Hello !
I'm designing 2 cell (8.4V) Li-Ion battery charger with bq2057W.
The charger is integral part from final battery module and is important very low current consumption
after charging termination and VCC removal.
The design with transistor chosen.
For VCC used step up converter (lmr64010) from 5V to 9V without diode like in AN with mosfet.
By data sheet -
Automatic Low-Power Sleep Mode When VCC Is Removed.
This doesn’t match absolute maximum ratings:
Input voltage, SNS, BAT, TS, COMP (all with respect to GND) −0.3 V to VCC+0.3 V
My questions:
Do I need diode between Step up converter and VCC like in AN with mosfet?
Is this design safe and optimum for low power consumption from battery.
What is approximated or max current consumption from battery after VCC removal.
Thanks!
If a p-ch is used as the pass FET then there is a body diode from the battery to the input and there can be much current if there is a load and a blocking diode may be needed.
If a pnp is uses as the pass transistor, there is a small leakage current fromt the emitter to base through the CC pin through an internal diode to the input so there would be a small current if there is a load on the input, maybe a couple of milliamps. One may need a diode in this case.