Datasheet LMP8271, LMP8276 Datasheet (National Semiconductor)

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PRELIMINARY

LMP8271, LMP8276
High Common Mode, Gain of 20, Bidirectional Precision
Voltage Difference Amplifiers

January 2005

LMP8271,LMP8276 High Common Mode, Gain of 20, Bidirectional Precision Voltage Difference

Amplifiers

General Description

The LMP™8271, LMP8276 are fixed gain differential ampli­fiers with a -2V to 27V input common mode voltage range
and a supply voltage range of 4.5V to 5.5V. The LMP8271,
LMP8276 are precision amplifiers which will detect, amplify
and filter small differential signals in the presence of high
common mode voltages. The gain is fixed at 20 and is
adequate to drive an ADC to full scale in most cases. This
fixed gain is achieved in two separate stages, a pre-amplifier
with gain of +10 and a second stage amplifier with a gain of
+2. The internal signal path is brought out on two pins that
provide a connection for a filter network.

The LMP8271, LMP8276 will function with reduced specifi­cations over the extended common mode input voltage
range of -5 to 36 Volts. This feature makes the device
suitable for applications with load dump in automotive sys­tems.

The midrail offset adjustment pin enables the user to utilize
this device for bidirectional current sensing. This is achieved
by adjusting an externally set voltage reference. Accurate
bidirectional load current measurements are achieved when
monitoring the output with respect to this reference voltage

Typical Application

Typical Application: Low side Current Sensing

Features

n Bidirectional Current Sense Capability
n Typical Values, TA = 25˚C
n Input Offset Voltage 1mV max
n TCVos (LMP8271) 15µV/˚C max
n TCVos (LMP8276) 30µV/˚C max
n CMRR 80dB Min
n Extended CMVR -5V to 36V
n Output Voltage Swing Rail to Rail
n Bandwidth 80KHz
n Operating Temperature Range (Ambient) -40˚C to 125˚C
n Operating Temperature Range (bare die) -40˚C to 150˚C
n Supply Voltage 4.5V to 5.5V
n Supply Current 1mA

Applications

n Fuel Injection Control
n Low Side Driver Configuration Current Sensing
n Power Management Systems

20130801

LMP™is a trademark of National Semiconductor Corporation.

© 2005 National Semiconductor Corporation DS201308 www.national.com

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.

ESD Tolerance (Note 2)

Junction Temperature (Note 3) +150˚C max

Soldering Information

Infrared or Convection (20 sec) 235˚C

Wave Soldering Lead Temp. (10

sec) 260˚C

Human Body Model

±

For input pins only

For All other pins

Machine Model 200V

Supply Voltage (V

- GND) 5.75V

S

4000V

±

2000V

Operating Ratings (Note 1)

Temperature Range (Note 3)

Packaged devices(Note 3) -40˚C to +125˚C

Bare Die Junction Temperature(Note

3) -40˚C to +150˚C

CMVR Continuous -5 to 42 Volts

Transient (300 ms) -TBD to 45 Volts

Storage Temperature Range -65˚C to +150˚C

Supply Voltage (V

Package Thermal Resistance (θ

8–Pin SOIC 190˚C/W

–GND) 4.5V to 5.5V

S

(Note 3))

JA

5V Electrical Characteristics (Note 7)

Unless otherwise specified, all limits guaranteed for TA= 25˚C, VS= 5V, GND= 0, -2V≤VCM≤27V. Boldface limits apply at the
temperature extremes.

Symbol Parameter Conditions Min Typ

V

OS

TC V

TC V

A2 I

I

S

Input Offset Voltage VCM= Vs/2

Input Offset Voltage Drift LMP8271

OS

Input Offset Voltage Drift LMP8276

OS

Input Bias Current of A2 (Note 5)

B

Supply Current 0.6

TBD

R

CM

Input impedance Common

160 200 240 KΩ

Mode

R

DM

Input impedance Differential

320 400 480 KΩ

Mode

CMVR Input Common-Mode Voltage

Continuous -2 +27 V

Range

ECMVR Extended Common-Mode

-5 36 V

Voltage Range

DC
CMRR

AC

LMP8271, LMP8276 High Common Mode, Gain of 20, Bidirectional Precision Voltage Difference Amplifier

CMRR

DC Common Mode Rejection
Ratio

AC Common Mode Rejection
Ratio

PSRR Power Supply Rejection Ratio 4.5V≤V

-2V≤V

-5V≤V

-2V≤V

-2V≤V

≤ 27V

CM

≤ 36V

CM

≤ 27V f = 1KHz TBD dB

CM

≤ 27V f = 10KHz TBD

CM

≤ 5.5V TBD

S

80
80

TBD

R

F-INT

TCR

Filter Resistor 97 100 103 KΩ

Filter Resistor Drift TBD ppm/˚C

F-INT

Midscale Offset Scaling
Accuracy (Pin 7)

