Hi all!
Below you can find my schematic for using the TPS77001 as a battery charger.
Its input is a voltage supply of around 5V or less, which is not always present and which can supply a maximum current of around 25mA. The output of the regulator is adjusted at 3.7V and the battery is connected directly to its output. The Enable control input is driven by a microcontroller. As you can see, I haven't used any diode between the regulator and the battery, in order to avoid its voltage drop. However, it has been proved that this point is a little bit problematic. Although I keep the EN input to LOW, when the voltage supply is not present, I have noticed that the voltage at the input of the regulator is around 2.7V, when the battery voltage is around 3.3V Since there is no other voltage source present (as I said, the voltage supply which charges the battery is not active during this phase of the test), I guess that there is some leakage from the battery through the VOUT pin of the TPS77001 going out from the VIN pin.
Can you verify, please, that this is possible? I guess that there is no real disconnection of the load during the period when the regulator is not enabled, is that true? Is this the reason that I see this problem?
In that case, I guess I should use some kind of switch between the regulator and the battery, which will be activated only during charging. Another alternative I was thinking is using another LDO instead of TPS77001 that can provide real load disconnect during shutdown. Is there such a part? Ideally, I would prefer to be pin to pin compatible with TPS77001, but I guess this would be really difficult. Nevertheless, any substitution with this load-disconnect feature would make me happy as well!
Thank you very much in advance!
Nikos
