On 29/08/2023 20:20, Paul - AI7JR
wrote:
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?
Yes, but typically modern processors have a variety of control
methods that can be configured, one of which is an 'open
collector' style where it only pulls the line low and leaves it to
float high. Hans seems to have decided to pull it high.
Chris, G5CTH
Paul -- AI7JR
On 8/29/23 11:54, Chris wrote:
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
