Using a switching regulator to step down voltage from 21,6V to 3.3V to power nRF52840

[Eirik Bodsberg]

Hi,

I am developing a PCB with the nrf52840 chip. The chip is implemented as described in the datasheet (Circuit configuration no. 6 for QIAA aQFN73), using the files that can be downloaded from the nordic webpage. The chip will act as a central unit, and communicate with other peripheral units via BLE over a relatively close range (<2 m). The chip will be powered by a battery with a nominal voltage of 21.6 volts. My plan is to step down the voltage to 3.3 volts, using a switching (buck) regulator, implemented with recommended circuitry for filtering and a frequency of 800 kHz. 

My main question is if it is suitable to power a nRF52840 chip with a switching regulator as described? (as this may cause greater power supply noise than a linear voltage regulator)

Secondly, the datasheet 7.3.15 describes that long power lines on the PCB should be avoided. Should I opt to place the voltage regulator close to the chip, or may this disturb RF signals?

Thanks for any reply!

Best Regards

Eirik

[ketiljo]

This shouldn't be a problem. The switching frequency is high enough to be properly filtered. Use a ferrite bead in series with the nRF52840 power supply in case there are high frequency components that's slipping through.

Use the recommended decoupling caps from both regulator and nRF52840 reference schematics and you should be fine.