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BQ24600: Powergood/Charging not activating when supply less than 2V above VPack

Sergei Lupashin
Prodigy 60 points
Part Number: BQ24600

Hi there,

We are using a BQ24600 to charge a 3s LiPO battery.

According to the datasheet, PowerGood is active (and charging becomes possible) if the voltage difference (VCC-SRN) is at least 100mV + 500mV (SLEEP threshold) + diode Vfwd (in our case, measured 200-400mV, matches datasheet) = ~800-1000mV

Unfortunately, experimental results show that VCC has to reach approx. VPACK+2V before PowerGood becomes valid and charging activates. At that point VCC can drop down approx 500-700mV before charging is cut off.

We are following the application circuit almost exactly -- but noticed that all the example designs use VCC that is significantly higher than VPack. Any hints for making this work better with a VCC that's not as high?

Thanks in advance!

-sergei

  • 0
    TI__Mastermind 20570 points
    What voltage is VCC at? and what is the battery voltage? Can you please show the scope capture?
    Also have you tested on the EVM?
  • 0 in reply to Jing Zou
    Prodigy 60 points
    Thanks for the reply!

    VCC is 13.2 as supplied by benchtop power supply. Battery is a 3s 1Ah lipo that is being charged via the BQ or discharged via electronic load. We load the battery to discharge, then occasionally plug in power supply for ~5s, which powers the load via switchover circuit and charges the battery. When battery discharges to 11.1V charging starts. Charging stops at 12V.

    Any hints as to what exactly might be helpful to scope?

    No, have not tested on EVM although implementation follows reference design exactly and hard to picture layout being an issue here.
  • 0 in reply to Sergei Lupashin
    TI__Mastermind 20570 points
    Sorry for the delay in response. Is the issue resolved? If not, please send the scope capture on VCC, SRN, SRP, VFB.