National Semiconductor LMP7721 Technical data

March 14, 2008

LMP7721
3 Femtoampere Input Bias Current Precision Amplifier

LMP7721 3 Femtoampere Input Bias Current Precision Amplifier

General Description

The LMP7721 is the industry’s lowest guaranteed input bias
current precision amplifier. The ultra low input bias current is
3 fA, with a guaranteed limit of ±20 fA at 25°C and ±900 fA at
85°C. This is achieved with the latest patent pending tech­nology of input bias current cancellation amplifier circuitry.
This technology also maintains the ultra low input bias current
over the entire input common mode voltage range of the am­plifier.

Other outstanding features, such as low voltage noise (6.5

), low DC offset voltage (±150 µV maximum at 25°C)

nV/
and low offset voltage temperature coefficient (−1.5 µV/°C),
improve system sensitivity and accuracy in high precision ap­plications. With a supply voltage range of 1.8V to 5.5V, the
LMP7721 is the ideal choice for battery operated portable ap­plications. The LMP7721 is part of the LMP® precision am­plifier family.

As part of National’s PowerWise® products, the LMP7721
provides the remarkably wide gain bandwidth product (GBW)
of 17 MHz while consuming only 1.3 mA of current. This wide
GBW along with the high open loop gain of 120 dB enables
accurate signal conditioning. With these specifications, the
LMP7721 has the performance to excel in a wide variety of
applications such as electrochemical cell amplifiers and sen­sor interface circuits.

The LMP7721 is offered in an 8-pin SOIC package with a
special pinout that isolates the amplifier’s input from the pow­er supply and output pins. With proper board layout tech­niques, the unique pinout of the LMP7721 will prevent PCB
leakage current from reaching the input pins. Thus system
error will be further reduced.

Features

Unless otherwise noted, typical values at TA = 25°C, VS = 5V.

Input bias current (VCM = 1V)

■

max @ 25°C ±20 fA

—

max @ 85°C ±900 fA

—

Offset voltage ±26 µV

■

Offset voltage drift

■

DC Open loop gain 120 dB

■

DC CMRR 100 dB

■

Input voltage noise (at f = 1 kHz) 6.5 nV/√Hz

■

THD 0.0007%

■

Supply current 1.3 mA

■

GBW 17 MHz

■

Slew rate (falling edge) 12.76 V/μs

■

Supply voltage 1.8V to 5.5V

■

Operating temperature range −40°C to 125°C

■

8-Pin SOIC

■

−1.5 μV/°C

Applications

Photodiode amplifier

■

High impedance sensor amplifier

■

Ion chamber amplifier

■

Electrometer amplifier

■

pH electrode amplifier

■

Transimpedance amplifier

■

Block Diagram of a Typical Application

Ion Chamber: Current to Voltage Converter

LMP® is a registered trademark of National Semiconductor Corporation.

PowerWise® is a registered trademark of National Semiconductor.

© 2008 National Semiconductor Corporation 202040 www.national.com

20204084

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/

LMP7721

Soldering Information
Infrared or Convection (20 sec) 235°C
Wave Soldering Lead Temp. (10 sec) 260°C

Distributors for availability and specifications.

ESD Tolerance (Note 2)
Human Body Model 2000V
Machine Model 200V
VIN Differential

Supply Voltage (VS = V+ – V−) (Note 10)

±0.3V

6.0V
Voltage on Input/Output Pins V+ +0.3V, V− −0.3V

Storage Temperature Range −65°C to 150°C

Operating Ratings (Note 1)

Temperature Range (Note 3) −40°C to 125°C
Supply Voltage (VS = V+ – V−)

0°C ≤ TA ≤ 125°C

−40°C ≤ TA ≤ 125°C

Package Thermal Resistance (θJA(Note 3))

8-Pin SOIC 190°C/W

Junction Temperature (Note 3) +150°C

2.5V Electrical Characteristics

Unless otherwise specified, all limits are guaranteed for TA = 25°C, V+ = 2.5V, V− = 0V, VCM = (V+ + V−)/2. Boldface limits apply
at the temperature extremes.

