BQ24650: Power reset feasibility

Ibrahim Qasim

Part Number: BQ24650

Hello,

I have designed my own charging circuit with the BQ24650 chip to accept a 20 Watt 7.4 V Solar panel and 4.2 V Lipo battery. This design works well until my battery runs out of charge when providing a load. The chip would terminate charge and would not start up again unless I physically move my solar panel away from the window or disconnect and reconnect the battery to my screw terminals. Why does this happen and can I use the chip's enable pin with a push button to momentarily resent the charge cycle without doing what was discussed earlier?

Here is the schematic for reference:

Thank you,

Ibrahim Qasim

over 4 years ago

0 Kedar Manishankar over 4 years ago

TI__Mastermind 24075 points

Hi Ibrahim,

Yes, toggling MPPSET to GND will reset and start a new charge profile. Most likely you are tripping the inbuilt 30 minute precharge timer (when battery is discharged) causing the charger to detect a fault. Only resetting so a new charge cycle begins (through POR which as you observed does the trick, or toggling MPPSET low) will allow you to continue charging.

0 Ibrahim Qasim over 4 years ago in reply to Kedar Manishankar

Intellectual 680 points

Hello Kedar,

Is there anyway to prevent the battery from being deeply discharged when loaded thus triggering the precharge timer?? I was thinking of implementing a battery protection IC which would cut the battery off at 3.4 V so that the BQ 24650 would not trigger the precharge timer and also prevent the battery from receiving solar charge.

Thanks

Ibrahim

0 Kedar Manishankar over 4 years ago in reply to Ibrahim Qasim

TI__Mastermind 24075 points

Hi Ibrahim,

Yes, you can use a battery protector IC, but you should make sure that the cutoff voltage is above the VLOWV voltage to prevent from entering precharge range.

0 Ibrahim Qasim over 4 years ago in reply to Kedar Manishankar

Intellectual 680 points

Kedar,

Thank you very much for your very useful feedback! Just on a side note, is VLOWV measured at the VFB pin?? if so my VFB is approximately 2.0V but the datasheet suggests its in a range between 1.54-1.56. Would adding an IC at charge protection between 2.3 to 2.5 V and release voltage between 2.9 to 3.0 V ensure that it wont enter the precharge range??

Thanks again!

0 Kedar Manishankar over 4 years ago in reply to Ibrahim Qasim

TI__Mastermind 24075 points

Hi Ibrahim,

Yes VLOW is measured at the VFB pin, as battery voltage is sensed by the charger IC form the midpoint of the resistor divider from battery to GND (midpoint tied to VFB). You can calculate what that voltage corresponds to by plugging in VLOWV value into the VFB equation. The specific voltage to have cutoff will correspond to your battery configuration and system requirements.

0 Ibrahim Qasim over 4 years ago in reply to Kedar Manishankar

Intellectual 680 points

Got it, Thanks!

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BQ24650: Power reset feasibility