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TPS1HC30-Q1: Switch enters fault mode on battery, fine on DC power supply

Alex Mills
Prodigy 10 points
Part Number: TPS1HC30-Q1

Tool/software:

Hey guys,

I have a custom PCB designed to run 6 of the TPS1HC30-Q1 switches that runs off of a 18V tool battery, a nominal voltage of 18-20V.

When connected to a desktop DC power supply set to 19.3V CV, the system works perfectly, drawing 0.2A as per the test load (two automotive LED position lamps).

When connected to the battery with the same voltage and the same test load, the system boots but as soon as EN is set high by the MCU, the FLT pin immediately goes low, with no output and no voltage on SNS.

I'm at a bit of a loss as to whats happening because once in maybe 20-25 connection attempts to the battery, it will work perfectly. 

The circuit is designed to match the datasheet for this chip with the exception of the ILIM pin floating and no TVS diode or Cvbb cap on battery input.

Any ideas? 

  • 0
    TI__Mastermind 34905 points

    Alex,

    Could you comment on what is on the load? Is it an actual load or an eLoad?

    We do not recommend to float ILIM as the internal current limit is considered a failsafe mode. Pretty much the only thing guaranteed with ILIM floating is that the device shuts off and protects itself before it is damaged (which is why we only give a typical value for the current limit).

    For pulling up DIAG_EN and LATCH, we recommend using a RPROT resistor and not connecting directly to 3.3V

    That being said, I don't think either of those two would actually describe what you are seeing. If it is an eLoad in constant current mode, it might cause some issues. If there is a DCDC converter somewhere and the inrush current is causing it to collapse, you could also potentially see an issue.

    Best Regards,
    Tim