Author Topic: Sigma Delta Diff. Inputs, Voltage Swing  (Read 1382 times)

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Offline arrestedmechanicsTopic starter

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Sigma Delta Diff. Inputs, Voltage Swing
« on: May 12, 2015, 12:14:51 pm »
I'm trying to use this sigma-delta ADC (MCP3911) for its quick settling time, and I'm a little confused about the input ratings.
http://ww1.microchip.com/downloads/en/DeviceDoc/22286A.pdf

The differential inputs are rated +/- 1V and are fed into a PGA before it gets to the modulator. Table 1-1 shows that the Analog Absolute Voltage on CH0+, CH0- can range from -1V to +1V, measured to AGND.

So can this ADC actually measure a 2Vp-p signal centered around GND? I'm confused because it's only a single-supply chip, and the block diagram doesn't show any internal voltage inverter for the PGA.
Do I supply -1V to REFIN-? Do I need to do the same for REFIN+, or can the ADC use the internal reference instead?

Thanks for your help!
 

Offline bktemp

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Re: Sigma Delta Diff. Inputs, Voltage Swing
« Reply #1 on: May 12, 2015, 12:24:30 pm »
This ic seems to have an internal chargepump for generating a negative supply voltage. The datasheet mentions somewhere the the negative input range is only valid when a clock is applied, otherwise a higher input current flows when a negative input voltage is applied.
 

Offline arrestedmechanicsTopic starter

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Re: Sigma Delta Diff. Inputs, Voltage Swing
« Reply #2 on: May 12, 2015, 07:17:09 pm »
I sure hope you're right! I guess I'll give it a go 😁
 


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