Test of Step-Up-Modules (sparkfun, Pololu & china-module) / any other?

[ericvdb]

Just took the time to shoot a pic of my Step-Up consumption, including a Voltage regulator MCP1702-3.3

As you can see, it's consuming 54uA with nothing connected.

Step-Up module: link

The capacitors are really important, one on the input of the step-up module, the other on the output of the MCP1702-3.3, both are 22uF. Without them, consumption is 2.20mA

[icebob]

@ericvdb great observation. But this board is not an MCP1702, because MCP1702 is a voltage regulator IC

[m26872]

Reading this thread again makes me remember another observation I did when was trying to get my mini PIR sensor up and running.

I was measuring load current and switched between the old "big" china step-up and the now more common smaller sized one. Identical load. The sleep current was a lot more for the newer smaller one. Could have been those 240uA, not sure but I remember it was the double or something. I was really confused since the two boards look to be populated with the same componets. I didn't look into this further cause I could bearly make the PIR stable on boost supply in any way.

Edit. Power Led disabled, of course.

[icebob]

On my custom node PCB, I will use MCP16251 chip to boost supply to 3.3V.
http://ww1.microchip.com/downloads/en/DeviceDoc/25173A.pdf

By docs, If I use it from one AA battery (1.5V), the efficiency is ~80%, consumes ~14uA. I think it is not bad.

[ericvdb]

@icebob said:

@ericvdb great observation. But this board is not an MCP1702, because MCP1702 is a voltage regulator IC

Where did you read that it's an MCP1702??

This test setup has a Step-Up module to 5V AND a voltage regulator to 3.3V. I never mentioned the MCP is included in the Step-Up module.

[icebob]

@ericvdb Sorry, I read somethingh wrong :)

[rvendrame]

@ericvdb , do you have any data sheet for this step-up? Or do you know which is the core chip?

[ericvdb]

No time to look for the datasheet atm, but here are some pics:

[scalz]

Hi.

maybe it could help some people to "evaluate theoretical" quiescent current...

if I remember right (I am not in front of my stuff), we can calculate the theoretical power consumption at Input like this:

I_input = (Vout * I_circuit)/(Vbat * Eff)

where
I_input = power consumption at Input
Vout = booster voltage output
I_circuit = power consumption of the circuit
Vbat = battery voltage
Eff = booster efficiency for Vout and Vbat

Now, if we take MCP1651, and says we have:

• a circuit which consumes 50uA (including booster quiescent current, sensors, leakage and a well designed circuit...)
• a MCP16251 booster with 3.3V output on a single 1.5V cell. Efficiency won't be the same during the whole life. And it is not an ultra high efficiency booster or it it would be named like "ultra high" (when they can, they do advertisement ;) ). This is why we can only see the efficiency at 1mA. But what is efficiency under very light loads (<100uA)? It should need to be tested. no matter, we assume it is like on datasheet.
  So here we have Eff=85% at VIN=1.5V and Eff=80% at 0.9V (near end of life)

Some maths gives us:
I_input = (Vout * I_circuit)/(Vbat * Eff)
I_input = (3.3V * 50uA)/(1.5V * 0.85)
I_input= 129uA
So it should use approximatively 129uA at Input/batt.

Another maths, if batt is at the end of life:
I_input = (3.3V * 50uA)/(0.9V * 0.80)
I_input= 229uA

So here we can see that quiescent current of booster is not always the biggest problem.

I hope it can help in your choice. And I hope to have not done a mistake lol!

[icebob]

@scalz: thank you for you calculation. It's interesting. I will measure it if I receive the MCP16251.

[Adi Vacaru]

This guy has actually tested the mcp16251 and posted his findings on YouTube https://m.youtube.com/watch?v=O5o6JUjz6Yc