Analog inputs ADS1015 5v or 3.3v?


#1

I’ve got an explorer phat and an enviro phat. Both have analog inputs using the ADS1015. The explorer phat docs say max 5v, while the enviro docs say 3.3v (and includes a whole section on 5v to 3.3v conversion).
The ADS1015 datasheet says anything up to 5v is ok.
I guess you only need to use 3.3v for those sensors that can’t handle 5v, and you might need the max voltage to calculate the value being read.
The enviro phat hasn’t blown up (as far as I can tell) when I accidentally used the very convenient 5v pin as power for a 10k pot to simulate an analogue sensor. I can read raw 0-4096 just fine on either phat with 5v inputs.
I am a little bit bemused by the different info, for the phats.
Is it okay to use 5v with the enviro phat analogues or not?


#2

On Enviro pHAT it’s technically not okay to use 5v, but I’ve generally found that the chip is tolerant of it.

The absolute max voltage that should be input to the analog pins is VDD + 0.3v. Enviro pHAT is powered at 3.3v so the maximum specified rating is 4.6v. This is close enough to 5v that in 99.99% of occasions it’ll probably be fine, but we’re careful to document the correct usage and not rely on chance.

The datasheet specifies this as a footnote on page 4: This parameter expresses the full-scale range of the ADC scaling. In no event should more than VDD + 0.3 V be applied to this device.

We’ve got a modified version of Enviro pHAT in the works which powers the ADC at 5v and includes logic level shifting on the i2c bus to talk to it. This grants it the full 0v to 5v input range, so wiring wont be such a kerfuffle.


#3

How do we know if we have the 5v envirophat or the 3.3v one?

Ta


#4

The 5v Enviro pHAT will have two transistor placements, they’re little black packages with 3 leads right near the ADC.

Oh, just remembered also that:

  • 3.3v Enviro pHAT has ADC on 0x48
  • 5v Enviro pHAT has ADC on 0x49

So i2c-detect -y 1 will tell you without you having to look at the underside.


#5

I can confirm that they don’t like 12v… Doh!!! Slaps face…

Time to practice some surface mount soldering. :) See, there is a silver lining too some clouds.


#6

Hi,
are the Enviro pHATs you have in store now the new 5v tolerant ones?

Best regards,
Daniel


#7

Absolutely!

The revised version must have been around for months now. Time flies!