LT6106
36V Low Cost High Side
Current Sense in a SOT-23
FEATURES
DESCRIPTION
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The LT®6106 is a versatile high side current sense amplifier. Design flexibility is provided by the excellent device
characteristics: 250µV maximum offset and 40nA maximum input bias current. Gain for each device is set by two
resistors and allows for accuracy better than 1%.
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Gain Configurable with Two Resistors
Low Offset Voltage: 250µV Maximum
Output Current: 1mA Maximum
Supply Range: 2.7V to 36V, 44V Absolute Maximum
Low Input Bias Current: 40nA Maximum
PSRR: 106dB Minimum
Low Supply Current: 65µA Typical, V+ = 12V
Operating Temperature Range: –40°C to 125°C
Low Profile (1mm) ThinSOT™ Package
APPLICATIONS
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Current Shunt Measurement
Battery Monitoring
Power Management
Motor Control
Lamp Monitoring
Overcurrent and Fault Detection
The LT6106 monitors current via the voltage across an
external sense resistor (shunt resistor). Internal circuitry
converts input voltage to output current, allowing for a
small sense signal on a high common mode voltage to
be translated into a ground referenced signal. The low DC
offset allows for monitoring very small sense voltages. As
a result, a small valued shunt resistor can be used, which
minimizes the power loss in the shunt.
The wide 2.7V to 44V input voltage range, high accuracy
and wide operating temperature range make the LT6106
ideal for automotive, industrial and power management
applications. The very low power supply current of the
LT6106 also makes it suitable for low power and battery
operated applications.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and
ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the property
of their respective owners.
TYPICAL APPLICATION
3V to 36V, 5A Current Sense with AV = 10
Measurement Accuracy vs Load Current
3V TO 36V
0.6
0.02Ω
100Ω
+IN
–IN
+
LOAD
ACCURACY (% OF FULL SCALE)
0.4
V–
–
V+
LIMIT OVER TEMPERATURE
0.2
0
TYPICAL PART AT TA = 25°C
–0.2
–0.4
–0.6
LIMIT OVER TEMPERATURE
–0.8
LT6106
OUT
1k
VOUT
200mV/A
5A FULL SCALE RIN = 100Ω
–1.0 RSENSE = 0.02Ω ROUT = 1k
AV = 10
V+ = 3V
–1.2
0
1
3
2
LOAD CURRENT (A)
4
5
6106 TA01b
6106 TA01a
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1
LT6106
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
Supply Voltage (V+ to V–)...........................................44V
Input Voltage (+IN to V–).............................................. V+
(–IN to V–)............................................. V+
Input Current.........................................................–10mA
Output Short-Circuit Duration........................... Indefinite
Operating Temperature Range (Note 4)
LT6106C/LT6106I..................................–40°C to 85°C
LT6106H............................................. –40°C to 125°C
Specified Temperature Range (Note 4)
LT6106C................................................... 0°C to 70°C
LT6106I.................................................–40°C to 85°C
LT6106H............................................. –40°C to 125°C
Storage Temperature Range................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec).................... 300°C
TOP VIEW
5 V+
OUT 1
V– 2
–IN 3
4 +IN
S5 PACKAGE
5-LEAD PLASTIC TSOT-23
TJMAX = 150°C, θJA = 250°C/W
ORDER INFORMATION
(http://www.linear.com/product/LT6106#orderinfo)
TAPE AND REEL (MINI)
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
SPECIFIED TEMPERATURE RANGE
LT6106CS5#TRMPBF
LT6106CS5#TRPBF
LTCWK
5-Lead Plastic TSOT-23
0°C to 70°C
LT6106IS5#TRMPBF
LT6106IS5#TRPBF
LTCWK
5-Lead Plastic TSOT-23
–40°C to 85°C
LT6106HS5#TRMPBF
LT6106HS5#TRPBF
LTCWK
5-Lead Plastic TSOT-23
–40°C to 125°C
*Temperature grades are identified by a label on the shipping container.
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Parts ending with PBF are RoHS and WEEE compliant.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/. Some packages are available in 500 unit reels through
designated sales channels with #TRMPBF suffix.
