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TPS61220 enable line

Other Parts Discussed in Thread: TPS61220

I have an very low power application powered from a solar cell buffering energy in an supercap for work during night time. The average current of my device is about 150 µA at 3V. Unfortunately the TPS start up current is too high to start while the capacitor is charging at low light conditions, so at about 0.8 - 0.9 V of capacitor voltage the start up attempts just use up the power coming in even if the solar cell current is well above the current requirements once the TPS started successfully.

As a result I decided to use one pin of my MSP430 to enable the TPS once the MSP430 came out of brown out reset. This needs about 1.9 V of input voltage to the TPS, output voltage is somewhat lower and provided by the clamping diode during this time. While the MSP430 is still in reset (and the outputs in high impedance state) I have to ensure the TPS is disabled, so I need a pull down resistor on the TPS enable input. Once the MSP430 is started the TPS is enabled by setting the output H, but the pull down resistor will add extra current flow all the time the TPS is ON.

From IEN<0.1 µA at VIN<1.5V you can calculate a maximum resistor of 15 MOhms for the pull down resistor.

At the moment I'm using an 1M Ohm resistor to GND in parallel to 10 nF capacitor (to prevent noise starting the TPS). This looks like working well but adds 3 µA of extra current to my application. This is not optimal but can be accepted if I can ensure the TPS will not start up by noise.

I did not find any recommended circuit fitting my need in the datasheet.

Best regards,

Roland

PS: A rough estimate of the efficiency shows about 80% which I find great under this low load condition.

  • Is there a question here or are you just posting a comment?
  • Yes, I would like to see an recommended circuit as my current approach is more or less try and error (hope the TPS will not start up by noise). Incrasing the pull down resistor would be fine, but I'm not sure it will work reliable.
    Roland
  • Roland

    i didn't see problem in your circuit. and i think maybe you can used higher pull down resistor. because when the TPS61220 is not working, the other IC device in the system don't work either. it seem there is not noise to enable the TPS61220 mistakenly, giving you have a 10nF capacitor in parallel with the EN pin. you can measure the EN pin voltage during you debug the circuit to check if a voltage couple to this pin.

    i would also suggest you should make sure 10nF capacitor in this pin is not a problem for the MCU when the PIN is pulled low.