Author Topic: MCP3425 input voltage range  (Read 850 times)

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Offline madwolfeTopic starter

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MCP3425 input voltage range
« on: June 03, 2019, 01:17:53 pm »
I'm having difficulties understanding the input voltage range for the MCP3425. I'm needing to measure a 0->3.3v range.

From the datasheet (description at top):
Quote
The on-board precision 2.048V reference voltage enables an input range of ±2.048V differentially (Δ voltage = 4.096V)

But also from the datasheet:
Quote
The differential input voltage should not exceed an absolute of (VREF/PGA) for accurate measurement, where VREF is the internal reference voltage (2.048V) and PGA is the PGA gain setting. The converter output code will saturate if the input range exceeds (VREF/PGA).

Where PGA is the gain (which would = 1).

I feel like it should be capable of measuring the voltage correctly, or would a voltage divider be necessary? (As the output is calibrated, the accuracy of the voltage divider wouldn't be important but the stability would be, so this could be an option).

Thanks
 

Offline madwolfeTopic starter

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Re: MCP3425 input voltage range
« Reply #1 on: June 03, 2019, 01:42:34 pm »
And of course, I forgot the link to the datasheet: http://ww1.microchip.com/downloads/en/DeviceDoc/22072b.pdf
 

Online SiliconWizard

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Re: MCP3425 input voltage range
« Reply #2 on: June 03, 2019, 01:49:06 pm »
As the internal reference is 2.048V and the internal PGA min gain is 1, there is no way you can measure a 0-3.3V input range without attenuating it first...
You can safely apply an input up to VDD but the ADC will saturate at 2.048V.

A quick suggestion would be to use an LTC2453 instead (similar specs and price).
« Last Edit: June 03, 2019, 01:56:25 pm by SiliconWizard »
 

Offline madwolfeTopic starter

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Re: MCP3425 input voltage range
« Reply #3 on: June 03, 2019, 08:03:34 pm »
Brilliant, thanks for that. The LTC2453 looks like it will be good, and better than using a voltage divider.
 


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