nRF52840 VDD output current maximum (Reg0 DCDC )

[Marien]

Hi,

We are going to evaluate:  nRF52840  with a large NOR flash.
This Flash has two options:  3.0V / 50 mA max,  Or 1.8V / 50 mA max.
We prefere to use the 1.8V type, as this is better low power.

But the nRF52840 datasheets specifies:  max external current at VDD  = 25 mA.
We gone use a 3.6V Li-ion battery, direct to VddH. Reg0 = DCDC mode.  VDD  = delaut = 1.8V.
The flash seems not to be power bij VDD as the DCDC seems not to deliver enough current.

The VDD shall supply the complete nRF chip:   Core, peripherals, BLE.
BLE will also require less battery energy if we set VDD to 1.8V.  BLE needs 16 mA
The Core activity is not known yet, but lets state 50%.  That will be 2 mA?
Then peripherals and IO.  Not known yet.

Our question is about the DCDC it's self.   How much current can it deliver?

Than we can calculate the remainig current for the flash.

[Robin M Saltnes]

Hi Marien 

As Jörg is pointing out the maximum external current the nRF52840 can provide is the 25 mA as specified in the datasheet. This is because the max current draw specified in the datasheet is the sum of all GPIO currents and is not affected by the chip's internal power consumption. The limiting factor is not how much power that's available to the chip, but how much current the chip can handle to put out through the GPIOS. Which is rated at 25 mA when the chips output power is set to 4 dBm or less. Anything more than this, i.e running the chip with even lower output powers, is outside of our spec and have not been validated by us.    

I would suggest powering your flash directly from the battery via an external Low-dropout regulator or DC-to-DC converter. 

Best regards 

Robin