Testing the CL4056 solar charger IC

2020-08-28, 03:12:00

There are lots of clones for the LTC4056 solar charger, I've bought the CL4056 from here. Some are even cheaper, but I've settled for this one since is has one of the highest tolerances from all that I've seen at LCSC.

I've already shown the circuit I made for it, but I want to point out a few things.

Bright leds

The charge and standby pins sink about 3mA for 1k @3.3V, without accounting how much do the leds draw.

I've used 0603 leds with 1k2 resistors and, for my taste, I find them too bright.

Non-consistent charged voltage

The finished 'charged status' is considered when the battery no longer pulls significant current, that is, 'it's full'.

If you try to measure the voltage reached, that small derivation will restart the charging cycle. 

The charged-voltage usually depends on the internal chemistry, called Vfloat. This floating voltage ranges 4.0XV to 4.3V without any control at all.

Slow charging or not charging at all

Rprog is supposed to control the charging current. Since what I want is to have an-under-the-sun-panel, which means receiving about 6 to 12 hours of sun, I set the current with a 4K resistor, for a 300mA current @5V, since my batteries' capacity is 1200mAh.

Well, charging from the usb port, with a 1.5A charger, the batteries where still discharged after an entire day.

So I've changed the resistor with a 750 ohm (out of specs) and my batteries were full in less than an hour at 1.6Ah.

Fussy output pin

I've discovered this issue with one of the boards, for whom the resistor didn't fixed the problem, and it turned out the charging pin wasn't properly soldered to the board and it probably had some resistance. I normally use bismuth paste and a heat gun, but I took the tin roll and the soldering iron to fix it. Moreover, there was voltage on the copper track and on the battery + metal pad, showing the 4.2V it shows without any load.

One way to test if the IC is working before connecting a battery is to check if it lights up both leds (the charging one because the output is functional and no resistance on it and the finished one because the current threshold is low).

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