I have a question about Trusted Platform Module header on PC motherboards. I want to install ESP8266 (standalone) inside of my PC, I know of 5VSB the the PSU supplies, but after looking at my mobo manual I saw TPM header with 3VSB pin, I could avoid using voltage regulator in that case. I'm only unsure how does that pin get 3V from the 5V, if it's capable of driving 200mA. I looked at some TPM datasheets and TPM consumes about 30mA to 50mA. Is there any legitimate way of acquiring motherboard "modern" schematics? I could study some of them and draw conclusions from there.
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2 Answers
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Every motherboard design is different. The designers choose various parameters to optimize the design for various factors including:
- BOM cost of motherboard.
- Reliability of components.
- Allowable temperature rise of components.
- Voltage regulator output capability design margins.
For sure the motherboard includes a voltage regulator for converting the 5VSB to 3V3SB. The design margin for that regulator could vary over a fairly large range from 50% to 90% or more. (Design margin being the load current requirement divided by the regulator's designed current supply capability). Because of these varied factors you could not generalize the available current from a TPM connector by any other means than evaluating a TPM module by itself.
You could try to determine by inspection whether the voltage regulator used on a particular board is a buck mode switcher or a low dropout linear regulator. Due to the increased efficiency and lower temperature operation of a modern switcher regulator it is more likely that the switcher would have more design margin than a linear regulator.
answered Apr 12, 2018 at 10:54
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\$\begingroup\$ My guess would be that it's buck, as they already have chokes mosfets and caps from vrm so buying 1 more of each should be more plausible instead of buying 1 ldr just for 3vsb.Or that would be overkill and took too much space on board. I tried looking at TPM specification but I couldn't see any information about requirements and tolerances for power delivery. \$\endgroup\$– OxmasterApr 13, 2018 at 6:14
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\$\begingroup\$ Like I said you cannot generalize. Do it and you may find you made the wrong assessment. \$\endgroup\$ Apr 13, 2018 at 22:02
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I checked 3 old motherboards schematics from around 2010 that are from 3 different reputable vendors and all of them use LDO that are capable of 3-5A. I think that should be enough.