UCC21710-Q1: UCC21710 OC Issue

Hi Noah,

Thanks for reaching out. I will provide a response by tomorrow.

Best regards,

Muiz.

Hi Noah,

Apologies for the late reply.

When you say that you tried shorting the pins and the device still had a fault. I assume that you're referring to shorting the OC pin to ground? If that is the case, OC detection is disabled and the device will not catch a fault. Can share waveforms showing RDY, FLT and power supply behaviors during this overcurrent condition. 

Best regards,

Muiz.

Hi Muiz,

Yes. When we startup the red LEDs flicker as if there is a fault being detected, but R200 is not present so there is no current flowing through the path. Additionally, when we replace the chip and lift the pins off the pad, then we maintain a solid red LED and no faults are detected. How would we have faults on the on the output side when there is no current flow?

Regards,

-Noah

Hi Noah, 

Can you please send me zoomed in waveforms showing FLT, output, DESAT and input signals for me to debug. Also, does this issue happen all the time with the unit or does it only happen under specific conditions?

In addition, you mentioned that when you don't see the issue when you place the chip and lift the pins off the pad. Are you saying that even a new unit showcases this unusual behavior until you float the pins? If so, what pins are you referring to?

Best regards,

Muiz.

Yes when you lift pin 1 and pin 2 and connect to pin 3 then the issue does not occur. When connecting Pin 1 and Pin 2 to the layout, the fault occurs even if the R200 is removed from the circuit. Therefore there should be no issues with FLT since it is not being utilized according to the datasheet.

The issue is very intermittent and occurs at various loading conditions or on a heatsink. I will try and provide FLT, Output and Desat signals during a dropout.

Regards,

-Noah

HI Noah,

I'll be on the lookout for your response with the waveforms.

Best regards,

Muiz

Hi Muiz,

Attached are the different dropouts related to these UCC21710 chips. As you can see the voltage is stable, and the data is being provided to the input of the gate drivers. FLT goes low even though it is completely disconnected as I previously stated. It seems that when the FLT goes low we usually have issues with the dropout of the gate signals. The Voltage appears stable via probing. We also looked at trying low pass filtering into the input and output side of the gate driver. Both of these did not fix our problem either. At higher loads all of the gate drivers dropout. We changed to the UCC5320SCDR and these work perfectly in the same setup. Can you please explain the difference in the isolation used or how the fault could be causing us these issues?

There is another E2E forum with several people with the same problem. Is there an issue with the chip?

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1552592/ucc21710-q1-issue-of-ucc21710-q1?tisearch=e2e-sitesearch&keymatch=UCC21710#

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1487858/ucc21710-gate-driver-tripping-on-over-current-fault-when-it-is-already-bypassed?tisearch=e2e-sitesearch&keymatch=UCC21710#

Image 1: Ch 1-3 Phase A-C LN, Ch 4-6 Phase A-C Current, Ch7 Modulation Waveform, Ch8 Output Gate Driver

Image 2: Ch 1-3 Phase A-C LN, Ch 4-5 Phase A-C Current, Ch6 In+ (LS_IN) Ch7 Modulation Waveform, Ch8 Output Gate Driver Dropout

Image 3: Ch 1 Phase B LN, Ch2 IN+ (LS_IN), Ch3 In- (HS_IN) Ch 4-5 Phase A, Phase B Current, Ch6 Nothing was PRobed, Ch7 FLT Open Collector Pin, Ch8 Output Gate Driver

Image 4: Ch 1 Nothing was Probed, Ch2 IN+ (LS_IN), Ch3 In- (HS_IN) Ch 4-5 Phase A, Phase B Current, Ch6 Nothing Probed, Ch7 FLT Open Collector Pin, Ch8 3.3V Signal