AFE7222 Rint

Hidetoshi Matsunami

Expert 2750 points

Other Parts Discussed in Thread: AFE7222

Hello Team,

I would like to ask the following questions.

(1)

Could you tell me the Rint setting values when IAUX_DAC=5mA、Rext=300Ω and Full Scale=1.5V?

Because Rext and FS AUX DAC setting values is written but Rint isn't written in the following sentences(P.90 of AFE7222 datasheet).

"For best linearity, limit the maximum voltage at AUXDAC_A to 1.5V.For example, with I AUX_DAC set to 5 mA, and R EXT set to 300 Ohm, the voltage on AUXDAC_A will swing from 0 to 1.5V."

(2)

I believe Rint is connected in parallel with Rext.

Could you tell me whether Rint affects the formula(AUXDAC_A＝IAUX_DAC x REXT)?

"For maximum input code, voltage on AUXDAC_A is equal to IAUX_DAC x REXT."(P.90 of AFE7222 datasheet)

Best Regards,

Hidetoshi Matsunami

over 9 years ago

0 Hidetoshi Matsunami over 9 years ago

Expert 2750 points

Hello Team,

I'm looking forward to hearing from you.

Best Regards,

Hidetoshi Matsunami

0 Ebenezer Dwobeng over 9 years ago in reply to Hidetoshi Matsunami

TI__Genius 9695 points

Hi Hidetoshi,

1) Rint should be chosen as close as possible to Rext. Since your Rext is 300ohms, you can select either 200ohms or 400ohms for Rint. Also consider using Rint=Rext=200ohms and then setting I AUX DAC to 7.5mA for best linearity performance.

2) Rint and Rext are not in parallel because the switches that connect these resistors to the current source (I AUX DAC) cannot be ON at the same time. Refer to Fig 10-17 on pg 90 in datasheet for AFE7222.

Since both of the switches cannot be on at the same time, Rint does not affect the formula AUXDAC_A＝IAUX_DAC x REXT

Thanks,

Eben.

0 Hidetoshi Matsunami over 9 years ago in reply to Ebenezer Dwobeng

Expert 2750 points

Hello Ebenezer,

I appreciate your help.

I understood.

Best Regards,

Hidetoshi Matsunami

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AFE7222 Rint