Hi,
We are using BQ2057W Battery Management IC to charge 7.4v Dual Cell LI-ion battery. Two LEDs are connected to STAT pin for battery charging and charging completed indication.
In the attached circuit, while battery is getting charged, ORANGE LED (D6) gets ON. It continues to glow until Battery gets fully charged. Once battery gets charged ORANGE LED (D6) goes off and RED LED (D5) gets ON.
The problem is occurring when board gets power only from battery (Charger disconnected).
In this condition both D6 and D5 are partially ON, irrespective of whether battery is fully charged or partially charged. As per the datasheet, the STAT pin should be tri-stated / Hi Impedance. Hence, both LEDs should be OFF as D5 should not be driven by +9V (Charger disconnected) and D6 should not be driven be STAT pin.
But, when charger is not connected we observed VBAT - 1V at +9V Net. That is, if battery has a voltage of 8V, 7V is measured at +9V net.
This in turn drives LEDs D5 & D6 and partially illuminates it.
Can some one help us in understanding
1. Why VBAT - 1V is appearing in VCC (9V net)? How to avoid it? Aim is to have RED LED on when "charger is connected and charging is completed", Orange LED ON when "Charger is connected and battery is charging", both LEDs off charger is not connected.
2. As per the BQ2057W datasheet Pg No 10, Fig 4, a 1K is connected in parallel to orange LED. Please explain its significance. Will RED LED not be ON continuously during hi-impedance of STAT Pin ?
Regards,
Murugavel.SSCHEMATIC1 PAGE1.pdf
