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:
Ceramic caps and thick film resistors.
Solar-Regualtor.pdf (275 KB)