Other Parts Discussed in Thread: INA190, INA818, ADS1115, , LM2576
Hi TI Technical Support Team,
Recently, I have design and produced a PCB for battery charging and discharging. I am charging and discharging rechargable li-ion battery with small capacity (around 40mAh ). The circuit is designed to apply constant current, constant voltage charge and discharge modes. The charging or discharging currents are 10mA at max and battery voltage I test is 4.2V at max. When charging or discharging I am pulling the bat_activate pin of U21 IC to high and when test is done I am pulling bat_activate to low to disconnect the battery from the circuit. I am selecting the test modes (constant current or constant voltage) through U17. I am measuring battery voltage through INA818 (gain 1) and I am using INA190 to monitor discharge or charge current. TS5A3359 is used to make current ranging. Using truth table given in TS5A3359 I am adjusting gain for current measurement. The ADCc I use is 16 bit ADC (ADS1115). The PCB is 4 layer PCB, Top and bottom layers are for signal routing and mid layers are 5V and GND planes. No track is passing through mid layers, they are solid planes. 5V is generated using LM2576-5, 12V using LM2576-12 and -12V is generated using LM2576 in inverting mode. All voltage levels are as expected. I also have LED on the board connected to 5V to indicate power. There is not any pull up or pull down resistors on control pins of U17, U21 and U25.
When the power is on, the circuit works as expected, it charges or discharges battery connected to the battery socket. However, when I cut the power and there is battery connected to the battery socket, the 5V LED does not turn off, it continues to be on. When I pull the battery from the socket and nothing connected to the socket, the LED is off. When the power off and there is battery connected to the socket, I measured the 5V point on the PCB as something around 2V. I think somehow the battery voltage couples to my 5V and when the power is off it starts to power the 5V, and as LED is connected there, it powers it, LED becomes ON and the battery that I left connected starts to discharge over LED. I removed INA818 and shorted 3 and 6 pins of INA818 footprint on the pcb, but the result is not changed.
Could you please comment on this problem and possible solution to this problem? Is it related to my poor PCB design like making one of mid layer as 5V plane? I did not know if this is related to TS5A3359 or not, so if the question is asked in wrong place, I am sorry for it.
I would like to thank you in advance for the help,
-Ahmet