Hi,
Below is the setup I'm using. An SPV1040 connected to a small 2Vmp solar panel charges two 50F supercapacitors connected in series up to Vout = 4.8V. The design is taken from the AN3319 application note of the STEVAL-ISV006V2.
Currently, I have many pcbs with this circuit working.
So far the circuit does what it is supposed to do: charges the supercaps up to 4.8V using the energy harvested from the solar panel. However, in some pcbs there seems to be a floating voltage in the SOURCE_INPUT node, here's a step-by-step example of what happens:
- The solar panel receives radiation and SPV1040 starts charging the supercaps.
- Supercaps are charge up to 4.8V
- The solar panel stops receiving radiation so its output voltage should be reduced to almost 0V, however, in the SOURCE_INPUT node there is ~0.5V even after disconnecting the solar panel from the circuit. It's like the SPV1040 lets voltage pass from output to input.
- Supercaps start to get drained by the SPV1040. I assumed it is because the SPV stays on.
For some other pcbs this situation is not detected, so when the solar panel stops receiving radiation, the SOURCE_INPUT node stays at ~0V and the supercaps are not drained by the SPV1040.
According to the SPV1040's datasheet, with a LOW (0.34V max) in the XSHUT pin the SPV1040 should go to off mode, since there's the 0.5V floating voltage this LOW condition isn't met so the SPV1040 stays on.
I've managed the situation by connecting a resistor between MPP-SET and GND so that the MPP-SET can be controlled and thus the XSHUT pin, however this causes an increase in the minimum solar panel voltage for the SPV to start charging the supercaps (which is undesired because we need more radiation to harvest energy).
What could be the reason for some SPVs to let voltage pass from output to input and others not?
Thanks
