LMP7312_14 Datasheet, PDF (16/29 Pages) National Semiconductor (TI) – Precision SPI-Programmable AFE with Differential/Single-Ended Input/Output

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⁺ = V_S) the Input Common mode voltage, V_{CM_ATT} = (+V_IN + (-
V_IN))/2 for the Attenuation inputs and V_{CM_AMP} = (+I_IN + (-I_IN))/2 for the Amplification inputs, has to stay between
the MIN and MAX values determined by these formulas:
CM_MAX = V_S + 1/K_V*(V_S - V_OCM)
CM_MIN = -1/K_V*V_OCM
K_V is a function of the Gain according to the table below:
Gain
K_V
0.096 V/V
0.12
0.192 V/V
0.218
0.384 V/V
0.414
0.768 V/V
0.806
1 V/V
1.065
2 V/V
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:
Gain
0.096 V/V
0.192 V/V
0.384 V/V
0.768 V/V
1 V/V
2 V/V
Table 1. Differential Input, Differential Output, V_S= 5V, V_OCM = 2.5V
Min
-15 V⁽¹⁾
V_{CM_ATT}
Max
+15 V⁽¹⁾
Min
V_{CM_AMP}
-11.5 V
+15 V
-6 V
+11 V
-3.1 V
+8.1 V
-2.3 V
-1.2 V
Max
+7.3 V
+6.2 V
(1) Limited by the operating ratings on input pins
In the case of a single ended input referred to ground (-V_IN = GND, -IN = GND) the table below summarizes the
voltage range allowed on the +VI_N and +I_IN inputs.
Table 2. Single Ended Input, Differential Output, V_S= 5V, V_OCM = 2.5V, -V_IN = GND, -I_IN = GND
Gain
0.096 V/V
0.192 V/V
0.384 V/V
0.768 V/V
1 V/V
2 V/V
Min
-15 V⁽¹⁾
-15 V⁽¹⁾
-12 V⁽²⁾
-6 V⁽²⁾
+V_IN
Max
+15 V⁽¹⁾
+15 V⁽¹⁾
+12 V⁽²⁾
+6 V⁽²⁾
+IN
Min
Max
-4.6 V⁽²⁾
-2.3 V⁽²⁾
+4.6 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 V_S-0.2V on both + V_OUT and -V_OUT)
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