circuit recommendation to switch between LiP battery and usb source?

[dotconnector]

RE: nrf52840QIAA - Can you recommend circuitry necessary to switch source between the usb and LiP battery?  Can you recommend inexpensive/small footprint boost circuitry to charge LiP? 

[awneil]

Look at Analog Devices (formerly Linear Technology), Texas Instruments, Maxim, et al ...

Fpr the switching between sources, "power path" is the search term you need ...

[dotconnector]

thanks for the reply.  I see the 52840 has a pmic of a sort built-in, but I notice only buck regulators.  I'd like to understand if the pmic internally decides which source to use, battery or usb.  Or how much of this circuitry has to provided externally?  I thought this would be a really common design issue with off-the-shelf solution.  

[awneil]

What does the datasheet tell you ?

[Andreas]

Hi,

 

There are two stages of voltage regulators in the nRF52840 (REG0 and REG1). REG0 from VDDH to VDD and REG1 from VDD to internal rails <=1.3V. VUSB powers the USB front-end only. This gives two alternatives:

• Apply 2.5-5.5V to VDDH, not shorted with VDD. Uses both regulator stages, and allows you to use the VDD pins to supply external circuitry as long as overall load on the regulator is <50mA (nRF52840 + external)
• Apply 1.7-3.6V to VDD, shorted with VDDH. This uses only the REG1 stage and does not allow supplying external circuitry from the nRF52840

Both regulator stages can be configured to operate in a 'LDO mode' and a 'DC/DC mode', independent of the mode in the other regulator stage. The DC/DC mode will have improved efficiency at the cost of additional external inductors. For the time being you should mind errata 197 and errata 202, a fix for these is coming later this year.

 

For more information see the POWER section of the nRF52840 PS.

 

Best regards,

Andreas