RFmax

RFmin

fmax

fmin

-----------1–

---------------------=

HVG t

LVG t

TDTD

18/36

Application information L6599

18/36

7.2 Operation at no load or very light load

When the resonant half-bridge is lightly loaded or unloaded at all, its switching frequency will

be at its maximum value. To keep the output voltage under control in these conditions and to

avoid losing soft-switching, there must be some significant residual current flowing through

the transformer's magnetizing inductance. This current, however, produces some

associated losses that prevent converter's no-load consumption from achieving very low

values.

To overcome this issue, the L6599 enables the designer to make the converter operate

intermittently (burst-mode operation), with a series of a few switching cycles spaced out by

long idle periods where both MOSFETs are in OFF-state, so that the average switching

frequency can be substantially reduced. As a result, the average value of the residual

magnetizing current and the associated losses will be considerably cut down, thus

facilitating the converter to comply with energy saving recommendations.

The device can be operated in burst-mode by using pin 5 (STBY): if the voltage applied to

this pin falls below 1.25 V the IC will enter an idle state where both gate-drive outputs are

low, the oscillator is stopped, the soft-start capacitor CSS keeps its charge and only the 2 V

reference at RFmin pin stays alive to minimize IC's consumption and VCC capacitor's

discharge. The IC will resume normal operation as the voltage on the pin exceeds 1.25 V by

50 mV.

To implement burst-mode operation the voltage applied to the STBY pin needs to be related

to the feedback loop. Figure 24 shows the simplest implementation, suitable with a narrow

input voltage range (e.g. when there is a PFC front-end).

Figure 24. Burst-mode implementation: narrow input voltage range

Figure 25. Burst-mode implementation: wide input voltage range

L6599

STBY

RFmin

Fmin RFmax RFmin RFmax

L6599 L6599

STBY

RFmin

RFmin RFmax

LINE

B+

RA+ RB >> RC

L6599 Application information

19/36

Essentially, RFmax will define the switching frequency fmax above which the L6599 will enter

burst-mode operation. Once fixed fmax, RFmax will be found from the relationship:

Note that, unlike the fmax considered in the previous section ("Chapter 7.1: Oscillator"), here

fmax is associated to some load PoutB greater than the minimum one. PoutB will be such that

the transformer's peak currents are low enough not to cause audible noise.

Resonant converter's switching frequency, however, depends also on the input voltage;

hence, in case there is quite a large input voltage range with the circuit of Figure 24 the

value of PoutB would change considerably. In this case it is recommended to use the

arrangement shown in Figure 25 where the information on the converter's input voltage is

added to the voltage applied to the STBY pin. Due to the strongly non-linear relationship

between switching frequency and input voltage, it is more practical to find empirically the

right amount of correction RA / (RA + RB) needed to minimize the change of PoutB. Just be

careful in choosing the total value RA + RB much greater than RC to minimize the effect on

the LINE pin voltage (see Chapter 7.6: Line sensing function).

Whichever circuit is in use, its operation can be described as follows. As the load falls below

the value PoutB the frequency will try to exceed the maximum programmed value fmax and

the voltage on the STBY pin (VSTBY) will go below 1.25V. The IC will then stop with both

gate-drive outputs low, so that both MOSFETs of the half-bridge leg are in OFF-state. The

voltage VSTBY will now increase as a result of the feedback reaction to the energy delivery

stop and, as it exceeds 1.3V, the IC will restart switching. After a while, VSTBY will go down

again in response to the energy burst and stop the IC. In this way the converter will work in a

burst-mode fashion with a nearly constant switching frequency. A further load decrease will

then cause a frequency reduction, which can go down even to few hundred hertz. The timing

diagram of Figure 26 illustrates this kind of operation, showing the most significant signals.

A small capacitor (typically in the hundred pF) from the STBY pin to ground, placed as close

to the IC as possible to reduce switching noise pick-up, will help get clean operation.

To help the designer meet energy saving requirements even in power-factor-corrected

systems, where a PFC pre-regulator precedes the DC-DC converter, the device allows that

the PFC pre-regulator can be turned off during burst-mode operation, hence eliminating the

no-load consumption of this stage (0.5 ÷ 1 W). There is no compliance issue in that

because EMC regulations on low-frequency harmonic emissions refer to nominal load, no

limit is envisaged when the converter operates with light or no load.

