A while ago it was suggested in this newsgroup that a Linear Technology LTC4150 Coulomb counter could be used with a 12V lead-acid battery by raising the GND pin so as to keep the IC's supply voltage under its maximum 8.5V. My first thought was simply to use a 7.5V voltage regulator connected to the GND pin of the LTC4150, however I'm worried that when the battery is connected that the 7.5V will take a small but finite time to rise, during which time the LTC4150 would see the full 12V of the battery. Any comments on this? Am I worrying about nothing?
Something as simple as a zener diode in place of the 7.5V supply would solve this, but as the LTC4150 typically uses around 115uA at 8.5V, I'm not sure if the zener would regulate properly with such a low current.
A voltage regulator that regulated from the 12V down would be nice, so that the voltage was equal to the battery voltage when the battery was connected and then settled to, say, 7.5V below the battery positive terminal and stayed constant as the battery discharged. But I just can't get my head round how to do this with simple circuitry. I can't help feeling theres's an easy adaptation of an existing regulator possibly. Must be low power due to battery operation. 7.5V power supply is based on an LP2951. Any ideas?