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TPS61200 start-up with single AA cell

Shlomi Yehezkia
Mastermind 6150 points
Other Parts Discussed in Thread: TPS61200

Hi,

We design out board using TI part number TPS61200 dc to dc. We have two input supplied one with one AA battery and the second using  two AA batteries connected with OR diode.  (see attach schematics)

When using the two AA battery input all working fine.

When we supply the board from  one AA battery (net name 1V5_BATT on the attach schematics)  we face turn on problems.

Our load is 2.7V 0.25Amp.

We found out that the dc to dc can't drive our load also when using TI demo board.

We also tried to connect the load direct to the dc to dc without the FET switching option.

We find that the current from  battery rise to peak of 0.8Amp maybe due to low efficiency , our load doesn’t reach that current peak.

Please advise TI recommendations to solve that problem.

Thanks,

Shlomi

  • 0
    TI__Mastermind 36110 points

    Can you provide your schematic? It did not appear to be attached.  Do you see the problem with a resistive load, or only with your system load?  What is your system load, and can you provide a V-I curve for it at startup?

     

    Also, it is very helpful to add more description to the subjec line to give a general idea of the post contents.  "TPS61200 startup problem" would be a good title for this forum post.

  • 0
    TI__Guru**** 150950 points

    I'm sorry, but your schematics were not attached to the post.  Please reattch them.

    What do you mean by "the dc to dc can't drive our load"?  What is the behavior you are seeing?  Can you attach a picture of Vin and Vout on a scope?

    0.8A is about right for the steady state input current at your load.  2.7V * 0.25A = 0.675W of output power.  At 70% efficiency, this is 0.964W of input power.  At 1.2V in, this is 0.8A.

    0.8A is a lot of current out of a AA battery.  It may be too much, when the internal impedance of the cell is taken into account.  Please confirm with the battery manufacturer or look at the battery datasheet and see if it can deliver 0.8A.

    One thing to try would be to supply Vin with a 1.2V lab power supply.  If the TPS61200 works fine, then it is your battery that is causing issues.

  • 0 in reply to Matthew Day
    Mastermind 6150 points

    7853.NL-93G.pdf

    Hi Michael,

    I will provide you the info soon.

    Attached the schematic.

    Best regards

    Shlomi

     

  • 0 in reply to Chris Glaser
    Mastermind 6150 points

    0676.NL-93G.pdf,

    Hi Chris,

    I will provide you the info soon.

    Attached the schematic.

    Best regards

    Shlomi

  • 0 in reply to Shlomi Yehezkia
    TI__Guru**** 150950 points

    Thank you for providing your schematic.  It looks ok, but 2 things to try:

    Add more ceramic input capacitance.  Say a 22uF across C8.  You will need more to overcome the impedance of the battery and to meet the minimum of 4.7uF of ceramic recommended in the datasheet.

    Retest with just the single battery but short out the diode, D3.  You are dropping about 0.3V across that diode at 0.8A, so your battery voltage would then be only 0.9V at the IC input.  At this Vin, you are much closer to reaching the maximum power capability of the IC.