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TPS61221: Maximum Output Current Issue

Part Number: TPS61221
Other Parts Discussed in Thread: TPS61220, TPS61220EVM-319


             I'm trying to incorporated a TPS61221 boost regulator with a fixed 3.3 V output into an embedded design to keep the supply voltage above 3 V as the battery drains. My design turns on and off. But, when it is on it draws a lot of current: 75 mA. I'm having trouble maintaining the 3.3 V output at the 75 mA of current. I've wired the device per the circuit diagram in the datasheet using 10 uF capacitors for C1 and C2 and a 4.7 uH inductor. When I connect the TPS61221 to a power supply and do not connect it to a load it's output voltage is 3.3 V, but when loaded with my circuit it can only sources about 50 mA and the output voltage drops to 2.8 V or so. Looking at Figure 1 in the datasheet I think that the output current should be in the 150-200 mA range for the range of input voltages that I plan on using: 2.2 - 3.7 V. I'm clearly missing something, but I can't figure out exactly what. Does anyone have any suggestions? Thanks!

  • could you share your schematic and layout, the issue you described is normally caused by the layout?
  • Hi,

             Thanks for your response. I've attached a file with a sketch of the circuit schematic that I'm using. Unfortunately, I don't have a great way of sharing my layout. I'm actually doing some prototyping with this part so I don't have a custom layout. I have it soldered to an SC-70 to 6-DIP adapter and then I've tried implementing the circuit both on a piece of breadboard and also soldered to a piece of protoboard. Either way I encountered the same issue with the output voltage dropping when the circuit is loaded. It sounds like the layout (or the fact that I don't have the correct one) may be causing issues. Is there anything else that I could try? I noticed that there is a Eval Board for the TPS61220, which has an output voltage of 3.3 V. Would it just be better if I tried using this? Thanks!TP61221 Schematic Sketch.pdf

  • you can apply the TPS61220EVM. change the IC to TPS61221 and also the feedback resistor. this is easier to evaluate the IC if you don't want to build real PCB.
  • Hello Luke,
    You need to Remove SC-70 6-DIP adapter because if you are using this means you places C1 and L 4.7uH inductor so far from the TPS6221 Booster IC so , if you are placing C1, C2 and inductor L1 so far from booster then voltgae drop is possible after apply load.
    You have Two solutions Luke
    1. You can hang C1, C2, L1 very close to U1 TPS61221 through the wires and test with the same SC-70 6-DIP after that voltage drop problem is solve may be oultput will not reach 150ma.
    2. You can design own PCB for evalution or Purchase TPS61220EVM-319 then change only U1 with TPS61221 and feedback Resistors also
    (R1-1M Ohm, R2- 175 to 200K Ohm) You will get approx 3.3v to 3.5v and 100ma current.