To do so, the device provides pin 9 (PFC_STOP): it is an open collector output, normally

open, that is asserted low when the IC is idle during burst-mode operation. This signal will

be externally used for switching off the PFC controller and the pre-regulator as shown in

Figure 27 When the L6599 is in UVLO the pin is kept open, to let the PFC controller start

first.

RFmax

---

RFmin

fmax

fmin

-----------1–

---------------------

⋅=

P o T s m P 20/36

Application information L6599

20/36

Figure 26. Load-dependent operating modes: timing diagram

Figure 27. How the L6599 can switch OFF a PFC controller at light load

LVG

HVG

1.25V

STBY

50 mV

hyster.

Resonant Mode Burst-m ode

fosc

Resonant Mode

PFC_STOP

PFC

GATE-DRIVE

L6599

PFC_STOP9

L6561/2

Vcc

ZCD

22 kΩ

100 kΩ

BC547

L6599 PFC_STOP9

L6563

PFC_OK

(AC_OK)

L6599 Application information

21/36

7.3 Soft-start

Generally speaking, purpose of soft-start is to progressively increase converter's power

capability when it is started up, so as to avoid excessive inrush current. In resonant

converters the deliverable power depends inversely on frequency, then soft- start is done by

sweeping the operating frequency from an initial high value until the control loop takes over.

With the L6599 converter's soft start-up is simply realized with the addition of an R-C series

circuit from pin 4 (RFmin) to ground (see Figure 28).

Initially, the capacitor CSS is totally discharged, so that the series resistor RSS is effectively

in parallel to RFmin and the resulting initial frequency is determined by RSS and RFmin only,

since the optocoupler's phototransistor is cut off (as long as the output voltage is not too far

away from the regulated value):

The CSS capacitor is progressively charged until its voltage reaches the reference voltage

(2V) and, consequently, the current through RSS goes to zero. This conventionally takes 5

time constants RSS·CSS but, before that time, the output voltage will have got close to the

regulated value and the feedback loop taken over, so that it will be the optocoupler's

phototransistor to determine the operating frequency from that moment onwards.

During this frequency sweep phase the operating frequency will decay following the

exponential charge of CSS, that is, initially it will change relatively quickly but the rate of

change will get slower and slower. This counteracts the non-linear frequency dependence

of the tank circuit that makes converter's power capability change little as frequency is away

from resonance and change very quickly as frequency approaches resonance frequency

(see Figure 29).

Figure 28. Soft-start circuit

fstart

3CF RF

min RSS

()()⋅⋅

---------------------------------------------------------------=

L6599

Css

RFmin

Fmin RSS

CSS

(

)

As a resuli, ihe average Wim linear frequency sw almost no overshooi. Typicaily, R55 and 055 where fs‘a,‘ is recomme quiie empirical and is a OCP (see nexi section) signiiicani signais durin 22/36

Application information L6599

22/36

Figure 29. Power vs frequency curve in an resonant half-bridge

As a result, the average input current will smoothly increase, without the peaking that occurs

with linear frequency sweep, and the output voltage will reach the regulated value with

almost no overshoot.

Typically, RSS and CSS will be selected based on the following relationships:

where fstart is recommended to be at least 4 times fmin. The proposed criterion for CSS is

quite empirical and is a compromise between an effective soft-start action and an effective

OCP (see next section). Please refer to the timing diagram of Figure 32 to see some

significant signals during the soft-start phase.

RESONANCE

FREQUENCY

| Z ( f ) | -1

Initial

frequency

Steady-state

frequency

RSS

RFmin

fstart

fmin

------------1–

----------------------=

Css

310

3–

⋅

RSS

-------------------=

Wm dJ

L6599 Application information

23/36

7.4 Current sense, OCP and OLP

The resonant half-bridge is essentially voltage-mode controlled; hence a current sense input

will only serve as an overcurrent protection (OCP).

