Other Parts Discussed in Thread: OPA1637,
Hi Team,
My customer is facing start-up issue that PWM switching doesn't start after /RESET is released. This occurs not every time but intermittently. There's OPA1637 in front of TPA3221 to convert current mode signal from DAC to voltage mode signal.
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Situation:
- PVDD=25V, VDD,AVDD,GVDD=5V(external. not from internal LDOs)
- Output of OpAMP looks fine. Inputs of TPA3221 are normal.
- PWM output of TPA3221 is unstable. sometimes it shows on both outputs but sometimes on only 1 CH or not at all.
- When the issue happens, /FAULT and /RESET are set to high at the same time.
- There's some bias voltage on the output while /CMUTE is set to Low. (From my understandings, there shouldn't be any signal on the output)
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Questions:
- Shouldn't /FAULT signal be turned high automatically after releasing /RESET when starting up? What does it mean that /FAULT is set high first than /RESET in datasheet below?
- Customer assumes start-up timings of OPA1637 and TPA3221 is a problem. Because Output only works when TPA3221 turned on faster than OPA1637. And The opposite doesn't work. Do you think this affects operation of TPA3221? If yes, Could you give me a short explanation why this error is occured?
- I read another similar thread that 1uF is the recommended for AC coupling capacitor. My customer is using 2uF. Is this possible to cause the issue? Please refer a schematic below
Thank very much you for reading this. I'll get back to you when I get more information and waveforms.
Best regards,
Jay
