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TPS65131 +15V Positive output shutdown

Go
Genius 4220 points
Other Parts Discussed in Thread: TPS65131

Hi,

Now I got the question about TPS65131 +15V Positive output problem.

+15V output shuts down during start-up as seen in attached wave form. but, -15V output will not have any problem.

+15V output will be connected to up to 3 Analog sub board and each board has about 100uF input cap.

This problem was observed only in the case when 3 analog sub boards were connected.

in the case that 1 or 2 analog sub boards  were connected, the +15V output started up correctly.

I suspected the over voltage event, but I'm not sure that the OVP event is Latch-Off type or not. is it Latch-off?

and I have no idea about a relevance between the OVP event and the capacitance connected to +15V rail.

Is there any limitation of  the maximum capacitance value connected to the TPS65131 positive rail?

I'd like to get an advice about the cause of this phenomenon.

Thanks,

Go

  • 0
    TI__Expert 8010 points
    Hi Go,

    The OVP- Event is latch-off, which means that if on FP-Voltage exceeds 1.274V the IC shuts down so lang until 1.213V is seen again.
    Can you send me your circuit to analyze?

    Thanks,
    Ilona
  • 0 in reply to Ilona
    Genius 4220 points

    Hi, Ilona

    Thank you for your comment.

    Here's the TPS65131 schematic.

    and regarding your comment below

    "FP-Voltage exceeds 1.274V the IC shuts down so lang until 1.213V is seen again."

    Does it mean that TPS65131 will re-start if FP-voltage decrease to 1.213V?

    If so, in this case TPS65131 doesn't re-start even though the FP-voltage decrease to 1.213V

    Any advice would be appreciated.

    Regards,

    GoTPS65131_circuit_pptx.pdf

  • 0 in reply to Go
    TI__Expert 8010 points
    Hi Go,

    First I need to be clear about your circuitry:
    - VNEG: You said that the -15V- Output is starting correctly --> is this output also connected to some load?
    - VPOS: Do you connect the sub boards before you switch on VIN or during operation mode? In case that the IC is starting correctly when 2 boards are connected, have you tried to connect the 3rd board after correct start-up?
    It is prejudicial applying an output capacitance of ~350uF for the IC, is it possible for you to reduce the input capacitance of the sub boards?
    What material do you use for the input caps of the sub boards (tantal, ceramic, post caps)? The parasitic effects can also effect the operating mode.
    I assume that you connect the boards between +15V and GND?

    Regarding to your comment : 'Does it mean that TPS65131 will re-start if FP-voltage decrease to 1.213V?'
    Yes it should restart when FP- voltage has reached to 1.213V

    Regards,
    Ilona
  • 0 in reply to Ilona
    Genius 4220 points
    Hi, Ilona

    Thank you for your comment.

    As for your questions, I'll confirm them to my customer and will let you know as soon as I get a feedback.

    Regarding your comment : "It is prejudicial applying an output capacitance of ~350uF for the IC"

    Do you have any target total output cap value for proper operation of TPS65131?

    Thanks

    Go
  • 0 in reply to Ilona
    Genius 4220 points

    Hi,  Ilona

    Thank you for your comment.

    I got some feedback for your questions, please see below in red.

    - VNEG: You said that the -15V- Output is starting correctly --> is this output also connected to some load?

    →yes, NEG output also connected to some load. and NEGoutput has same capacitance value as POS output line.

    - VPOS: Do you connect the sub boards before you switch on VIN or during operation mode? In case that the IC is starting correctly when 2 boards are connected, have you tried to connect the 3rd board after correct start-up?

    →the sub boards are connected before switch on VIN. and we can't test the case that connect the 3rd board after correct start-up

       because the system doesn't support hot plug. 

    It is prejudicial applying an output capacitance of ~350uF for the IC, is it possible for you to reduce the input capacitance of the sub boards?

    →Yes, now we're considering reducing the input capacitance of the sub boards as one of the countermeasure for the phenomenon.

       so We'd like to know the target total output cap value for proper operation of TPS65131

    What material do you use for the input caps of the sub boards (tantal, ceramic, post caps)? The parasitic effects can also effect the operating mode.

    →As for the largest input bulk cap, they use below, 

       type：Aluminum electrolytic cap
    　part No：UWX1E101MCL1（Nichi-Con）
    　Value：100uF/25V

    and the total value of input caps (including several ceramic bypass caps) is 136.38uF for each sub board.

    I assume that you connect the boards between +15V and GND?

    →Yes.


    Thanks

    Go

  • 0 in reply to Ilona
    Genius 4220 points

    Hi, Ilona

    How's it going? 

    Do you have any update for the questions?

    Thanks

    Go

  • 0 in reply to Go
    TI__Expert 8010 points
    Hi Go,
    I am sorry that i havent answered yet, but I accidently skipped out the question regarding max. output capacitance. I made some measurements with Cout of 500uF and it is ramping up properly. It is hard to say what the max. COUT is as it depends of the load current, dynamics. How much load current do the sub boards require?
    When the load current increases rapidly which the big output capacitance cannot provide as it is not charged in the starting moment then the failure is presumable. Have you done any progress minimizing the COUT?
  • 0 in reply to Ilona
    Genius 4220 points

    Hi,  Ilona

    Thank you for your comment.

    Regarding your questions,

    About 300mA is required for 3 sub boards.

    and  the +15V Output is starting correctly if reducing the COUT to 47uF for each board.

    Thanks

    Go 

  • 0 in reply to Ilona
    Genius 4220 points
    Hi, Ilona

    Regarding the waveforms I've attached before,

    If the switching stopped due to the OVP event, Why the switching didn't re-start even though the output voltage decreased?

    Thanks

    Go
  • 0 in reply to Go
    TI__Expert 8010 points

    Hi Go,

    The IC is then in latch-up-state, so you need to reset the input voltage. My answer above was maybe not clear regarding this.

    Regards,

    Ilona

  • 0 in reply to Ilona
    Genius 4220 points

    Hi, Ilona

    Thank you for your support.

    I'm not sure that why TPS65131 was in latch-up state.

    Have you ever seen this kind of phenomenon before?

    Thanks

    Go