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TPS61252: Output voltage unstable

Mert Aysoy
Prodigy 100 points
Part Number: TPS61252

I would like to use TPS61252 on my project but I run into some problems. I want 5v output but output voltage is unstable. I used exactly the same schematic in datasheet. I tried different IC and board but no luck.

Inductor: TDK VLS3015ET-1R0N, 1uH, 58 mOhm, 2A

Input cap: Murata GRM219R60J106KE19D, 10 uF, 6.3V, X5R

Output cap: Samsung CL21A226MQQNNNE, 22uF, 6.3V, X5R

Feedback resistors: 768k, 243k

Input voltage: 4V

Output voltage: Fluctuates between 4v and 6.3v

Feedback pin: Fluctuates between 1.24v and 1.28v

Load current: 100mA

Please help me. Thank you.

  • 0
    TI__Mastermind 46905 points
    1. try several boards to check if the behavior is the same.
    2. remove the C1 and check again
    3. measure the VIN and VOUT waveform when the problem happen. (please note that attach probe in FB could cause problem if the impedance of the probe is not large eough)
  • 0 in reply to Jasper Li
    Prodigy 100 points

    1) I tried two different board, one protoboard and two different IC. Behavior is the same.

    2) Removing C1 made no difference.

    3)

  • 0 in reply to Mert Aysoy
    Prodigy 100 points
    I changed the inductor value to 1.5uH.

    At first output voltage was 5.02v. Within 20 minutes output slowly rise to 5.05v. Than suddenly output dropped to 4.67v. After 10 seconds output come back to 5.01v. But after 15 minutes output dropped to 4.0v, which is input voltage. I waited 5 min but output never rise to 5v.
    I disconnect and reconnected the power (Vin), after that output voltage is 1.6v
  • 0 in reply to Mert Aysoy
    TI__Mastermind 46905 points
    the behavior seem to be caused by the solder problem. i found similar strange behavior in other device because of using bad "solder paste". no sure if you had clean the board after finishing assemble the components.

    i would also suggest you apply an EVM. do the same experiment in the EVM. The swap the IC of the EVM and your system board to check if the problem is caused by the IC or external components.

    about the waveform, please set it to DC coupling.