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bq25570EVM-206 Eval. Board, Change in Behavior

Ansync
Prodigy 10 points
Other Parts Discussed in Thread: BQ25570EVM-206

Hello,

I'm using the bq25570EVM-206 evaluation board with a kinetic energy harvester to power a circuit. It seems that the behavior of the evaluation board changes after about four hours of use.

In particular, the setup follows:

  • 1 kohm resistor at VOUT
  • 220 uF at VBAT
  • Kinetic energy harvester leads at VIN

Initially, as the kinetic energy harvester is excited, the voltage across the capacitor at VBAT rises until it suddenly drops. This coincides with a spike in voltage at the VOUT pins.

After about fours of use of the board, as the kinetic energy harvester is excited, the voltage across the capacitor at VBAT rises until it stops at about 1.2 V. No signal is ever received at VOUT.

I'm using an input voltage within the range specified in the datasheet and have tried swapping out the IC of the board with a new one. The behavior remains the same.

What is the reason for this change in behavior? What can I do to ensure that the board continues to work as it initially does? Any help is appreciated.

Thank you.

  • 0
    TI__Mastermind 20570 points

    First of all, the the buck regulator is not enabled during cold start (VSTOR voltage lower than 1.8V). Thus you do not see any signal at VOUT when VBAT 1.2V.
    From your discription, it also indicates that your source does not provide enough power to charge up the 200uF cap above 1.2V. Try lower the capacitor to see if the voltage rises up.
    Since you are using capacitor at VBAT which can be discharged to 0V, the once you connect a valid input source, the IC will enter cold start. The input voltage needs to be higher than 330mV. To get out of the coldstart, your input source needs to provide at least 15uW (typ) or higher. So even if the input voltage is within the range, the current might not be enought to charge up 220 uF cap.
    One way to try verify if the board function correctly is use a DC power supply with a resistor in series. Adjust the input voltage and current limit until it works for your particular setting. Then you will find out what the minimum power needed for your setting.

    Vout is set to 1.8V by default setting on the EVM. 1Kohm results in a 1.8mA load current. When the Buck converter is enabled, it seems like it quick discharges the 220uF cap at thetime buck turns on.