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TehWoomiestRPI
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Joined: Thu Apr 07, 2016 7:39 pm

Power Management Chip on RPI3B+

Tue Apr 03, 2018 9:43 pm

Hey everyone,

Was curious about what functions that Power Management Chip does on the Raspberry Pi 3B+, I know it says it allows for better Signal transmission for power, but what else does it help Manage. If thats all it actually does, how does it do it compared to just using the fuses/resistors that was used previously?

Does the OS/Kernel have access to the PMC or does it do its own thing?

Thanks!

klricks
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Joined: Sat Jan 12, 2013 3:01 am
Location: Grants Pass, OR, USA
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Re: Power Management Chip on RPI3B+

Tue Apr 03, 2018 11:57 pm

TehWoomiestRPI wrote:
Tue Apr 03, 2018 9:43 pm
Hey everyone,

Was curious about what functions that Power Management Chip does on the Raspberry Pi 3B+, I know it says it allows for better Signal transmission for power, but what else does it help Manage. If thats all it actually does, how does it do it compared to just using the fuses/resistors that was used previously?

Does the OS/Kernel have access to the PMC or does it do its own thing?

Thanks!
Here is the data sheet of the new power chip for your enjoyment: https://www.exar.com/ds/mxl7704.pdf
The older RPi's B+, 2B & 3B had more than just fuses and resistors in the power circuitry.
Older RPi used this power chip: https://www.diodes.com/assets/Datasheets/PAM2306.pdf
The 3B and 3B+ have the same 'polyfuse' rated at 2.6A (hold current).
The 3B and 3B+ have the same over-voltage device - TVS diode.
The 3B+ does not seem to have the ideal diode circuit that older models have.
One thing to note is that the 3V3 current output on the 3B+ is now 1.5A. Older RPi's were 1.0A per datasheets.

Probably most of the interaction with firmware is for configuring the chip at boot time.
The new chip does have two 8 bit ADC inputs and a temperature sensor. The ADC inputs are grounded out per schematic so not usable. Possibly the temp sensor could be accessed if firmware allows it?

Reference schematics
3B+: https://www.raspberrypi.org/documentati ... ematic.pdf
3B: https://www.raspberrypi.org/documentati ... matics.pdf
Unless specified otherwise my response is based on the latest and fully updated Raspbian Buster w/ Desktop OS.

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