pH ELECTRODE

100:

V

+

V

-

0.1 µF

0.1 µF

0.1 µF

0.1 µF

TRIAX

-

+

-

+

LMP7721

LMP7715

LMP7721

SNOSAW6E – JANUARY 2008 – REVISED DECEMBER 2014

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Application Information (continued)

If using "water soluble" or "no clean" flux, a second cleaning step is needed. These fluxes still leave a film behind

that can attract contaminates and dust. The board should be washed with fresh isopropyl alcohol or methanol

and baked to make sure all remaining traces of moisture are removed from the board. Areas between the

component leads should be scrubbed and areas under surface mount devices thoroughly flushed. The board

should be re-cleaned after any rework to components within the guarded areas. Boards should be handled by the

edges and stored in sealed containers with desiccant.

8.2 Typical Application

The following application examples highlight only a few of the circuits where the LMP7721 can be used.

A CMOS input stage with ultra-low input bias current, negligible input current noise, and low input voltage noise

allows the LMP7721 to provide high fidelity amplification. In addition, the LMP7721 has a 17 MHz gain bandwidth

product, which enables high gain at wide bandwidth. A rail-to-rail output swing at 5.5-V power supply allows

detection and amplification of a wide range of input currents. These properties make the LMP7721 ideal for

transimpedance amplification.

Figure 50. LMP7721 as pH Electrode Amplifier

8.2.1 Design Requirements

The output of a pH electrode is typically 59.16 mV per pH unit at 25°C, for an output range of 414 mV to

−414

mV as the pH changes from 0 to 14 at 25°C.

22

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