LM74700D-Q1: LM74700D Vgs Stress issue

Hi Rock,

This is not expected. Is this happening on multiple devices and boards?

Also, I see that the CH2 (PSU VOUT) is around 30V whereas VCAP is at ~12V only. 

Is CH3 measured at pin1 or pin1-pin6.

Regards,

Shiven Dhir

Hi Shiven,

I'm not sure about the number of customer tests. I will on side support yesterday and double the test result.

The CH3 measured at pin1 Vcap.

Please refer to the schematic on secondary side.

Hi Rock,

Is the device already damaged or something? VCAP does not seem to work. Ideally when working, pin1 should see VIN+12V.

Please verify this.

Regards,

Shiven Dhir

Hi Shiven,

I  have checked with the customer and double-checked the MOSFET Vgs voltage, in the different outputs of the PSU, and there were different results. 

In the 12V Vout PUS application, the MOSFET Vgs were normal

CH2: Vgs

In the 36V Vout PUS application, the  MOSFET Vgs were abnormal

CH2: Vgs, CH3: Vds

Is LM74700 can be used in the redundant power application? Thanks.

Hi Rock,

LM74700-Q1 can be used in redundant power application.

In 2nd scope shot, what were the test conditions?

Was it connected in ORing? VSD looks negative and GATE falls to zero as soon as VSD goes negative.

Regards,

Shiven Dhir