LMP8601MAEVAL/NOPB - NATIONAL SEMICONDUCTOR

LMP8601

LMP8601/LMP8601Q 60V Common Mode, Bidirectional Precision Current Sensing

Amplifier

Literature Number: SNOSAR2D

LMP8601/LMP8601Q

July 16, 2009

60V Common Mode, Bidirectional Precision Current

Sensing Amplifier

General Description

The LMP8601 and LMP8601Q are fixed 20x gain precision

amplifiers. The part will amplify and filter small differential sig-

nals in the presence of high common mode voltages. The

input common mode voltage range is –22V to +60V when op-

erating from a single 5V supply. With 3.3V supply, the input

common mode voltage range is from –4V to +27V. The

LMP8601 and LMP8601Q are members of the Linear Mono-

lithic Precision (LMP®) family and are ideal parts for unidirec-

tional and bidirectional current sensing applications. All

parameter values of the part that are shown in the tables are

100% tested and all bold values are also 100% tested over

temperature.

The part has a precise gain of 20x which is adequate in most

targeted applications to drive an ADC to its full scale value.

The fixed gain is achieved in two separate stages, a pream-

plifier with a gain of 10x and an output stage buffer amplifier

with a gain of 2x. The connection between the two stages of

the signal path is brought out on two pins to enable the pos-

sibility to create an additional filter network around the output

buffer amplifier. These pins can also be used for alternative

configurations with different gain as described in the applica-

tions section .

The mid-rail offset adjustment pin enables the user to use

these devices for bidirectional single supply voltage current

sensing. The output signal is bidirectional and mid-rail refer-

enced when this pin is connected to the positive supply rail.

With the offset pin connected to ground, the output signal is

unidirectional and ground-referenced .

The LMP8601Q incorporates enhanced manufacturing and

support processes for the automotive market, including defect

detection methodologies. Reliability qualification is compliant

with the requirements and temperature grades defined in the

AEC Q100 standard.

Features

Unless otherwise noted, typical values at TA = 25°C,

VS = 5.0V, Gain = 20x

■TCVOS 10μV/°C max

■CMRR 90 dB min

■Input offset voltage 1 mV max

■CMVR at VS = 3.3V −4V to 27V

■CMVR at VS = 5.0V −22V to 60V

■Operating ambient temperature range −40°C to 125°C

■LMP8601Q available in Automotive AEC-Q100 Grade 1

qualified version

■Single supply bidirectional operation

■All Min / Max limits 100% tested

Applications

■High side and low side driver configuration current sensing

■Bidirectional current measurement

■Current loop to voltage conversion

■Automotive fuel injection control

■Transmission control

■Power steering

■Battery management systems

Typical Applications

20157101

LMP™ is a trademark of National Semiconductor Corporation.

LMP8601/LMP8601Q 60V Common Mode, Bidirectional Precision Current Sensing Amplifier

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 4)

Human Body

For input pins only ±4000V

For all other pins ±2000V

Machine Model 200V

Charge Device Model 1000V

Supply Voltage (VS - GND) 6.0V

Continuous Input Voltage ((−IN and

+IN) −22V to 60V

Transient (400 ms) −25V to 65V

Maximum Voltage at A1, A2,

OFFSET and OUT Pins

VS +0.3V and

GND -0.3V

Storage Temperature Range −65°C to 150°C

Junction Temperature (Note 3) 150°C

Mounting Temperature

Infrared or Convection (20 sec) 235°C

Wave Soldering Lead (10 sec) 260°C

Operating Ratings (Note 1)

Supply Voltage (VS – GND) 3.0V to 5.5V

Offset Voltage (Pin 7 ) 0 to VS

Temperature Range (Note 3)

Packaged devices −40°C to +125°C

Package Thermal Resistance (Note 3)

8-Pin SOIC (θJA)190°C/W

3.3V Electrical Characteristics (Note 2)

Unless otherwise specified, all limits guaranteed at TA = 25°C, VS = 3.3V, GND = 0V, −4V ≤ VCM ≤ 27V, and RL = ∞, Offset (Pin

7) is grounded, 10nF between VS and GND. Boldface limits apply at the temperature extremes.

