Sim7000E High current draw knocks out Voltage regulator (MCP1700-3302E LDO)

Hi all ,

I was wondering if someone would be able to help me with my circuit.

I am trying to make a low current sleeping device so I am using the MCP1700-3302E with a large 3.7v battery. I am powering the SIM7000 directly via Vbat and then powering the Arduino pro mini 3.3v via the MCP1700.

I currently have the issue that the high current draw of the sim7000e (2amps peak) knocks out my voltage regulator I am using to power my Arduino and causes a reset.

The LDO has inbuilt surge protection and I believe this is why it is restarting.

Does anyone know how I could put a circuit before the regulator to protect it from the high switch on the current of the sim7000?



Thats only capable of 250mA.

You could try some very large electrolytic capacitors, or a super cap, but thats really the wrong regulator for the job.

Always best to state which Arduino you are using as well, it can make a big difference.

I am guessing its a bare bones Atmega328P setup, in which case what bootloader did you program it with ?

I need a regulator that has a low operating current as the Arduino will be asleep a lot of the time. (1.6uA as per the data sheet)

I do have a large cap for the sim7000 supply of 4700uF but it doesn't seem to help.

Also, I am not driving the high current draw device with the mcp1700 so I am not sure why it drops out as that current is only being pulled by the sim7000.

I have tried to use another PSU for the sim7000 but it still knocks the mcp1700 out...

The Arduino I am currently using is a standard Arduino pro mini 3.3v on a board powered via the 3.3V VCC not the RAW as the onboard voltage regulators dont allow for a low enough sleep current.

Obviously I would like to add that having two batteries fixes the issue but this is not really preferred and I would like to stick with one.

How do you know the MCP1700 is 'dropping out' ?

Well its a theory I guess but I saw on the data sheet this - image

But it is stating only for output current ...

However it makes sense to what I am seeing as when the Arduino resets because of this , the relay is switched off at the start and so the current draw isn't happening and the cycle repeats it self...

Maybe its something to do with the relay.. but that doesn't make sense as they are not being driven by the Arduino and have fly back diodes

I strongly suspect your guess is wrong.

If the Arduino is resetting, its far more likley that its brown out detection circuit is seeing a spike on the supply and resetting, as intended.

You can, with the minicore for Atmega328P, reprogram the bootloader so that the appropriate brownout voltage is selected, 1.8V for a 3.3V Pro Mini or disable it all together. This might help, but there is no guarantee that the supply glitches wont crash the processor.

Power the Atmega328P with its own regulator .....................

Okay , so there isn't there hardware that I could use to limit the current to the LDO and stop the spike to the arduino?

I can't use the onboard one it is not suitable for the low current draw.

something like this?

You get the same issue when powering up some GPS, the switch on current spike resets the Arduino. To remove this issue I slow down the turn on of the MOSFET that switches the power;

Slow Down Circuit

Ah okay , sorry I have little knowledge of MOSFETs but how have you gone about slowing it down ? can I do that with my relay setup?

I have also just checked I may be able to use the onboard MIC5205-3.3YM5-TR but yes as you say , I think the issue will still happen as its Arduino related not PSU.

Can you post a picture of your project so we can see your component layout.
Do you have the SIM power wires connected directly to the battery? (including gnd)
Do you have the regulator power wires connected directly to the battery?(including gnd)

In other words are your power connection star configured so no SIM supply current flows in the regulator supply wires.

Tom... :grinning: :+1: :coffee: :australia:

Time to do some searching on the Internet then.

The capacitor slows down the turn on of the MOSFET.

The sim power wires are connected directly yes as well as the regulator.

Star configured...? I need to research this...

To conclude this topic - the problem was the track width of the GND on my PCB (needed to be 2mm) to not cause a voltage drop which in turn caused the psu to drop out.

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