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LT6106
36V Low Cost High Side
Current Sense in a SOT-23
FEATURES
■
■
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■
■
■
■

DESCRIPTION

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) ThinSOTTM Package

APPLICATIONS
■
■
■
■
■
■

Current Shunt Measurement
Battery Monitoring
Power Management
Motor Control
Lamp Monitoring
Overcurrent and Fault Detection

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%.
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.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
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
ACCURACY (% OF FULL SCALE)

0.4
100Ω
0.02Ω
+IN

–IN

–

LOAD
V–

V+

LT6106

OUT

VOUT
200mV/A
1k

LIMIT OVER TEMPERATURE

0.2
0

TYPICAL PART AT TA = 25°C

–0.2
–0.4
–0.6

LIMIT OVER TEMPERATURE

–0.8

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)

5
6106 TA01b

6106 TA01a

6106fa

LT6106
ABSOLUTE MAXIMUM RATINGS

PIN CONFIGURATION

(Note 1)

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............................................... –40°C to 85°C
LT6106H ............................................ –40°C to 125°C
Speciﬁed Temperature Range (Note 4)
LT6106C................................................... 0°C to 70°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

4 +IN

–IN 3

S5 PACKAGE
5-LEAD PLASTIC TSOT-23
TJMAX = 150°C, θJA = 250°C/W

ORDER INFORMATION
Lead Free Finish
TAPE AND REEL (MINI)

TAPE AND REEL

PART MARKING*

PACKAGE DESCRIPTION

TEMPERATURE RANGE

LT6106CS5#TRMPBF
LT6106CS5#TRPBF
LTCWK
5-Lead Plastic TSOT-23
LT6106HS5#TRMPBF
LT6106HS5#TRPBF
LTCWK
5-Lead Plastic TSOT-23
TRM = 500 pieces. *Temperature grades are identiﬁed by a label on the shipping container.
Consult LTC Marketing for parts speciﬁed with wider operating temperature ranges.
Consult LTC Marketing for information on lead based ﬁnish parts.
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/

0°C to 70°C
–40°C to 125°C

ELECTRICAL CHARACTERISTICS

The ● 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

ΔVOS/ΔT

Input Offset Voltage Drift

VSENSE = 5mV

Input Bias Current (+IN)

V+ = 12V, 36V

IOS

Input Offset Current

V+ = 12V, 36V

IOUT

Maximum Output Current

(Note 2)

●

PSRR

Power Supply Rejection Ratio

V+ = 2.7V to 36V, V

●

106

VSENSE(MAX)

Input Sense Voltage Full Scale

RIN = 500Ω (Notes 2, 7)

●

0.5

VSENSE = 500mV, RIN = 500Ω, ROUT

= 10k, V+ = 12.5V

●

–0.65

–0.25

VSENSE = 500mV, RIN = 500Ω, ROUT

= 10k, V+ = 36V

●

–0.45

–0.14

0.1

1.2
1.4

V
V

AV Error
VOUT(HIGH)

CONDITIONS

MIN
●

VSENSE = 5mV

TYP

2.7
150

●
●

Output Swing High
(Referred to V+)

VSENSE = 120mV

250
350

μV
μV
μV/°C

40
65
1

SENSE = 5mV

●

UNITS

●

Gain Error (Note 3)

MAX

nA
nA
nA

6106fa

LT6106
ELECTRICAL CHARACTERISTICS

SYMBOL

PARAMETER

CONDITIONS

MIN

Minimum Output Voltage
(Note 5)

VSENSE = 0mV, RIN = 100Ω, ROUT = 10k

TYP

MAX

45
65

mV
mV

16
22

mV
mV

●

VSENSE = 0mV, RIN = 500Ω, ROUT = 10k, V+ = 12V, 36V

●

UNITS

Signal Bandwidth (–3dB)

IOUT = 1mA, RIN = 100Ω, ROUT = 5k

200

kHz

Input Step Response (to 50% of
Output Step)

ΔVSENSE = 100mV Step, RIN = 100Ω, ROUT = 5k,
Rising Edge

3.5

μs

Supply Current

V+ = 2.7V, IOUT = 0μA, (VSENSE = –5mV)
V+ = 12V, IOUT = 0μA, (VSENSE = –5mV)

85
115

μA

95
120

μA

100
130

μA

●

V+ = 36V, IOUT = 0μA, (VSENSE = –5mV)
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,

