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Original question:

PMP9256: Output Ripple

PMP9256: PMP9256

Ch Ramakrishna
Prodigy 240 points
Part Number: PMP9256

Dear sir,

We have completed successfully our proto unit development of qty 2no.s of DC DC converters by following the PMP9256..

These two units are working from 9V to more than 40V DC input voltages with output current of 5Amp at 12V.

Recently we launched the units for production of qty more than 50no.s We are facing the problem that at 5amp load the input power supply source is tripping from 9V to 11V inputs. But the no load voltage is fine.

And the unit is meeting full load specifications from 11V to more than 40V DC inputs.

We request suggestion to overcome this problem at input voltages from 9 to 11 V..

  • 0
    TI__Expert 6620 points

    Hi CH,

    Based on your description it sounds like the power supply could be hitting current limit early.

    This could be because of noise or other issues, can you please check the current sense and see if there is noise.

    Also, do you notice that the level of current you can put out is related to the input voltage? At 9V can you put out less than 10V?

    I am also copying the original designer to follow up as well.


    Thanks,

    Robert

  • 0 in reply to Robert Taylor1
    TI__Intellectual 1235 points

    Hi CH,

    In the test report you can find the input current in the efficiency data. At 9V input the current is 7.75A while at 12V it is 5.58A.

    Best Regards,

    Bob

  • 0 in reply to Robert Taylor1
    Prodigy 240 points

    Hi Robert,

    We thank for your response.

    We also observed that due to noise, the power supply is hitting to current limit early. And also the input power supply source is trickling ON-OFF-ON-OFF during 5 Amp load with input voltage from 9V to 11V.

    We found that the power supply stable with 4Amp load from 10V to 11 V input voltage. And it is stable with 3.5 A from 9V to 10 V input voltage. There is slight variation from board to board in our production lot.

    Reagards

  • 0 in reply to Bob Sheehan
    Prodigy 240 points

    Hi Bob,

    Thank you  for the information.

    Our initial proto models Qty 2 no.s are in-line with the design parameters and are meeting the 5 Amp load with 9V to 40 V DC input variation.

    However during recent production lot, we are facing this problem. There could be some design margins, which are causing this problem.

    Regards

  • 0 in reply to Ch Ramakrishna
    TI__Intellectual 1235 points

    Hi Ch,

    To help track down the variation, you can measure the DC voltage with a meter across the input current sense resistor, shown as Rs1 and Rs2 on the schematic. This will give you a measurement of the average input current that is drawn from your input power source.

    Best Regards,

    Bob

  • 0 in reply to Bob Sheehan
    Prodigy 240 points

    Dear Bob,

    We thank for your support..

    We could able to resolve the issue by replacing Rs1 and Rs2 resistors with 1% tolerant resistors..

    During our production, the vendor supplied 5% tolarence resistors, which was informed to our QA department after analyzing the problem.

    We thank for your support..

    Ramarkishna