PPK2 Insertion Impedance

[JLThompson]

What is the insertion impedance when using the PPK2 to monitor power consumption? My project uses a CR2450 battery and runs fine directly from that power source. It also runs fine using the PPK2 to supply power. But when I use the PPK2 to monitor the power my project draws from its battery, the project will not boot up and the PPK2 shows a sequence of current pulses that hit a peak, then rapidly decay.

[hmolesworth]

Maybe try forcing the PPK2 to a less sensitive range, as the range-switch on the PPK2 is slowish. I made these notes some time ago to show the range series impedance. To test simply place a bypass resistor across the DUT which will force the PPK2 to be in low-impedance mode before the DUT is connected; if it boots ok then this is probably the issue.

// note the resistor (labelled DUT) must connect to the PPK-II Gnd and not just the battery negative.
// The PPK-II is not a 2-wire current meter but a 3-terminal voltage monitor which reads the voltage
// across the internal series resistor RC where Rc is used for current sense
// Resistor Rc for current sense is 1k0 in parallel with none or more of 110R, 11R0, 1R0 and 0R051
//
//              <- +ve Supply to DUT From VOUT                               External Battery +ve To VIN
//             +------------------------------+                             +-----------------------+
//             |                              |                             |                       |
//             |              +---------+     |                             |     +---------+       |
//             |              |     GND |     | VOUT                   VIN  |     | GND -ve |       | CR2450
//   +=========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
//             +--------------+

[JLThompson]

I was trying to use the PPK2 as a simple ammeter in series with the battery, a 2-wire connection.. I didn’t realize I needed to use all 4 wires. Now it works! Thanks!!