nRF52840 HFCLK

[Al Bundy]

What kind of high frequency clock source is less current 'hungry', internal RC or external XO? I can not find any information in nRF52840 product specification?

It is possible to provide CPU core with 16 MHz or 32 MHz instead of 64 MHz for saving power consumption?

[Roger Clark]

Don't the reference designs already use 32Mhz. Check the PDK schematic, it shows 32Mhz and 32Khz crystal

I'm not sure how much power you would save using an external 16Mhz instead of 32Mhz. Ultimately the internals of the MCU and RF section will need to run at 64Mhz, so everything after the PLL multplier will take the same amount of power as they will all be running at 64Mhz.

So power savings by using an external 16Mhz crystal are going to be limited (even if 16Mhz is supported)

[Sigurd]

Hi,

Q1: What kind of high frequency clock source is less current 'hungry', internal RC or external XO?

A1: The internal RC uses less power, but the RC clock accuracy is much lower compared to using a crystal. If you are using BLE/Radio peripheral, you have to use an external crystal with a frequency tolerance of max 40 ppm.

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Q2: It is possible to provide CPU core with 16 MHz or 32 MHz instead of 64 MHz for saving power consumption?

A2: You can only run the CPU at 64MHz. Using a 64MHz clock will execute your tasks faster and overall you wont save power reducing the clock speed. We chose not to implement a clock divider because we found 64MHz to be most effective in terms of current consumption.