LMP8603 [NSC]
60V Common Mode, Fixed Gain, Bidirectional Precision Current Sensing Amplifier; 60V共模，固定增益，双向精密电流感应放大器
| 型号： | LMP8603 |
| 厂家： | 
National Semiconductor |
| 描述： | 60V Common Mode, Fixed Gain, Bidirectional Precision Current Sensing Amplifier |
| 文件： | 总24页 (文件大小：572K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
July 17, 2009
LMP8602/LMP8603
60V Common Mode, Fixed Gain, Bidirectional Precision
Current Sensing Amplifier
General Description
Features
The LMP8602 and LMP8603 are fixed gain precision ampli-
fiers. The parts will amplify and filter small differential signals
in the presence of high common mode voltages. The input
common mode voltage range is –22V to +60V when operating
from a single 5V supply. With a 3.3V supply, the input com-
mon mode voltage range is from –4V to +27V. The LMP8602
and LMP8603 are members of the Linear Monolithic Precision
(LMP®) family and are ideal parts for unidirectional and bidi-
rectional current sensing applications. All parameter values
of the parts that are shown in the tables are 100% tested and
all bold values are also 100% tested over temperature.
Unless otherwise noted, typical values at TA = 25°C,
VS = 5.0V, Gain = 50x (LMP8602), Gain = 100x (LMP8603)
TCVos
10μV/°C max
90 dB min
1 mV max
−4V to 27V
−22V to 60V
■
■
■
■
■
■
■
■
CMRR
Input offset voltage
CMVR at VS = 3.3V
CMVR at VS = 5.0V
Operating ambient temperature range −40°C to 125°C
Single supply bidirectional operation
All Min / Max limits 100% tested
The parts have a precise gain of 50x for the LMP8602 and
100x for the LMP8603, which are adequate in most targeted
applications to drive an ADC to its full scale value. The fixed
gain is achieved in two separate stages, a preamplifier with a
gain of 10x and an output stage buffer amplifier with a gain of
5x for the LMP8602 and 10x for the LMP8603. The connection
between the two stages of the signal path is brought out on
two pins to enable the possibility 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 applications section.
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
■
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 LMP8602 and LMP8603 are available in a 8–Pin SOIC
package and in a 8–Pin MSOP package.
Typical Applications
30083401
LMP™ is a trademark of National Semiconductor Corporation.
© 2009 National Semiconductor Corporation
300834
www.national.com
Storage Temperature Range
Junction Temperature (Note 3)
Mounting Temperature
Infrared or Convection (20 sec)
Wave Soldering Lead (10 sec)
−65°C to 150°C
150°C
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
235°C
260°C
ESD Tolerance (Note 4)
Human Body
Operating Ratings (Note 1)
Supply Voltage (VS – GND)
For input pins only
For all other pins
Machine Model
±4000V
±2000V
200V
3.0V to 5.5V
0 to VS
Offset Voltage (Pin 7 )
Temperature Range (Note 3)
Packaged devices
Charge Device Model
Supply Voltage (VS - GND)
1000V
6.0V
−40°C to +125°C
Package Thermal Resistance (Note 3)
Continuous Input Voltage (−IN
and +IN) (Note 6)
Transient (400 ms)
Maximum Voltage at A1, A2,
OFFSET and OUT Pins
−22V to 60V
−25V to 65V
VS +0.3V and
GND -0.3V
8-Pin SOIC (θJA
)
190°C/W
203°C/W
8-Pin MSOP (θJA
)
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.
