LDO and DC/DC of nRF52840 can be configured to drive the external memory device working at 3V, 25mA?

[Dhara]

Hi,

The Ch. 16 Power Supply Section of  "nRF52840 Objective Product Specification v0.5" mentions the two power supply mode of nRF52840. This supply is available on the respective power pins of the IC.

Can these be implemented as a power source to drive the memory IC operating at 3V, 25mA and analog front end device working at 3V, 15mA..? Also, note that at the same time can I operate the nRF52840 at 1.8V input voltage?

Please let me know if somebody has worked upon the similar scenario and utilized the internal power supply of the nRF52840 to drive the external devices.

Thanks.

[Andreas]

Hi,

 

Objective Product Specification v0.5 is outdated, get the updated one here.

 

You can supply up to 25 mA without concerning yourself with how much current the nRF52840 itself draws (provided RF output power is 4dBm or less). You might be able to exceed this slighty, but only at times where the nRF52840 is at low draw, and never exceed 50 mA.

 

The voltage output at VDD is also the voltage that the nRF52840 'operates at'. You can not supply 3.0V to your memory device and operate 1.8V, you need to supply and operate at the same voltage.

 

Best regards,

Andreas

[Dhara]

Hi Andreas

Many thanks for your reply.

As per my application, I have estimated that nRF52840 will require around 21~22mA operated at 1.8V. I want to interface the following devices with nRF52840.

a) NAND flash 2GB SPI memory running at 3V, 25mA

b) Ànalog front End IC at 3V, 15mA

Can I still drive these (a) and (b) using the nRF's internal LDO or DC/DC power supply..?

-Dhara.

[Andreas]

Hi,

 

No, you can not operate the nRF52840 at 1.8V and supply 3V at the same time. You need to supply VDDH, between 2.5V and 5.5V, and use VDD to both supply external circuitry and the nRF52840 at VDD voltage, either 1.8V or 3V, but not both at the same time. With VDDH as input, VDD becomes output for supplying external circuitry and input for the nRF52840 main systems. If you need to run at 1.8V for GPIO level compatiblity then you need to regulate the 3V for the flash and front-end with a separate regulator if your main power rail is higher than 3V.

Even if it would be possible, the external current draw is still exeeding our specifications. WIth radio output power lower than 4 dBm (which would be with an external FEM), max external current draw should not exceed 25 mA. You either need to supply these outside the nRF, or make sure the NAND flash is shut down when the radio is running, and vice-versa.

 

Best regards,

Andreas