Hi,
I'm making a new design. I want to use the NRF52840. I also want a low power microphone interface.
PDM seems like a good idea, modern PDM mics have low power modes at reduced clock rates with currents much less than 300uA.
The NRF52840 has a PDM input but it appears to have two obstacles preventing it working for my application based on all the information I could find:
1) It doesn't support low power modes with reduced clock frequency.
I found information related to increasing the clock rate. But I need to reduce the clock rate to ~750kHz for devices like the SPH0641LM4H-1
2) It only supports clock generation from the HFCLK
I think this means the power consumption will be much higher than I need since the HFCLK is power hungry and requires continuous power for the PDM to work. A possible workarround would be to enable an external clock or to be able to use the LFCLK as the clock generator (albeit at a fixed 1MHz)
Please can someone confirm the limitations or provide a work-around or clarification?
Thanks
Karim