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Problems in setting up power profiler kit PPK

Aravinth

We have a product that uses nrf51422_CE_AA, Revision 3, 256KB ROM, 16KB RAM, PCA10028, SDK 8.0.0, S110. We are now in the stage of power optimization. Therefore we bought Nordic Power Profiler Kit. We have problems in setting it up to show accurate readings. Therefore decided to test it with a known load and measurement was way beyond the actual current. I have adjusted the calibration resistors and brought the current measurement close to the real. However, if i change the load to consume less current, the current measurement on PPK doesn't change. Following is my setup.

As shown in the image 3-led-load.jpg

I have connected three LEDs with 330 Ohm resistors respectively. PPK's SW2 is set to "External", SW4 is set to "Reg" and COM is set to "EXT". Multimeter in mA range is connected in series with positive of P16 (External DUT) and positive rail of breadboard. PPK is powered via USB and J-Link is connected via COM to computer. In PPK Voltage regulator VDD is set at 3V and resistor calibration "Hi" is changed from 1.8 to 19.4 get 7.73 mA where multimeter shows 7.73 mA. That was pretty successful.

However, one LED and a resistor was removed as shown in the image 2-led-load.jpg

and there was no change in the measurement. It just stays at 7.73 mA even after restarted and powered on/off where multimeter shows 5.63 mA. What should be done to make it work?

image description

Additionally, power profiling should be done on our real system. Our product uses 3.7 V (nominal voltage) LiPo battery (max voltage is 4.2 V and min voltage is 2.7 V). When i use our LiPo battery and put SW4 to "External", will software voltage regulator work? or voltage from the battery should be regulated to 3.6V before applying to P22 (External DUT Supply)?

UPDATE on 10-Nov-2016

If i disconnect PPK and reconnect, then it starts from 0mA but then goes to 7.7 mA even though Multimeter measures 5.6 mA (2 LEDs) as shown in the image.

image description

If i disconnect external DUT, then it shows noise as shown in the image.

image description

If i remove one more LED and Multimeter measures 2.9 mA, then i see noise and average of 4.5 mA (still wrong) as shown in the image.

image description

UPDATE on 14-Nov-2016

Started without Load. Measurement is around 0 mA with noise.

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While connecting the load and HI resistor calibration updated at 2 and it is around 0 mA with noises goes from 0 to 74 mA.

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After connected the load with HI resistor calibration updated at 2. Measurement stays at 74 mA. Actual load is 2 LEDs with 330 Ohm resistors which consume 5.63 mA.

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UPDATE on 15-Nov-2016

1 MΩ (998 KΩ) resistor load measures average 3.04 uA.

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470 KΩ (466 KΩ) resistor load measures average 6.39 uA

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UPDATE on 18-Nov-2016

270 Ω (268 Ω) resistor load measures 83.32 mA

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    It doesn't make much sense when it stuck to 7.7mA even after restarting. If you disconnect the PPK and connect it again with power would it still stuck to the initial 7.7mA or change to 0mA ? Also, if you actually disconnect the external circuit, would the measurement stick to 7.7mA ?

    Do you see any change or noise when it's measuring ? I suspect it's a software issue.

    Regarding your question, as in the userguide stated, you should only connect 1.8V to 3.6V to the external DUT supply. If you want to connect 4.2V I would suggest to connect it via the USB port or via V5V pin (pin 5 Port P1,P2,P3) please see the schematic. Make sure you compensated the difference in the input voltage (4.2V instead of 5V).

  • 0

    @Hung Bui : If i disconnect PPK and reconnect, then it starts from 0mA but then goes to 7.7 mA even though Multimeter measures 5.6 mA (2 LEDs) as shown in the image above under UPDATE on 10-Nov-2016. If i disconnect external DUT, then it shows noise as shown in the image above under UPDATE on 10-Nov-2016. If i remove one more LED and Multimeter measures 2.9 mA, then i see noise and average of 4.5 mA (still wrong) as shown in the image above under UPDATE on 10-Nov-2016.

    When i was starting ppk.py, there was a warning that ppk software was tested with numpy 1.9.2 and my version is 1.11.2. I have downgraded numpy to 1.9.2 and it doesn't show me the warning anymore. Other than that i don't see any software errors.

  • 0

    @Hung Bui : This question is to know whether I'm doing resistor calibration correctly. With default calibration and my test load with 3 LEDs with VDD set 3000 mV, shows average current of 80mA. Then i set "Hi" to 19.4 to match 7.7 mA. Is it right what i have done? Do i have to change anything physically in the board for calibration?

  • 0

    The measurement resistor should never have to be adjusted that much, so if it goes higher than 3ohm there is definately something wrong. Does your software do a calibration at the startup, and you can see zero current drawn (just noise) with the external DUT removed? Please try to set the resistor value to e.g 2Ohm and restart with the DUT disconnected. Insert the tests you have and report back, just so that we can verify if there are some offset error in the system.

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    Also, please measure the VDD on the DUT connector to verify that we actually have 3V. This is very important! When doing the calibration, please just use a known resistor and don't bother with a multimeter in-between.

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