ppk2 ampere meter measure error.not correct

[3Rsteven]

hi nordic,

when ppk2 entry Ampere meter.
the measure current not correct.(it seem the scale and offset error ,but can be enable/disable output)

(test circuit only vdd(3.3 extern power)->resistor5.1k->ppk2(in)-->ppk2(out)-->gnd(ppk2 gnd)
it should be 0.6mA,but the ppk2 only 60uA.? and other case it get error value(nrf52840 dk blinkly example  same issue*1)

when ppk2 entry soure meter.it be work
it is right value.
(it test use nrf52840 dk ,blinkly example)
https://i.imgur.com/pMqRzEY.png

measure example(error):
https://i.imgur.com/o41SGHp.png

app version:
https://i.imgur.com/TlxZCIo.png

ppk2 F.W version:
15:37:32.160 Validating firmware for device with s/n D55B03750145
15:37:32.177 Opening device with s/n D55B03750145

os:
# nRFConnect System Report - 2020-12-30T10-21-15.621Z

- System:     xxxx
- BIOS:       xxxx
- CPU:        1 x Intel Core i5-8265U 1.60 GHz 8 cores (4 physical)
- Memory:     1.2 GB free of 7.9 GB total
- Filesystem: C: (NTFS) 120 GB 94.9% used

- OS:         Microsoft Windows 10 Pro (10.0.19041) win32 ia32

- Versions
    - kernel: 10.0.19041
    - git: 2.21.0.windows.1
    - node: 12.13.0
    - python: 2.7.13
    - python3:

*1:

https://infocenter.nordicsemi.com/index.jsp?topic=%2Fug_ppk2%2FUG%2Fppk%2Fmeasure_current_ampere_meter.html

---

2020-12-30T02:18:09.168Z INFO Deselecting device
2020-12-30T02:18:27.807Z INFO Validating firmware for device with s/n D55B03750145
2020-12-30T02:18:27.814Z INFO Opening device with s/n D55B03750145
2020-12-30T02:18:28.606Z INFO PPK started
2020-12-30T02:18:28.624Z INFO PPK opened
2020-12-30T02:18:36.925Z INFO DUT ON
2020-12-30T02:18:40.149Z INFO Sampling started
2020-12-30T02:18:51.021Z INFO Sampling stopped
2020-12-30T02:18:59.541Z INFO DUT OFF
2020-12-30T02:19:54.636Z INFO Deselecting device
2020-12-30T02:19:54.698Z INFO PPK closed
2020-12-30T02:19:58.355Z INFO Validating firmware for device with s/n D55B03750145
2020-12-30T02:19:58.362Z INFO Opening device with s/n D55B03750145
2020-12-30T02:19:58.729Z INFO PPK started
2020-12-30T02:19:58.748Z INFO PPK opened
2020-12-30T02:20:06.226Z INFO DUT ON
2020-12-30T02:20:07.538Z INFO Sampling started
2020-12-30T02:20:14.812Z INFO Sampling stopped
2020-12-30T02:20:15.640Z INFO DUT OFF

[Øyvind]

Due to Christmas holidays our technical support team is lower staffed, and the response time will be longer. Also, most of our R&D our out of office until January 4th. We apologize for any inconvenience this may cause.

---

Hello, 
The PPK team is currently out of office. Please expect an answer within next week. 

Kind regards,
Øyvind

[Øyvind]

Here is the result of connecting my nRF52840 DK running Blinky to source meter:

While here is the result I get when connected in Ampere Meter

Why do you have a 5k1 resistor connected as well? 

"The PPK2 is driven by the nRF52840 System on Chip (SoC), which uses its analog-to-digital converter (ADC) to measure a voltage drop over a series of measurement resistors. Resistor values are used to calculate the power consumption. The PPK2 has five different measurement ranges, which are managed by an automatic switch circuitry."

Kind regards,
Øyvind

[hmolesworth]

I just tested the Power Profiler Kit II (PPK2) with fixed 1% wire-ended resistors and short leads. I repeated the value used in the question of 5.1k (5k1) and also 510k. I set the source voltage to 3.314 volts, and measured the voltage across the resistor with a 5-digit DVM as well as measuring the resistor value (out of circuit) with a 5-digit meter.

I see 1.5% error on 5k1 and 0.3% error on 510k, assuming my quick calculation is accurate, which is good enough I think.

PPK2 PPK-II
Setting     Resistor Display DVM 5-digit          Actual   Error
=========== ======== ======= ==================== ======== =====
3.314 volts   5k1 1%  647uA  3.336 volts   5.116k 656.76uA  1.5%
3.314 volts 510k  1% 6.47uA  3.338 volts 514.400k   6.49uA  0.3%

This test was performed in Source Mode.

