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TPS61221: Problem, sometimes the device doesn't start and the output voltage is ~1.5V

Periklis Karavaggelis
Prodigy 20 points
Part Number: TPS61221

Hi everyone,

I have a (typical) circuit with TPS61221, 3V coin cell battery as input and a slide switch in series as you can see below in the schematic. The load current is 1~20mA in normal operation. I have noticed that sometimes when I turn the switch ON, the TPS61221 doesn't start and the output voltage is approximately 1.5V and the battery consumption is 200mA. I read some similar posts in forum so I added more input capacitors, but the problem remains. Why is this happening and how can be solved? Thank you in advance. I look forward to your response.

  • 0
    TI__Mastermind 46905 points
    The reason should be that the source is weak and output capacitor is very large. could you try to set the EN to high logic after connecting the battery?
  • 0 in reply to Jasper Li
    Prodigy 20 points

    I will try it and tell you the results. Moreover, I will try to change the output capacitor to 47uF, if that helps.

    EDIT:

    I tried the solution that you suggested and, as you can see below in the schematic, I added a simple RC circuit with a pnp-BJT to set the EN pin of TPS61221 to high logic after a period of time depending on the RC (in this case after about a second), also I changed the output capacitor. So far, this circuit seems to work. But I'm just curious, how much delay time do you think is needed? (more or less). In addition, if you have any other suggestions, or if you think this one is not suitable, please let me know. Once again thank you very much for your help.