This is a revision of a post from a few days ago. I'm currently working on designing a solar charge controller using the LT3652 chip that takes a solar panel input, charges a battery pack, and also delivers a voltage output to a micro controller board.

Circuit Diagram (LT3652 Datasheet)

Everything mostly works, however I had some questions about the CHRG pin / CHRG led and also the battery charging current and was wondering if someone could help me.

For reference:

My solar panel input is about 11V and 320mA. I use a DC power supply set to this in place of the solar panels for testing in order to be more consistent. The input is at the top left screw terminal

My Li-Ion battery is 2S of 3.6 V cells. It is at approximately 7.3 V at the moment. It is a L74A26-2-1-3WA3 battery pack

I have omitted the use of a thermistor for testing purposes, so please ignore that in the schematic

Vin_reg is also connected to Vin (like how SHDN is connected to Vin), omitting the use of the potentiometer at Vin_reg

At the output of my board I am connected to a Pololu 5V 1A Step-up/Step-down voltage converter in order to power my microcontroller board, the BeagleBone Black

Questions :

When I only have the solar panel input plugged in and the battery disconnected, the CHRG pin is consistently on, rather than blinking like the datasheet says it should when the battery is disconnected. Are there any ideas to why this is happening?


Battery Removal

When reading the current at the battery, with the power supply detected it is approximately -7 mA, however when I removed the power supply the battery begins discharging at around +200-300 mA (what the micro controller board needs to be on) and solely powers the micro controller board. I am confused to why the battery is seemingly not being charged at all when the supply is plugged in, as I have the R sense configured to deliver a charge current of approximately 100 mA, less than my input, but the battery still reads -7 mA. Did I configure something wrong here? The CHRG LED is on during this process which should mean it is being charged, but that doesn't seem to be the case when reading the current.

Charge current resistor

Any help, guidance, or suggestions would be greatly appreciated. Thank you for your time!

  • \$\begingroup\$ Is yours configured for C/10 termination? It sounds like the blinking only happens in that mode. \$\endgroup\$
    – Hearth
    Commented Jul 24, 2023 at 19:43
  • \$\begingroup\$ Yep! I have the timer plugged into ground. \$\endgroup\$
    – John G.
    Commented Jul 24, 2023 at 21:05

1 Answer 1


Update: Everything now works! It looks like the problem was with the breadboard.

I ordered a circuit board to test on and now everything works fine. The LED blinking works and the battery charging works. I haven't got a chance to test it with the BeagleBone also attached but I presume it would work.

Circuit Schematic


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