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TPS798-Q1: output voltage error

Big Bill
Expert 1980 points

Part Number: TPS798-Q1

Dear  All:

   I  used the TPS79801 to output voltage 4.5V， but sometimes the  output voltage is only 1.5V，the  R138 is damaged, it seems  like short circuit. i change the new part ， it recover nto normal， what cause the result？ I measure the Vin & Vout pin , they to GND is normal.  Thanks for your help.

  

  • 0
    TI__Genius 10490 points
    Hi Bill,

    You may need to change the power rating for R138 if it is getting damaged in your application. The current limit for the TPS798-Q1 is a maximum of 200 mA. As such, R138 needs to be rated to dissipate P = I^2 * R = 0.2^2 * 10 = 0.4 W

    Another thing to note in your schematic is the number of components in series between VBAT and VDD. These can cause the output to drop out of regulation at lower input voltages. There is a combined voltage drop across D45, D6, and D44. R138 will also have a voltage drop of Vd,max = Io,max * R138 = 50 mA * 10 ohms = 0.5 V. The drops across these components all increase the minimum input voltage required for the TPS798-Q1 to regulate the 4.5 V output.

    What is your minimum input voltage for this application?

    Thanks,
    Gerard
  • 0
    TI__Genius 10490 points
    Hi Bill,

    Since it has been a couple weeks without a reply, I assume this thread is resolved. If not, you can respond at any time.

    Thanks,
    Gerard