PKK2 inaccurate readings in ampere mode

[ioko]

Hello!

I am trying to monitor the GPIO pull-up drive capability of a microprocessor using a PPK2 module in "Ampere meter" mode.

PPK2 VIN is connected to the GPIO pin and VOUT to a 1Kohm resistor to ground.

Although the current verified with a multi-meter to be around 25uA, PPK2  is measuring values around 5uA:

Is this a limitation? Using 10K resistor seems to solve the issue.

Thanks!

[Priyanka]

Hi Ioannis,

Which DK are you trying this with? 

Best Regards,

Priyanka

[ioko]

Hi Priyanka!

I am using a "Power Profiled Kit II", HW version 1.0.1 and running "Power Profiler" v 3.5.3. The test device is a custom board with ARM processor but I can also reproduce the issue using a resistor net - simulating the pull-up resistor with a 68KOhm resistor to Vcc and adding an 1Kohm load resistor to ground in series.

Vcc <-> 68K <-> PPK2_VIN  -  PPK2_VOUT <-> 1K <-> GROUND

Thanks!

[Priyanka]

Hi Ioannis,

Could you also tell how much is the Vcc supply that you give to the DUT (Device Under Test) ? Is it between 0.8V and 5V?

-Priyanka

[ioko]

Hi Priyanka,

the Vcc was at 1,8V.

Thanks!

[Priyanka]

Hi Ioannis,

The GPIO pullup internal resistance is 13k, and hence the resistance for the VIN of PPK2. So when you connect a 1k resistor to the VOUT, it's actually acting as a voltage divider to the 1.8V VIN that you give, i.e.

VIN becomes VIN x (1k / (1k + 13k)) = 1.8V x 0.071 = 0.129V

This is too less VIN compared to the requirement of 0.8V - 5V

Hope this helps.

-Priyanka

[ioko]

Hi Priyanka,

Thank you very much for your analysis!

Sorry, I missed the 0,8V min VIN requirement.

Best regards,

Ioannis

[Priyanka]

No Problem.