Symbol Parameter Conditions Min

(Note 5)

V

OS

TC VOSInput Offset Voltage Drift

Input Offset Voltage ±50 ±180

–1.5 –4

(Note 6)

I

BIAS

Input Bias Current VCM = 1V

(Notes 7, 8)

25°C ±3 ±20

−40°C to 85°C ±900

−40°C to 125°C ±5 pA

I

OS

Input Offset Current VCM = 1V

(Note 8)

CMRR Common Mode Rejection Ratio

0V ≤ VCM ≤ 1.4V

83

80

PSRR Power Supply Rejection Ratio

CMVR Input Common-Mode Voltage

Range

A

VOL

V

O

Large Signal Voltage Gain VO = 0.15V to 2.2V

Output Swing High

1.8V ≤ V+ ≤ 5.5V
V− = 0V, VCM = 0

CMRR ≥ 80 dB
CMRR ≥ 78 dB

RL = 2 kΩ to V+/2

VO = 0.15V to 2.2V

RL = 10 kΩ to V+/2

RL = 2 kΩ to V+/2

84

80

−0.3

–0.3

88

82

92

88

70

77

RL = 10 kΩ to V+/2

60

66

Output Swing Low

RL = 2 kΩ to V+/2

RL = 10 kΩ to V+/2

I

O

Output Short Circuit Current Sourcing to V

VIN = 200 mV (Note 9)

Sinking to V
VIN = −200 mV (Note 9)

I

S

Supply Current 1.1 1.5

−

36

30

+

7.5

5.0

SR Slew Rate AV = +1, Rising (10% to 90%)

AV = +1, Falling (90% to 10%)

6 40 fA

30 70

15 60

Typ

(Note 4)

100

92

1.5

107

120

25

20

46

15

9.3

10.8

Max

(Note 5)

±480

1.5

73

62

1.75

1.8V to 5.5V

2.0V to 5.5V

Units

μV

μV/°C

fA

dB

dB

V

dB

mV

from V

mV

mA

mA

V/μs

+

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LMP7721

Symbol Parameter Conditions Min

(Note 5)

Typ

(Note 4)

Max

(Note 5)

Units

GBW Gain Bandwidth Product 15 MHz

e

n

i

n

THD+N Total Harmonic Distortion + Noise

Input-Referred Voltage Noise f = 400 Hz 8

f = 1 kHz 7

Input-Referred Current Noise f = 1 kHz 0.01

f = 1 kHz, AV = 2, RL = 100 kΩ
VO = 0.9 V

PP

f = 1 kHz, AV = 2, RL = 600Ω
VO = 0.9 V

PP

0.003

0.003

nV/

pA/

%

5V Electrical Characteristics

Unless otherwise specified, all limits are guaranteed for TA = 25°C, V+ = 5V, V− = 0V, VCM = (V+ + V−)/2. Boldface limits apply at
the temperature extremes.

Symbol Parameter Conditions Min

(Note 5)

V

OS

TC VOSInput Offset Average Drift

Input Offset Voltage ±26 ±150

–1.5 –4

(Note 6)

I

BIAS

Input Bias Current VCM = 1V

(Notes 7, 8)

