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PSM Current 0.7uA

bsams

We're using the UDP SDK example on the NRF9160DK with modem fw 1.2.3 (10 minute sleep, 0 second active timer), and we're seeing a current of 0.7uA when measuring on the header on the dev kit with the dk in PSM mode. The device behaves as expected, waking up every 10 minutes and sending packets, and we see the expected current waveform for these times when the device is awake. For the sleep though, we are expecting to see around 2.7uA (from the datasheet). Is something going wrong? Or is the datasheet out of date? We're also using the most recent modem hardware revision. We're using a Keysight N6705 Power analyzer to measure the current, and a CMW500 for the cell communication, so it seems unlikely that the measurements are incorrect. 

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    Hi, yes, 0.7 uA sounds too low. You can try to use the N6705 as a power supply, not as an ampere meter. It will give more accurate results since you bypass the (noisy) switching regulators on the DK.

    Here's how I usually connect the DK for current measurements using a N6705 power analyzer:

    (edit: I see now that the power switch in the picture is set to OFF. It should be in the ON position)

    Then configure the power analyzer to "2 quadrant power supply" and 3.7V voltage output.

    It's important to use automatic range switching.

    Here's how the PSM current should look like (running the UDP sample from NCS):

    Use 250 ms/div and 512k sampling points to get the best resolution (5us) (if you choose to capture using the scope function, not data logger). Click on the "Ranges..." button and make sure that the channel is set to "Current: Auto"

    If you still see 0.7 uA in PSM, can you measure the floor current between the regulator refresh spikes (all the spikes you see in the plot above are from the internal regulator). It should be around 1 uA. If you see less or a negative value, I'm thinking that the 91 is powered from something externally. Not sure what that could be. What is the DK version? I can try the exact same setup here

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  • 0

    Hi, yes, 0.7 uA sounds too low. You can try to use the N6705 as a power supply, not as an ampere meter. It will give more accurate results since you bypass the (noisy) switching regulators on the DK.

    Here's how I usually connect the DK for current measurements using a N6705 power analyzer:

    (edit: I see now that the power switch in the picture is set to OFF. It should be in the ON position)

    Then configure the power analyzer to "2 quadrant power supply" and 3.7V voltage output.

    It's important to use automatic range switching.

    Here's how the PSM current should look like (running the UDP sample from NCS):

    Use 250 ms/div and 512k sampling points to get the best resolution (5us) (if you choose to capture using the scope function, not data logger). Click on the "Ranges..." button and make sure that the channel is set to "Current: Auto"

    If you still see 0.7 uA in PSM, can you measure the floor current between the regulator refresh spikes (all the spikes you see in the plot above are from the internal regulator). It should be around 1 uA. If you see less or a negative value, I'm thinking that the 91 is powered from something externally. Not sure what that could be. What is the DK version? I can try the exact same setup here

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