Unlike PWM-controlled converters, where energy flow is controlled by the duty cycle of the

primary switch (or switches), in a resonant half-bridge the duty cycle is fixed and energy flow

is controlled by its switching frequency. This impacts on the way current limitation can be

realized. While in PWM-controlled converters energy flow can be limited simply by

terminating switch conduction beforehand when the sensed current exceeds a preset

threshold (this is commonly now as cycle-by-cycle limitation), in a resonant half-bridge the

switching frequency, that is, its oscillator's frequency must be increased and this cannot be

done as quickly as turning off a switch: it takes at least the next oscillator cycle to see the

frequency change. This implies that to have an effective increase, able to change the energy

flow significantly, the rate of change of the frequency must be slower than the frequency

itself. This, in turn, implies that cycle-by-cycle limitation is not feasible and that, therefore,

the information on the primary current fed to the current sensing input must be somehow

averaged. Of course, the averaging time must not be too long to prevent the primary current

from reaching too high values.

In Figure 30 and Figure 31 a couple of current sensing methods are illustrated that will be

described in the following. The circuit of Figure 30 is simpler but the dissipation on the sense

resistor Rs might not be negligible, hurting efficiency; the circuit of Figure 31 is more

complex but virtually lossless and recommended when the efficiency target is very high.

Figure 30. Current sensing technique with sense resistor

L6599

6 ISEN

τ ≈ 10

fmin

Vspk

ICr L6599

24/36 The deVice is equipped wi1h a currenf sensing inpu1 (pin 6, ISEN) and a sophisficaled overcurrem managemem sys1em. The ISEN pin is imernally connec1ed101he mom of a firs1 comparalor, referenced 1o 0.8 V, and lo 1haf of a second comparalor referenced lo 1.5 V. If fhe vol1age exlernally applied lo 1he pm by ei1her CeruH in Figure 30 or Figure 31 exceeds 0.8 V 1he firs1 comparafor is fripped and lhis causes an imernal swmch 1o be 1urned on and discharge 1he soﬂrslarl capaci1or 053 (see Chapter 7.3: Softrstart). This will quickly increase fhe osCillafor frequency and fhereby limil energy lransfer. The discharge Wl” go on un1il1he vollage on fhe ISEN pin has dropped by 50 mV; lhis, wi1h an averaging lime in me range of 10/fmm, ensures an eﬂeclive frequency rise. Under ou1puf shon circuil, 1his operalion resulfs in a nearly cons1an1 peak primary current I1 is normal fhal lhe vol1age on me ISEN pin may overshoo1 above 0.8 V; however, if 1he volfage on me ISEN pin reaches 1.5 V, 1he second comparafor will be friggered, 1he L6599 Will shuldown and la1ch off wi1h bolh fhe galerdrive oufpuls and lhe PFC_STOP pin low, hence fuming olf fhe emire uni1. The supply vollage of me It) musl be pulled below fhe UVLO fhreshold and lhen again above lhe s1ar17up level in order lo res1ar1. Such an evem may occur if fhe sollrsfarf capacilor C55 is foo large, so 1ha1 ils discharge is no11as1 enough or in case of 1ransformer's magnelizing inducfance saluralion or a shoned secondary reclifier. In 1he Circuil shown in Figure 30 where a sense resislor Fig in series lo 1he source of me lowiside MOSFET is used, no1e1he panicular connecfion of fhe resonam capacilor. In fhis way 1he vollage across H5 is relaled lo 1he currenf floWing lhrough fhe highrside MOSFET and is posilive mosl of me swilching period, excepl for fhe lime needed for me resonam currem lo reverse aller lhe lowiside MOSFET has been swi1ched OFF. Assuming fhaf fhe lime cons1an1o11he FlC filler is al leas11en1imes lhe minimum swi1ching frequency fmm, fhe approximale value of RS can be found using lhe empirical equalion: where lCmKX is me maximum desired peak curren1 flowing fhrough 1he resonam capacilor and fhe primary winding of fhe 1ransformer, which is rela1ed lo fhe maximum load and me minimum inpu1vol1age. £7

Application information L6599

24/36

Figure 31. Lossless current sensing technique, with capacitive shunt

The device is equipped with a current sensing input (pin 6, ISEN) and a sophisticated

overcurrent management system. The ISEN pin is internally connected to the input of a first

comparator, referenced to 0.8 V, and to that of a second comparator referenced to 1.5 V. If

the voltage externally applied to the pin by either circuit in Figure 30 or Figure 31 exceeds

0.8 V the first comparator is tripped and this causes an internal switch to be turned on and

discharge the soft-start capacitor CSS (see Chapter 7.3: Soft-start). This will quickly

increase the oscillator frequency and thereby limit energy transfer. The discharge will go on

until the voltage on the ISEN pin has dropped by 50 mV; this, with an averaging time in the

range of 10/fmin, ensures an effective frequency rise. Under output short circuit, this

operation results in a nearly constant peak primary current.

