I have a circuit with a single AD7820A cell balance IC which we are prototyping for an automated battery management system for 6S Li-Ion batteries. We have it setup as shown in the datasheet reference, with the upper connection pins (for daisy chain) tied to VDD. ALERThi and SDIhi are tied to VDD via 1K resistors as mentioned in the datasheet, and all was going well until suddenly the ALERThi and SDIhi pins started sinking current. With an 18V supply they are sinking 10 and 15mA respectively. I can't seem to see a reason why, no changes were being made when the problem occurred - a read all operation was being carried out every 5 seconds at the time, with no cells connected to the board. Any assistance would be greatly appreciated, please see attached schematic for reference.
Fixed: found that the ICs were being damaged by a transient voltage spike when connecting the battery. Voltage was swinging up to 46V for a few uS, switching voltage damped by adding a TVS diode and some series resistance on the VDD side of the circuit. Voltage now ramps up and does not overshoot, when powered down the IC draws very little current.