A1

V

+

1

LM35

V

+

pH ELECTRODE

pH ELECTRODE TEMPERATURE

10 k:

10 k:

+

-

A2

V

+

10 k:

10 k:

V

-

V

-

+

-

ADC12034

0.01 PF

0.1 PF

10 PF

+

CH0

CH1

DGND

0.01 PF

10 PF

AGND

+

V

+

V

+

LM4140A

6

2

1,4,7,8

3

10 k:

3.3 k:

0.1 PF

-V

+

1 PF

75:

10

1k

100k

10M

0.1

1

10

1000

1M

10k

100

100

LMP7701, LMP7702, LMP7704

www.ti.com

SNOSAI9I – SEPTEMBER 2005 – REVISED NOVEMBER 2015

Application Information (continued)

The input current noise of the LMP770x is so low that it will not become the dominant factor in the total noise

unless source resistance exceeds 300 M

Ω, which is an unrealistically high value.

mentioned before, the current noise will not be the dominant noise factor for any practical application.

Figure 48. Total Input Noise

9.2 Typical Application

Figure 49. pH Measurement Circuit

Copyright © 2005–2015, Texas Instruments Incorporated

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