# TP4056 battery output (charging voltage) is not constant

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

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.

• What battery are you using? How much voltage does it put out by itself (not connected to the charger)? – Bruce Abbott Sep 5 '20 at 6:14
• haven't checked the TP4056 datasheet, but these 0.7 V between in- and output might simply be the minimum drop. How are you measuring the voltage if you're not attaching a battery? Obviously, the free-running voltage is not what you'll see when you attach anything that actually loads the charger's output. – Marcus Müller Sep 5 '20 at 7:31
• unshort ibatt and connet an ammeter there, observe current during the tests. – Jasen Sep 5 '20 at 9:02
• Why should it be 4.2 V without load? – Marcus Müller Sep 6 '20 at 16:58
• You said "the battery outputs 4.3V" but you didn't connect the battery. Please edit your question to correct this incorrect information. – Bruce Abbott Sep 6 '20 at 21:32