Symbol Parameter Conditions Min

(Note 6)

Typ

(Note 5)

Max

(Note 6)

Units

Overall Performance (From -IN (pin 1) and +IN (pin 8) to OUT (pin 5) with pins A1 (pin 3) and A2 (pin 4) connected)

ISSupply Current 0.6 11.3 mA

AVTotal Gain 19.9 20 20.1 V/V

Gain Drift (Note 14)−40°C ≤ TA ≤ 125°C −2.7 ±20 ppm/°C

SR Slew Rate (Note 7) VIN = ±0.165V 0.4 0.7 V/μs

BW Bandwidth 50 60 kHz

VOS Input Offset Voltage VCM = VS / 2 0.15 ±1 mV

TCVOS Input Offset Voltage Drift (Note 8)−40°C ≤ TA ≤ 125°C 2 ±10 μV/°C

enInput Referred Voltage Noise 0.1 Hz − 10 Hz, 6 Sigma 16.4 μVP-P

Spectral Density, 1 kHz 830 nV/√Hz

PSRR Power Supply Rejection Ratio DC, 3.0V ≤ VS ≤ 3.6V, VCM = VS/2 70 86 dB

Mid−scale Offset Scaling Accuracy ±0.15 ±0.5 %

Input Referred ±0.413 mV

Preamplifier (From input pins -IN (pin 1) and +IN (pin 8) to A1 (pin 3))

RCM Input Impedance Common Mode −4V ≤ VCM ≤ 27V 250 295 350 kΩ

RDM Input Impedance Differential Mode −4V ≤ VCM ≤ 27V 500 590 700 kΩ

VOS Input Offset Voltage VCM = VS / 2 ±0.15 ±1 mV

DC CMRR DC Common Mode Rejection Ratio −2V ≤ VCM ≤ 24V 86 96 dB

AC CMRR AC Common Mode Rejection Ratio

(Note 9)

f = 1 kHz 80 94 dB

f = 10 kHz 85

CMVR Input Common Mode Voltage Range for 80 dB CMRR −4 27 V

A1VGain (Note 14) 9.95 10.0 10.05 V/V

RF-INT Output Impedance Filter Resistor 99 100 101 kΩ

TCRF-INT Output Impedance Filter Resistor Drift ±5 ±50 ppm/°C

A1 VOUT A1 Output Voltage Swing VOL RL = ∞ 2 10 mV

VOH 3.2 3.25 V

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LMP8601/LMP8601Q

Symbol Parameter Conditions Min

(Note 6)

Typ

(Note 5)

Max

(Note 6)

Units

Output Buffer (From A2 (pin 4) to OUT( pin 5 ))

VOS Input Offset Voltage 0V ≤ VCM ≤ VS−2

−2.5 ±0.5 2

2.5 mV

A2VGain (Note 14) 1.99 2 2.01 V/V

IBInput Bias Current of A2 (Note 10), −40 fA

±20 nA

A2 VOUT A2 Output Voltage Swing

(Note 11, Note 12)

VOL RL = 100 kΩ 4 20 mV

VOH 3.28 3.29 V

ISC Output Short-Circuit Current (Note 13) Sourcing, VIN = VS, VOUT = GND -25 -38 -60 mA

Sinking, VIN = GND, VOUT = VS30 46 65

5V Electrical Characteristics (Note 2)

Unless otherwise specified, all limits guaranteed for at TA = 25°C, VS = 5V, GND = 0V, −22V ≤ VCM ≤ 60V, and RL = ∞, Offset (Pin

7) is grounded, 10nF between VS and GND. Boldface limits apply at the temperature extremes.

Symbol Parameter Conditions Min

(Note 6)

Typ

(Note 5)

Max

(Note 6)Units

Overall Performance (From -IN (pin 1) and +IN (pin 8) to OUT (pin 5) with pins A1 (pin 3) and A2 (pin 4) connected)

