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PMP9256: PMP9256

Ch Ramakrishna
Prodigy 240 points
Part Number: PMP9256

1. We designed the board as per available gerber in the application note PMP9256.

2. The design includes some of DNP (Do Not Place) components and the PCB is provided with mounting locations for these components also. As per the assembly instructions, we assembled the PCB. And DNP components are not populated.

3. In the schematic, Rsb5, Rsb6, 34 Ohms each and Csb3 (220pF) are shown and they are not marked as DNP but the mounting positions for these components are not available on the board. As per the image available for this board, these components are mounted on the board by doing rework. We also accommodated these components on our board.

4. In the Schematic SW pin is connected to GND : Is it inline with the design of unit or not..

5. After power up, we checked at 12 V DC input and 24V DC input, the expected 12V DC output is not present.

6. We cross checked the PCB assembly, components mounting and their values, all are as per the design guidelines.

7. We checked following voltages (with Vin = 12 V DC)

 EN(UVLO) = 2.194 V, SS(Soft-Start) = 4.086 V, COMP = 3.365 V.  The HO and LO signals are pulses with frequency around 230 kHz. The waveforms at PRI and SEC locations are not proper (Not as per the PMP9256 technical manual)

8. You are requested to extend technical support for resolving this issue..

  • 0
    TI__Intellectual 1235 points
    Hello Ch,

    From your notes it sounds like the controller is switching properly, probably at maximum duty cycle since the COMP voltage is high. The SW pin should be grounded, as HO must drive the secondary through the gate transformer.

    There is probably some issue with the power stage or secondary gate drive. As a test you can disconnect the secondary gate drive by opening R20 and shorting R30. This will allow the secondary rectifier Q2 to operate using its body diode.

    Please send all documentation and test results for my review. Make sure to include part numbers for the components used, and any relevant drawings or specifications.

    Regards,

    Bob Sheehan
    Texas Instruments
    robert.sheehan@ti.com
  • 0 in reply to Bob Sheehan
    Prodigy 240 points

    Dear Bob Sheehan,

    Thank you for the suggestion..

    We could able to localize problem with switching circuit, both Q1 and Q2 terminals are not soldered properly. We corrected this problem but still the output voltage is not as per the required.

    If VIN=9V then VOUT=0.9 V , If VIN=12V then VOUT=1.2V, if VIN=24V then VOUT=2.4V, if VIN=30V then VOUT=3.0V.

    The measured values of SS, UVLO and COMP are same as above. The Pulse at SEC terminal is with 10% duty cycle only and the PRI is just 180 degrees out of phase.

    We have used the same BOM as suggested in the design guide.

    We need still clarification on the placement of Rsb5, Rsb6, Csb3 and C24 components.

  • 0 in reply to Ch Ramakrishna
    TI__Intellectual 1235 points

    Hello Ch,

    I will need to see scope plots of the gate drive and switch waveforms in order to help you. Please take photos of the board and send with your scope plots to robert.sheehan@ti.com

    The  components Rsb5, Rsb6 and Csb3 were added by rework to the board. You can stack them on top of the parallel parts or cut the copper to install them as shown in the test report picture. C24 is not installed. The BOM has QTY 0 for DNP (do not populate) components.

    Regards,

    Bob Sheehan

  • 0 in reply to Bob Sheehan
    Prodigy 240 points

    Dear Bob Sheehan,

    We thank for your support..

    Finally we could bale to localize the problem and it is our assembly mistake. In place of 100K at R13 location, 100 Ohm resistor was placed.

    The output is around 11.87 V DC is coming.

    Thank you..

    Regards