UCC27211A: How to reduce reverse current of internal boot diode?

Hi Harry,

There are several things that could lead to the internal diode becoming reverse biased. To reduce the reverse current, you can add a 1 ohm resistor in series with the boot capacitor, but please check the following first:

1. Please check to see if VDD or HB voltage is not exceeding abs max ratings.

2. The boot capacitor and VDD bypass capacitor may also be sized improperly, so can you share a full schematic that includes the component values and FETs?

3. Did the system fail at a specific operating time, such as startup, steady state, or shutdown?

Thanks,
Rubas

Hi Rubas

Thanks for your respond. I don't have the operation status now because end-customer test it with system. but we saw the same fail phenomenon in the startup.

And 

1. the resistor should be in series with cap or diode?

2. Can customer add an external diode to address this issue? if yes, is there some app not for the external diode choosing.

Update schematic

Hi Harry,

The current limiting resistor would go in series between the HB pin and bootstrap capacitor.

Yes, you can use an external bootstrap diode, and it may help in preventing damage due to reverse current. This app note explains how to design and select for a bootstrap diode and bootstrap capacitor. You can also use that app note to doublecheck if the current bypass capacitor value fits the requirement.

Please let me know when you receive the system characteristics, and make sure HB and VDD are not exceeding abs. max specs.

Thanks,
Rubas