ISSupply Current 0.7 1.1 1.5 mA

AVTotal Gain (Note 14) 19.9 20 20.1 V/V

Gain Drift −40°C ≤ TA ≤ 125°C −2.8 ±20 ppm/°C

SR Slew Rate (Note 7) VIN = ±0.25V 0.6 0.83 V/μs

BW Bandwidth 50 60 kHz

VOS Input Offset Voltage 0.15 ±1 mV

TCVOS Input Offset Voltage Drift (Note 8)−40°C ≤ TA ≤ 125°C 2 ±10 μV/°C

eNInput Referred Voltage Noise 0.1 Hz − 10 Hz, 6 Sigma 17.5 μVP-P

Spectral Density, 1 kHz 890 nV/√Hz

PSRR Power Supply Rejection Ratio DC 4.5V ≤ VS ≤ 5.5V 70 90 dB

Mid−scale Offset Scaling Accuracy ±0.15 ±0.5 %

Input Referred ±0.625 mV

Preamplifier (From input pins -IN (pin 1) and +IN (pin 8) to A1 (pin 3))

RCM Input Impedance Common Mode 0V ≤ VCM ≤ 60V 250 295 350 kΩ

−20V ≤ VCM ≤ 0V 165 193 250 kΩ

RDM Input Impedance Differential Mode 0V ≤ VCM ≤ 60V 500 590 700 kΩ

−20V ≤ VCM ≤ 0V 300 386 500 kΩ

VOS Input Offset Voltage VCM = VS / 2 ±0.15 ±1 mV

DC CMRR DC Common Mode Rejection Ratio −20V ≤ VCM ≤ 60V 90 105 dB

AC CMRR AC Common Mode Rejection Ratio

(Note 9)

f = 1 kHz 80 96 dB

f = 10 kHz 83

CMVR Input Common Mode Voltage Range for 80 dB CMRR −22 60 V

A1VGain (Note 14) 9.95 10 10.05 V/V

RF-INT Output Impedance Filter Resistor 99 100 101 kΩ

TCRF-INT Output Impedance Filter Resistor Drift ±5 ±50 ppm/°C

A1 VOUT A1 Ouput Voltage Swing VOL RL = ∞ 2 10 mV

VOH 4.95 4.985 V

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LMP8601/LMP8601Q

Symbol Parameter Conditions Min

(Note 6)

Typ

(Note 5)

Max

(Note 6)Units

Output Buffer (From A2 (pin 4) to OUT( pin 5 ))

VOS Input Offset Voltage 0V ≤ VCM ≤ VS−2

−2.5 ±0.5 2

2.5 mV

A2VGain (Note 14) 1.99 2 2.01 V/V

IBInput Bias Current of A2 (Note 10) −40 fA

±20 nA

A2 VOUT A2 Ouput Voltage Swing

(Note 11, Note 12)

VOL RL = 100 kΩ 4 20 mV

VOH 4.98 4.99 V

ISC Output Short-Circuit Current (Note 13) Sourcing, VIN = VS, VOUT = GND –25 –42 –60 mA

Sinking, VIN = GND, VOUT = VS30 48 65

Note 1: “Absolute Maximum Ratings” indicate limits beyond which damage to the device may occur, including inoperability and degradation of the device reliability

and/or performance. Functional operation of the device and/or non-degradation at the Absolute Maximum Ratings or other conditions beyond those indicated in

the Recommended Operating Conditions is not implied. The Recommended Operating Conditions indicate conditions at which the device is functional and the

device should not be beyond such conditions. All voltages are measured with respect to the ground pin, unless otherwise specified.

Note 2: The electrical Characteristics tables list guaranteed specifications under the listed Recommended Operating Conditions except as otherwise modified or

specified by the Electrical Characteristics Conditions and/or Notes. Typical specifications are estimations only and are not guaranteed.

Note 3: The maximum power dissipation must be derated at elevated temperatures and is dictated by TJ(MAX), θJA, and the ambient temperature, TA. The maximum

allowable power dissipation PDMAX = (TJ(MAX) - TA)/ θJA or the number given in Absolute Maximum Ratings, whichever is lower.

Note 4: Human Body Model per MIL-STD-883, Method 3015.7. Machine Model, per JESD22-A115-A. Field-Induced Charge-Device Model, per JESD22-C101-

Note 5: Typical values represent the most likely parameter norms at TA = +25°C, and at the Recommended Operation Conditions at the time of product

characterization and are not guaranteed.

Note 6: Datasheet min/max specification limits are guaranteed by test.

Note 7: Slew rate is the average of the rising and falling slew rates.

Note 8: Offset voltage drift determined by dividing the change in VOS at temperature extremes into the total temperature change.

