Powering an arduino mkr from a 2S li-ion pack

Thread Starter

Snotvalling

Joined Aug 12, 2023
7
I'm building a battery operated device using an Arduino MKR WAN 1310 and a HX711 load cell board.
I'm using a 2S li-ion battery pack (I also need higher voltage for other parts of the project which is why I'm using a 2S setup).

Now I'm looking for an LDO voltage regulator with low quencient power to power both the Arduino and the HX711.
The Arduino can take 3.3V or 5V. The HX711 needs 5V.

I was not very successful at finding voltage regulators that are available, have a low quencient power and a current rating above 600ma.
I did find the LT1129 that can deliver 5V 700ma, which should be good ?

Now my question is: Is the LT1129 a good choice?
Someone else told me it's an old one, and he said there will surely be newer ones with much lower self-consumption.
I think they guy was incorrect because I was unable to find a better LDO alternative and with a quencient current of 50uA it should be good for a battery operated device too...

My project needs long battery life. So the Arduino will be in sleep mode most of the time.
So, I need to make sure the voltage regulator has a low self-consumption too offcourse.
 

ericgibbs

Joined Jan 29, 2010
18,826
Hi Sn,
Welcome to AAC.
Are you powering down the HX711 module and bridge during the Sleep mode.
The HX711 will work on 3.3v

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EG57_ 1054.png
 

Thread Starter

Snotvalling

Joined Aug 12, 2023
7
Yes, the HX711 will be powered down when the arduino is in sleep mode.
You're right the HX711 will work with 3.3V too. I always thought they were 5V because last time I used them I needed 5V for a specific load cell that didn't work with a voltage below 4.5V

Ok. So I can go for the LT1129 3.3V variant and power the arduino and HX711 from 3.3 instead. Skipping the arduino's built-in voltage regulators. Should consume a little less power this way, right?
 

ericgibbs

Joined Jan 29, 2010
18,826
Hi,
According to the LT1129 d/s Shut Down current is 16uA, it looks OK.
E

  • 400mV Dropout Voltage
  • 700mA Output Current
  • 50μA Quiescent Current
  • No Protection Diodes Needed
  • Adjustable Output from 3.8V to 30V
  • 3.3V and 5V Fixed Output Voltages
  • Controlled Quiescent Current in Dropout
  • Shutdown
  • 16μA Quiescent Current in Shutdown
  • Stable with 3.3μF Output Capacitor
  • Reverse Battery Protection
  • No Reverse Output Current
  • Thermal Limiting
  • Surface Mount SOT-223 and DD-Pak Packages
 

Thread Starter

Snotvalling

Joined Aug 12, 2023
7
Thanks. If not mitaken I can use the shutdown pin of the LT1129 with 3.3V logic too?
So I can use LT1129 to power on/off other parts of the project, from an arduino pin.
 

ericgibbs

Joined Jan 29, 2010
18,826
Hi,
The d/s states the following.
Use a resistive divider from the 3.3v pin, also ensures the pin doesn't float when MCU powered into sleep

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EG57_ 1055.png
 

Thread Starter

Snotvalling

Joined Aug 12, 2023
7
In the datasheet I read " . This allows the shutdown pin to be driven directly by 5V logic or by open collector logic with a pull-up resistor. " But It does indeed also show that it'll turn ON with a voltage above 2.8V on SHDN.

That's why I was thinking I can just turn it on/off with 3.3V logic signals? I'm not quiet sure where the resistive divider comes in.
 

ericgibbs

Joined Jan 29, 2010
18,826
Hi,
Can you confirm if the MCU pin that drives the shut down assumes a low state during sleep?
Or an Open circuit output, if so the shut down pin may 'float'
E
 

ericgibbs

Joined Jan 29, 2010
18,826
If you are sure that pin will be held as an active Low during Sleep, it should be OK.
If there was a possibility it could become an open state, a 10k resistor to 0v would ensure a low state for shut down.
 
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