Edit: I have tested the same board and resistors in Ampere Mode using a CR2032 coin cell with curious results:

PPK2 PPK-II
Setting     Resistor Display DVM 5-digit          Actual   Error
=========== ======== ======= ==================== ======== =====
3.160 volts   5k1 1%  680uA  3.160 volts   5.116k 617.67uA  9.2%
3.231 volts 510k  1% 6.28uA  3.231 volts 514.400k   6.28uA  0.0%

This test performed in Ampere Mode had no measurable error at 510k load but a massive 9.2% error at 5k1 load. Perhaps someone might repeat this test to verify my findings; I ran the test a few times.

[hmolesworth]

This is more of a problem than at first sight. Alternating between Source Mode and Ampere Mode with Source Mode voltage set to the same as the CR2032 coin cell in Source Mode indicates 20uA in Source Mode and 10uA in Ampere Mode. (I tried to edit original response but the Reply/More/Edit stuff defeats me). This test is with nRF52832 in sleep, all outputs static no peripherals enabled, no connections to any pins, just LDO skipping and all 32 pins as outputs low driving . All 32 pins left as on reset figures are 18uA Source Mode and 7uA Ampere Mode when in both cases actual current is 1.16uA.

EXT+POWER_IN and VLDO on the PPK2 have the same 10uF capacitor on the PPK2, but the LDO impedance will be less than a coin cell; maybe the SAADC sampling requires adjustment to compensate for this although both readings are high which implies LDO skipping pulse peak "looks" longer than reality..

Edit: The original problem about not measuring in Ampere Mode is caused because the PPK2 has been incorrectly connected to the board you are testing:

Change (3.3 extern power)->resistor5.1k->ppk2(in)-->ppk2(out)-->gnd(ppk2 gnd)

To     (3.3 extern power)->ppk2(in)    ppk2(out)->resistor5.1k->gnd(ppk2 gnd)

The PPK2 takes the diffference in measured voltages because the measurement loads the input and output with 120k+30k each.

//                  <- Supply to DUT From VOUT                            External Battery To VIN
//             +------------------------------+                        +-------------------------+
//             |                              |                        |                         |
//             |              +---------+     |                        |     +-----------+       |
//             |              |     GND |     | VOUT              VIN  |     | GND       |       |
//   +---------O---------+    |    +----O-----O------------------------O-----O----+      |       | Battery
//   |        Vdd        |    |    |    |     |                        |     |    |      |       | + 3 volts
//   |                   |    |    |    |     |          AMPERE \      |     |    |      |     +-O-+
//   |                   |    |    |    |     |                  \     |     |    |      |     |   |
//   |                   |    |    |    |     #----#-----------O  O----#     |    |      |     |   |
//   | Device Under Test |    |    |    |     |    |                   |     |    |      |     |   |
//   |       DUT         |    |    |    | 120k|    |                   |120k |    |      |     |   |
//   |                   |    |    |    |    +++   |  \  SOURCE       +++    |    |      |     |   |
//   |                   |    |    |    |    | |   |   \              | |    |    |      |     +-O-+
//   |                   |    |    |    |    | |   +-O  O-- PPK LDO   | |    |    |      |       | Gnd
//   |                   |    |    |    |    | |                      | |    |    |      +-------+
//   |                   |    |    |    |    +++                      +++    |    |
//   |                   |    |    |    |     |                        |     |    |
//   |                   |    |    |    |     #-- VDUT           VIN --#     |    |
//   |                   |    |    |    |     |  Sense           Sense |     |    |
//   |                   |    |    |    |    +++                      +++    |    |
//   |                   |    |    |    |    | |                      | |    |    |
//   |                   |    |    |    |    | |                      | |    |    |
//   |                   |    |    |    |    | |                      | |    |    |
//   |                   |    |    |    |    +++                      +++    |    |
//   |                   |    |    |    |     | 30k                30k |     |    |
//   |                   |    |    |    +--#--+                        +--#--+    |
//   |                   |    |    |       |                              |       |
//   |                   |    |    |     =====                          =====     |
//   |                   |    |    |      ===                            ===      |
//   |        Gnd        |    |    |       =                              =       |
//   +---------O---------+    |    +----------------------------------------------+
//             |              |     PPK-II
//             +--------------+

[hmolesworth]

The original problem about not measuring in Ampere Mode is caused because the PPK2 has been incorrectly connected to the board you are testing:

Change (3.3 extern power)->resistor5.1k->ppk2(in)-->ppk2(out)-->gnd(ppk2 gnd)

To     (3.3 extern power)->ppk2(in)    ppk2(out)->resistor5.1k->gnd(ppk2 gnd)

The PPK2 takes the difference in measured voltages because the measurement loads the input and output with 120k+30k each.

[sonic74]

Thanks for the circuit diagram! Would be great as silkscreen on the next PCB revision instead of the simplified one.