Note 9: AC Common Mode Signal is a 5VPP sine-wave (0V to 5V) at the given frequency.

Note 10: Positive current corresponds to current flowing into the device

Note 11: For this test input is driven from A1 stage.

Note 12: For VOL, RL is connected to VS and for VOH, RL is connected to GND.

Note 13: Short-Circuit test is a momentary test. Continuous short circuit operation at elevated ambient temperature can result in exceeding the maximum allowed

junction temperature of 150°C

Note 14: Both the gain of the preamplifier A1V and the gain of the buffer amplifier A2V are measured individually. The over all gain of both amplifiers AV is also

measured to assure the gain of all parts is always within the AV limits

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LMP8601/LMP8601Q

Block Diagram

20157105

K2 = 2

Connection Diagram

8-Pin SOIC

20157102

Top View

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LMP8601/LMP8601Q

Pin Descriptions

Pin Name Description

Power Supply 2 GND Power Ground

6 VSPositive Supply Voltage

Inputs 1 −IN Negative Input

8 +IN Positive Input

Filter Network 3 A1 Preamplifier output

4 A2 Input from the external filter network and / or A1

Offset 7 OFFSET DC Offset for bidirectional signals

Output 5 OUT Single ended output

Ordering Information

Package Part Number Package Marking Transport Media NSC Drawing

8-Pin SOIC

LMP8601MA LMP8601MA 95 Units/Rail

M08A

LMP8601MAX 2.5K Units Tape and Reel

LMP8601QMA LMP8601QMA 95 Units/Rail

LMP8601QMAX 2.5K Units Tape and Reel

Automotive Grade (Q) product incorporates enhanced manufacturing and support processes for the automotive market, including

defect detection methodologies. Reliability qualification is compliant with the requirements and temperature grades defined in the

AEC Q100 standard. Automotive Grade products are identified with the letter Q. Fully compliant PPAP documentation is available.

For more information go to http://www.national.com/automotive.

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LMP8601/LMP8601Q

Typical Performance Characteristics Unless otherwise specified, all limits guaranteed for at TA = 25°C,

VS = 5V, GND = 0V, −22 ≤ VCM ≤ 60V, and RL = ∞, Offset (Pin 7) connected to VS, 10nF between VS and GND.

VOS vs. VCM at VS = 3.3V

20157124

VOS vs. VCM at VS = 5V

20157125

Input Bias Current Over Temperature (+IN and −IN pins)

at VS = 3.3V

20157141

Input Bias Current Over Temperature (+IN and −IN pins)

at VS = 5V

20157142

Input Bias Current Over Temperature (A2 pin)

at VS = 5V

20157127

Input Bias Current Over Temperature (A2 pin)

at VS = 5V

20157126

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LMP8601/LMP8601Q

Input Referred Voltage Noise vs. Frequency

20157110

PSRR vs. Frequency

20157117

Gain vs. Frequency at VS = 3.3V

20157111

Gain vs. Frequency at VS = 5V

20157112

CMRR vs. Frequency at VS = 3.3V

20157128

CMRR vs. Frequency at VS = 5V

20157129

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LMP8601/LMP8601Q

Step Response at VS = 3.3V

20157118

Step Response at VS = 5V

20157119

Settling Time (Falling Edge) at VS = 3.3V

20157120

Settling Time (Falling Edge) at VS = 5V

20157121

Settling Time (Rising Edge) at VS = 3.3V

20157122

Settling Time (Rising Edge) at VS = 5V

20157123

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LMP8601/LMP8601Q

Positive Swing vs. RLOAD at VS = 3.3V

20157113

Negative Swing vs. RLOAD at VS = 3.3V

20157114

Positive Swing vs. RLOAD VS = 5V

20157115

Negative Swing vs. RLOAD at VS = 5V

20157116

VOS Distribution at VS = 3.3V

20157134

VOS Distribution at VS = 5V

20157135

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LMP8601/LMP8601Q

TCVOS Distribution

20157136

Gain Drift Distribution

20157137

Gain error Distribution at VS = 3.3V

20157138

Gain error Distribution at VS = 5V

20157139

CMRR Distribution at VS = 3.3V

20157132

CMRR Distribution at VS = 5V

20157133

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LMP8601/LMP8601Q

Application Information

GENERAL

The LMP8601 and LMP8601Q are fixed gain differential volt-

age precision amplifiers with a gain of 20x and a -22V to +60V

input common mode voltage range when operating from a

single 5V supply or a -4V to +27V input common mode voltage

range when operating from a single 3.3V supply. The

LMP8601 and LMP8601Q are members of the LMP family

and are ideal parts for unidirectional and bidirectional current

sensing applications. Because of the proprietary chopping

level-shift input stage the LMP8601/LMP8601Q achieve very

low offset, very low thermal offset drift, and very high CMRR.

