nRF9160 has two power inputs: VDD for internal parts and VDD_GPIO for GPIO pins. VDD_GPIO consumption should be observed in measurements, because load on any GPIO pin is visible on VDD_GPIO.
nRF9160 contains an internal DC/DC converter operating in a hysteretic mode when the device is in a low power consumption state. In this mode, the internal DC/DC periodically charges supply capacitors. The charging cycle creates spikes in current consumption. During a charging period, current consumption is typically in the mA range, but during a quiet period it can be less than 1 µA.
The performance of the test equipment should be carefully considered when setting up a power consumption measurement system. The most important criteria are good sensitivity for low currents, high dynamic range, and good sample rate. For example, Keysight 6715C power analyzer with auto-ranging power modules and Keithley DMM7510 multimeter are viable options. Nordic Semiconductor's Power Profiler Kit II can also be used for current consumption measurements.
Temperature has a significant impact on current consumption in the low power mode. The current consumption is higher in high temperatures and lower in cold temperatures. Accurate and repeatable measurements require stable temperature in the test environment.
The measured current depends on the battery voltage. The current consumption decreases with higher battery voltage. As a result, the consumed power in watts is approximately constant.
It is important to verify transient behavior in VDD voltage under maximum power RF transmission and ensure that the VDD level stays within expected values. Too low VDD during RF transmission may degrade signal quality and cause a Device Under Test (DUT) reset.
PSM, cDRX, and iDRX current consumption example shows an example of nRF9160 waking up from the Power Saving Mode (PSM) mode, performing a Tracking Area Update (TAU) towards the LTE network, entering connected mode Discontinuous Reception (DRX) for three seconds, and finally entering idle mode DRX. The RF transmission is done with maximum power. The resulting peak current consumption is approximately 300 mA in this example measurement.
Power consumption between the idle mode DRX paging periods is in the µA range. In PSM, cDRX, and iDRX current consumption example, the zoomed-in image from that period shows typical PSM mode consumption with a DC/DC converter charging pulses.
For typical current consumption in different operational states, see Current consumption in nRF9160 Product Specification.
For more information on measuring current consumption on the nRF9160 Development Kit (DK), see Measuring current in nRF9160 DK User Guide.
For estimating current consumption and battery life at an early stage of design, see the Online Power Profiler tool in Nordic Semiconductor DevZone.