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BQ24072 - EN1, EN2 floating?

Geoff Salter
Prodigy 30 points
Other Parts Discussed in Thread: BQ24072

Hello


I am using the BQ24072 charger with a lithium polymer battery. The EN1, EN2 and /CE pins are connected directly to the GPIO of a MSP430 (no pull-down resistors). The MSP430 and the rest of the circuit is powered through a 3.3V buck-boost, with an UVLO of 2.7V. (I.E. the load circuit switches off if the battery reaches the minimum voltage of 2.7V).

I have experienced an intermittent problem when the battery is fully discharged (2.7V) and the circuit is switched off. If I plug in the charger (USB), I am expecting the output of the BQ24072 to go to 3.4V and the load to switch back on. This doesn't always happen. I end up having to unplug the battery and reconnect the battery for the circuit to reset.


Am I correct in thinking that the EN1, EN2 and /CE lines are effectively floating when I have a flat battery, as the MSP430 is unpowered? Do I require pull down resistors on these three signals to give them an initial defined state when the load circuit is switched off? 


Thank you for your assistance.

Regards,
Geoff

  • 0
    TI__Mastermind 20570 points
    Yes, when a valid input is plugged in, the voltage on OUT pin should be 3.4V if battery voltage is less than 3.2V. EN1, EN2 and /CE are internally pulled down with approximately 285 kOhm. As state in the datasheet, to ensure proper operation, do not leave EN1, EN2 or /CE unconnected.