LMP7312MASLASHNOPB datasheet(16/29 Pages) TI1

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LMP7312

SNOSB32B – MARCH 2010 – REVISED MARCH 2013

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INPUT VOLTAGE RANGE

The LMP7312 has an internal OpAmp with rail-to-rail input voltage range capability. The requirement to stay

within the V-and V+ rail at the OpAmp input translates in an Input Voltage Range specification as explained in this

application section.

Differential Output

Considering a single positive supply (V-= GND, V+ = VS) the Input Common mode voltage, VCM_ATT = (+VIN + (-

VIN))/2 for the Attenuation inputs and VCM_AMP = (+IIN + (-IIN))/2 for the Amplification inputs, has to stay between

the MIN and MAX values determined by these formulas:

CMMAX = VS + 1/KV*(VS - VOCM)

CMMIN = -1/KV*VOCM

KV is a function of the Gain according to the table below:

Gain

0.096 V/V

0.192 V/V

0.384 V/V

0.768 V/V

1 V/V

2 V/V

0.12

0.218

0.414

0.806

1.065

2.096

Regardless to the values derived by the formula, the voltage on each input pin must never exceed the specified

Absolute Maximum Ratings.

Below are some typical values:

Table 1. Differential Input, Differential Output, VS= 5V, VOCM = 2.5V

VCM_ATT

VCM_AMP

Gain

Min

Max

Min

Max

0.096 V/V

-15 V(1)

+15 V(1)

0.192 V/V

-11.5 V

+15 V

0.384 V/V

-6 V

+11 V

0.768 V/V

-3.1 V

+8.1 V

1 V/V

-2.3 V

+7.3 V

2 V/V

-1.2 V

+6.2 V

(1)

Limited by the operating ratings on input pins

In the case of a single ended input referred to ground (-VIN = GND, -IN = GND) the table below summarizes the

voltage range allowed on the +VIN and +IIN inputs.

Table 2. Single Ended Input, Differential Output, VS= 5V, VOCM = 2.5V, -VIN = GND, -IIN = GND

+VIN

+IN

Gain

Min

Max

Min

Max

0.096 V/V

-15 V(1)

+15 V(1)

0.192 V/V

-15 V(1)

+15 V(1)

0.384 V/V

-12 V(2)

+12 V(2)

0.768 V/V

-6 V(2)

+6 V(2)

1 V/V

-4.6 V(2)

+4.6 V(2)

2 V/V

-2.3 V(2)

+2.3 V(2)

(1)

Limited by the operating ratings on input pins.

(2)

Limited by the output voltage swing (0.2V to VS-0.2V on both + VOUT and -VOUT)

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