ELECTRICAL
CHARACTERISTICS
The
l denotes the specifications which apply over the full specified
+
+
operating temperature range, otherwise specifications are at TA = 25°C. V = 12V, V = VSENSE+, RIN = 100Ω, ROUT = 10k, Gain = 100
unless otherwise noted. (Note 6)
SYMBOL
PARAMETER
V+
Supply Voltage Range
VOS
Input Offset Voltage
CONDITIONS
MIN
l
TYP
MAX
36
V
150
250
350
µV
µV
2.7
VSENSE = 5mV
l
ΔVOS/ΔT
Input Offset Voltage Drift
VSENSE = 5mV
IB
Input Bias Current (+IN)
V+ = 12V, 36V
1
l
µV/°C
40
65
l
UNITS
nA
nA
IOS
Input Offset Current
V+ = 12V, 36V
IOUT
Maximum Output Current
(Note 2)
l
1
mA
PSRR
Power Supply Rejection Ratio
V+ = 2.7V to 36V, VSENSE = 5mV
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106
dB
VSENSE(MAX)
Input Sense Voltage Full Scale
RIN = 500Ω (Notes 2, 7)
l
0.5
V
AV Error
Gain Error (Note 3)
VSENSE = 500mV, RIN = 500Ω, ROUT
1
= 10k, V+ = 12.5V
VSENSE = 500mV, RIN = 500Ω, ROUT = 10k, V+ = 36V
nA
l
–0.65
–0.25
0
%
l
–0.45
–0.14
0.1
%
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LT6106
ELECTRICAL
CHARACTERISTICS
The
l denotes the specifications which apply over the full specified
+
+
operating temperature range, otherwise specifications are at TA = 25°C. V = 12V, V = VSENSE+, RIN = 100Ω, ROUT = 10k, Gain = 100
unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
VOUT(HIGH)
Output Swing High
(Referred to V+)
VSENSE = 120mV
Minimum Output Voltage
(Note 5)
VSENSE = 0mV, RIN = 100Ω, ROUT = 10k
TYP
UNITS
1.2
1.4
V
V
12
45
65
mV
mV
7
16
22
mV
mV
l
l
VSENSE = 0mV, RIN = 500Ω, ROUT = 10k, V+ = 12V, 36V
MAX
l
BW
Signal Bandwidth (–3dB)
IOUT = 1mA, RIN = 100Ω, ROUT = 5k
200
kHz
tr
Input Step Response (to 50% of
Output Step)
ΔVSENSE = 100mV Step, RIN = 100Ω, ROUT = 5k,
Rising Edge
3.5
µs
IS
Supply Current
V+ = 2.7V, IOUT = 0µA, (VSENSE = –5mV)
60
85
115
µA
65
95
120
µA
70
100
130
µA
l
V+ = 12V, IOUT = 0µA, (VSENSE = –5mV)
l
V+ = 36V, IOUT = 0µA, (VSENSE = –5mV)
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Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime. In addition to the Absolute Maximum Ratings, the
output current of the LT6106 must be limited to insure that the power
dissipation in the LT6106 does not allow the die temperature to exceed
150°C. See the applications information section “Power Dissipation
Considerations” for further information.
Note 2: Guaranteed by the gain error test.
Note 3: Gain error refers to the contribution of the LT6106 internal
circuitry and does not include errors in the external gain setting resistors.
Note 4: The LT6106C is guaranteed functional over the operating
temperature range of –40°C to 85°C. The LT6106C is designed,
characterized and expected to meet specified performance from –40°C to
85°C but is not tested or QA sampled at these temperatures. The LT6106I
is guaranteed to meet specified performance from –40°C to 85°C. The
LT6106H is guaranteed to meet specified performance from –40°C to
125°C.
Note 5: The LT6106 output is an open collector current source. The
minimum output voltage scales directly with the ratio ROUT/10k.
Note 6: VSENSE+ is the voltage at the high side of the sense resistor,
RSENSE. See Figure 1.
Note 7: VSENSE (MAX) is the maximum sense voltage for which the Electrical
Characteristics will apply. Higher voltages can affect performance but will
not damage the part provided that the output current of the LT6106 does
not exceed the allowable power dissipation as described in Note 1.
