CRD300DA12E-XM3 with CGD1700HB2M-UNA overcurrent protection threshold

ak47

Hello Experts,

We were looking at the CGD1700HB2M-UNA schematic and we had a few queries on the UCC21710 OC protection circuit,

Firstly what is the threshold it is designed for? (In terms amps not in Vce(sat) or Vds)

Looking at the UCC21710 data sheet , the Vocdet comes to around 5.7v, so the current threshold comes to 875 Amps, Could you experts verify this?

Also how have you assumed the Vf of the diode is 1v constantly, wouldn't it change with temperature and the current flowing through the diodes.?

Thanks ,

AK

TBhatia

Hello, thank you for your message. A member of our technical team is looking into your questions and we will respond shortly. 

AustinC

Hi AK,

It's important to keep in mind that the overcurrent protection circuit is intended to prevent short circuit events from damaging the power module and is not a precisely tunable current limit. We typically select a high trip level to prevent false trips during normal operation while catching the extreme cases from short circuit or shoot through events.

Yes, the voltage drop across the two high voltage diodes will change with current and temperature. We've used the IV curve on the US3M-13 diode's datasheet at TA = 25 C and the estimated current through the diodes to approximate ~0.5 V drop on each of the diodes. With the stock gate driver board, the trip point will be around 6.7 V just as the image of your calculator shows.

For the CRD300DA12E-XM3, which uses the CAB450M12XM3, the trip point will be around 1300 A at 175 C. If we were to further tune the CGD1700HB2M-UNA gate driver board to be used with the CAB450M12XM3 power module, we'd set the trip point closer to around 900 A at 175 C (2x the nameplate current at max junction temp.).

Best Regards,

Austin C.

ak47

Thankyou Austin for your feedback,

We will let you know if we have any further clarifications.