External enable for NRF9160 boost converter

[jeremyherbert]

Hi,

I'm looking at using the NRF9160 in a system where every microamp counts. The NRF9160 already includes a DC/DC converter, but as I understand it is step down only, so when the battery is low I will need to use an external boost converter. This is a big waste of power when the rest of the system can run directly off the battery or at 1.8V, especially because the converter needs to support ~500mA in worst case, which generally rules out most ultra-low Iq options. Is there some way that I can run the device at 1.8V (or a weak 3.3V boost converter with only ~100mA supply), and only enable the higher power boost when the radio needs to transmit (ie during the initial join, message transmit and eDRX/PSM period expiration) with an external enable pin on the boost converter or similar?

I think the COEX2 pin could be used, but I am unsure about the exact criteria for it being set high, as well as the delay between COEX2 high and the actual peak current draw (the boost converter will need some time to start up)

[ketiljo]

No, that's not possible. The DCDC converters are controlled partly by HW and partly by the modem. Changes here will require custom modem FW. In any case, the power hungry part, the PA, is powered by a separate DCDC converter and completely disabled when the TX is is not active. 

[jeremyherbert]

Thanks. It would be good if you could perhaps consider this for the future in the modem firmware, much like how the COEX0 pin can be switched between LTE and GPS by an AT command. Even just knowing whether the modem is in sleep or not on an external pin would be very useful.

Right now my device wastes >80% of the standby current on the boost converter Iq and efficiency loss.