A

V

Total Gain 20 V/V

Gain Error

Gain Drift

A1 V

A1 Output Voltage Swing RL= 100KΩ on Output VOL 0.01 Volts

OUT

VOH 4.80

A2 V

A2 Output Voltage Swing RL= 100KΩ on Output VOL 0.01 Volts

OUT

VOH 4.80

(Note

±

0.25 1.0 mV

±
±

1.0 1.2

Max Units

4)

6

6

TBD

±

15 µV/˚C

±

30 µV/˚C

±

20 µA

mA

dB

dB

1%

±

1%

±

25 ppm/˚C

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5V Electrical Characteristics (Note 7) (Continued)

Unless otherwise specified, all limits guaranteed for TA= 25˚C, VS= 5V, GND= 0, -2V≤VCM≤27V. Boldface limits apply at the
temperature extremes.

Symbol Parameter Conditions Min Typ

Max Units

(Note

4)

SR Slew Rate (Note 6) 0.7 V/µs

BW Bandwidth 80 KHz

Noise 0.1Hz ro 10Hz TBD µVpp

Spectral Density TBD nV/

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, 1.5 kΩ in series with 100 pF. Machine model: 0Ω in series with 200 pF.

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

P

=(T

D

J(MAX)-TA

Note 4: Typical values represent the most likely parametric norm.

Note 5: Positive current corresponds to current flowing into the device.

Note 6: Slew rate is the average of the rising and falling slew rates.

Note 7: Electrical table values apply only for factory testing conditions at the temperature indicated. Factory testing conditions result in very limited self-heating of

the device.

)/ θJA. All numbers apply for packages soldered directly onto a PC board.

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

J(MAX)

√

Connection Diagram

8–Pin SOIC

LMP8271, LMP8276 High Common Mode, Gain of 20, Bidirectional Precision Voltage Difference Amplifier

Hz

Application Note

The LMP8271, LMP8276 are single supply amplifier with a
fixed gain of 20 and an extended common mode voltage
range of -2V to 36V. The fixed gain is achieved in two
separate stages, a pre-amplifier with gain of +10 and a
second stage amplifier with gain of +2. A block diagram of
the LMP8271, LMP8276 is shown in Figure 1.

20130803

FIGURE 1.

Top View

20130802

The overall offset of the LMP8271, LMP8276 is minimized by
trimming amplifier A1. This is done so that the output re­ferred offset of A1 cancels the input referred offset of A2 or

OS1

=-V

OS2

10V
Because of this offset voltage relationship, the offset of each

individual amplifier stage maybe more than the limit speci­fied for the overall system in the datasheet tables. Care must
be given when pin 3 and 4, A1 and A2, are connected to
each other. If the signal going from A1 to A2 is amplified or
attenuated (by use of amplifiers and resistors), the overall
LMP8271, LMP8276 offset will be affected as a result. Fil­tering the signal between A1 and A2 or simply connecting the
two pins will not change the offset of the LMP8271,
LMP8276.

Referencing input referred offset voltages, the following re­lationship holds:

If the signal on pin 3 is scaled, attenuated or amplified, by a
factor X then the offset of the overall system will become:

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Application Note (Continued)

This represents a value that the LMP8271 and LMP8276
have not been optimized and trimmed for and may very well
be above the limits indicated in the electrical characteristics
tables.

Midrail Offset Adjustment Pin

The external midrail offset adjustment pin enables the user
to utilize this device for bidirectional current sensing. If the
offset pin, pin 7, is connected to ground then the LMP8271,
LMP8276 are capable of sensing positive signals. When the
offset pin is connected to V
output and under this condition the amplifier can sense both
positive and negative signals. If this offset pin is connected
to any voltage between ground and V
increased by a voltage equal to half of that offset, e.g. If the
offset is connected to V

. The following figure shows how this works:

1/2V

X

then 1/2VSis added to the

S

, then the output is

S

, then the output increases by

X

Note that the offset pin, pin 7, needs to be connected at all
times. If the pin is left floating, the LMP8271 and LMP8276
will be operating in an undefined mode. Also pin 7 should be
driven from a low impedance source.

20130806

FIGURE 2.

LMP8271, LMP8276 High Common Mode, Gain of 20, Bidirectional Precision Voltage Difference Amplifier

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Notes

LMP8271,LMP8276 High Common Mode, Gain of 20, Bidirectional Precision Voltage Difference

Amplifiers

National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves
the right at any time without notice to change said circuitry and specifications.

For the most current product information visit us at www.national.com.

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