PCA10040 power measurement

[Steve H]

I've modded the PCA10040 DK for current measurement with an ampere-meter (TTi 1604), using a program which turns an LED on and off every 5 seconds. The measured current stays at around 3uA regardless of whether the LED is on or off. However, the power supply shows a 3mA drain when the LED is on.

Any idea where the disparity is coming from - is the LED supply not drawn through the DK current measurement connection?

[Stian Røed Hafskjold]

Hi,

The LEDs are powered by VDD, which is from the external power pins, Battery or USB. The nRF chip is powered by VDD_nRF. The link between VDD and VDD_nRF is P22 where you are measuring current, so the only thing you are measuring on P22 is the current going in to the nRF.

When you are turning on the LEDs from the nRF chip, you are pulling the GPIO to ground. Which means that current is flowing directly from VDD (power supply) through the LED, down to GND. Not going through the chip, or P22.

[Steve H]

Great, thanks for the clarification Stian.