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Small Motor Drivers Slide 13

The L6202 is a Full Bridge with logic level inputs. The device includes the level shift to drive the gate of the upper N-channel power MOS as well as a dead time generator to eliminate the possibility of cross conduction. To drive the gate of the upper N-Channel MOS device we need to generate a voltage that is higher than the power supply voltage. In the L6205 this is done by a combination of an internal charge pump and an external bootstrap capacitor. The charge pump is completely internal, and is only turned on when it is needed to turn on one of the upper transistors and requires no additional components. However, the values of capacitance that can be implemented on the IC are not large enough to be able to guarantee a good switching time. The external bootstrap provides sufficient energy to get a good switching performance but can not sustain a 100% duty cycle on the upper device as the leakage will eventually drain off the charge. The combination of the charge pump plus bootstrap provides good switching and the ability to maintain the upper transistor on indefinitely. One big advantage of an integrated driver IC is the ability to also implement some protection features in the device. The thermal shut down is an example of a protection function easily implemented on a monolithic IC that is difficult to implement with discrete devices. In the IC the thermal sensing element, typically a diode, can be placed very close to the power transistors and has a very good thermal coupling to the power transistor so it can very reliably sense the die temperature.

PTM Published on: 2011-12-14