TYPICAL PERFORMANCE CHARACTERISTICS
12
10
8
6
4
2
0
–200
–120
120
–40 0 40
INPUT OFFSET VOLTAGE (µV)
200
6106 G23
70
60
50
40
30
20
10
0
–10
–20
–30
–40
–50
–60
–70
400
VSENSE = 5mV
RIN = 100Ω
ROUT = 10k
TYPICAL UNITS
INPUT OFFSET VOLTAGE (µV)
PERCENT OF UNITS (%)
14
V+ = 12V
VSENSE = 5mV
RIN = 100Ω
ROUT = 10k
1068 UNITS
CHANGE IN INPUT OFFSET VOLTAGE (µV)
16
Input Offset Voltage vs
Temperature
Input Offset Voltage vs
Supply Voltage
VOS Distribution
VSENSE = 5mV ROUT = 10k
+
AV = 100
300 V = 12V
TYPICAL UNITS
RIN = 100Ω
200
100
0
–100
–200
–300
0
5
10 15 20 25 30
SUPPLY VOLTAGE (V)
35
40
6106 G02
–400
–55
–25
35
65
5
95
TEMPERATURE (°C)
125
6106 G03
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LT6106
TYPICAL PERFORMANCE CHARACTERISTICS
Power Supply Rejection Ratio
vs Frequency
120
110
–0.10
V+ = 36V
–0.15
V+ = 12V
–0.20
V+ = 5V
–0.25
–0.30
V+ = 2.7V
–0.35
–0.40
–0.45
VOUT = 1V
IOUT = 1mA
ROUT = 1k
TYPICAL UNIT
–0.50
–0.55
–0.60
–45 –25 –5
V+ = 12.5V
AV = 20
RIN = 100Ω
ROUT = 2k
100
90
80
70
60
50
40
30
20
10
0
100
15 35 55 75 95 115 130
TEMPERATURE (°C)
VOUT = 0.5V
VOUT = 1V
VOUT = 2V
1k
10k
100k
FREQUENCY (Hz)
Gain Error Distribution
16
14
12
10
8
6
4
2
0
–0.60
–0.48
–0.36 –0.24
GAIN ERROR (%)
–0.12
0
45
40
35
30
25
20
15
10
5
0
–5
–10
–15
–20
–25
–30
80
70
60
50
40
30
20
10
VOUT = 10V
VOUT = 2.5V
1k
10k
100k
FREQUENCY (Hz)
10k
20
1M
Gain vs Frequency
AV = 100
RIN = 100Ω
ROUT = 10k
100k
1M
FREQUENCY (Hz)
10M
45
40
35
30
25
20
15
10
5
0
–5
–10
–15
–20
–25
–30
VOUT = 10V
V+ = 12.5V
AV = 20
RIN = 500Ω
ROUT = 10k
VOUT = 2.5V
1k
10k
100k
1M
FREQUENCY (Hz)
10M
6106 G14
Step Response 0mV to 10mV
(RIN = 100Ω)
Step Response 10mV to 20mV
(RIN = 100Ω)
VSENSE
20mV/DIV
18
1k
6106 G09
Input Bias Current vs Supply
Voltage
VSENSE = 5mV
19 RIN = 100Ω
VOUT = 2.5V
VOUT = 5V
VOUT = 10V
6106 G06
V+ = 12.5V
6106 G24
INPUT BIAS CURRENT (nA)
90
0
100
1M
GAIN (dB)
PERCENT OF UNITS (%)
18
GAIN (dB)
VSENSE = 500mV
RIN = 500Ω
ROUT = 10k
11,072 UNITS
TA = 25°C
20
100
Gain vs Frequency
V+ = 12.5V
22
V+ = 12.5V
AV = 20
RIN = 500Ω
ROUT = 10k
110
6106 G08
6106 G04
24
Power Supply Rejection Ratio
vs Frequency
120
POWER SUPPLY REJECTION RATIO (dB)
0
–0.05
POWER SUPPLY REJECTION RATIO (dB)
GAIN ERROR (%)
Gain Error vs Temperature
VSENSE
20mV/DIV
17
VOUT
500mV/DIV
16
15
14
13
TA = –40°C
TA = 25°C
TA = 70°C
TA = 85°C
TA = 125°C
12
11
10
0
5
10 15 20 25 30 35 40 45 50
SUPPLY VOLTAGE (V)
VOUT
500mV/DIV
0V
0V
AV = 100
VOUT = 0V TO 1V
ROUT = 10k
V+ = 12V
5µs/DIV
6106 G10
AV = 100
VOUT = 1V TO 2V
ROUT = 10k
V+ = 12V
5µs/DIV
6106 G11
6106 G05
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LT6106
TYPICAL PERFORMANCE CHARACTERISTICS
Step Response 0mV to 100mV
(RIN = 100Ω)
Step Response 50mV to 100mV
(RIN = 500Ω)
Step Response 10mV to 100mV
(RIN = 100Ω)
VSENSE
200mV/DIV
VSENSE
200mV/DIV
VSENSE
100mV/DIV
VOUT
2V/DIV
VOUT
2V/DIV
VOUT
500mV/DIV
0V
