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adafruit / Adafruit-nRF52-Bluefruit-Feather-PCB

PCB files for the Adafruit nRF52 Bluefruit Feather
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nRF52840 question: why is the AP2112 present on the board? #3

Closed lbdroid closed 5 years ago

lbdroid commented 5 years ago

The specifications for the nRF52840 include DCDC and LDO power regulators onboard capable of being supplied by any voltage from 1.7 to 5.5, including the ability to drive external 3.3v components (specifically, the multi-color LED and the external flash). The AP2112 has a quiescent current of 55-80 uA, which appears to be an unnecessary waste since the datasheet for the nRF52840 suggest that it can consume as little as 1 uA while being supplied by 5V.

It seems to me that the circuit would be simplified and efficiency improved by removing the AP2112, and instead of tying the nRF52840's VDDH to VDD, connect VDDH to the cathode of D1.

ladyada commented 5 years ago

we need 300mA minimum for accessories, whats the spec of the nRF52840 LDO?

lbdroid commented 5 years ago

Ah, ok. Then it makes sense since the nRF is maximum 25 mA. I suppose then that it would be nice to be able to operate without the AP2112 when external accessories are not required.

lbdroid commented 5 years ago

@ladyada : could you consider for future revisions, instead of connecting VDDH to VDD inside the footprint of the nRF, using a 0R beside it? This would make it possible for it to be switched from external to internal regulator for extreme low power needs when the higher current isn't needed for accessories.