Hello,
We are using the LTM8078 to produce a 5V and 3V3 output. The schematic is detailed below. The input voltage is 24V.
Most of the units we receive behave as expected, with output voltages very close to the desired values. However, we are having the problem that some of the received units have much lower outputs (~4.6 and ~3.15V) which is incompatible with our downstream ICs. The PCBs are from the same batch so we assume it is not a systematic use of incorrect resistors etc. All of the resistors are 1% tolerance.
My question is, is there something about this design that might be susceptible to slight manufacturing defects (e.g. something close to a threshold) that could explain the deviations? We were concerned that the bias pin was not receiving >3.2V so we increased the voltage via the feedback resistor (75k) which pushed the (still low) voltage up to 3.28V but did not appear to fix the problem.
This could very well be a layout/soldering quality issue, but we would of course like to rule out schematic problems first.
Thanks in advance!
Rohan.