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TPS7A11: wrong output behavior

Roman Leduc
Prodigy 10 points
Part Number: TPS7A11

Hello all,

I am using the TPS7A1118 to provide1.8V with the following set up, to supply an ADC:

-Vin = 3.3V

-Vbias = 3.3V

-EN = 3.3V (all 3 pins are tied to 3.3V power plane)

-The NC pin is not connected, and GND pin tied to thermal pad to ground.

I can measure on Vout with multimeter 2.4V when supplying with 3.3V. with a range from 0 to 4V for Vin, Vout will vary from 0.12 to 2.58, and Vout will be 0 whenever Vin < 2.1V.

I checked for everything on pcb (shorts, some residual flux,...) nothing wrong... Is there something I am missing, with input pins range ?

I would be glad if you could enlighten me !

  • +1
    TI__Genius 12930 points

    Hello,

             This device requires at least 2.2uF capacitance between IN pin & GND (CIN) and between OUT pin & GND (COUT). It is also good design practice to have at least 100nF of capacitance between BIAS pin and GND (CBIAS). Could you verify if your schematic has these capacitors? Thanks!

    Regards,

    Srikanth 

  • +1 in reply to Srikanth Lolla Venkata
    Prodigy 10 points

    Hello Srikanth,

    Thank you for your help, in deed I included these biasing capacitors, but I found the answer to my problem that is a good lesson ... Definitely to use a multimeter for measuring such voltages is not a good option, and through oscilloscope I have steady 1.8V ! 

    I found a similar topic on your forum with someone having the same issue, and wrote that he used a multimeter...

    As a conclusion, more important thing than knowning if your design works, is knowning that your measurement also does !

    Best regards