-

+

+

-

+

-

A

B

C

LMP7312

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SNOSB32B – MARCH 2010 – REVISED MARCH 2013

APPENDIX

Offset Voltage and Offset Voltage Drift calculation

Listed in the table below are the calculated values for Offset Voltage and Offset Voltage Drift based on the max

specifications of these parameters for the core op-amp (for all gain configurations).

Parameter

Unit

Value

Gain

V/V

0.096

0.192

0.384

0.768

1

2

Total Offset Input Referred (MAX)

µV

±1141

±620

±360

±230

±200

±150

Total Offset Output Referred (MAX)

µV

±109

±119

±138

±176

±200

±300

µV/°C

±32.3

±18.6

±10.8

±6.9

±6

±4.5

µV/°C

±3.3

±3.6

±4.1

±5.3

±6

±9

Noise calculation

Listed in the table below are the calculated values for Voltage Noise based on the spectral density of the core

op-amp at 10kHz (for all gain configurations).

Parameter

Unit

Value

Gain

V/V

0.096

0.192

0.384

0.768

1

2

Total Noise Referred to Input

nV/

√Hz

211

150

112

89

53

46

Total Noise Referred to Output

nV/

√Hz

20

29

43

68

53

92

Input resistance calculation

The common mode input resistance is the resistance seen from node “A” when

ΔV1 = ΔV2 = 0 and a common

mode voltage

ΔVCM is applied to both inputs of the LMP7312. The differential input resistance is the resistance

seen from the nodes “B” and “C” when

ΔVCM=0 and a differential voltage ΔV1 = ΔV2 = V/2 is applied to the

inputs of the LMP7312.

Figure 42. Circuit for Input Resistance calculation

Mode of Operation

Unit

Gains

Attenuation Mode

0.096

0.192

0.384

0.768

Common Mode Resistance

k

Ω

57.08

62.08

72.08

92.08

Differential Resistance

k

Ω

228.30

248.30

288.30

368.30

Amplification Mode

1

2

Common Mode Resistance

k

Ω

40.0

60.0

Differential Resistance

k

Ω

160.0

240.0

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