The LMP8601 and LMP8601Q will amplify and filter small dif-

ferential signals in the presence of high common mode volt-

ages.

The LMP8601/LMP8601Q use level shift resistors at the in-

puts. Because of these resistors, the LMP8601/LMP8601Q

can easily withstand very large differential input voltages that

may exist in fault conditions where some other less protected

high-performance current sense amplifiers might sustain per-

manent damage.

PERFORMANCE GUARANTIES

To guaranty the high performance of the LMP8601/ LM-

P8601Q, all minimum and maximum values shown in the

parameter tables of this data sheet are 100% tested where all

bold limits are also 100% tested over temperature.

THEORY OF OPERATION

The schematic shown in Figure 1 gives a schematic repre-

sentation of the internal operation of the

LMP8601/LMP8601Q.

The signal on the input pins is typically a small differential

voltage across a current sensing shunt resistor. The input

signal may appear at a high common mode voltage. The input

signals are accessed through two input resistors. The propri-

etary chopping level-shift current circuit pulls or pushes cur-

rent through the input resistors to bring the common mode

voltage behind these resistors within the supply rails. Subse-

quently, the signal is gained up by a factor of 10 and brought

out on the A1 pin through a trimmed 100 kΩ resistor. In the

application, additional gain adjustment or filtering compo-

nents can be added between the A1 and A2 pins as will be

explained in subsequent sections. The signal on the A2 pin is

further amplified by a factor of 2 and brought out on the OUT

pin. The OFFSET pin allows the output signal to be level-

shifted to enable bidirectional current sensing as will be ex-

plained below.

20157105

K2 = 2

FIGURE 1. Theory of Operation

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LMP8601/LMP8601Q

ADDITIONAL SECOND ORDER LOW PASS FILTER

The LMP8601/LMP8601Q has a third order Butterworth low-

pass characteristic with a typical bandwidth of 60 kHz inte-

grated in the preamplifier stage of the part. The bandwidth of

the output buffer can be reduced by adding a capacitor on the

A1 pin to create a first order low pass filter with a time constant

determined by the 100 kΩ internal resistor and the external

filter capacitor.

It is also possible to create an additional second order Sallen-

Key low pass filter by adding external components R2, C1 and

C2. Together with the internal 100 kΩ resistor R1 as illustrated

in Figure 2, this circuit creates a second order low-pass filter

characteristic.

When the corner frequency of the additional filter is much

lower than 60 kHz, the transfer function of the described am-

plifier van be written as:

Where K1 equals the gain of the preamplifier and K2 that of

the buffer amplifier.

The above equation can be written in the normalized frequen-

cy response for a 2nd order low pass filter:

The cutt-off frequency ωo in rad/sec (divide by 2π to get the

cut-off frequency in Hz) is given by:

and the quality factor of the filter is given by:

With K2 = 2x, the above equation transforms results in:

With this filter gain K2= 2x, the design procedure can be very

simple if the two capacitors are chosen to be equal, C1=C2=C.

In this case, given the predetermined value of R1 = 100kΩ

( the internal resistor), the quality factor is set solely by the

value of the resistor R2.

R2 can be calculated based on the desired value of Q as the

first step of the design procedure with the following equation:

For instance, the value of Q can be set to 0.5√2 to create a

Butterworth response, to 1/√3 to create a Bessel response,

or a 0.5 to create a critically damped response. Once the

value of R2 has been found, the second and last step of the

design procedure is to calculate the required value of C to give

the desired low-pass cut-off frequency using:

Note that the frequency response achieved using this proce-

dure will only be accurate if the cut-off frequency of the second

order filter is much smaller than the intrinsic 60 kHz low-pass

filter. In other words, to have the frequency response of the

LMP8601/LMP8601Q circuit chosen such that the internal

poles do not affect the external second order filter.