Min
(Note 7) (Note 5) (Note 7)
Overall Performance (From -IN (pin 1) and +IN (pin 8) to OUT (pin 5) with pins A1 (pin 3) and A2 (pin 4) connected)
Typ
Max
Symbol
Parameter
Conditions
Units
IS
Supply Current
Total Gain
1.3
1
mA
V/V
AV
LMP8602
LMP8603
49.75
99.5
50
50.25
100.5
±20
100
−2.7
Gain Drift (Note 15)
ppm/°C
−40°C ≤ TA ≤ 125°C
SR
Slew Rate (Note 8)
Bandwidth
VIN = ±0.165V
0.4
50
0.7
60
V/μs
kHz
mV
BW
VOS
Input Offset Voltage
Input Offset Voltage Drift (Note 9)
VCM = VS / 2
0.15
2
±1
TCVOS
±10
−40°C ≤ TA ≤ 125°C
0.1 Hz − 10 Hz, 6 Sigma
μV/°C
μVP-P
en
Input Referred Voltage Noise
16.4
830
Spectral Density, 1 kHz
nV/√Hz
dB
PSRR
Power Supply Rejection Ratio
70
86
DC, 3.0V ≤ VS ≤ 3.6V, VCM = VS/2
LMP8602
Mid−scale Offset Scaling Accuracy
±0.25
±1
%
Input Referred
±0.33
±1.5
mV
%
LMP8603
±0.45
Input Referred
±0.248
mV
Preamplifier (From input pins -IN (pin 1) and +IN (pin 8) to A1 (pin 3))
RCM
RDM
VOS
Input Impedance Common Mode
Input Impedance Differential Mode
Input Offset Voltage
250
500
295
590
350
700
−4V ≤ VCM ≤ 27V
−4V ≤ VCM ≤ 27V
kΩ
kΩ
mV
dB
VCM = VS / 2
±0.15
±1
DC CMRR DC Common Mode Rejection Ratio
86
96
94
85
−2V ≤ VCM ≤ 24V
f = 1 kHz
AC CMRR AC Common Mode Rejection Ratio
(Note 10)
80
dB
f = 10 kHz
CMVR
K1
Input Common Mode Voltage Range
Gain (Note 15)
for 80 dB CMRR
−4
9.95
99
27
10.05
101
±50
10
V
V/V
10.0
100
±5
RF-INT
Output Impedance Filter Resistor
Output Impedance Filter Resistor Drift
A1 Output Voltage Swing
kΩ
TCRF-INT
A1 VOUT
ppm/°C
mV
VOL
VOH
2
RL = ∞
3.2
3.25
V
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2
Min
Typ
Max
Symbol
Parameter
Conditions
Units
(Note 7) (Note 5) (Note 7)
Output Buffer (From A2 (pin 4) to OUT( pin 5 ))
VOS
K2
Input Offset Voltage
Gain (Note 15)
−2
−2.5
2
2.5
0V ≤ VCM ≤ VS
±0.5
mV
V/V
LMP8602
LMP8603
4.975
9.95
5
5.025
10.05
10
IB
Input Bias Current of A2 (Note 11)
−40
fA
±20
40
nA
A2 VOUT
A2 Output Voltage Swing (Notes 12, 13) VOL
RL = 100 kΩ
VOH
RL = 100 kΩ
,
LMP8602
LMP8603
10
10
mV
V
80
,
3.28
3.29
ISC
Output Short-Circuit Current (Note 14)
Sourcing, VIN = VS, VOUT = GND
Sinking, VIN = GND, VOUT = VS
-25
30
-38
46
-60
65
mA
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.
Min
(Note 7) (Note 5) (Note 7)
Overall Performance (From -IN (pin 1) and +IN (pin 8) to OUT (pin 5) with pins A1 (pin 3) and A2 (pin 4) connected)
Typ
Max
Symbol
Parameter
Conditions
Units
IS
Supply Current
1.1
50
1.5
mA
V/V
AV
Total Gain (Note 15)
LMP8602
LMP8603
49.75
99.5
50.25
100.5
±20
100
−2.8
Gain Drift
ppm/°C
−40°C ≤ TA ≤ 125°C
SR
Slew Rate (Note 8)
Bandwidth
VIN = ±0.25V
0.6
50
0.83
60
V/μs
kHz
mV
BW
VOS
Input Offset Voltage
Input Offset Voltage Drift (Note 9)
0.15
2
±1
TCVOS
±10
−40°C ≤ TA ≤ 125°C
0.1 Hz − 10 Hz, 6 Sigma
μV/°C
μVP-P
eN
Input Referred Voltage Noise
17.5
890
Spectral Density, 1 kHz
nV/√Hz
dB
PSRR
Power Supply Rejection Ratio
70
90
DC 4.5V ≤ VS ≤ 5.5V
Mid−scale Offset Scaling Accuracy
LMP8602
±0.25
±1
%
Input Referred
Input Referred
±0.50
±1.5
mV
%
LMP8603
±0.45
±0.375
mV
Preamplifier (From input pins -IN (pin 1) and +IN (pin 8) to A1 (pin 3))
RCM
RDM
VOS
Input Impedance Common Mode
Input Impedance Differential Mode
Input Offset Voltage
250
165
500
300
295
193
350
250
700
500
±1
0V ≤ VCM ≤ 60V
−20V ≤ VCM< 0V
0V ≤ VCM ≤ 60V
kΩ
kΩ
kΩ
590
386
−20V ≤ VCM < 0V
VCM = VS / 2
kΩ
mV
dB
±0.15
DC CMRR DC Common Mode Rejection Ratio
90