25°C ±3 ±20

−40°C to 85°C ±900

−40°C to 125°C ±5 pA

I

OS

CMRR Common Mode Rejection Ratio

Input Offset Current (Note 8) 6 40 fA

0V ≤ VCM ≤ 3.7V

84

82

PSRR Power Supply Rejection Ratio

CMVR Input Common-Mode Voltage

Range

A

VOL

V

O

Large Signal Voltage Gain VO = 0.3V to 4.7V

Output Swing High

1.8V ≤ V+ ≤ 5.5V
V− = 0V, VCM = 0

CMRR ≥ 80 dB
CMRR ≥ 78 dB

RL = 2 kΩ to V+/2

VO = 0.3V to 4.7V

RL = 10 kΩ to V+/2

RL = 2 kΩ to V+/2

84

80

−0.3

–0.3

88

82

92

88

70

77

RL = 10 kΩ to V+/2

60

66

Output Swing Low

RL = 2 kΩ to V+/2

RL = 10 kΩ to V+/2

I

O

Output Short Circuit Current Sourcing to V

−

VIN = 200 mV (Note 9)

Sinking to V

+

VIN = −200 mV (Note 9)

I

S

Supply Current 1.3 1.7

31 70

20 60

46

38

10.5

6.5

SR Slew Rate AV = +1, Rising (10% to 90%) 10.43

AV = +1, Falling (90% to 10%)

GBW Gain Bandwidth Product 17 MHz

Typ

(Note 4)

100

96

4

111

120

30

20

60

22

12.76

Max

(Note 5)

±450

4

73

62

1.95

Units

μV

μV/°C

fA

dB

dB

V

dB

mV

from V

mV

mA

mA

V/μs

+

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Symbol Parameter Conditions Min

e

n

LMP7721

Input-Referred Voltage Noise f = 400 Hz 7.5

(Note 5)

Typ

(Note 4)

Max

(Note 5)

f = 1 kHz 6.5

i

n

THD+N Total Harmonic Distortion +

Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is
intended to be functional, but specific performance is not guaranteed. For guaranteed specifications and the test conditions, see the Electrical Characteristics
Tables.

Note 2: Human Body Model, applicable std. MIL-STD-883, Method 3015.7. Machine Model, applicable std. JESD22-A115-A (ESD MM std. of JEDEC)

Field-Induced Charge-Device Model, applicable std. JESD22-C101-C (ESD FICDM std. of JEDEC).

Note 3: The maximum power dissipation is a function of T
PD = (T

Note 4: Typical values represent the most likely parametric norm as determined at the time of characterization. Actual typical values may vary over time and will
also depend on the application and configuration. The typical values are not tested and are not guaranteed on shipped production material.

Note 5: Limits are 100% production tested at 25°C. Limits over the operating temperature range are guaranteed through correlations using the Statistical Quality
Control (SQC) method.

Note 6: Offset voltage average drift is determined by dividing the change in VOS at the temperature extremes by the total temperature change.

Note 7: Positive current corresponds to current flowing into the device.

Note 8: This parameter is guaranteed by design and/or characterization and is not tested in production.

Note 9: The short circuit test is a momentary open loop test.

Note 10: The voltage on any pin should not exceed 6V relative to any other pins.

Input-Referred Current Noise f = 1 kHz 0.01

f = 1 kHz, AV = 2, RL = 100 kΩ

Noise

VO = 4 V

PP

f = 1 kHz, AV = 2, RL = 600Ω
VO = 4 V

- TA)/θJA. All numbers apply for packages soldered directly onto a PC Board.

J(MAX)

PP

, θJA. The maximum allowable power dissipation at any ambient temperature is

J(MAX)

0.0007

0.0007

Units

nV/

pA/

%

Connection Diagram

8-Pin SOIC

Top View

20204083

Ordering Information

Package Part Number Package Marking Transport Media NSC Drawing

8-Pin SOIC

LMP7721MA

LMP7721MAX 2.5k Units Tape and Reel

LMP7721MA

95 Units/Rail

M08A

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LMP7721

Typical Performance Characteristics Unless otherwise specified: T

Input Bias Current vs. V

Input Bias Current vs. V

CM

20204094

CM

Input Bias Current vs. V

Input Bias Current vs. V

= 25°C, VCM = (V+ + V−)/2.

A

CM

20204087

CM

Input Bias Current vs. V

CM

20204095

20204085

20204086

Offset Voltage Distribution

20204039

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