PNP Transistor Not Passing Current

[Noah517]

Hi there,
I created a custom PCB for a project that has a GPS module that can be powered down through a PNP transistor. The RTC is connected to VCC, but the actual VCC for the GPS goes through a PNP transistor so the GPS can be put into a "sleep" mode via an Arduino.

The issue is, I can't get the transistor to power the GPS. No matter what I do, the transistor won't break down to power the GPS. I'm sure this was likely an issue with me just picking the wrong value transistor or something. The Arduino is a 3.3v Pro Mini

Here is the datasheet for the transistor:

1810181212_ROHM-Semicon-2SB1198KT146R_C266246.pdf

I have attached my schematic below.

Is there anything obvious that I missed?

Noah

[LarryD]

Let’s see a good image of the PCB.

[Noah517]

larryd:
Let’s see a good image of the PCB.

I'm not home at the moment, so this is the best image I have. I will reply again once I'm able to take a better photo. The transistor goes on the bottom right of the PCB. I have removed the transistor and bridged the contacts so I am able to power the GPS.

[jremington]

Show all the Arduino connections on the schematic.
Where is the required common ground connection? Why is it not shown on the serial interface header?
What voltage for Vcc?

[Noah517]

jremington:
Show all the Arduino connections on the schematic.
Where is the required common ground connection? Why is it not shown on the serial interface header?
What voltage for Vcc?

The entire schematic has been attached
The interface headers are for debugging purposes only, so they don't have a ground pin on the connector. The common ground of the PCB is a GND copper layer on both the top and bottom layers of the PCB.
As I said in my original post, the system runs on 3.3v.
Noah

Schematic_simple_hab_2021-04-09.pdf (88.5 KB)

[Noah517]

larryd:
Let’s see a good image of the PCB.

Here is a better image that I forgot I had

[JCA34F]

The transistor Ic rating is 500mA, how much current does the GPS require?
Post a datasheet link for "the GPS".

[Noah517]

JCA34F:
The transistor Ic rating is 500mA, how much current does the GPS require?

Definitely less 500mA. But the transistor won't activate even for a moment, so I doubt that it's a current issue.

Here is the datasheet
https://www.u-blox.com/en/docs/UBX-16000093

[LarryD]

Please confirm what happens to the transistor if you manually take the ‘base’ to GND using a low value external resistor.

A image of traces top and bottom from the PCB design program would be useful.

Have you look for or done any continuity measurements to see if nearby signals/power rails are interfering with the base current ?

Have you check what the signal (GPSPD) to the base resistor looks like with a scope ?

[LarryD]

[Noah517]

larryd:

Goodness gracious-
Lesson learned, don't blatantly trust the PCB footprint in the design software-
Thanks for the help, I should be able to just flip the transistor upside down and get it to work, I'll respond again if it does!
Thanks!
Noah

[LarryD]

“ I should be able to just flip the transistor upside down and get it to work”

Yes, there might be enough lead length for you to do this, just document this on your schematic ;).

[MarkT]

Why are you switching only some of the Vcc pins of the GPS unit? Surely they all need
to be switched together?

[Danois90]

Just out of curiosity; Would it not be much better to switch the ground? If ground is available current from data pins may be wasted in the GPS module..

[MarkT]

Such phantom powering should be avoided whether switching low-side (ground) or high-side (Vcc),
it can burn out the data pins.