105
96
−20V ≤ VCM ≤ 60V
f = 1 kHz
AC CMRR AC Common Mode Rejection Ratio
(Note 10)
80
dB
f = 10 kHz
83
CMVR
K1
Input Common Mode Voltage Range
Gain (Note 15)
for 80 dB CMRR
−22
9.95
99
60
V
10
10.05
101
V/V
kΩ
RF-INT
Output Impedance Filter Resistor
100
3
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Min
Typ
Max
Symbol
Parameter
Conditions
Units
(Note 7) (Note 5) (Note 7)
TCRF-INT
A1 VOUT
Output Impedance Filter Resistor Drift
A1 Ouput Voltage Swing
±5
2
±50
10
ppm/°C
mV
VOL
VOH
RL = ∞
4.95
4.985
V
Output Buffer (From A2 (pin 4) to OUT( pin 5 ))
VOS
Input Offset Voltage
−2
−2.5
2
2.5
0V ≤ VCM ≤ VS
±0.5
mV
V/V
K2
Gain (Note 15)
LMP8602
LMP8603
4.975
9.95
5
5.025
10.05
10
IB
Input Bias Current of A2 (Note 11)
−40
fA
±20
40
nA
A2 VOUT
A2 Ouput Voltage Swing (Notes 12, 13)
VOL
RL = 100 kΩ
VOH
RL = 100 kΩ
,
LMP8602
LMP8603
10
10
mV
V
80
,
4.98
4.99
ISC
Output Short-Circuit Current (Note 14)
Sourcing, VIN = VS, VOUT = GND
Sinking, VIN = GND, VOUT = VS
–25
30
–42
48
–60
65
mA
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-
C.
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: For the MSOP package, the bare board spacing at the solder pads of the package will be to small for reliable use at higher voltages (VCM >25V) Therefore
it is strongly advised to add a conformal coating on the PCB assembled with the LMP8602 and LMP8603.
Note 7: Datasheet min/max specification limits are guaranteed by test.
Note 8: Slew rate is the average of the rising and falling slew rates.
Note 9: Offset voltage drift determined by dividing the change in VOS at temperature extremes into the total temperature change.
Note 10: AC Common Mode Signal is a 5VPP sine-wave (0V to 5V) at the given frequency.
Note 11: Positive current corresponds to current flowing into the device
Note 12: For this test input is driven from A1 stage in uni directional mode (Offset pin connected to GND).
Note 13: For VOL, RL is connected to VS and for VOH, RL is connected to GND.
Note 14: 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 15: 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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Block Diagram
30083405
K2 = 5 for LMP8602, K2 = 10 for LMP8603
Connection Diagram
8-Pin SOIC / MSOP
30083402
Top View
Pin Descriptions
Pin
Name
Description
Power Supply
Inputs
2
6
1
8
3
4
7
5
GND
VS
Power Ground
Positive Supply Voltage
Negative Input
−IN
+IN
Positive Input
Filter Network
A1
Preamplifier output
A2
Input from the external filter network and / or A1
DC Offset for bidirectional signals
Single ended output
Offset
OFFSET
OUT
Output
5
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Ordering Information
Package
Part Number
Package Marking
Transport Media
95 Units/Rail
NSC Drawing
LMP8602MA
LMP8602MAX
LMP8602MM
LMP8602MMX
LMP8603MA
LMP8603MAX
LMP8603MM
LMP8603MMX
8-Pin SOIC
LMP8602MA
M08A
2.5K Units Tape and Reel
95 Units/Rail
8–Pin MSOP
8-Pin SOIC
8–Pin MSOP
LMP8602MM
LMP8603MA
LMP8603MM
MUA08A
M08A
3.5K Units Tape and Reel
95 Units/Rail
2.5K Units Tape and Reel
95 Units/Rail
MUA08A
3.5K Units Tape and Reel
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Typical Performance Characteristics Unless otherwise specified, all limits guaranteed for at TA = 25°C,
VS = 5V, GND = 0V, −22V ≤ VCM ≤ 60V, and RL = ∞, Offset (Pin 7) connected to VS, 10nF between VS and GND.
