Li-Ion Battery charger LED problem

[Majek Ondrovic]

I'm having an issue with a circuit I'm testing that uses a simple Li-ion charger IC. I'm using a Chinese brand TP4054 IC from LCSC that I assume is a clone of the LTC4054. I'm only using the knock-off because it's a Basic part for JLCPCB assembly service. See my crude schematic attached

The issue is with my charge status LED circuit. With the battery attached, everything works fine, however when there's no battery and VCC is supplied, the LED toggles on and off rapidly at a dim level, and the Charge status pin reads about 2.6v. Unfortunately I do not have access to a scope. The datasheet says that the Charge status should be 10ma pull-down when charging, and a weak 20µA pull-down when complete, but in undervoltage lockout it goes high impedance. I'm not sure what the pin does when no battery is present.

I notice the datasheet mentions to use an output capacitor to reduce ripple voltage when no battery is present. It also says to add a 1 ohm series resistor if low ESR caps are used.

I put in a 10uF ceramic cap by the battery but forgot about adding any resistor. Should I add that resistor ?, and how does that effect the battery when it's plugged in?

Thanks

[Peabody]

I'm not sure the TP and LTC parts are the same. They are not the same for the 4056.  So I'd suggest you use the TP4054 datasheet in case there are any differences.  But it's possible the blinking LED is the intended behavior if the charger is powered but no battery is present.  The TP4056 has separate pins for the charging and charge termination LEDs, and it turns both on if there's no battery.

[kjr18]

If there is no battery connected, Stand-by led should be lit, and charging led should flash at about 1 to 4 Hz. At least that what datasheet says.