Hello everyone,
I am writing this because lately we have had two issues with LT8705 component. In both cases changing the component resulted in the fix.
The final application is a small PLC for earth-moving machines. The supply is a battery, usually 24V (could be also 12V) and the output is 12V 1A. The mosfets are BSC070N10NS3G and we put a 3,3Ohm gate resistor. The inductor is 47uH and the switching frequency around 350kHz.
- First problem: two boards with INTVcc in short circuit. We got back two (in around 200 boards) and found that the INTVcc pin measured a short to ground. Substituting the component fixed the short. We are not able to replicate the problem on the lab and. Does anyone had the same problem ?
- Second problem: we have other 2 boards that function normally at ambient temperature. BUT if we heat the LT8705 up just a little the start behaving erratic:
- One board's output voltage oscillates between around 22V (with 24V input) and zero. Measuring INTVcc voltage we see that while we heat it up the voltage rises. When it reaches around 7,9V the IC starts to oscillate. Looking at the CLOKOUT pin the die temperature sould be around 91°C
- The other board instead we heat it up and nothing happens until we try to switch off and then on the board. At this point the board is dead and the output of the converter is 0V. Only when the chip cools down the board starts to work back properly. This behaviour appears far below the "Overtemperature shutdown" since by heating other boards the same we do not see this behaviour. Looking at the CLOKOUT pin the temperature of the die sould be around 111°C.
Any idea of what could it be?
If you need any other information let mw know. Thank you