VOS vs. VCM at VS = 3.3V
VOS vs. VCM at VS = 5V
30083424
30083425
Input Bias Current Over Temperature (+IN and −IN pins)
at VS = 3.3V
Input Bias Current Over Temperature (+IN and −IN pins)
at VS = 5V
30083441
30083442
Input Bias Current Over Temperature (A2 pin)
at VS = 5V
Input Bias Current Over Temperature (A2 pin)
at VS = 5V
30083427
30083426
7
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Input Referred Voltage Noise vs. Frequency
PSRR vs. Frequency
30083410
30083417
Gain vs. Frequency LMP8602
Gain vs. Frequency LMP8603
30083411
30083412
CMRR vs. Frequency at VS = 3.3V
CMRR vs. Frequency at VS = 5V
30083428
30083429
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8
Step Response at VS = 3.3V
Step Response at VS = 5V
RL = 10kΩ LMP8602
RL = 10kΩ LMP8602
30083418
30083419
Settling Time (Falling Edge) at VS = 3.3V
LMP8602
Settling Time (Falling Edge) at VS = 5V
LMP8602
30083420
30083421
Settling Time (Rising Edge) at VS = 3.3V
LMP8602
Settling Time (Rising Edge) at VS = 5V
LMP8602
30083422
30083423
9
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Step Response at VS = 3.3V
Step Response at VS = 5V
RL = 10kΩ LMP8603
RL = 10kΩ LMP8603
30083443
30083444
Settling Time (Falling Edge) at VS = 3.3V
LMP8603
Settling Time (Falling Edge) at VS = 5V
LMP8603
30083445
30083446
Settling Time (Rising Edge) at VS = 3.3V
LMP8603
Settling Time (Rising Edge) at VS = 5V
LMP8603
30083447
30083448
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Positive Swing vs. RLOAD at VS = 3.3V
Positive Swing vs. RLOAD VS = 5V
30083413
30083415
Negative Swing vs. RLOAD at VS = 3.3V
Negative Swing vs. RLOAD at VS = 5V
30083414
30083416
Gain Drift Distribution LMP8602
5000 parts
Gain Drift Distribution LMP8603
5000 parts
30083483
30083437
11
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Gain error Distribution at VS = 3.3V LMP8602
5000 parts
Gain error Distribution at VS = 3.3V LMP8603
5000 parts
30083484
30083438
Gain error Distribution at VS = 5V LMP8602
5000 parts
Gain error Distribution at VS = 5V LMP8603
5000 parts
30083485
30083439
CMRR Distribution at VS = 3.3V
5000 parts
CMRR Distribution at VS = 5V
5000 parts
30083433
30083432
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12
VOS Distribution at VS = 3.3V
5000 parts
VOS Distribution at VS = 5V
5000 parts
30083434
30083435
TCVOS Distribution
5000 parts
30083436
13
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THEORY OF OPERATION
Application Information
The schematic shown in Figure 1 gives a schematic repre-
sentation of the internal operation of the LMP8602/
LMP8603.
GENERAL
The LMP8602 and LMP8603 are fixed gain differential volt-
age precision amplifiers with a gain of 50x for the LMP8602,
and 100x for the LMP8603. The input common mode voltage
range is -22V to +60V when operating from a single 5V supply
or -4V to +27V input common mode voltage range when op-
erating from a single 3.3V supply. The LMP8602 and
LMP8603 are members of the LMP family and are ideal parts
for unidirectional and bidirectional current sensing applica-
tions. Because of the proprietary chopping level-shift input
stage the LMP8602 and LMP8603 achieve very low offset,
very low thermal offset drift, and very high CMRR. The
LMP8602 and LMP8603 will amplify and filter small differen-
tial signals in the presence of high common mode voltages.
