AN2785 datasheet(39/51 Pages) STMICROELECTRONICS

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AN2785

Below-ground voltage on the OUT pin

Doc ID 14785 Rev 1

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Figure 29.

Use of OUT resistor to limit the below ground voltage spike on OUT pin

Note that this resistor is in series with both the turn ON and the turn OFF path, so it must be

considered in the sizing of overall turn-ON and turn-OFF resistance.

In case neither the OUT resistor would not be enough to limit the below ground voltage, the

following final resolving action could be taken:

●

Add a high voltage fast diode (e.g. STTH1L06) between the GND pin and the OUT pin

(very close to the device pins) in order to clamp directly on the gate driver OUT pin the

below ground voltage spike. Note that, in any case, this diode must be used together

with the OUT resistance suggested in the previous tip, because it must be avoided that

the diode brings the very large load current during low side recirculation, in order to

increase the clamping action of the diode itself (see following Figure 30).

HVG

H.V.

OUT

LVG

BOOT

CBOOT

VCC

HB_OUT

RGH_ON

RGH_OFF

RGL_ON

RGL_OFF

RBOOT

DBOOT

HB_OUT

OUT

BOOT

VBOOT without Rout

ROUT

AN2785 Datasheet(PDF) 39 Page - STMicroelectronics