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TPS7A90: No proper output voltage

Part Number: TPS7A90

Dear Teams,

I am helping my customer test the LDO TPS7A9001 with following schematic diagram. What I found the output voltage is only 0.85V and Vfb is only 0.2V. Do you think the chip is already broken? Or do you have any other suggestions?

Thanks!

Dylan

  • Hey Dylan,

    each unit is tested before shipping out so it should have arrived in working condition. Can you re-upload your schematic so we can evaluate it, it didn't post correctly. 

  • Hi Renterghem,

    I have re-uploaded my schematic diagram here. 

    Thanks!

    Dylan

  • Hey Dylan,

    I don't notice any concerns with this portion of the schematic but there are two things I would check:

    1. Is the device going into thermal shutdown? 6V to 3.3V at 500ma (assuming you are using it at full load) would be 1.35W which the device can support depending on the ambient temp and the PCB layout. Assuming a JEDEC layout the junction would heat up 77C above the ambient temperature. 
      1. does a scope show the output at a DC 0.85V? If it is thermal shutdown then the output will look more like a square wave turning on and off. 
    2. Verify that there aren't situations which exceed Abs Max (Vin>7V or Vout>Vin+0.3V would be the most likely)
      1. Use a scope to measure, Vin, Vout, and Iout (if possible) during startup, shutdown, load transients, or any fault scenarios. 

    I hope this helps. 

  • Hi Renterghem,

    Thanks a lot for your help! I found the root cause of this one. The reason is because the later stage on C2K has been short to GND, which caused the output capacitor short the 3.3V to GND direcly.

    Thansk!

    Dylan