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LMP8601/LMP8601Q

20157155

K1 = 10, K2 = 2

FIGURE 2. Second Order Low Pass Filter

GAIN ADJUSTMENT

The gain of the LMP8601/LMP8601Q is 20; however, this

gain can be adjusted as the signal path in between the two

internal amplifiers is available on the external pins.

Reduce Gain

Figure 3 shows the configuration that can be used to reduce

the gain of the LMP8601/LMP8601Q.

20157156

K2 = 2

FIGURE 3. Reduce Gain

Rr creates a resistive divider together with the internal

100 kΩ resistor such that the reduced gain Gr becomes:

Given a desired value of the reduced gain Gr, using this equa-

tion the required value for Rr can be calculated with:

Increase Gain

Figure 4 shows the configuration that can be used to increase

the gain of the LMP8601/LMP8601Q.

Ri creates positive feedback from the output pin to the input

of the buffer amplifier. The positive feedback increases the

gain. The increased gain Gi becomes:

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LMP8601/LMP8601Q

From this equation, for a desired value of the gain, the re-

quired value of Ri can be calculated with:

It should be noted from the equation for the gain Gi that for

large gains Ri approaches 100 kΩ. In this case, the denomi-

nator in the equation becomes close to zero. In practice, for

large gains the denominator will be determined by tolerances

in the value of the external resistor Ri and the internal 100

kΩ resistor. In this case, the gain becomes very inaccurate. If

the denominator becomes equal to zero, the system will even

become instable. It is recommended to limit the application of

this technique to gain values of 50 or smaller.

20157157

K2 = 2

FIGURE 4. Increase Gain

BIDIRECTIONAL CURRENT SENSING

The signal on the A1 and OUT pins is ground-referenced

when the OFFSET pin is connected to ground. This means

that the output signal can only represent positive values of the

current through the shunt resistor, so only currents flowing in

one direction can be measured. When the offset pin is tied to

the positive supply rail, the signal on the A1 and OUT pins is

referenced to a mid-rail voltage which allows bidirectional

current sensing. When the offset pin is connected to a voltage

source, the output signal will be level shifted to that voltage

divided by two. In principle, the output signal can be shifted

to any voltage between 0 and VS/2 by applying twice that

voltage to the OFFSET pin.

With the offset pin connected to the supply pin (VS) the oper-

ation of the amplifier will be fully bidirectional and symmetrical

around 0V differential at the input pins. The signal at the out-

put will follow this voltage difference multiplied by the gain and

at an offset voltage at the output of half VS.

Example:

With 5V supply and a gain of 20x, a differential input signal of

+10mV will result in 2.7V at the output pin. similarly -10mV at

the input will result in 2.3V at the output pin.

Note: The OFFSET pin has to be driven from a very low-impedance source

(<10Ω). This is because the OFFSET pin internally connects directly

to the resistive feedback networks of the two gain stages. When the

OFFSET pin is driven from a relatively large impedance (e.g. a re-

sistive divider between the supply rails) accuracy will decrease.

POWER SUPPLY DECOUPLING

In order to decouple the LMP8601/LMP8601Q from AC noise

on the power supply, it is recommended to use a 0.1 µF by-

pass capacitor between the VS and GND pins. This capacitor

should be placed as close as possible to the supply pins. In

some cases an additional 10 µF bypass capacitor may further

reduce the supply noise.

DRIVING SWITCHED CAPACITIVE LOADS

Some ADCs load their signal source with a sample and hold

capacitor. The capacitor may be discharged prior to being

connected to the signal source. If the LMP8601/LMP8601Q

is driving such ADCs the sudden current that should be de-

livered when the sampling occurs may disturb the output

signal. This effect was simulated with the circuit shown in

Figure 5 where the output is to a capacitor that is driven by a

rail to rail square wave.

20157160

FIGURE 5. Driving Switched Capacitive Load

This circuit simulates the switched connection of a discharged

capacitor to the LMP8601/LMP8601Q output. The resulting

VOUT disturbance signals are shown in Figure 6

and Figure 7.

