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Internal DC/DC Operating Voltage?

Hello I have what I hope is a simple question regarding the Internal DC/DC on the nRF52832 and thus nRF52810.  I am assuming it is the same internal design, correct between these 2 devices...

Use Case: -12dBm Tx Power, Beacon interval 2seconds, VBat/Vdd = 1.8-3.1V, Internal DC/DC Enabled, External DC/DC Boost is Enabled only upon Beacon Connecting to Client Vdd Boost = 3.3V.  

What is the minimum Vdd that the internal DC/DC can operate from.  The nRF52832 indicates that it can operate from 1.7-3.6V but I don't see any specific mention as to what the minimum voltage that the DC/DC requires to still function correctly?  

My question stems from a scenario that I am observing in which we are powered from 2 AAA batteries and using an external DC/DC Boost in Bypass Mode 98% of the time(just passes battery voltage when the external DC/DC boost is disabled).  What I am seeing is that at VBat < ~2.0 the IDD rises significantly in which I would expect the IDD to continue to drop if the Core voltage the internal DC/DC is regulating to is 1.3V as is shown on the Diagrams such as Figure 14: in the nRF52832 datasheet.

Measurements taken are shown below.  The Minimum IDD(in between Tx) stays relatively steady at ~12-14uA.

VDD = 2.4V Peak IDD = 210uA

VDD = 2.3V Peak IDD = 214uA

VDD = 2.2V Peak IDD = 219uA

VDD = 2.1V Peak IDD = 226uA

VDD = 2.0V Peak IDD = 231uA

VDD = 1.9V Peak IDD = 242uA

VDD = 1.8V Peak IDD = 255uA

Based on this is there a crossover where the DC/DC should be disabled because of inefficiencies at lower voltages?  

Secondarily is it safe to Enable/Disable the internal DC/DC on the fly?

Regards,

Sensor Maestros

  • The minimum operating voltage is 1.7 V, for both LDO and DCDC operation.

    The current draw will increase when the operating voltage gets lower. This is because the efficiency of the DCDC converter gets lower when the difference between the input and output gets lower. But the DCDC converter will be more efficient than the LDO even at 1.7 V. So there's no reason to switch to LDO mode even at 1.7 V.

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