0V
0V
6106 G12
AV = 100
5μs/DIV
VOUT = 0V TO 10V
ROUT = 10k
V+ = 12V
6106 G13
AV = 100
5µs/DIV
VOUT = 1V TO 10V
ROUT = 10k
V+ = 12V
Step Response 0mV to 50mV
(RIN = 500Ω)
AV = 20
VOUT = 1V TO 2V
ROUT = 10k
V+ = 12V
Step Response 50mV to 500mV
(RIN = 500Ω)
VSENSE
100mV/DIV
6106 G15
5µs/DIV
Step Response 0mV to 500mV
(RIN = 500Ω)
VSENSE
1V/DIV
VSENSE
1V/DIV
VOUT
2V/DIV
VOUT
2V/DIV
0V
0V
VOUT
500mV/DIV
0V
6106 G16
5µs/DIV
11.00
900
800
10.95
10.90
10.85
10.80
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
6106 G07
Output Voltage vs Input Sense
Voltage (0mV ≤ VSENSE ≤ 10mV)
220
V+ = 12V
AV = 100
RIN = 100Ω
ROUT = 10k
1000
VOUT (mV)
OUTPUT VOLTAGE (V)
11.05
1100
V+ = 12V
AV = 100
RIN = 100Ω
ROUT = 10k
VSENSE = 120mV
180
160
600
500
400
140
120
100
80
300
60
200
40
100
20
0
1
2
V+ = 12V
AV = 20
RIN = 500Ω
ROUT = 10k
200
700
0
3
4 5 6 7
VSENSE (mV)
8
9
6106 G18
AV = 20
5µs/DIV
VOUT = 0V TO 10V
ROUT = 10k
V+ = 12V
Output Voltage vs Input Sense
Voltage (0mV ≤ VSENSE ≤ 10mV)
Output Voltage Swing vs
Temperature
11.10
6106 G17
AV = 20
5µs/DIV
VOUT = 1V TO 10V
ROUT = 10k
V+ = 12V
VOUT (mV)
AV = 20
VOUT = 0V TO 1V
ROUT = 10k
V+ = 12V
10
6106 G19
0
0
1
2
3
4 5 6 7
VSENSE (mV)
8
9
10
6106 G20
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5
LT6106
TYPICAL PERFORMANCE CHARACTERISTICS
12
Output Voltage vs Input Sense
Voltage (0mV ≤ VSENSE ≤ 1V)
12
V+ = 12V
AV = 100
RIN = 100Ω
ROUT = 10k
10
100
8
VOUT (V)
VOUT (V)
AV = 20
RIN = 500Ω
ROUT = 10k
10
8
6
6
4
4
2
2
0
Supply Current vs Supply Voltage
120
V+ = 12V
SUPPLY CURRENT (µA)
Output Voltage vs Input Sense
Voltage (0mV ≤ VSENSE ≤ 200mV)
0
0
20 40 60 80 100 120 140 160 180 200
VSENSE (mV)
80
60
40
TA = –40°C
TA = 25°C
TA = 70°C
TA = 85°C
TA = 125°C
20
0
0 100 200 300 400 500 600 700 800 900 1000
VSENSE (mV)
0
5
10
15 20 25 30 35
SUPPLY VOLTAGE (V)
6106 G22
6106 G21
40
45
6106 G01
PIN FUNCTIONS
V+ (Pin 5): Positive Supply Pin. The V+ pin should be connected directly to either side of the sense resistor, RSENSE.
Supply current is drawn through this pin. The circuit may
be configured so that the LT6106 supply current is or is
not monitored along with the system load current. To
monitor only the system load current, connect V+ to the
more positive side of the sense resistor. To monitor the
total current, including that of the LT6106, connect V+ to
the more negative side of the sense resistor.
OUT (Pin 1): Current Output. OUT will source a current
that is proportional to the sense voltage into an external
resistor.
V– (Pin 2): Normally Connected to Ground.
–IN (Pin 3): The internal sense amplifier will drive –IN to
the same potential as +IN. A resistor (RIN) tied from V+
to –IN sets the output current IOUT = VSENSE/RIN. VSENSE
is the voltage developed across RSENSE.
+IN (Pin 4): Must be tied to the system load end of the
sense resistor, either directly or through a resistor.
