We have been useing the BQ24702 for five years with one irritating issue which is now becoming intolerable with a small design change. The recent change have been to 'steal' about 10 mA of current constantly and directly from the battery ( Vbatt). Doing this causes the 24702 to never quite stop the PWM signal from trying to delivery charge current, once the battery charge has started, even though the battery reaches full and/or is removed. SInce we use the PWM signal to also light an LED to indicate chagring is in process, we always now have 'charge' happening.
Details: Input rail is 19V and AC is detected properly. The BATP is set to cut charge at 16.8V, and there is 16.8V on the Battery ( Vbatt) line even with the 10mA load (with a full battery or no battery). But the PWM keeps driving. At power up, with no battery or a full battery, the system is stable with no PWM ( high)and so no LED indicating 'charge'. Once PWM starts running to delivery charge current, then the PWM never stops, even if the battery reaches full or is removed. "Reseting" the charge by momentrily disableing charge ( ENABLE = LOW) will get the PWM to stop and so the charge indicator LED goes off. This condition again ( as during power up) remains stable ( no PWM ) until charge current is demanded by connection to a undercharged battery, starting the PWM. But again , pulling the battery or letting it reach full, will not stop the PWM from running.
Any ideas????
Roger
