Until the microprocessor comes up, LIN_REG_EN will be pulled up
to +12 by R101. Once it's up and initialized, it will be fed by
the microprocessor output from it's 3.3 volt supply.
Does that fit what's observed?
Paul -- AI7JR
On 8/29/23 11:54, Chris wrote:
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Nothing.? The Linear continues to
produce 3.3V relative to it's 'GND' pin. if the supply produced
by the SMPS is more then it provides nothing.? All this is
confused by D102 andD103 which prevent the linear getting a
voltage on its output which it can't cope with.
Chris, G5CTH
On 29/08/2023 19:40, Jonathan
Burchmore wrote:
What is the mechanism that reduces the voltage on LIN_REG_IN
during that half-way state from the supply voltage to 3.3V? ?It
seems to me that the supply voltage passes through Q103 &
Q105 (on the 5V board), then R101 on the 3v3 board and is
directly connected from there to PD7 on the processor.
Jonathan KN6LFB
Paul - AI7JR