Mismatching pin description between schematics and datasheet


#1

Who can know this mismatching pin between Arrow’s schematics and Qualcomm’s datasheet?

Schematics: Schematics_DragonBoard410c.pdf, August 31, 2015
Datasheet: lm80-p0436-7_b_apq8016_devicespec.pdf, August 2015

An example of mismatching pins:

Schematics: AP19 = VDDAL_BBRX_CH0_1 on page 12
Datasheet: AP19 = GND for APQ on page 48

Which one is correct?


#2

Hmnnn…

I’d be astonished if the pin numbers on the schematic were wrong so, having looked, I’d say that AP19 is not connected to ground on a DB410c (rev A) but connected instead to one of the PMIC power supply lines. My electronics knowledge is fairly rudimentary but because the board works I also think it unlikely that AP19 is part of the main ground supply to SoC.

The above is by no means conclusive but I suspect this is an error in the datasheet.


#3

Hi @XenFrancicso

Great catch…

I checked several other APQ8016 schematics (including the prototype DragonBoard 410c) and all of them have pin AP19 wired to ground. This matches the datasheet. I believe the published schematics have the error. I have asked Arrow to confirm.

Full Disclosure: I am an employee of Qualcomm Canada. Any opinions I may have expressed in this or any other post may not reflect the opinions of my employer.


#4

Thanks for the update.

Sorry for calling it wrong. Still can’t figure out quite how that sort of error could propagate through the EDA without being spotted! Still, like I said, my knowledge is pretty basic here.


#5

Thanks,

Schematics is used for designing PCB layout.
If there were a mistake the board won’t work, so I believe that the schematics is correct.
The datasheet is just a document.


#6

So is a schematic :wink: . There’s always scope for version skew between the schematic and the board itself. Like you I originally thought that to be less likely than a mistake in a document but it looks like I was wrong.


#7

In this case the layout came from the prototype (which is the schematic I checked). The early revisions of the board had AP19 pin was tied to a supply, but by connecting the pin to ground, power consumption is (slightly) decreased. The posted schematic was not updated when the change was made. The early versions of the board did work with pin AP19 tied to a supply.

Full Disclosure: I am an employee of Qualcomm Canada. Any opinions I may have expressed in this or any other post may not reflect the opinions of my employer.


#8

Hi ljKing,

Thanks for the update.
I understood that the datasheet is correct and the posted schematics has not been updated.
I however cannot understand why the early versions of the board did work even with pin AP19 tied to a supply.
What is pin AP19 for?

Can you answer this question?