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Original question:

PMP22343: PMP22343 design issue

PMP22343: Converter input going into CC protection under NO LOAD at output

Stefano Alfredo La Spina
Prodigy 240 points

Part Number: PMP22343

Following PMP22343 design I have built a board for 12V to +/-30V conversion. During testing when i am powering up the circuit through a Keysight bench lab power supply DC at 12V with a 1,5A max CC current limitation it is immediately going to CC limit without any load at the output. EN pin is tied to GND at boot, when TPS turns on it goes into CC mode.

I have read 's post regarding same problem she had but the post doesn't show any solution apparently.

Please help me where to investigate.

Here the schematic I have used, following slavishly the design rules at https://www.ti.com/tool/PMP22343

TIDM445-Schematic.PDF

Best regards

  • 0
    TI__Intellectual 1570 points

    Hi Stefano,

    Can I get a schematic for the board you built? Also if you have more information on how the design is connected that would be useful.

    Thanks,

    John

  • 0 in reply to John Dorosa
    Prodigy 240 points

    Hi John. Thank You for Yor reply. Here attached the schematic. The problem appears in the LAB during testing at NO LOAD; the input is attached to a 230V/12V switching Lab bench PSU. If I do not limit the input current during pulling the EN pin (H24), the  converter acts normally but this means a high spike inrush current. Limiting to 1.5A the converter puts the PSU in CC protection mode. What do You recommend? Increase the input capacitor?

    Best regards and thanks

    PSU_DUAL30V_RAIL_Rev.0.pdf

  • 0 in reply to Stefano Alfredo La Spina
    TI__Intellectual 1570 points

    Are you level-shifting the enable signal? If the EN_HCP_PSU signal is coming from a MCU referenced to GND it may not be reliable for start-up.

    For the inrush current, the soft-start feature is controlled internally. So it is either a problem with the output capacitance or overall system. Is there any other circuit in the system that runs of of the +/-40 V output at start-up? Is it possible to sequence those?

  • 0 in reply to John Dorosa
    Prodigy 240 points

    Thank You John for the valuable info about the EN_HCP_PSU. but the PSU starts with ENABLE connected to VIN 12V.

    No MCU has been in this phase connected to the pin

    What do You mean by output capacitance? the schema has been taken from TI's REFERENCE DESIGN GUIDEs, so I was supposing that it was correct.

    I repeat that there is NO LOAD connected. The problem is in the characterizing phase by testing the PSU on a LAB bench.

    Best regards

  • 0 in reply to Stefano Alfredo La Spina
    TI__Intellectual 1570 points

    Thank you for the additional information. It sounds like something may be damaged or placed incorrectly. Can you measure the input with an ohm-meter? There should be some impedance but from the sounds of it there could be an unexpected short.