60
●

●

characterized and expected to meet speciﬁed performance from –40°C to
85°C but is not tested or QA sampled at these temperatures. 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 (%)

V+ = 12V
VSENSE = 5mV
RIN = 100Ω
ROUT = 10k
1068 UNITS

CHANGE IN INPUT OFFSET VOLTAGE (μV)

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

10 15 20 25 30
SUPPLY VOLTAGE (V)

6106 G02

–400
–55

–25

35
65
5
95
TEMPERATURE (°C)

125
6106 G03

6106fa

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 (%)

100
90
80
70
60
50
40
30
20
10
0
100

–0.12

VOUT = 2.5V
VOUT = 5V
VOUT = 10V
1k

10k
100k
FREQUENCY (Hz)

45
40
35
30
25
20
15
10
5
0
–5
–10
–15
–20
–25
–30

Gain vs Frequency
V+ = 12.5V

VOUT = 10V
VOUT = 2.5V

10k

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

10k

100k
1M
FREQUENCY (Hz)

10M
6106 G14

6106 G09

6106 G24

Step Response 0mV to 10mV
(RIN = 100Ω)

Input Bias Current vs Supply
Voltage

1M
6106 G06

GAIN (dB)

PERCENT OF UNITS (%)

GAIN (dB)

VSENSE = 500mV
RIN = 500Ω
ROUT = 10k
11,072 UNITS
TA = 25°C

V+ = 12.5V
AV = 20
RIN = 500Ω
ROUT = 10k

110

Gain vs Frequency

V+ = 12.5V

120

6106 G08

6106 G04

Power Supply Rejection Ratio
vs Frequency
POWER SUPPLY REJECTION RATIO (dB)

0
–0.05

POWER SUPPLY REJECTION RATIO (dB)

GAIN ERROR (%)

Gain Error vs Temperature

Step Response 10mV to 20mV
(RIN = 100Ω)

INPUT BIAS CURRENT (nA)

VSENSE = 5mV
19 RIN = 100Ω

VSENSE
20mV/DIV

17
VOUT
500mV/DIV

16
15
VOUT
500mV/DIV
0V

14
13
TA = –40°C
TA = 25°C
TA = 70°C
TA = 125°C

12
11
10

10 15 20 25 30 35 40 45 50
SUPPLY VOLTAGE (V)

0V
AV = 100
VOUT = 0V TO 1V
ROUT = 10k
V+ = 12V

5μs/DIV

6106 G1

AV = 100
VOUT = 1V TO 2V
ROUT = 10k
V+ = 12V

5μs/DIV

6106 G1

6106 G05

6106fa

LT6106
TYPICAL PERFORMANCE CHARACTERISTICS
Step Response 0mV to 100mV
(RIN = 100Ω)

Step Response 10mV to 100mV
(RIN = 100Ω)

Step Response 50mV to 100mV
(RIN = 500Ω)

VSENSE
200mV/DIV

VSENSE
100mV/DIV

VOUT
2V/DIV

VOUT
500mV/DIV

6106 G1

AV = 100
5μs/DIV
VOUT = 0V TO 10V
ROUT = 10k
V+ = 12V

6106 G1

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

VOUT
2V/DIV

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

140
120
100

400

300

200

100

20
0

V+ = 12V
AV = 20
RIN = 500Ω
ROUT = 10k

200

700

4 5 6 7
VSENSE (mV)

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

6106 G19

4 5 6 7
VSENSE (mV)

6106 G20

6106fa

LT6106
TYPICAL PERFORMANCE CHARACTERISTICS
Output Voltage vs Input Sense
Voltage (0mV ≤ VSENSE ≤ 1V)

V+ = 12V
AV = 100
RIN = 100Ω
ROUT = 10k

AV = 20
RIN = 500Ω
ROUT = 10k

100

8
VOUT (V)

Supply Current vs Supply Voltage
120

V+ = 12V

SUPPLY CURRENT (μA)

Output Voltage vs Input Sense
Voltage (0mV ≤ VSENSE ≤ 200mV)

40
TA = –40°C
TA = 25°C
TA = 70°C
TA = 125°C

0 100 200 300 400 500 600 700 800 900 1000
VSENSE (mV)

20 40 60 80 100 120 140 160 180 200
VSENSE (mV)

15 20 25 30 35
SUPPLY VOLTAGE (V)

6106 G22

6106 G21

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+

–IN

14k

–

+IN

14k

+
IOUT
V–
2

OUT

VOUT = VSENSE •

6106 F01

ROUT
RIN

ROUT

Figure 1. LT6106 Block Diagram and Typical Connection
6106fa

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 by orders of

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

6106fa

LT6106
APPLICATIONS INFORMATION
magnitude. A sense resistor with integrated Kelvin sense
terminals will give the best results. Figure 2 illustrates the
recommended method.
+

RSENSE

RIN
+IN

This approach can be helpful in cases where occasional
bursts of high currents can be ignored.
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.