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 (K1) and
brought out on the A1 pin through a trimmed 100 kΩ resistor.
In the application, additional gain adjustment or filtering com-
ponents 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 (K2) which equals a factor of 5 for
the LMP8602 and a factor of 10 for the LMP8603. The output
signal of the final gain stage is provided on the OUT pin. The
OFFSET pin allows the output signal to be level-shifted to
enable bidirectional current sensing as will be explained be-
low.
The LMP8602/LMP8603 use level shift resistors at the inputs.
Because of these resistors, the LMP8602/LMP8603 can eas-
ily withstand very large differential input voltages that may
exist in fault conditions where some other less protected high-
performance current sense amplifiers might sustain perma-
nent damage.
PERFORMANCE GUARANTIES
To guaranty the high performance of the LMP8602/LMP8603,
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.
30083405
K2 = 5 for LMP8602, K2 = 10 for LMP8603
FIGURE 1. Theory of Operation
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14
ADDITIONAL SECOND ORDER LOW PASS FILTER
It is also possible to create an additional second order Sallen-
Key low pass filter as shown in Figure 2 by adding external
components R2, C1 and C2. Together with the internal
100 kΩ resistor R1, this circuit creates a second order low-
pass filter characteristic.
The LMP8602/LMP8603 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.
30083455
K1 = 10, K2 = 5 for LMP8602, K2 = 10 for LMP8603
FIGURE 2. Second Order Low Pass Filter
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:
For any filter gain K > 1x, the design procedure can be very
simple if the two capacitors are chosen to in a certain ratio.
Inserting this in the above equation for Q results in:
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:
Which results in:
The Cutt-off frequency ωo in rad/sec (divide by 2π to get the
cut-off frequency in Hz) is given by:
In this case, given the predetermined value of R1 = 100 kΩ
( the internal resistor), the quality factor is set solely by the
value of the resistor R2.
and the quality factor of the filter is given by:
15
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R2 can be calculated based on the desired value of Q as the
first step of the design procedure with the following equation:
For C2 the value is calculated with:
Or for a gain=5:
For the gain of 5 for the LMP8602 this results in:
For the gain of 10 for the LMP8603 this is:
and for a gain=10:
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
LMP8602/LMP8603 circuit chosen such that the internal
poles do not affect the external second order filter.
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:
For a desired Q = 0.707 and a cut off frequency = 3 kHz, this
will result for the LMP8602 in rounded values for R2 = 51
kΩ, C1 = 1.5 nF and C2 = 3.9 nF
And for the LMP8603 this will result in rounded values for R2
= 22 kΩ, C1 = 3.3 nF and C2 = 0.39 nF
Which for the gain=5 will give:
and for the gain=10:
GAIN ADJUSTMENT
The gain of the LMP8602 is 50 and the gain of the LMP8603
is 100, however, this gain can be adjusted as the signal path
in between the two internal amplifiers is available on the ex-
ternal pins.
Reduce Gain
Figure 3 shows the configuration that can be used to reduce
the gain of the LMP8602 and the LMP8603.
30083456
FIGURE 3. Reduce Gain
Rr creates a resistive divider together with the internal
100 kΩ resistor such that, for the LMP8602, the reduced gain
Gr becomes:
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16
and for the LMP8603:
For the LMP8603:
From this equation, for a desired value of the gain, the re-
quired value of Ri can be calculated for the LMP8602 with:
Given a desired value of the reduced gain Gr, using this equa-
tion the required value for Rr can be calculated for the
LMP8602 with:
and for the LMP8603 with:
and for the LMP8603 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 increases of a factor 2.5 or smaller.
Increase Gain
Figure 4 shows the configuration that can be used to increase
the gain of the LMP8602/LMP8603.
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 for the LMP8602 becomes:
30083457
FIGURE 4. Increase Gain
17
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BIDIRECTIONAL CURRENT SENSING
driving such ADCs the sudden current that should be deliv-
ered 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.
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 from a low impedance source (Note 16) to the OFF-
SET pin.
30083460
FIGURE 5. Driving Switched Capacitive Load
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.
This circuit simulates the switched connection of a discharged
capacitor to the LMP8602/LMP8603 output. The resulting
VOUT disturbance signals are shown in Figure
and Figure 7.
