Battery Current Charging MCP73831 - LiPo

[made2hack]

Hello all,

Here's the circuit I have built. Vin is 4.96V from a regulated supply (computer PSU). Rprog is 2K (1%).



The charging current Output is only 140mA approximately. According to datasheet, it should be at around 500mA?  Am I doing something incorrectly?

I have the MCP soldered to a SOT23-5 to DIP board and that DIP board soldered to a circuit on a phenolic board I etched. According to the datasheet, they recommend placing battery leads as close to the circuit as possible to avoid major voltage drops. My battery has AWG24 (solid) soldered to the leads that then solder to the circuit. Approx 15cm length each, so total 30 cm length. Could this be generating such high voltage drop? I mean, I'm getting essentially 1/3 of the charging current?

Thanks,

[Kilrah]

What's the voltage on the battery at that point? LiPo charge is CC-CV, so once the battery reaches the terminal voltage (4.2V for most types) current will gradually reduce. Your battery might simply be near full...

[made2hack]

Started with a battery that had 3.4V around. When it goes into what I think is CV charging, I think it drops to around 20mA - 30mA.

[mariush]

You have an error in your design.
You must connect Vss directly to ground.

Connect Prog to Ground through a resistor, to limit the current: Ireg = 1000V / Rprog (kOhm)  so basically with 2k ohm you'd get 1000/2 = 500mA


The way it is shown in your picture, you're basically limiting the input current to the chip.

Here's the datasheet example:

[made2hack]

Hi Mariush,

I connected the PROG pin to VSS through the 2K and connected VSS to GND. It seems to be ok now. My Fluke 21 maxes out at 300mA and it is OverLoaded, so, I think that was it.