–IN

Selection of External Output Resistor, ROUT

–

LOAD
V–

V+

The output resistor, ROUT, determines how the output current is converted to voltage. VOUT is simply IOUT • ROUT.

OUT

LT6106

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

VOUT = VSENSE •

ROUT
; VSENSE = RSENSE • ISENSE
RIN

6106 F03

LOAD

Figure 3. Shunt Diode Limits Maximum Input Voltage to Allow
Better Low Input Resolution Without Overranging

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.
6106fa

LT6106
APPLICATIONS INFORMATION
V+

Output Error Due to the Ampliﬁer DC Offset
Voltage, VOS
R
EOUT( VOS) = VOS • OUT
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.

RSENSE

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

EOUT(IBIAS)

⎛
⎞
R
= ROUT ⎜IB + • SENSE – IB – ⎟
RIN
⎝
⎠

Assuming IB+ ≅ IB– = IBIAS, and RSENSE << RIN then:
EOUT(IBIAS) ≅ –ROUT • IBIAS
It is convenient to refer the error to the input:
EIN(IBIAS) ≅ –RIN • IBIAS
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 << RIN, the bias current error can be similarly
reduced if an external resistor RIN+ = (RIN – RSENSE) is
connected as shown in Figure 4. Under both conditions:
EIN(IBIAS) = ±RIN • IOS; where IOS = IB+ – IB–
If the offset current, IOS, of the LT6106 ampliﬁer is 6nA,
the 60μV error above is reduced to 6μV.
Adding RIN+ as described will maximize the dynamic
range of the circuit. For less sensitive designs, RIN+ is
not necessary.
Output Error Due to Gain Error
The LT6106 exhibits a typical gain error of –0.25% at 1mA
output current. The primary source of gain error is due to
the ﬁnite gain to the PNP output transistor, which results in
a small percentage of the current in RIN not appearing in the
output load ROUT.

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.
Power Dissipation Considerations
The power dissipated by the LT6106 will cause a small
increase in the die temperature. This rise in junction temperature can be calculated if the output current and the
supply current are known.
The power dissipated in the LT6106 due to the output
signal is:
POUT = (VIN– – VOUT) • IOUT
Since VIN– ≅ V+, POUT ≅ (V+ – VOUT) • IOUT
The power dissipated due to the quiescent supply current is:
PQ = IS • (V+ – V–)
The total power dissipated is the output dissipation plus
the quiescent dissipation:
PTOTAL = POUT + PQ
The junction temperature is given by:
TJ = TA + θJA • PTOTAL
At the maximum operating supply voltage of 36V and the
maximum guaranteed output current of 1mA, the total
6106fa

LT6106
APPLICATIONS INFORMATION
power dissipation is 41mW. This amount of power dissipation will result in a 10°C rise in junction temperature
above the ambient temperature.
It is important to note that the LT6106 has been designed
to provide at least 1mA to the output when required, and
can deliver more depending on the conditions. Care must
be taken to limit the maximum output current by proper
choice of sense resistor and RIN– and, if input fault conditions exist, external clamps.
Output Filtering
The output voltage, VOUT, is simply IOUT • ZOUT. This makes
ﬁltering straightforward. Any circuit may be used which
generates the required ZOUT to get the desired ﬁlter response. For example, a capacitor in parallel with ROUT
will give a lowpass response. This will reduce unwanted
noise from the output, and may also be useful as a charge
reservoir to keep the output steady while driving a switching circuit such as a MUX or ADC. This output capacitor
in parallel with an output resistor will create a pole in the
output response at:
f–3dB =

