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TPS61322: TPS61322

alex alex
Prodigy 40 points
Part Number: TPS61322 
Hello, have a question about TPS61322. I need to get 3.6V (100mA max load). I have two solutions:
1) TPS613226A Use 3.3V input voltage (supplying the CPU) formed by LDO connected to Li-ion battery
2) Use a direct connection to the battery and get 5V output with the TPS613222A. And then use LDO at 3.6V
Which of these is the best solution and up to what load current can I use the TPS613226A without an external diode?
  • +1
    TI__Genius 9046 points

    Hi Alex,

    May I confirm if your power block diagram looks like below?

    Solution 1)

    Solution 2)

    From systematical view, solution 1 has better efficiency than solution 2. The reason is large conversion ratio between li-ion battery and TPS613222A's output poses lower efficiency, and for LDO its efficiency equals to 1-Vdo/Vin so when dropout is smaller the efficiency is higher. For solution 1 you can use TPS613226A for better light load efficiency.

    You can use below equation to calculate maximum output current of TPS61322 given a specified Vin, Vout and efficiency:

    Iout,max=Vin*efficiency*(Ilim,min-100mA)/Vout

    Ilim.min can be read from below

    For example, 3.3Vin to 3.6Vout, TPS63226A, it can output maximum output current is around 560mA;

    3.7Vin to 5Vout, TPS613222A, it can output maximum output current to 690mA;

    Another way is to use buck-boost converter. Let me check if it is feasible for your case.

    -Wenhao

  • 0 in reply to Wenhao Wu
    TI__Genius 9046 points

    Hi Alex,

    TPS63900 can be used for your case and replace LDO+TPS61322, solution size will be smaller but cost may be a concern.

    Another point is output noise, if your load really cares about power supply noise, then LDO is recommended to be used close to load side. Please specify what spec you cares the most. 

    -Wenhao

  • 0 in reply to Wenhao Wu
    Prodigy 40 points

    Hello. Thanks for the answer. Yes, both diagrams are correct. 3.6V is needed only for the subsequent charging of supercapacitor / battery, so I think the power noise is not critical here. That is, I understood correctly that in the case of a conversion from 3.3V to 3.6V, I can get a maximum output current of about 560mA without using an external diode? What will be the input current draw (on 3.3V side) if the load (on 3.6V side) is not connected to the TPS63226A?

  • 0 in reply to Wenhao Wu
    Prodigy 40 points 
    I thought to use a buck-boost converter, but their price is much higher and they are not in stock.
  • 0 in reply to alex alex
    TI__Genius 9046 points

    Hi Alex,

    You can use efficiency charts in datasheet to calculate input current draw. Thanks!

    -Wenhao