Other Parts Discussed in Thread: INA818,
Hi TI Technical Support Team,
I have designed discrete constant current charge discharge circuit. I am adjusting current between 1mA and 10mA using DAC (output voltage corresponding to current). My aim is as follows: I would like to set charge current between 1mA - 10mA by setting DAC output between 2.6V and 3.5V. And to adjust discharge current between 1mA and 10mA, I am setting DAC output between 2.4V and 1.5V.
When I am using 1k ohm resistor instead of battery to test circuit, the circuit works as expected. For example, my aim is to achieve 1mA charge current, then I am measuring 100mV across 100 ohm current sense resistor and 1V in the output of INA818. When I am setting -1mA current by setting DAC out to 2.4V, I am again measurinv -1V at the output of INA818 and -100mV across 100 ohm current sense resistor. But when using battery instead of resistor, I cannot achieve my target value. For example to achieve 1mA current value I am setting DAC out to 2.6V, but I am measuring 0.170mV across current sense resistor (or 2.670V at the inverting input of the opamp U1A). I also applied different set points using DAC (between 2.4V and 1.5V and also between 2.6V and 3.5V) and it worked as expected when using resistor to test the lopp instead of battery. But when I am connecting battery (3.6V rechargable Li-ion coin cell), the loop fails and opamps noninverting (DAC input U1A) and inverting (current feedback U1A) input do not become equal. I am guessing maybe the loop is not negative (but then why it works with 1k resistor value?)
Could you please help me to identify the reason why the circuit fails to work with battery and also if possible, suggest me some solutions.
Thank you in advance for your help.
Ahmet