BLOCK DIAGRAM
ILOAD
–
VSENSE
+
VBATTERY
RSENSE
L
O
A
D
5
RIN
V+
3
4
–IN
14k
–
+IN
14k
+
V–
2
OUT
IOUT
VOUT = VSENSE •
1
6106 F01
ROUT
RIN
ROUT
Figure 1. LT6106 Block Diagram and Typical Connection
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LT6106
APPLICATIONS INFORMATION
Introduction
The LT6106 high side current sense amplifier (Figure 1) provides accurate monitoring of current through a user-selected
sense resistor. The sense voltage is amplified by a userselected gain and level shifted from the positive power supply to a ground-referred output. The output signal is analog
and may be used as is, or processed with an output filter.
Theory of Operation
An internal sense amplifier loop forces –IN to have the
same potential as +IN. Connecting an external resistor,
RIN, between –IN and V+ forces a potential across RIN
that is the same as the sense voltage across RSENSE. A
corresponding current, VSENSE/RIN, will flow through RIN.
The high impedance inputs of the sense amplifier will not
conduct this current, so it will flow through an internal
PNP to the output pin as IOUT.
The output current can be transformed into a voltage by
adding a resistor from OUT to V–. The output voltage is
then VO = V– + IOUT • ROUT.
Table 1. Useful Gain Configurations
GAIN
20
50
100
GAIN
20
50
100
RIN
499Ω
200Ω
100Ω
RIN
249Ω
100Ω
50Ω
ROUT
10k
10k
10k
ROUT
5k
5k
5k
VSENSE at VOUT = 5V
IOUT at VOUT = 5V
250mV
500µA
100mV
500µA
50mV
500µA
VSENSE at VOUT = 2.5V IOUT at VOUT = 2.5V
125mV
500µA
50mV
500µA
25mV
500µA
must be small enough that VSENSE does not exceed the
maximum input voltage specified by the LT6106, even
under peak load conditions. As an example, an application
may require that the maximum sense voltage be 100mV.
If this application is expected to draw 2A at peak load,
RSENSE should be no more than 50mΩ.
Once the maximum RSENSE value is determined, the minimum sense resistor value will be set by the resolution or
dynamic range required. The minimum signal that can be
accurately represented by this sense amplifier is limited by
the input offset. As an example, the LT6106 has a typical
input offset of 150µV. If the minimum current is 20mA, a
sense resistor of 7.5mΩ will set VSENSE to 150µV. This is
the same value as the input offset. A larger sense resistor will reduce the error due to offset by increasing the
sense voltage for a given load current. Choosing a 50mΩ
RSENSE will maximize the dynamic range and provide a
system that has 100mV across the sense resistor at peak
load (2A), while input offset causes an error equivalent to
only 3mA of load current. Peak dissipation is 200mW. If a
5mΩ sense resistor is employed, then the effective current
error is 30mA, while the peak sense voltage is reduced to
10mV at 2A, dissipating only 20mW.
The low offset and corresponding large dynamic range of
the LT6106 make it more flexible than other solutions in
this respect. The 150µV typical offset gives 60dB of dynamic range for a sense voltage that is limited to 150mV
maximum, and over 70dB of dynamic range if the rated
input maximum of 0.5V is allowed.
Selection of External Current Sense Resistor
Sense Resistor Connection
The external sense resistor, RSENSE, has a significant effect
on the function of a current sensing system and must be
chosen with care.
Kelvin connection of the –IN and +IN inputs to the sense
resistor should be used in all but the lowest power applications. Solder connections and PC board interconnections that carry high current can cause significant error
in measurement due to their relatively large resistances.
One 10mm × 10mm square trace of one-ounce copper
is approximately 0.5mΩ. A 1mV error can be caused by
as little as 2A flowing through this small interconnect.
This will cause a 1% error in a 100mV signal. A 10A load
current in the same interconnect will cause a 5% error
for the same 100mV signal. By isolating the sense traces
from the high current paths, this error can be reduced
First, the power dissipation in the resistor should be
considered. The system load current will cause both heat
and voltage loss in RSENSE. As a result, the sense resistor should be as small as possible while still providing
the input dynamic range required by the measurement.
Note that input dynamic range is the difference between
the maximum input signal and the minimum accurately
measured signal, and is limited primarily by input DC offset
of the internal amplifier of the LT6106. In addition, RSENSE
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7
LT6106
APPLICATIONS INFORMATION
by orders of magnitude. A sense resistor with integrated
Kelvin sense terminals will give the best results. Figure 2
illustrates the recommended method.
V
+
RSENSE
RIN
+IN
–IN
+
LOAD
The output resistor, ROUT, determines how the output current is converted to voltage. VOUT is simply IOUT • ROUT.
