Platform forum

About Enable for 3V3_S5

mulfycrowh , 11-11-2022, 04:12 PM
Hi everyone,

There is something I don't understand.
I've got this schematic about 3V3_S5 on COM Express module.
The RUN_V_3V3_S5 is tied to the RUN input of the LTC 3869 used to deliver 3V3_S5.

According to the datasheet:
LTC3869 LTC3869-2 - Dual, 2-Phase Synchronous Step-Down DC/DC Controllers (analog.com)

the RUN input is active high.

When the computer is in S5 state, SUS_S5# is low which means, according to the schematic, RUN_V_3V3_S5 also low.
If RUN is low, the output is disabled, which is not coherent.

Any idea?

qdrives , 11-12-2022, 09:26 AM
Isn't the # an indication of invert (not)?
Signals are inverted twice, so a low on the input (sus_s5#) will cause a low on run_v_3v3_s5.
mulfycrowh , 11-12-2022, 10:09 AM
@qdrivesyou're right. What I do not understand is that when the system is in S5 state (sus_s5# low), the power supply is disabled.
I thought that during this state, everything is OFF except that power supply that is for example tied to the power button.
If the power supply is disabled, you won't never be able to start the system while pushing the button.
There is a misunderstanding and I don't know where.

qdrives , 11-13-2022, 08:07 AM
Do note that I have no knowledge of COM or other computer related (power) elements.
I just look at the supplied schematic and dataheet of regulator.
Then again, it would explain the amount of 'power' related issues there are in PCs were sleep and hibernation cause crashes.
robertferanec , 11-14-2022, 01:23 AM
Try to find and check the processor reference schematic - especially look for power up timing diagram, that should explain it. Sometimes signaling/naming may be a little bit different from what we expect. Notice the SBY power (STANDBY), they are doing also something else there.
Use our interactive Discord forum to reply or ask new questions.
Discord invite
Discord forum link (after invitation)

Didn't find what you were looking for?