Maximum Voltage NRF51822 in Low Voltage Mode (External DCDC)

RE: Maximum Voltage NRF51822 in Low Voltage Mode (External DCDC)

Håkon Alseth — Tue, 27 May 2014 09:10:23 GMT

It doesn't make sense to deactivate the LDO, as the voltage you're getting from your external DCDC is around 2.0V.

Let's say that you lower this to 1.95V (just on the limit of what the low-voltage mode can support, assuming no voltage ripple), then you will save: 1 - (1.95/2) = 2.5 % power.

However, if the other ICs on your board does not support this voltage (temp sensors min voltage is 2.0V), you are forced to run the nRF-device on >=2.0V with LDO power scheme to ensure that your temperature sensor works within spec.

Cheers, Håkon

RE: Maximum Voltage NRF51822 in Low Voltage Mode (External DCDC)

Mathias — Tue, 27 May 2014 08:32:12 GMT

Hi Hakon,

thanks again for your reply!

So it isn't possible to deactivate the LDO when using an external DCDC, since I assume the LDO has an standby current in the range of some 100nA to sume uA?

RE: Maximum Voltage NRF51822 in Low Voltage Mode (External DCDC)

Håkon Alseth — Tue, 27 May 2014 08:17:59 GMT

If you're using the 1.8V or the LDO (anywhere from VDD = 1.8 to 3.6V), the current consumption will be equal to the numbers in the datasheet. As it's an LDO, meaning that it drops to a given voltage internally and "burns" off the rest, the current consumption of the LDO will be equal to: Pldo = (VDD - VDDinternal) * I Where VDDinternal is around 1.7V.

I would recommend running on LDO power scheme at 2.0V, as the current that you "burn off" in the LDO is not very much.

Cheers, Håkon

RE: Maximum Voltage NRF51822 in Low Voltage Mode (External DCDC)

Mathias — Mon, 05 May 2014 11:46:05 GMT

Hi Hakon,

do you know the additional current consumption of the internal LDO?

Another option might be to use 1,95V and to hope that the ADS1118 will work at this voltage.

Best regards, Mathias

RE: Maximum Voltage NRF51822 in Low Voltage Mode (External DCDC)

Håkon Alseth — Fri, 02 May 2014 11:28:49 GMT

If your board uses 1.8 V low voltage mode, then powering the device with 2.0V is out-of-spec, and should not be used. You should configure it with power-scheme "schematic with internal LDO regulator" as shown in the product specification, chapter 11.2.1.

BR Håkon

RE: Maximum Voltage NRF51822 in Low Voltage Mode (External DCDC)

Mathias — Fri, 02 May 2014 11:23:34 GMT

Hi, thanks for your quick response.

So would you say 2.0V is critical regarding the lifetime?

Best regards Mathias

RE: Maximum Voltage NRF51822 in Low Voltage Mode (External DCDC)

Håkon Alseth — Fri, 02 May 2014 11:19:20 GMT

Hi Mathias,

It would then be better to run the nRF51-chip with internal LDO regulator power scheme. The current draw will be the same as in 1V8 mode. Exceeding the VDD_1V8 limit will most likely work (note: it's out of spec), but it will also decrease the lifetime of the device.

Best regards Håkon