ADS1293: Question about CMVR

Takumi Suzuki1

Mastermind 8610 points

Part Number: ADS1293

Hi,

I would like to ask you a basic question about following explanation. (datasheet page16)

What is the value of "1.75" and "0.25"? Input bias voltage of INA??

And about VINmax is 0.4V, right?

Sorry for my basic question, thank you in advance.

Best Regards,

over 8 years ago

0 Brian Pisani over 8 years ago

TI__Mastermind 38745 points

Hello Takumi-san,

The value 1.75 comes from the gain. Each side of the inequality takes on half of the gain of 3.5. The 0.25 V comes from the output range of the INA. The output can range from 0.25 V to VDD - 0.25 V. Yes, the maximum input is 0.4 V.

Brian

0 Takumi Suzuki1 over 8 years ago in reply to Brian Pisani

Mastermind 8610 points

Hi Brian-san,

I understood well, thank you very much for your explanation!

Best Regards,

0 Takumi Suzuki1 over 8 years ago in reply to Brian Pisani

Mastermind 8610 points

Hi Brian-san,

Sorry let me ask you again as below if my understanding is correct.

As CMVR is from 0.95 to Vdd-0.95, both +V amd -V of INA must be 0.95V to Vdd-0.95V.
For example, in case +V = GND and -V = +/- 0.4V (mid point is GND), this is out of range and INA does not work correctly.
In this case, mid point should be greater than 0.95V, that is to say, +V should be 0.95V and -V sould be +1.35V/+0.55V.
Is my idea correct?

Regards,

0 Brian Pisani over 8 years ago in reply to Takumi Suzuki1

TI__Mastermind 38745 points

Takumi-san

You are correct. The INA will not work if one of the inputs is ground.

Brian

0 Takumi Suzuki1 over 8 years ago in reply to Brian Pisani

Mastermind 8610 points

Brian-san,

Thank you so much!

Regards,

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ADS1293: Question about CMVR