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LMP8601/LMP8601Q

20157130

FIGURE 6. Capacitive Load Response at 3.3V

20157131

FIGURE 7. Capacitive Load Response at 5.0V

These figures can be used to estimate the disturbance that

will be caused when driving a switched capacitive load. To

minimize the error signal introduced by the sampling that oc-

curs on the ADC input, an additional RC filter can be placed

in between the LMP8601/LMP8601Q and the ADC as illus-

trated in Figure 8.

20157161

FIGURE 8. Reduce Error When Driving ADCs

The external capacitor absorbs the charge that flows when

the ADC sampling capacitor is connected. The external ca-

pacitor should be much larger than the sample and hold

capacitor at the input of the ADC and the RC time constant of

the external filter should be such that the speed of the system

is not affected.

LOW SIDE CURRENT SENSING APPLICATION

Figure 9 illustrates a low side current sensing application with

a low side driver. The power transistor is pulse width modu-

lated to control the average current flowing through the in-

ductive load which is connected to a relatively high battery

voltage. The current through the load is measured across a

shunt resistor RSENSE in series with the load. When the power

transistor is on, current flows from the battery through the in-

ductive load, the shunt resistor and the power transistor to

ground. In this case, the common mode voltage on the shunt

is close to ground. When the power transistor is off, current

flows through the inductive load, through the shunt resistor

and through the freewheeling diode. In this case the common

mode voltage on the shunt is at least one diode voltage drop

above the battery voltage. Therefore, in this application the

common mode voltage on the shunt is varying between a

large positive voltage and a relatively low voltage. Because

the large common mode voltage range of the

LMP8601/LMP8601Q and because of the high AC common

mode rejection ratio, the LMP8601/LMP8601Q is very well

suited for this application.

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LMP8601/LMP8601Q

20157152

RSENSE = 0.01Ω, K2 = 2, VOUT = 0.2 V/A

FIGURE 9. Low Side Current Sensing Application

HIGH SIDE CURRENT SENSING APPLICATION

Figure 10 illustrates the application of

the LMP8601/LMP8601Q in a high side sensing application.

This application is similar to the low side sensing discussed

above, except in this application the common mode voltage

on the shunt drops below ground when the driver is switched

off. Because the common mode voltage range of

the LMP8601/LMP8601Q extends below the negative rail,

the LMP8601/LMP8601Q is also very well suited for this ap-

plication.

20157153

K2 = 2

FIGURE 10. High Side Current Sensing Application

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LMP8601/LMP8601Q

BATTERY CURRENT MONITOR APPLICATION

This application example shows how the LMP8601/LM-

P8601Q can be used to monitor the current flowing in and out

a battery pack. The fact that the LMP8601/LMP8601Q can

measure small voltages at a high offset voltage outside the

parts own supply range makes this part a very good choice

for such applications. If the load current of the battery is higher

then the charging current, the output voltage of the LMP8601/

LMP8601Q will be above the “half offset voltage” for a net

current flowing out of the battery. When the charging current

is higher then the load current the output will be below this

“half offset voltage”.

20157154

K2 = 2

FIGURE 11. Battery Current Monitor Application

ADVANCED BATTERY CHARGER APPLICATION

The above circuit can be used to realize an advanced battery

charger that has the capability to monitor the exact net current

that flows in and out the battery as show in Figure 12. The

output signal of the LMP8601/LMP8601Q is digitized with the

A/D converter and used as an input for the charge controller.

The Charge controller can me used to regulate the charger

circuit to deliver exactly the current that is required by the load,

avoiding overcharging a fully loaded battery

www.national.com 18

LMP8601/LMP8601Q

20157103

K2 = 2

FIGURE 12. Advanced Battery Charger Application

CURRENT LOOP RECEIVER APPLICATION

Many industrial applications use 4 to 20 mA transmitters to

send a sensor’s analog value to a central control room. The

LMP8601/LMP8601Q can be used as a current loop receiver

as shown in Figure 13.

20157151

K2 = 2

FIGURE 13. Current Loop Receiver Application

19 www.national.com

LMP8601/LMP8601Q

Physical Dimensions inches (millimeters) unless otherwise noted

8Pin SOIC

NS Package Number M08A

www.national.com 20

LMP8601/LMP8601Q

Notes

21 www.national.com

LMP8601/LMP8601Q

Notes

LMP8601/LMP8601Q 60V Common Mode, Bidirectional Precision Current Sensing Amplifier

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