LMP7312MASLASHNOPB datasheet(14/29 Pages) TI1

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SCK

SDI

SDO

VIO

-VIN

+IN

+VIN

VOCM

SPI

Controller

+VOUT

-VOUT/VR

100 k:

ADC

VREF

ADC

-IN

VCM

LMP7312

SNOSB32B – MARCH 2010 – REVISED MARCH 2013

www.ti.com

APPLICATION SECTION

GENERAL DESCRIPTION

The LMP7312 is a single supply programmable gain difference amplifier with two input pairs: Attenuation pair (-

VIN, +VIN) 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 voltage industrial buses and the

low voltage digital converters.

OUTPUT MODE CONFIGURATION

The LMP7312 is able to work in both single ended and differential output mode. The selection of the mode is

made through the VOCM (output common mode voltage) pin.

Differential Output

This mode of operation is enabled when the output common mode voltage pin (VOCM) is connected to a voltage

higher than 1V, for instance the common mode voltage supplied by an ADC, (Figure 34) or a voltage reference. If

the VOCM pin is floating an internal voltage divider biases it at the half supply voltage. In this configuration the

output signals are set on the VOCM voltage level.

Single-Ended Output

This mode of operation is enabled when the VOCM 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 amplifier, where the +VOUT pin is the single-

ended output while the –VOUT /VR is the reference voltage.

1. In the case of bipolar input signal the non inverting output will be connected to an external reference through

a buffer (Figure 35).

2. In the case of unipolar input signal the non inverting output will be connected to ground (Figure 36).

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

Figure 34. Differential ADC Interfacing with VCM provided by the ADC

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