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TPS62840: TPS62841DLCR debug

Vishak Narayanan
Prodigy 20 points
Part Number: TPS62840

Tool/software:

Hi

I use a TPS62841DLC in one of my designs to switch and output a 1.5V from 3.3V input. But for some reason, when I enable the regulator the output seems to be at ~2.6 - 3.3V ( and there seems to be a direct short between Vout and Vin pins when the regulator is enabled). I have verified my boards for any direct short between the pins (post soldering) and there seems to be none and the EN receives a 3.3V (same as that of the input Vin). I have tried to follow the webench designer and datasheet specifications as closely as possible,  but I not able to debug as to why this is happening.  I have attached the schematic and layout here. I would appreciate any help or suggestion.

I also have a TPS2841 eval board (with a DGR package), and the same settings provides a 1.5V in the eval board.  
TPS62841DLCR debug.pdf

  • 0
    TI__Mastermind 23030 points

    Hello Vishak,

    thanks for using E2E.

    The RSET value in your schematic is incorrect for the desired 1.5V output voltage. According to Table 1 in the datasheet RSET of 102kΩ should be selected for VOUT of 1.5V.

    Could you please also verify if you really used a TPS62841DLC and not by mistake a TPS62840DLC or TPS62849DLC? On these devices the same RSET is resulting in a different VOUT.

    Let me know if you have any questions.

    Best regards,

    Andreas.

  • 0 in reply to Andreas Mueller
    Prodigy 20 points

    Andreas,

    Sorry the value of Rset was a typo in the schematic. I am indeed using a 102K resistor and TPS62841DLC. I have verified the package marking with the datasheet to verify its a TPS62841DLC.

  • 0
    TI__Mastermind 23030 points

    Hello Vishak,

    thanks for the clarification.

    Could you please check your startup timing? The TPS62841 is sensing the RSET value during startup. A slow power or EN signal ramp up could cause wrong sensing.

    Also the external parasitic capacitance at VSET pin should be less than 100 pF for correct RSET sensing.

    Please let me know your feedback.

    Bets regards,

    Andreas.