Why the inrush current at startup is about 500mA

[Frederic]

When I use a power supply, (3.0Volts-60mA limitation) with the DevKit boards nRF51 or nRF52 the input voltage is clamped at around 2.0 V and the current is 60mA : the SoC doesn’t start.

By increasing the current limitation, step by step, the SoC start, with the current threshold of 80mA.

After the start up, the current of the devKit is low as expected. (With the software ble_peripheral>ble_app_hts s110 for nRF51 or s132 for nRF52).

I've checked the inrush current with a scope. I've seen a pulse of 500mA and 30µs width .

[Stefan Birnir Sverrisson]

Hi Frederic

There are two chips on the nRF51-DK board. One is nRF5x, the other is Segger chip. Nordic does not provide specification for the Segger chip. To measure the current on the nRF51 chip, you should follow section 5.7 in the nRF51-DK user guide. These methods you can use for measuring current for the nRF51 chip on the nRF51-DK board. Information on measuring current for the nRF52 kit is given on the following links (1) (2) (3)

The startup current consumption however for the nRF5x is not specified, i.e. until the chip comes out of reset state. When nRF5 comes out of reset state, the current consumption is specified.

[Frederic]

Hi Stefan,

Indeed on these DK boards there is the Segger but I didn't measure it, just the nRF5x. I've also my own boards without the Segger and I have the same peak of current at startup. The current consumption after the nRF5x comes out of reset state is as specified in the datasheet.

During the VCC rising I have to know the worst case because I have an external power supply with a limited current. The inrush current I've measured (500mA during 30µs) is not acceptable for most of our applications. Please could you make the same measure at startup to be able to specify this current.

Best regards Frederic.