What we observe is that the LIN_REG_EN
line goes from floating high to being pulled to the 3.3V MCU high
state which as far as the V_IN line is concerned is low.? Hans has
done this in his setup code. The effect is to turn the SMPS on
without turning the Linear off. No one other than Hans can have
done this or can say why.
There are two logic Off levels here,
for the FETs in the positive supply lines off corresponds to close
to the positive line and on is a lower voltage while for the FETS
connected to the GND line and the MCU logic low is 0V and logic
high is +3.3 V.
In most places the transition between
these is managed using additional FETs such as Q101 for LIN_REG_EN
and the linear supply, Q106 for the PWM_5V signal and Q107 for the
PWM_3V3 signal but in the case of Q111 and Q110 this doesn't
happen, they can both be on at the same time.
Chris, G5CTH
On 29/08/2023 20:41, Paul - AI7JR
wrote:
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That's true, but it wasn't really the question, as I recall it.
The question was about what made the lower voltage segment on
the LIN_REG_EN line. Since I don't know the microprocessor, I
can't comment on what Hans could have done, only comment
on what is observed!
73, Paul -- AI7JR
On 8/29/23 12:35, Chris wrote:
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
