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TPS61200: TPS6120x Constant Output Current Calculation

Vicente
Prodigy 70 points
Part Number: TPS61200
Other Parts Discussed in Thread: TPS61222, TPS61220, TPS61240

Hello, I'm using the TPS6120 which will be powered by a 3.7V LiPo battery and I want a constant (not adjustable!) output of 5V to power an ATmega32U4. In the datasheet, it establishes that the maximum output current for a Vout of 5V is 600mA and I don't want the uC to be fried. It says that the output current depends on the input to output voltage Down Conversion Mode ratio which I didn't understand very well, and I want to know how can I calculate for R1 and R2 for an output current of maximum 25mA with constant 5V.

In addition, if I want a constant output voltage, would R1 be 0 ohms? If this is true, how would I calculate the value of R2? 

 

  • 0
    TI__Mastermind 46905 points
    YOU can just select R1=1M and R2=110K to get 5V output.

    the load of the 5V is 25mA? if yes, you can select TPS61222, which is much easier to use. just follow the datasheet and EVM user guide for the schematic and layout
  • 0 in reply to Jasper Li
    Prodigy 70 points
    But if I want a constant output voltage, shouldn't R1=0 because FB needs to be connected directly to Vout ? Then, what would be the value for R2?
  • 0 in reply to Vicente
    Prodigy 70 points

    Oh, I see, in the datasheets it says R2 won't be used neither if I want a fixed output. But according the first graph if my LiPo voltages levels go from 2.4V up to 4.2V I would have 100mA-200mA (blue line) as maximum output current. 

    Then in the typical fixed output voltage supply application, it says that it can have a maximum output current of 60mA. 

    Does this mean that if my ATmega supports a maxmimum input current of 25mA I will be ok because the boost converter can deliver up to 60mA in any needed moment?

  • 0 in reply to Vicente
    TI__Mastermind 46905 points
    from lithium-ion battery input, the output current capability of TPS61220 is 60mA. so if the load current is lower than 60mA, you can select TPS61220. if the load current is higher, then i would suggest other device, like TPS61240