CCS/PGA411-Q1: Some confusion about EXTOUT, and how to adjust the resistance so that IEx meets the 0.5-4V range

zhiwen wu

Prodigy 60 points

Part Number: PGA411-Q1

Tool/software: Code Composer Studio

There are two different explanations for the output waveform of OEx, which confuse me.

Case 1:

EXTOUT is described as the minimum OEx voltage in the application manual TIDUBI2A.

Case 2:

EXTOUT adjusts the common mode voltage of OEx as found in pg 21 of DS, and my case is consistent with this one.

I calculate the OEx(min) by formula " OEx(min) = 4.25 - Vexco/4 " instead of " OEx(min) = EXTOUT ". And my calculations are consistent with the oscilloscope tests described in my reply later.

over 5 years ago

0 zhiwen wu over 5 years ago

Prodigy 60 points

The waveforms of OE1 and OE2 . EXTMODE = 4VRMS , EXTOUT_GL = 0xF , EXTOUT = 0x0

Theoretical OExmax and OExmin were calculated using differential voltage (13.85V) and common mode voltage (4.25V).And the calculated results are consistent with the oscilloscope test results.

OExmax = 4.25 + 13.85/4 = 7.7125V

OExmin = 4.25 – 13.85/4 = 0.7875V

The appropriate resistance value will then be calculated using formula 21.

To make IEx greater than 0.5V, Rmax = 40 * (0.7875 - 0.5) / 0.5 = 23KΩ

To make IEx smaller than 4V , Rmin = 40 * (7.7125 - 4) / 4 = 37.125KΩ

Because of “Rmax < Rmin”, there is no suitable R for IEx to meet the range of 0.5V-4V

Is there something wrong with my OEx waveform or my calculation process ?

0 Arjun_Prakash over 5 years ago in reply to zhiwen wu

TI__Expert 7599 points

Hello,

Thanks for your post.

Please refer to the datasheet for guidance on the Exciter amplifier and its equation. You can also refer to our AFE design guide that is here

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CCS/PGA411-Q1: Some confusion about EXTOUT, and how to adjust the resistance so that IEx meets the 0.5-4V range