It is normal that the voltage on the ISEN pin may overshoot above 0.8 V; however, if the

voltage on the ISEN pin reaches 1.5 V, the second comparator will be triggered, the L6599

will shutdown and latch off with both the gate-drive outputs and the PFC_STOP pin low,

hence turning off the entire unit. The supply voltage of the IC must be pulled below the

UVLO threshold and then again above the start-up level in order to restart. Such an event

may occur if the soft-start capacitor CSS is too large, so that its discharge is not fast enough

or in case of transformer's magnetizing inductance saturation or a shorted secondary

rectifier.

In the circuit shown in Figure 30 where a sense resistor RS in series to the source of the

low-side MOSFET is used, note the particular connection of the resonant capacitor. In this

way the voltage across RS is related to the current flowing through the high-side MOSFET

and is positive most of the switching period, except for the time needed for the resonant

current to reverse after the low-side MOSFET has been switched OFF. Assuming that the

time constant of the RC filter is at least ten times the minimum switching frequency fmin, the

approximate value of RS can be found using the empirical equation:

where ICrpkx is the maximum desired peak current flowing through the resonant capacitor

and the primary winding of the transformer, which is related to the maximum load and the

minimum input voltage.

L6599

6 ISEN

RB1N4148

1N4148

τ ≈ 10

fmin

VCrp

ICr

Vspkx

ICrpkx

--------------- 50.8⋅

ICrpkx

----------------4

ICrpkx

---------------

≈≈=

L6599 Application information

25/36

The circuit shown in Figure 31 can be operated in two different ways. If the resistor RA in

series to CA is small (not above some hundred Ω, just to limit current spiking) the circuit

operates like a capacitive current divider; CA will be typically selected equal to CR/100 or

less and will be a low-loss type, the sense resistor RB will be selected as:

and CB will be such that RB·CB is in the range of 10 /fmin.

If the resistor RA in series to CA is not small (in this case it will be typically selected in the ten

kΩ ), the circuit operates like a divider of the ripple voltage across the resonant capacitor Cr,

which, in turn, is related to its current through the reactance of Cr. Again, CA will be typically

selected equal to CR/100 or less, this time not necessarily a low-loss type, while RB

(provided it is << RA) according to:

where the reactance of CA (XCA) and CR (XCr) should be calculated at the frequency where

ICrpk = ICrpkx. Again, CB will be such that RB·CB is in the range of 10 /fmin.

Whichever circuit one is going to use, the calculated values of RS or RB should be

considered just a first cut value that needs to be adjusted after experimental verification.

OCP is effective in limiting primary-to-secondary energy flow in case of an overload or an

output short circuit, but the output current through the secondary winding and rectifiers

under these conditions might be so high to endanger converter's safety if continuously

flowing. To prevent any damage during these conditions it is customary to force converter's

intermittent operation, in order to bring the average output current to values such that the

thermal stress for the transformer and the rectifiers can be easily handled.

With the L6599 the designer can program externally the maximum time TSH that the

converter is allowed to run overloaded or under short circuit conditions. Overloads or short

circuits lasting less than TSH will not cause any other action, hence providing the system

with immunity to short duration phenomena. If, instead, TSH is exceeded an overload

protection (OLP) procedure is activated that shuts down the device and, in case of

continuous overload/short circuit, results in continuous intermittent operation with a user-

defined duty cycle.

0.8π

ICrpkx

--------------- 1Cr

-------+

⎝⎠

⎛⎞

0.8π

ICrpkx

---------------

2XCA

XCr

----------------------------

⋅=

Application information L6599

26/36

Figure 32. Soft-start and delayed shutdown upon overcurrent timing diagram

This function is realized with pin 2 (DELAY), by means of a capacitor CDelay and a parallel

resistor RDelay connected to ground. As the voltage on the ISEN pin exceeds 0.8 V the first

OCP comparator, in addition to discharging CSS, turns on an internal current generator that

sources 150 µA from the DELAY pin and charges CDelay. During an overload/short-circuit

the OCP comparator and the internal current source will be repeatedly activated and CDelay

will be charged with an average current that depends essentially on the time constant of the

current sense filtering circuit, on CSS and the characteristics of the resonant circuit; the

discharge due to RDelay can be neglected, considering that the associated time constant is

typically much longer.

