2
\$\begingroup\$

Circuit

In this circuit I'm using an MCP73832 for battery charging and an AP2210 LDO. The mosfet is a DMP3099L. With the USB disconnected, VBAT set to 4.2V and the MCU (STM32F030F4P6) in standby mode (drawing < 10uA), the total current graph looks like this:

enter image description here

The average current is around 50uA, which seems very high. Candidates for this high average current are the mosfet, the LDO and maybe the MCP73832 (but VCC is not connected, not sure if it can run from VBAT alone, the datasheet doesn't say anything about this that I can see).

This high average current consumption is the main problem, but perhaps the spikes are related?

The frequency of the spikes decreases with VBAT voltage, and their cadence is not fixed. For example, here's the graph when VBAT = 3.8V, where the spikes are between 6 seconds and about 0.8 seconds apart.

3.8v

The STAT pin is connected to a GPIO on the MCU which is in high impedance mode while the MCU is in standby mode.

So the questions are:

  • Why is the average current consumption so high?
  • What is causing the intermittent current draw?
\$\endgroup\$
3
  • \$\begingroup\$ What's the reverse leakage current in D1? \$\endgroup\$
    – Andy aka
    Mar 25 at 11:53
  • \$\begingroup\$ datasheet.lcsc.com/lcsc/2202131900_CBI-RB551V-30-D_C2836062.pdf At 20V the datasheet says 100uA but the only path to ground is via a 100K resistor. If we assume linear relationship between reverse voltage and leakage current (although I have no idea if that's a valid assumption), then it should be 20uA being dissipated mostly in that resistor \$\endgroup\$
    – Charlie Skilbeck
    Mar 25 at 12:41
  • \$\begingroup\$ Charlie --> look at figure 2 in the data sheet. At 25 degC the quiescent current is around 10 uA at 5 volts. But, if you operate your circuit at an elevated temperature you might get much more but, like you said, it's limited by the resistor (but that assumes nothing is being consumed by the 73832. See my answer also for what I believe is the main cause. \$\endgroup\$
    – Andy aka
    Mar 25 at 12:46

1 Answer 1

Reset to default
1
\$\begingroup\$

The average current is around 50uA, which seems very high.

The AP2210_3V3 has a quiescent current (aka ground current) specified as being 100 μA typically. It's also shown in this graph: -

enter image description here

And, in case there's any doubt what ground pin current means, read note 10: -

enter image description here

Why is the average current consumption so high?

It's the quiescent current of the LDO voltage regulator as outlined above. If you were building a batch of these circuits I'd advise that the current consumption in MCU standby might be over 100 μA in many.

What is causing the intermittent current draw?

It might be your MCU coming out of deep-sleep now and then to perform some housekeeping task.

\$\endgroup\$
1
  • 1
    \$\begingroup\$ Gotcha, thanks, I'll swap out the LDO for something with a low Iq, should get me where I need to be \$\endgroup\$
    – Charlie Skilbeck
    Mar 25 at 12:53

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.