Tool/software:
Dear Support Team,
We attempted to drive a BLDC in open-loop using an external MCU and the DRV8311H, but were unsuccessful.
Although we applied power to the circuit and supplied INHx signals, we observed no change in the voltage at the OUTx pins with no fault signal.
Circuit configuration
External MCU
• 3.3 V logic
• Inputs: nFAULT, SOx
• Outputs: nSLEEP(set HIGH), INHx
DRV8311H
• VIN_AVDD = VM = 12 V
• AVDD = nSLEEP = MODE = INLx = 3.3 V
Measurements
- All 12 V supply rails measure correctly.
- Because we also provide 3.3 V externally, we cannot verify the AVDD regulator’s operation in operating mode.
- The nFAULT pin never goes low, even when nSLEEP changes state.
- The CP voltage stays around 11.7 V regardless of nSLEEP state, suggesting the charge-pump is not running.
- The voltage between each pair of OUTx pins is about 0.2 mV—just noise level.
From these observations, it appears the DRV8311H is not operating normally.
We would appreciate any guidance on possible errors or concerns in our setup.
Best regards,
Gunwoo Ahn
