LMP7312 datasheet(13/22 Pages) NSC

13 / 22 page

Application Section

GENERAL DESCRIPTION

The LMP7312 is a single supply programmable gain differ-

ence amplifier with two input pairs: Attenuation pair (-V

IN,

IN) and Amplification pair (-IN, +IN). The output can be

configured in both single-ended and differential modes with

the output common mode voltage set by the user. The input

selection, the gains and the mode of operation of the

LMP7312 are controlled through a 4- wire SPI interface (SCK,

CS, SDI, SDO). These features combined make the

LMP7312 a very easy interface between the analog high volt-

age industrial buses and the low voltage digital converters.

OUTPUT MODE CONFIGURATION

The LMP7312 is able to work in both single ended and differ-

ential output mode. The selection of the mode is made

through the V

OCM (output common mode voltage) pin.

Differential Output

This mode of operation is enabled when the output common

mode voltage pin (V

OCM) is connected to a voltage higher than

1V, for instance the common mode voltage supplied by an

ADC, (Figure 1) or a voltage reference. If the V

OCM pin is

floating an internal voltage divider biases it at the half supply

voltage. In this configuration the output signals are set on the

OCM voltage level.

Single-Ended Output

This mode of operation is enabled when the V

OCM pin is tied

to a voltage less than 0.5 V, for example to ground. In this

mode of operation the LMP7312 behaves as a difference am-

plifier, where the +V

OUT pin is the single-ended output while

the –V

OUT /VR is the reference voltage.

In the case of bipolar input signal the non inverting output

will be connected to an external reference through a

buffer (Figure 2).

In the case of unipolar input signal the non inverting

output will be connected to ground (Figure 3).

In both cases the inverting output pin is configured as an input

pin.

30075503

FIGURE 1. Differential ADC Interfacing with V

CM provided by the ADC

LMP7312 Datasheet(PDF) 13 Page - National Semiconductor (TI)

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