Hi Guys, Thanks for your precious time and insight. Let me try to explain what we did,
We have developed a custom board After assembling the board, we do a bare board test where we check all impedance's including those across VDD, AVDD and capacitors provided for the Chips internal voltage regulators.
- In all instance across four boards we have tested(bare boards before power up) , impedance were above 100K.
- Then we Power up the board and test voltages. The board is powered up using a coin cell battery or a 3V supply. Measurement of voltage shows 3V. The board is disconnected and impedance checked, results when checked using a multi-meter resistance mode shows above 100K. 3)Board is powered up again, connected to a Jlink programmer and is flashed with blinky LED program. It works fine for few tries.
- Then randomly after few tries, its no longer able to program the chip and when you check power supply impedance it shows typically less than 10 ohms(Not short but very low impedance).
- The chip can no longer be programmed after this stage.