Electronic – TP4056 battery output (charging voltage) is not constant

battery-charginglipotp4056

I tried to design a charging circuit based on the TP4056 li-po chip. At a usb voltage of 5V, the battery charging output (Pin 5 of TP4056) 4.3V. This seems acceptable, but there seems to be no regulation in my circuit as the battery voltage will vary with the input voltage

VCC-Vbatt
4.50--3.87
4.75--4.12
5.00--4.34
5.25--4.61
5.50--4.82

Can anyone suggest what the problem is? I'm too reluctant to plug in my li-pos until I get safe readings from a multimeter. Schematic included below
enter image description here

IBATT connector is shorted for voltage tests.

I do not want to overcharge my batteries with a voltage too high. The TP40456 dosent seem to be doing its job properly.

Best Answer

The TP4065 could be detecting there is no battery, or a battery that is out-of-spec for normal charging, and do as it sees fit.

It could also be going into CC-charging mode, and then it's a current source and not regulating voltage. Its behaviour in the absence of a battery may well be described in its datasheet, I haven't checked.

Anyway: it will be hard to test properly without a battery connected. Pros use a Battery Simulator; when in doubt, I just take the whole rig outside, use a battery, and stand well back; not as safe, but much cheaper.

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