V+
OUT
LT6106
Care should be taken when designing the board layout for
RIN, especially for small RIN values. All trace and interconnect resistances will increase the effective RIN value,
causing a gain error.
Selection of External Output Resistor, ROUT
–
V–
This approach can be helpful in cases where occasional
bursts of high currents can be ignored.
VOUT
ROUT
6106 F02
Figure 2. Kelvin Input Connection Preserves Accuracy with
Large Load Currents
Selection of External Input Resistor, RIN
RIN should be chosen to allow the required resolution
while limiting the output current to 1mA. In addition, the
maximum value for RIN is 500Ω. By setting RIN such that
the largest expected sense voltage gives IOUT = 1mA, then
the maximum output dynamic range is available. Output
dynamic range is limited by both the maximum allowed
output current and the maximum allowed output voltage,
as well as the minimum practical output signal. If less
dynamic range is required, then RIN can be increased
accordingly, reducing the maximum output current and
power dissipation. If low sense currents must be resolved
accurately in a system that has a very wide dynamic range,
a smaller RIN than the maximum current spec allows may
be used if the maximum current is limited in another way,
such as with a Schottky diode across RSENSE (Figure 3).
This will reduce the high current measurement accuracy
by limiting the result, while increasing the low current
measurement resolution.
In choosing an output resistor, the maximum output voltage must first be considered. If the following circuit is a
buffer or ADC with limited input range, then ROUT must be
chosen so that IOUT(MAX) • ROUT is less than the allowed
maximum input range of this circuit.
In addition, the output impedance is determined by ROUT. If
the circuit to be driven has high enough input impedance,
then almost any useful output impedance will be acceptable. However, if the driven circuit has relatively low input
impedance, or draws spikes of current such as an ADC might
do, then a lower ROUT value may be required in order to
preserve the accuracy of the output. As an example, if the
input impedance of the driven circuit is 100 times ROUT,
then the accuracy of VOUT will be reduced by 1% since:
VOUT = IOUT •
ROUT • RIN(DRIVEN)
ROUT +RIN(DRIVEN)
= IOUT • ROUT •
100
= 0.99 •IOUT • ROUT
101
Error Sources
The current sense system uses an amplifier and resistors
to apply gain and level shift the result. The output is then
dependent on the characteristics of the amplifier, such as
gain and input offset, as well as resistor matching.
Ideally, the circuit output is:
V+
RSENSE
DSENSE
6106 F03
LOAD
Figure 3. Shunt Diode Limits Maximum Input Voltage to Allow
Better Low Input Resolution Without Overranging
VOUT = VSENSE •
ROUT
; VSENSE = RSENSE •ISENSE
RIN
In this case, the only error is due to resistor mismatch,
which provides an error in gain only. However, offset voltage and bias current cause additional errors.
6106fb
8
For more information www.linear.com/LT6106
LT6106
APPLICATIONS INFORMATION
Output Error Due to the Amplifier DC Offset
Voltage, VOS
ROUT
RIN
The DC offset voltage of the amplifier adds directly to the
value of the sense voltage, VSENSE. This is the dominant
error of the system and it limits the low end of the dynamic
range. The paragraph “Selection of External Current Sense
Resistor” provides details.
V+
RSENSE
EOUT(VOS) = VOS •
RIN–
RIN+
+IN
–IN
+
LOAD
–
V–
V+
LT6106
OUT
VOUT
ROUT
RIN+ = RIN– – RSENSE
6106 F04
Output Error Due to the Bias Currents, IB+ and IB–
Figure 4. Second Input R Minimizes Error Due to Input Bias Current
The bias current IB+ flows into the positive input of the
internal op amp. IB– flows into the negative input.
Minimum Output Voltage
It is convenient to refer the error to the input:
The curves of the Output Voltage vs Input Sense Voltage
show the behavior of the LT6106 with low input sense
voltages. When VSENSE = 0V, the output voltage will always
be slightly positive, the result of input offset voltages and
of a small amount of quiescent current (0.7µA to 1.2µA)
flowing through the output device. The minimum output
voltage in the Electrical Characteristics table include both
these effects.
EIN(IBIAS) @ –RIN • IBIAS
Power Dissipation Considerations
For instance if IBIAS is 60nA and RIN is 1k, the input referred
error is 60µV. Note that in applications where RSENSE @
RIN, IB+ causes a voltage offset in RSENSE that cancels the
error due to IB– and EOUT(IBIAS) @ 0mV. In most applications, RSENSE
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