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DRV8302: Generating fault for few PCBs

Part Number: DRV8302
Other Parts Discussed in Thread: DRV8301

we are facing problem while testing the DRV8302 IC with our custom design.

As of now we are thinking the problem is with the OC_ADJ pin (PIN11). Since if we are giving 0.21V with potential divider (R1 =10K, R2 =680 Ohm) we are observing an error (nFAULT pin going to LOW and observing 0.05V at OC_ADJ pin (Pin 11)). And observed that nOCTW pin is not generating error while nFAULT pin is LOW.

However, if we do any one of among the following changes, the Board is working fine.

  1. If we replace R1 =1K and R2 = 68 Ohms.
  2. If we give 0.21V from external power supply.
  3. if we short OC_ADJ pin directly to DVDD pin (Disabling the current limit).

So finally, we observed the impedance of that pin 11(OC_ADJ) with respect to GND for a separate IC, it is observed that 11MΩ. However, if we observe the faulty board it is around 200Ω (Calculated from OC_ADJ=0.05V).

So here we are doubting on the IC, at Pin 11 and arising the queries:

  1. what should be normal impedance of that pin 11?
  2. Under what circumstances the impedance becomes smaller? and what are the chances to reduce the impedance of the Pin 11 from 11MΩ to 200Ω?
  3. What are the major reasons could be, to reduce the voltage from 0.21V to 0.05V at Pin11(OC_ADJ)?

Note: R207 and C57 are not mounted on PCB. Required Current for Motor is less than 5A.  Set current limit is 28A at OC_ADJ pin.