This operation will go on until the voltage on CDelay reaches 2 V, which defines the time TSH.

There is not a simple relationship that links TSH to CDelay

, thus it is more practical to

determine CDelay experimentally. As a rough indication, with CDelay = 1 µF TSH will be in the

order of 100 ms.

Once CDelay is charged at 2 V the internal switch that discharges CSS is forced low

continuously regardless of the OCP comparator's output, and the 150 µA current source is

continuously on, until the voltage on CDelay reaches 3.5 V. This phase lasts:

with TMP is expressed in ms and CDelay in µF. During this time the L6599 runs at a frequency

close to fstart (see Chapter 7.3: Soft-start) to minimize the energy inside the resonant circuit.

As the voltage on CDelay is 3.5 V, the device stops switching and the PFC_STOP pin is

pulled low. Also the internal generator is turned off, so that CDelay will now be slowly

discharged by RDelay

. The IC will restart when the voltage on CDelay will be less than 0.3V,

which will take:

Vcc

Css

DELAY

START-UP OVER

LOAD OVERLOAD

Primary

Current

NORMAL

OPERATION

NORMAL

OPERATION SHUTDOWN

Vout

SOFT-START SOFT-START

3.5V

0.3V

MIN. POWER

PFC_STOP

ISEN

0.8V

TSH TSTOP

TMP

Tss

TMP 10 CDelay

⋅=

TSTOP RDelay CDelay

⋅=ln3.5

0.3

--------2.5RDelay

≈CDelay

⋅

L6599 Application information

27/36

The timing diagram of Figure 32 shows this operation.

Note that if during TSTOP the supply voltage of the L6599 (Vcc) falls below the UVLO

threshold the IC keeps memory of the event and will not restart immediately after VCC

exceeds the start-up threshold if V(DELAY) is still higher than 0.3 V. Also the PFC_STOP pin

will stay low as long as V(DELAY) is greater than 0.3 V. Note also that in case there is an

overload lasting less than TSH, the value of TSH for the next overload will be lower if they are

close to one another.

7.5 Latched shutdown

The device is equipped with a comparator having the non-inverting input externally available

at pin 8 (DIS) and with the inverting input internally referenced to 1.85 ‘V. As the voltage on

the pin exceeds the internal threshold, the IC is immediately shut down and its consumption

reduced at a low value. The information is latched and it is necessary to let the voltage on

the Vcc pin go below the UVLO threshold to reset the latch and restart the IC.

This function is useful to implement a latched overtemperature protection very easily by

biasing the pin with a divider from an external reference voltage, where the upper resistor is

an NTC physically located close to a heating element like the MOSFET, or the secondary

diode or the transformer.

An OVP can be implemented as well, e.g. by sensing the output voltage and transferring an

overvoltage condition via an optocoupler.

7.6 Line sensing function

This function basically stops the IC as the input voltage to the converter falls below the

specified range and lets it restart as the voltage goes back within the range. The sensed

voltage can be either the rectified and filtered mains voltage, in which case the function will

act as a brownout protection, or, in systems with a PFC pre-regulator front-end, the output

voltage of the PFC stage, in which case the function will serve as power-on and power-off

sequencing.

L6599 shutdown upon input undervoltage is accomplished by means of an internal

comparator, as shown in the block diagram of Figure 33, whose non-inverting input is

available at pin 7 (LINE). The comparator is internally referenced to 1.25 V and disables the

IC if the voltage applied on the LINE pin is below the internal reference. Under these

conditions the soft-start is discharged, the PFC_STOP pin is open and the consumption of

the IC is reduced. PWM operation is re-enabled as the voltage on the pin is above the

reference. The comparator is provided with current hysteresis instead of a more usual

voltage hysteresis: an internal 1 µA current sink is ON as long as the voltage on the LINE pin

is below the reference and is OFF if the voltage is above the reference.

This approach provides an additional degree of freedom: it is possible to set the ON

threshold and the OFF threshold separately by properly choosing the resistors of the

external divider (see below). With voltage hysteresis, instead, fixing one threshold

automatically fixes the other one depending on the built-in hysteresis of the comparator.

