Possibilities of LTC3331 VIN output null given a working piezo as harvester. DC source into VIN gives VOUT
No reading at Vin or no reading at Vout? If your Vin is shorted to GND, the IC may have been damaged.
Note that there are some current limits to the LTC3331. The AC inputs can take a max of +/- 50mA, so if your piezo device has more capability than that, there is a chance it can damage the part (even if the DC load on Vout will not pull 50mA). There is also an internal shunt on VIN (see block diagram in the datasheet) that engages at about 19V, and this shunt has a current limit of 25mA; so, if your input voltage is greater than ~19V, your current capability must be less than 25mA or the part will be damaged. Either of these scenarios may result in a short on VIN, which would explain why you wouldn't see any voltage there with your piezo connected.
It sounds like you are putting piezo power into your LTC3331 and Vout is unable to regulate, but when you input a DC source (power supply?) it regulates as expected. Is that correct?
This is due to power limiting. Your piezo input is not powerful enough or not consistent enough to make sure Vout remains high. This could be due to too much load on Vout relative to your piezo output, or perhaps that the piezo is not being regulated at its max power point correctly.
Can you give more details here about what you are putting into the device and what you are trying to power from Vout?
The setup I'm using was giving a regulated output as expected and charging the battery(used a 10uf cap for test).
I was testing Vout with an led. A while later I was unable to get any reading at Vin. I'm attaching my piezo datasheet link here.
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