We have a 12v output (from flyback) with load current of up to 100 mA. To simulate this 100 mA, I used a 120 ohm resistor.
The power supervisor I am using is LTC2907ITS8. It monitors a Vcc = 5v and this Vdd = 12v output. I have probed previously that normally disconnecting the AC plug input (to flyback) will always result to Vdd falling and triggering the power supervisor's RST signal and NOT the 5v output (ie, the 5v output crosses the ~4.5v trigger pt much later compared to 12v crossing the ~10v trigger pt).
The problem I encounter as follows:
Case 1:
Vdd has no 120 ohm load. I probe both 12v and RST signal to check if RST signal goes low (RST is active low) when the 12v signal crosses the threshold of ~10v (upon disconnecting AC plug). The result is good because RST signal goes low at this expected Vdd signal level ~10v.
Case 2:
Vdd has 120 ohm load to simulate 100 mA current load. Again, I probe both 12v and RST signal to check if RST signal goes low at ~10v. The problem occurs here because RST signal goes low at ~6.40v instead. Note that we have not changed the values of the resistive divider (R67 and R68) for monitoring the 12v Vdd output.
Our hypothesis as of now is that somehow, the 120 ohm load is affecting the values of the resistive divider that monitors the Vdd load. We just started investigating this however. I'll continually update whenever we find more hints. I'll try to probe the midpoint of the divider next.
Any suggestion is appreciated.
Thank you
