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  • Case ID: 329958
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Power Profile Kit II doesn't show current value when it is testing the current in GND

huapage

I am testing the current consumption of SIM cards with PPK2.


When PPK2 is connected to VCC ( voltage 1.8 v or 3 v ), the PPK2 can display the current properly ( around 9 mA ).


But when PPK2 is connected to GND ( voltage 0 ), the PPK2 cannot display the current properly ( display as 1 mA, but actually it should be 9 mA ). With oscilloscope I can see correct current value.

PPK2 current measurement cannot work properly in low voltage?

Application Version is 4.1.2

  • 0

    Possible related the GND connection. In Power Profiler Kit II, I see 4 pins. GND1, VIN, VOUT and GND2 ( from left to right ).

    The connection of GND1 and GND2 may impact the test result. (Why AMP mode need connect GND? strange ).

    When testing the current near GND case, since VOUT also connect to GND, possible Power Profile Kit II is confused by these 3 GNDs then cannot get correct value.

  • 0

    Hello,

    Could you perhaps share a picture of your set-up/the connections that you made.?

    Regards,

    Swathy

  • 0 in reply to SwRa

    Hi,

    I found I can reproduce this issue in a simple setup.

    Use a 5V power and 500 ohm resistor.

    If connect in this way ( connection_type_01 )

    Power 5V --> 500 ohm resistor --> PPK2 VIN --> PPK2 VOUT --> Power GND, you will see the following wave, sure the current is wrong ( should be 10 mA )

    Then if you connect PPK2 GND ( near the PPK2 VOUT ) to GND, you can get good wave, but the current is only 1 mA, which is not correct, should be 10 mA.

    See the test result:

    If connect in this way ( connection_type_02 )

    Power 5V --> PPK2 VIN --> PPK2 VOUT--> 500 ohm resistor --> Power GND

    Without connect PPK2 GND to Power GND, the test result is similar to connection_type_01.

    But when PPK2 GND is connected to Power GND, the result is OK, it shows the current is around 10 mA.

    So the PPK2 GND is useful for testing, if the PPK2 GND and PPK2 VOUT both connect to Power GND (connection_type_01 case), the result is not correct.

  • 0 in reply to huapage

    The strange things is why AMP mode need to connect 3 lines then can measure current ( VIN and VOUT can understand, GND not sure what is the usage in AMP mode). When I use multimeter to test current, only need to connect two lines then can get result.

  • 0 in reply to huapage

    The PPK2 is based on a nRF52840 which has no current measurement feature, only voltage measurement via the internal SAADC. The internal code is not released, but this may be ether a single-ended or a differential measurement. Current I = (VIN-VOUT)/Rc where Resistor Rc for current sense is 1k0 in parallel with one or more of 110R, 11R0, 1R0 and 0R051 for the different measurement ranges. The nRF52840 SAADC may not perform well when measuring an input voltage connected to GND, which might give erroneous results for current if not compensated for in the software (which we do not have details of). The PPK2 is designed to measure current in the load on VOUT, not on the load on VIN; connection type 2 with VIN->500R->GND is correct provided the GNDS are all common.

    // Resistor Rc for current sense is 1k0 in parallel with one or more of 110R, 11R0, 1R0 and 0R051
//
//              <- +ve Supply to DUT From VOUT                               External Battery +ve To VIN
//             +------------------------------+                             +-----------------------+
//             |                              |                             |                       |
//             |              +---------+     |                             |     +---------+       |
//             |              |     GND |     | VOUT                   VIN  |     | GND -ve |       |
//   +=========O=========+    |    +====O=====O=============================O=====O====+    |       | Battery
//   |        Vdd (+)    |    |    |    |     #----+                        |     |    |    |       | + 3 volts
//   |                   |    |    |    |     |    |Rc        AMPERE \      |     |    |    |     +-O-+
//   |                   |    |    |    |     |   +++                 \     |     |    |    |     |   |
//   |                   |    |    |    |     |   | |   +-----------O  O----#     |    |    |     |   |
//   | Device Under Test |    |    |    |     |   | |   |                   |     |    |    |     |   |
//   |       DUT         |    |    |    | 120k|   | |   |                   |120k |    |    |     |   |
//   |                   |    |    |    |    +++  +++   |   \  SOURCE      +++    |    |    |     |   |
//   |                   |    |    |    |    | |   |    |    \             | |    |    |    |     +-O-+
//   |                   |    |    |    |    | |   +----#--O  O-- PPK LDO  | |    |    |    |       | Gnd (-)
//   |                   |    |    |    |    | |                           | |    |    |    +-------+
//   |                   |    |    |    |    +++                           +++    |    |
//   |                   |    |    |    |     |                             |     |    |
//   |                   |    |    |    |     #-- VDUT                VIN --#     |    |
//   |                   |    |    |    |     |  Sense                Sense |     |    |
//   |                   |    |    |    |    +++                           +++    |    |
//   |                   |    |    |    |    | |                           | |    |    |
//   |                   |    |    |    |    | |                           | |    |    |
//   |                   |    |    |    |    | |                           | |    |    |
//   |                   |    |    |    |    +++                           +++    |    |
//   |                   |    |    |    |     | 30k                     30k |     |    |
//   |                   |    |    |    +--#--+                             +--#--+    |
//   |                   |    |    |       |                                   |       |
//   |                   |    |    |     =====      <<== Common Gnd ==>>     =====     |
//   |                   |    |    |      ===           (Common -ve)          ===      |
//   |        Gnd (-)    |    |    |       =                                   =       |
//   +=========O=========+    |    +===================================================+
//             |              |     PPK-II
//             +--------------+

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