Author Topic: Wide supply voltage range input voltage tolerance  (Read 1083 times)

0 Members and 1 Guest are viewing this topic.

Offline czk9527

  • Contributor
  • Posts: 5
  • Country: au
Wide supply voltage range input voltage tolerance
« on: November 28, 2016, 05:28:09 am »
Hi guys, just a quick question. If say my MCU is capable of running under wide supply voltage range (1.6V - 3.6V). If I power it with 2V and interface it to an ADC which is powered by 3.3V. Will the MCU blow up? Cheers.
 

Offline MK14

  • Super Contributor
  • ***
  • Posts: 2273
  • Country: gb
Re: Wide supply voltage range input voltage tolerance
« Reply #1 on: November 28, 2016, 05:51:19 am »
You need to check the datasheet for the specific MCU you are using.
Often/usually, the inputs are limited to the supply voltage rails. So if you run it at 2 Volts, the inputs must not exceed 2 volts.

But some MCU's have inputs, which can tolerate higher voltages, such as 5V or 3.3V. Again, best to refer to the datasheet.
If they do, be careful, because it may only apply to some of its inputs, and may have other requirements as well.

The problem is that many inputs have ESD/static protection built in to them, which means that there are diodes, connecting it (protecting it) to the ground and Vcc pins. They are connected up in such a way, that if more than about half a volt or so difference (below ground, or above Vcc), between the supply pins and the input(s), significant/huge currents can flow.
There is a good EEVblog video about it.

« Last Edit: November 28, 2016, 06:05:41 am by MK14 »
 
The following users thanked this post: czk9527

Online Rerouter

  • Super Contributor
  • ***
  • Posts: 4525
  • Country: au
  • Question Everything... Except This Statement
Re: Wide supply voltage range input voltage tolerance
« Reply #2 on: November 28, 2016, 10:01:58 am »
Perhaps tell us the interface your adc will use, if it's i2c, you can have your liftups to 2v and it will work just fine, if it's an spi one then add a resistor divider on the inputs and direct connect the outputs

Most devices will tell you there accepted high and low input thresholds, and most 3.3v devices I have seen use 1.8v to register a high. Which for a modern micro should be ok.
 
The following users thanked this post: czk9527


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf