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BQ24073 output oscillating without battery and at low Vin?

Other Parts Discussed in Thread: BQ24073, TPS63030, TPS62560

What is the expected behavior of bq24073 if the battery is absent and the input supply is around 4.4-4.5V?

 I notice oscillation on the output while sweeping input from 3V to 6V and hitting that range. It then goes away as voltage increases. It also goes away if battery is connected. Is that expected or am I missing something here? Thanks!

  • If the battery is absent, the output will track the input voltage with a voltage drop of IOUT*Ron (~300mohm). There will be battery detection routine happening at BAT pin, which is a square wave between 0 to 4.2V but it should not affect the OUT pin signal.

    I used an EVM and forced the same condition but didn't see the oscillation at output, can you send me the waveform of the OUT pin, VIN pin and BAT pin?

    Thanks,
    Wenjia
  • At 4.5V Vin PGood goes off, output oscillates at 2-3KHz around 2V . if I disable downstream power converters feeding off the part (I have a TPS63030 buck-boost followed by TPS62560 buck with maybe 200mA load) things calm down and I see Pgood signal once again.
    Can't seem to attach a scope plot here- I'll PM it directly
  • This device has a input DPM threshold (Vin_dpm on the datasheet) below which the input current will reduce to zero to prevent the input voltage from collapsing. When the input voltage is close to 4.5V, the current limit will reduce and the input power may not be enough to support the output power, so you saw the up and down of the output signal. When the battery is connected, the output can be supplied from the battery so the signal became stable again.

    Thank,
    Wenjia
  • Thank you very much - that clears it up!