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The high side current shunt monitor fault goes high as soon as power is turned on preventing the P-MOSFET from turning on, its not faulting because of over current but as soon as the Enable signal goes high the Fault also goes high with it. the 3.3V is the first signal that comes on after the 18V.

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  • \$\begingroup\$ Please show schematic. “Fault goes high” what’s that? Signal goes high? Shunt goes high impedance? \$\endgroup\$ – winny Aug 17 '18 at 5:53
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    \$\begingroup\$ Probably unrelated but C1 and R7 are just talking to each other and doing nothing for the rest of the circuit. BTW, are you aware that when you use the CircuitLab button on the editor toolbar an editable schematic is saved inline with your post? No account needed. No need for screengrabs. \$\endgroup\$ – Transistor Aug 17 '18 at 14:14
  • \$\begingroup\$ I think that at least R7 needs to be connected to ground - I cant see what R7 and C1 do otherwise. \$\endgroup\$ – Tim Mottram Aug 17 '18 at 14:15
  • \$\begingroup\$ R7 and C1 connected to GND \$\endgroup\$ – tilengneer Aug 17 '18 at 14:29
  • \$\begingroup\$ Without looking in too much detail, I would contend that the start up behaviour of the INA200 is undefined and could be causing the trip. \$\endgroup\$ – Peter Smith Aug 17 '18 at 16:01
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Figure 1. Problems with logic levels?

I haven't looked at the INA200 datasheet at this stage but it seems to me that you have a few potential issues.

Q1's emitter is pulled up to 3.3 V at (3) and (4)but the very most its base can reach is 2.5 V at (2) even if (1) is running on 5 V logic.

Is this intended design?

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  • \$\begingroup\$ only CMPout drives high it high and low, if RESET is sequenced right its defaulted to low \$\endgroup\$ – tilengneer Aug 17 '18 at 16:21

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