pebblywicket
Posts: 1
Joined: Thu Oct 12, 2017 2:11 pm

Compute Module IO Board Schematic

Thu Oct 12, 2017 2:26 pm

Regarding the PAM2306 multi-output DC-DC converter circuit (Compute Module IO Board v3.0):
- R22, R23 have a value of 0R (jumpers)
- C21, C22, R24, R25 have a value of NF
What does NF stand for?
Also, what purpose does this circuit serve, when would it be necessary and how would the component values be determined?
Lastly, what does PP stand for? Probe point?? Used for electrical checks of the PCB during production?
Thanks!

PhilE
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Raspberry Pi Engineer & Forum Moderator
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Re: Compute Module IO Board Schematic

Thu Oct 12, 2017 3:32 pm

"NF" stands for "Not Fitted" - i.e. no component should be placed there, and it remains open-circuit.
"PP" is definitely a test point - I think it stands for "Probe Point".

Somebody else will have to explain the function of the circuit.

6by9
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Re: Compute Module IO Board Schematic

Thu Oct 12, 2017 4:25 pm

The PAM2306 datasheet explains it.
" The dual output voltages are available for 3.3V, 2.8V, 2.5V, 1.8V, 1.5V, 1.2V or adjustable"
If adjustable, then you fit C21/R25 and C22/R24 to set the voltage. See Figure 1.
If fixed voltage, then you connect directly back hence the 0 ohm links.

Page 13 then tells you that as the fitted part number is PAM2306AYPKE, V1 is fixed at 3.3V, and V2 is fixed at 1.8V.

I guess someone early on thought they might use a PAM2306AYPAA (adjustable on both rails), and hence put the pads there to allow fitting the relevant resistors.
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