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Original question:

TPS922052: Is it possible to prevent sleep mode without external trigger pulses?

TPS922052: Start-up issue - Inductor current no present at first PWM pulse

Philipp D
Prodigy 40 points
Part Number: TPS922052


Tool/software:

Hi,

we are facing an issue with TPS922052 during start-up. The inductor current needs several pulses on PWM pin to settle at the set 1A.

To avoid soft start a 6us pulse is sent to the PWM pin during start-up. To avoid sleep mode a 200ns pulse is sent every 50ms.

This setting was working in an older prototype but with a new one (layout changes only, same schematics) we are seeing the issue. It looks like the driver is running in any limit because the SW pin is immediately release when pulled down. 

Yellow: Switch node during first PWM pulse.

 Please check and let me know what might be the issue.

Thanks,

Philipp

  • 0
    Prodigy 40 points

    I have captures more images. The PWM signal is high for 100us. Duty-cycle not defined as I am controlling manually.

    Input 48V

    Output 10x white LEDs ~30V

    Current: 1A

    Blue: PWM Input:

    Red: LED current

    Green: Switch node

    1. Trigger - LED driver does not start switching.

    5. Trigger - Seeing a transition but no proper rectangle signal

    20. Trigger - Current rises to 1A

  • 0
    TI__Mastermind 23310 points

    Hi Philipp,

    Philipp D said:

    we are facing an issue with TPS922052 during start-up. The inductor current needs several pulses on PWM pin to settle at the set 1A.

    To avoid soft start a 6us pulse is sent to the PWM pin during start-up. To avoid sleep mode a 200ns pulse is sent every 50ms.

    If this only happens during the first several EN/PWM pulses after the device have been enabled, then I would say this behavior is expected since the COMP voltage have not yet been built up and the device needs some time to charge up the COMP voltage and enters into CCM from DCM.

    Philipp D said:
    This setting was working in an older prototype but with a new one (layout changes only, same schematics) we are seeing the issue.

    Could you have a double check with the older prototype? Is the only change the layout? Is there any other change like schematic components, input/output conditions, etc.?

    Best Regards,

    Steven