6
Example:
With 5V supply and a gain of 50x for the LMP8602, a differ-
ential input signal of +10 mV will result in 3.0V at the output
pin. similarly -10 mV at the input will result in 2.0V at the output
pin.
With 5V supply and a gain of 100x for the LMP8603, a differ-
ential input signal of +10 mV will result in 3.5V at the output
pin. similarly -10 mV at the input will result in 1.5V at the output
pin.
Note 16: 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 resistive divider
between the supply rails) accuracy will decrease.
POWER SUPPLY DECOUPLING
In order to decouple the LMP8602/LMP8603 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.
30083430
FIGURE 6. Capacitive Load Response at 3.3V
LAYOUT CONSIDERATIONS
The two input signals of the LMP8602/LMP8603 are differen-
tial signals and should be handled as a differential pair. For
optimum performance these signals should be closely togeth-
er and of equal length. Keep all impedances in both traces
equal and do not allow any other signal or ground in between
the traces of this signals.
The connection between the preamplifier and the output
buffer amplifier is a high impedance signal due to the 100
kΩ series resistor at the output of the preamplifier. Keep the
traces at this point as short as possible and away from inter-
fering signals.
The LMP8602/LMP8603 is available in a 8–Pin SOIC pack-
age and in a 8–Pin MSOP package. For the MSOP package,
the bare board spacing at the solder pads of the package will
be too small for reliable use at higher voltages (VCM > 25V) In
this situation it is strongly advised to add a conformal coating
on the PCB assembled with the LMP8602/LMP8603 in MSOP
package.
30083431
FIGURE 7. Capacitive Load Response at 5.0V
DRIVING SWITCHED CAPACITIVE LOADS
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
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 LMP8602/LMP8603 is
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18
in between the LMP8602/LMP8603 and the ADC as illustrat-
ed in Figure 8.
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 LMP8602/
LMP8603 and because of the high AC common mode rejec-
tion ratio, the LMP8602/LMP8603 is very well suited for this
application.
30083461
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.
For this application the following example can be used for the
calculation of the output signal:
When using a sense resistor, RSENSE, of 0.01 Ω and a current
of 1A, then the output voltage at the input pins of the LMP8602
is: RSENSE * ILOAD = 0.01 Ω * 1A = 0.01V
With the gain of 50 for the LMP8602 this will give an output of
0.5V. Or in other words, VOUT = 0.5V/A.
LOW SIDE CURRENT SENSING APPLICATION WITH
LARGE COMMON MODE TRANSIENTS
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
For the LMP8603 the calculation is similar, but with a gain of
100, giving an output of 1 V/A.
30083452
FIGURE 9. Low Side Current Sensing Application with Large Common Mode Transients
19
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LOW SIDE CURRENT SENSING APPLICATION WITH
NEGATIVE COMMON MODE TRANSIENTS
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 LMP8602/LMP8603 ex-
tends below the negative rail, the LMP8602/LMP8603 is also
very well suited for this application.
Figure 10 illustrates the application of the LMP8602/
LMP8603 in a high side sensing application. This application
is similar to the low side sensing discussed above, except in
30083453
FIGURE 10. High Side Current Sensing Application with Negative Common Mode Transients
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20
BATTERY CURRENT MONITOR APPLICATION
for such applications. If the load current of the battery is higher
then the charging current, the output voltage of the
LMP8602/LMP8603 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”.
This application example shows how the LMP8602/
LMP8603 can be used to monitor the current flowing in and
out a battery pack. The fact that the LMP8602/LMP8603 can
measure small voltages at a high offset voltage outside the
parts own supply range makes this part a very good choice
30083454
FIGURE 11. Battery Current Monitor Application
21
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ADVANCED BATTERY CHARGER APPLICATION
A/D converter and used as an input for the charge controller.
The charge controller can be used to regulate the charger
circuit to deliver exactly the current that is required by the load,
avoiding overcharging a fully loaded battery.
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 LMP8602/LMP8603 is digitized with the
30083403
K2 = 5 for LMP8602
K2 = 10 for LMP8603
FIGURE 12. Advanced Battery Charger Application
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22
Physical Dimensions inches (millimeters) unless otherwise noted
8Pin SOIC
NS Package Number M08A
8Pin MSOP
NS Package Number MUA08A
23
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