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#### m12lrpv

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##### Need help understanding ADC datasheet
« on: May 29, 2012, 03:53:26 am »
I've got a couple of 16bit ADC's ( A Burr Brown ADS1110 and a Microchip MCP3425 ) and while I think I have a handle on what they're capable of I need know if I've read the datasheets right.

They are basically the same specs but the microchip datasheet is more verbose and says the following...

Quote
The on-board precision 2.048V reference voltage
enables an input range of ±2.048V differentially
(? voltage = 4.096V)

I take this to read that the maximum absolute voltage difference between the inputs is 2.048V. Initially I thought that this restricted me to measuring from ground on one input to 2.048v on another.

I became unsure of myself when I take into account that both devices allow the inputs to go (just above) the supply voltage. Now I'm assuming that the 2.048V absolute voltage difference can be between input voltages that are anywhere within the supply rails. So I can measure the difference between an input at 4.5v and one at 2.5v. It's a logical assumption that the inputs can float within the rails but assumptions are more likely to get me in trouble than not hence I'm asking.

Is my current thinking correct?

MCP3425 datasheet

#### free_electron

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##### Re: Need help understanding ADC datasheet
« Reply #1 on: May 29, 2012, 04:06:03 am »
The inputs can indeed float between the rails. you can't really go 'over' as the input stage will saturate and distort...
so , if you power the device with 5 volts one input could be at 0.5 volt and the other at 4.596 volts and you would still fall in the 4096 range ..
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#### ejeffrey

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##### Re: Need help understanding ADC datasheet
« Reply #2 on: May 29, 2012, 04:23:42 am »
so , if you power the device with 5 volts one input could be at 0.5 volt and the other at 4.596 volts and you would still fall in the 4096 range ..

The range is only +/-2.048.

Other than that, yes: the inputs can go anywhere within the common-mode range as long as they are within 2.048 V of each other.

#### m12lrpv

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##### Re: Need help understanding ADC datasheet
« Reply #3 on: May 29, 2012, 04:39:36 am »
Thanks guys.

Smf