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TPS53667: PMBUS register 78H - Other faults meaning

Suhant Raval1
Prodigy 20 points
Part Number: TPS53667
Other Parts Discussed in Thread: CSD

Hi, There, 

We are using  TPS53667 for I/P 12 VDC to O/P 0.85 VDC @144 Amps design with 6 phase in operation.  On my first prototype for this design TPS 53667 with 6 nos of CSD 95490 for 6 phase, stops working immediately at power on. Type of behaviour it shows is "it is experiencing O/P OV".  As its controller try to restart after Hiccup delay of 22 mSec, 3 times.

We have used above chip set combination on other design and it has worked well couple of design for 5 phase designs.  Also we have web benched designed and checked all component and its value very well on this board so we are not suspecting on layout or design values at this point of time. But we still seek your quick advise on the same.

As Internal regulator in above condition are showing healthy voltages, we tried to read PMBUS register on PMBUS. In PMBUS Register also we observed device has logged Over voltage fault and not  OC, UV or Temp faults. 

So when we read PMBUS Register, following were results.

  1. Register 78H  Value 61H. 
  2. Register 7BH  Value 08H. 
  3. Register 80H  Value 30H. 

We are a bit surprised to receive these values.

  1. In register 78H we should get value - 60H for OVP, Why are we getting 61H. What does it mean to have other fault in this chip?

  2. In register 7BH we should get value - 00H, Why are we getting 08H. What does it mean?

  3. In register 80H we should get value - 00H, Why are we getting 30H. What does it mean?

We repeated the above fault condition so many times and also read registers so many times all time it gives same above value. Also value for lot of other registers are coming up correct as per datasheet of the TPS53667. 

Can someone, quickly guide us what this register value means and what type of next steps we should take to quickly move forward.

Your quick response will be well appreciated. 

Regards, 

Suhant. 

  • 0
    TI__Genius 11095 points

    Hello, The datasheet appears to be marking bits as unsupported which are actually supported. 

    Register 78h (STATUS_BYTE)

    • The OTHER bit here just means that a condition other than (VOUT_OV, IOUT_OC, VIN_UV, OTF, or CML) occurred. It is just an indicator that you should look to the other status registers for more information. 
    • The value 61h indicates you saw IOUT_OC, VOUT_OV and OTHER. 

    Register 7Bh (STATUS_IOUT)

    • 08h means that current share warning was latched. This should be why you see the OTHER bit being set. 

    Register 80h (STATUS_MFR)

    • 30h here means that current sharing warning occurred in the 6th phase. 

    To further debug, It would be helpful if you collected some waveforms of the board behavior. 

  • 0 in reply to Matt Schurmann
    Prodigy 20 points

    Hi, Matt,

    Thanks for clarifying bit behaviours. Today we Probed more and identified issue with channel 6 misbehaving due to prototype assembly issue.

    Now we resolved it, Thanks again for your quick help.

    Regards,

    Suhant.