HVln m bus RM LNE R‘ Vcc «2 wow L6599 HV \an bus me vmorr UNE vaK \ws ‘5 M Van we HVG vou|

Application information L6599

28/36

Figure 33. Line sensing function: internal block diagram and timing diagram

With reference to Figure 33 the following relationships can be established for the ON

(VinON) and OFF (VinOFF) thresholds of the input voltage:

which, solved for RH and RL, yield:

While the line undervoltage is active there is no PWM activity, thus the VCC voltage (if not

supplied by another source) continuously oscillates between the start-up and the UVLO

thresholds, as shown in the timing diagram of Figure 33.

As an additional measure of safety (e.g. in case the low-side resistor is open or missing, or

in non-power factor corrected systems in case of abnormally high input voltage) if the

VinON 1.25–

---------------------------------- 15 10 6–1.25

-----------+⋅=

VinOFF 1.25–

-------------------------------------1.25

-----------=

VinON VinOFF

–

15 10 6–

⋅

------------------------------------------=

RLRH

1.25

VinOFF 1.25–

-------------------------------------

⋅=

h E 7+7 —- 7 14 our The diode prevents any current can flow from the VBOOT pin back supply is quickly turned oft when the internal capacitor 01 the pum To drive the synchronous DMOS it is necessary a voltage highert Vcc- This voltage is obtained by means ol an internal charge pum The bootstrap structure introduces a voltage drop while recharging side driver is on), which increases with the operating frequency an external power MOSFET. It is the sum of the drop across the FtDS‘ across the series diode. At low frequency this drop is very small a as the operating frequency increases, it must be taken into accoun reduces the amplitude of the driving signal and can signiﬁcantly in external highrside MOSFET and then its conductive loss.

L6599 Application information

29/36

voltage on the pin exceeds 7 V the device is shutdown. If its supply voltage is always above

the UVLO threshold, the IC will restart as the voltage falls below 7 V.

The LINE pin, while the device is operating, is a high impedance input connected to high

value resistors, thus it is prone to pick up noise, which might alter the OFF threshold or give

origin to undesired switch-off of the IC during ESD tests. It is possible to bypass the pin to

ground with a small film capacitor (e.g. 1-10 nF) to prevent any malfunctioning of this kind. If

the function is not used the pin has to be connected to a voltage greater than 1.25 V but

lower than 6V (worst-case value of the 7 V threshold).

7.7 Bootstrap section

The supply of the floating high-side section is obtained by means of a bootstrap circuitry.

This solution normally requires a high voltage fast recovery diode to charge the bootstrap

capacitor CBOOT

. In the L6599 a patented integrated structure, replaces this external diode.

It is realized by means of a high voltage DMOS, working in the third quadrant and driven

synchronously with the low side driver (LVG), with a diode in series to the source, as shown

in Figure 34.

Figure 34. Bootstrap supply: internal bootstrap synchronous diode

The diode prevents any current can flow from the VBOOT pin back to VCC in case that the

supply is quickly turned off when the internal capacitor of the pump is not fully discharged.

To drive the synchronous DMOS it is necessary a voltage higher than the supply voltage

VCC. This voltage is obtained by means of an internal charge pump (Figure 34).

The bootstrap structure introduces a voltage drop while recharging CBOOT (i.e. when the low

side driver is on), which increases with the operating frequency and with the size of the

external power MOSFET. It is the sum of the drop across the RDS(on) and the forward drop

across the series diode. At low frequency this drop is very small and can be neglected but,

as the operating frequency increases, it must be taken into account. In fact, the drop

reduces the amplitude of the driving signal and can significantly increase the RDS(on) of the

external high-side MOSFET and then its conductive loss.

L6599

14 OUT

16 VBOOT

Vcc 12

LVG

CBOOT

Application information L6599

30/36

This concern applies to converters designed with a high resonance frequency (indicatively,

> 150 kHz), so that they run at high frequency also at full load. Otherwise, the converter will

run at high frequency only at light load, where the current flowing in the MOSFETs of the

half-bridge leg is lower, so that, generally, an RDS(on) rise is not an issue. However, it is wise

to check this point anyway and the following equation is useful to compute the drop on the

bootstrap driver:

where Qg is the gate charge of the external power MOS, RDS(on) is the on-resistance of the

bootstrap DMOS (150, typ.) and Tcharge is the ON-time of the bootstrap driver, which equals

about half the switching period minus the dead time TD. For example, using a MOSFET with

a total gate charge of 30 nC, the drop on the bootstrap driver is about 3 V at a switching

frequency of 200 kHz:

If a significant drop on the bootstrap driver is an issue, an external ultra-fast diode can be

used, thus saving the drop on the RDS(on) of the internal DMOS.

