Trouble with solar battery charger (LT3652EMSEPBF)

I’ve been trying to set up a solar battery charger, but I’m having trouble getting it to work. I’m using a Linear Technologies IC - LT3652EMSEPBF, datasheet attached.

Here is my schematic - it’s almost the same as the example on the first page of the datasheet. I’ll be running it from a 12V 125mA solar panel, but for now I’ve been testing with my autoranging power supply. I’m charging a 7.2V NiMH so I’ve set a float voltage at this level.

All grounds are connected through a ground pour.

The system load successfully gets power when I apply it to either the VCC or VBAT inputs, or when both are connected. But I can’t seem to get charging to initiate. Although I don’t have the CHRG and FAULT pins connected, I’ve probed them with a probe pulled up to VCC and they both read high, so the IC doesn’t seem to be registering a fault. I’m testing with a depleted battery, so the VBAT is about 5V and the VFB pin is at about 2V, so charging (or preconditioning) should start. Similarly, VIN_REG is reading in the appropriate range, and I’ve been inputting >12V so the charging current shouldn’t be lowered, and should be running at 2A (R-sense = 0.05).

At VCC the circuit is drawing ~10mA, which is about the same as it is drawing when I power it through VBAT - the battery voltage isn’t shifting and I’m not seeing increased current draw that I’d expect to when charging.

Any help would be greatly appreciated!

For completeness, here’re the schottkys I’m using:
Here’s the inductor:
The diode:
Ceramic caps and thick film resistors.

Solar-Regualtor.pdf (275 KB)


Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?

Can you please post a copy of your sketch, using code tags?
They are made with the </> icon in the reply Menu.
See section 7,148850.0.html

Thanks … Tom… :slight_smile:

EAGLE files below - note that the problem is with the LT3652EMSEPBF so top left of the board. There isn't a sketch as yet, I've gone through and verified that the ATMEGA328P is powered up, can read the inputs, and can communicate over Serial, but that's all - this isn't a problem.

EAGLE files:


I have some experience with the LT3652, you may want to look over my board design and see how I did things.

Also, look at the problems I ran into while trying to figure out what I wanted it to do.

Frankly I did not know what I wanted and tried a lot of stuff until things started to make sense. I really only had one issue with the LT3652, and that was where I put the .1uF bypass. For some reason I thought it was needed on the PV input but it was really needed right at the LT3652 input just like any bypass. I have worked with power supplies for a long time so I made sure the circulating currents did not flow under the control chip from the beginning. All power paths run into the bottom plane, and LT3652 is soldered on a top plane that has no power flows (though the bypass is connected to it). I did this with two layers so had to break some rules, but the main rule is to have a clean (no switched power flow) plane under the control chip.

This is some of the tests that I did to it.

I have also integrated it onto another board if you want to see how that looks (though it is not tested yet).

Hi, Rather than post a schematic off site and that needs a specific program to read.

Eagle should be able to export a jpg file, which you can ATTACH to your post.

REPLY rather than QUICK REPLY and it has an attachment facility, so you can post your file as an attachment.

Tom.... :)

I'm not going to open a zip file on another site, to view your pcb.

Happy to upload an image, but it will be significantly less useful than opening the EAGLE file would be.

Unfortunately, I have to provide the design as a ZIP as the forum won’t allow the native extension.

Thanks Ron, I’ll have a look at your pages. It seems you’ve gone for a more sophisticated charger than I was, so hopefully I can follow what you’re doing.

Cheers, (91.9 KB)