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Suitability of D36V6F3 as an LDO replacement

Hi folks,

I’ve had good success using Pololu step-down regulators in conjunction with 7.4 V LiSOCl2 batteries over the past few years to power the Iridium satellite transceivers in my instrumentation deployed in the Arctic.

With both SparkFun and Adafruit almost universally adopting the AP2112 LDO regulator for all of their microcontrollers, I’m now faced with a 6 V input voltage restriction. This has led me to explore the possibility of bypassing the AP2112 and powering the 3.3 V rail directly using a D36V6F3 3.3V, 600mA Step-Down Voltage Regulator (manually replacing the LDO isn’t desirable).

I’ve been running some tests over the past couple of weeks, and the D36V6F3 appears to be doing a good job of powering my circuit. When enabled, the current draw of the regulator at 7.4 V is measured to be ~64 uA (0.5 mW), which is comparable to the AP2112. The overall draw of the circuit shoudn’t exceed 50 mA, so voltage dropouts aren’t a concern.

My main query pertains to efficiency. I am cognizant of the fact the D36V6F3 is not intended for extremely low quiescent loads (my circuit has a sleep current of ~50 uA). Based on the provided graph, it seems that the step-down regulator should be between 60-70% efficient under the circumstances.

My questions are:

  1. Would the D36V6F3 be a feasible alternative to the AP2112?
  2. If so, is there any way to quantify how much power is actually wasted?

image

Cheers,
Adam

Hi.

The 50uA draw of your project while it is asleep is low enough to basically count as quiescent, so in that state it sounds like you have already compared the D36V6F3 and AP2112. For currents near 50mA, the data we used to make the graphs shows efficiencies between 75-80%. The datasheet you posted for the AP2112 does not have any efficiency graphs, so I cannot say how much better or worse it might be.

If you have a meter that can accurately measure sub-milliamp units, you could measure the input and output current and voltage to find the efficiency at any particular state of your system. Ideally, you would use four meters so everything is measured at the same time, but you could probably get a pretty good sense by measuring all four one after the other.

-Claire

Hi Claire,

Thanks for your reply.

I should clarify that the ~50 uA quiescent draw was measured between the 3.3 V output of the D36V6F3 and the Arduino’s 3.3 V rail. At 7.4 V, I measure a total system quiescent draw of ~78 uA. Still good results, given that the bulk of this (~64 uA) can be attributed to the D36V6F3.

My uncertainty was mainly regarding how efficiency losses can be measured/calculated. I appreciate the tips on how to go about doing so.

Cheers,
Adam