VDrop ICh earg rDS()ON VF

TCh earg

-------------------- RDS()ON VF

+=+=

VDrop

30 10 9–

⋅

2.5 10 6–0.3 10 6–

⋅–⋅

------------------------------------------------------- 150 0.6 2.7V=+=

h 4:7 23 a a: 430‘ 542.4 ﬂ .5 .u r v . [Eu N v . I _ v

L6599 Application information

31/36

7.8 Application example

Figure 35. EVAL6599-90W demo board, 90W adapter with L6563 and L6599: electrical schematic

Application information L6599

32/36

Table 6. EVAL6599-90W demo board, 90W adapter with L6563 & L6599: evaluation

data

Vin = 115 Vac Vin = 230 Vac

Vout Iout Pout Pin Eff. Vout Iout Pout Pin Eff.

[V] [A] [W] [W] % [V] [A] [W] [W] %

18.95 4.71 89.25 99.13 90.04 18.95 4.71 89.25 97.23 91.80

18.95 3.72 70.49 78.00 90.38 18.96 3.72 70.53 76.74 91.91

18.97 2.7 51.22 56.55 90.57 18.97 2.7 51.22 55.85 91.71

18.98 1.71 32.46 36.00 90.16 18.98 1.71 32.46 35.57 91.24

18.99 1.0 18.99 21.70 87.51 18.99 1.0 18.99 21.30 89.15

18.99 0.5 9.50 11.30 84.03 19.00 0.5 9.50 10.87 87.40

19.00 0.25 4.75 5.86 81.06 19.00 0.25 4.75 5.77 82.32

19.01 0.080 1.52 3 50.70 19.01 0.080 1.52 2.4 63.37

19.01 0.053 1.01 2 50.38 19.01 0.053 1.01 1.68 59.97

19.01 0.027 0.51 1.08 47.53 19.01 0.027 0.51 1 51.33

19.01 0.013 0.25 0.66 37.44 19.01 0.013 0.25 0.67 36.89

19.01 0 0 0.28 --- 19.01 0 0 0.34 ---

Ul—ll—lLll—IUUU

L6599 Package mechanical data

33/36

8 Package mechanical data

In order to meet environmental requirements, ST offers these devices in different grades of

ECOPACK® packages, depending on their level of environmental compliance. ECOPACK®

specifications, grade definitions and product status are available at: www.st.com.

ECOPACK® is an ST trademark.

Table 7. Plastic DIP-16 mechanical data

Dim.

mm. inch

Min Typ Max Min Typ Max

a1 0.51 0.020

B 0.77 1.65 0.030 0.065

b 0.5 0.020

b1 0.25 0.010

D 20 0.787

E 8.5 0.335

e 2.54 0.100

e3 17.78 0.700

F 7.1 0.280

I 5.1 0.201

L 3.3 0.130

Z 1.27 0.050

Figure 36. Plastic DIP-16 package dimensions

”Hf i: 1— 8: In 0016020 D £7

Package mechanical data L6599

34/36

Figure 37. Package dimensions

Table 8. SO16N mechanical data

Dim.

mm. inch

Min Typ Max Min Typ Max

A 1.75 0.069

a1 0.1 0.25 0.004 0.009

a2 1.6 0.063

b 0.35 0.46 0.014 0.018

b1 0.19 0.25 0.007 0.010

C 0.5 0.020

c1 45° (typ.)

D(1) 9.8 10 0.386 0.394

E 5.8 6.2 0.228 0.244

e 1.27 0.050

e3 8.89 0.350

F(1) 3.8 4.0 0.150 0.157

G 4.60 5.30 0.181 0.208

L 0.4 1.27 0.150 0.050

M 0.62 0.024

S 8°(max.)

L6599 Revision history

35/36

9 Revision history

Table 9. Document revision history

Date Revision Changes

15-May-2006 1 Initial release

18-Jul-2006 2 Typo in cover page

11-Feb-2009 3 Not recommended for new designs, the device has been

replaced by L6599A

L6599

36/36

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