normal operation, VSENSE should not exceed 500mV (see
VSENSE(MAX) under Electrical Characteristics). This additional constraint can be stated as V+ – (+IN) ≤ 500mV.
Referring to Figure 5, feedback will force the voltages
at the inputs –IN and +IN to be equal to (VS – VSENSE).
Connecting V+ to the load side of the shunt results in equal
voltages at +IN, –IN and V+. Connecting V+ to the supply
end of the shunt results in the voltages at +IN and –IN to
be VSENSE below V+.
If the V+ pin is connected to the supply side of the shunt
resistor the supply current drawn by the LT6106 is not
included in the monitored current. If the V+ pin is connected to the load side of the shunt resistor (Figure 5),
the supply current drawn by the LT6106 is included in
the monitored current. It should be noted that in either
conﬁguration, the output current of the LT6106 will not
be monitored since it is drawn through the RIN resistor
connected to the positive side of the shunt. Contract the
factory for operation of the LT6106 with a V+ outside of
the recommended operating range.
VS

RIN

1
RSENSE

2 • π • ROUT • COUT

+IN

–IN

+
LOAD

Useful Equations

V–

–
V+

Input Voltage: VSENSE = ISENSE • RSENSE
Voltage Gain:

VOUT
R
= OUT
VSENSE
RIN

LT6106

OUT

VOUT
ROUT

6106 F05

Current Gain:

IOUT
ISENSE

Transconductance:
Transimpedance:

RSENSE
RIN

Figure 5. LT6106 Supply Current Monitored with the Load

Reverse Supply Protection

IOUT
1
=
VSENSE RIN
VOUT

ISENSE

= RSENSE •

ROUT
RIN

Power Supply Connection
For normal operation, the V+ pin should be connected to
either side of the sense resistor. Either connection will
meet the constraint that +IN ≤ V+ and –IN ≤ V+. During

Some applications may be tested with reverse-polarity
supplies due to an expectation of the type of fault during
operation. The LT6106 is not protected internally from external reversal of supply polarity. To prevent damage that
may occur during this condition, a Schottky diode should
be added in series with V– (Figure 6). This will limit the
reverse current through the LT6106. Note that this diode
will limit the low voltage performance of the LT6106 by
effectively reducing the supply voltage to the part by VD.
6106fa

LT6106
APPLICATIONS INFORMATION
In addition, if the output of the LT6106 is wired to a device that will effectively short it to high voltage (such as
through an ESD protection clamp) during a reverse supply condition, the LT6106’s output should be connected
through a resistor or Schottky diode (Figure 7).

Response Time
The photos in the Typical Performance Characteristics show
the response of the LT6106 to a variety of input conditions
and values of RIN. The photos show that if the output current is very low or zero and an input transient occurs, there
will be an increased delay before the output voltage begins
changing while internal nodes are being charged.

Demo Board
Demo board DC1240 is available for evaluation of the
LT6106.

RSENSE

+IN

–IN

+ –

V–

L
O
A
D

+IN

R1
100Ω

V–

L
O
A
D

V+
VBATT

+ –

LT6106

OUT

LT6106

R1
100Ω

–IN

VBATT

V+

OUT

R3
1k
ADC
R2
4.99k

D1
R2
4.99k

6106 F07

6106 F06

Figure 7. Additional Resistor R3 Protects Output
During Supply Reversal

Figure 6. Schottky Diode Prevents Damage During Supply Reversal

PACKAGE DESCRIPTION
S5 Package
5-Lead Plastic TSOT-23
0.62
MAX

0.95
REF

(Reference LTC DWG # 05-08-1635)

2.90 BSC
(NOTE 4)

1.22 REF

1.4 MIN

3.85 MAX 2.62 REF

2.80 BSC

1.50 – 1.75
(NOTE 4)

PIN ONE
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR

0.30 – 0.45 TYP
5 PLCS (NOTE 3)

0.95 BSC
0.80 – 0.90

0.20 BSC

0.01 – 0.10
1.00 MAX

DATUM ‘A’

0.30 – 0.50 REF
NOTE:
1. DIMENSIONS ARE IN MILLIMETERS
2. DRAWING NOT TO SCALE
3. DIMENSIONS ARE INCLUSIVE OF PLATING

0.09 – 0.20
(NOTE 3)

1.90 BSC
S5 TSOT-23 0302 REV B

4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
5. MOLD FLASH SHALL NOT EXCEED 0.254mm
6. JEDEC PACKAGE REFERENCE IS MO-193
6106fa

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.

LT6106
TYPICAL APPLICATION
Simple 400V Current Monitor
DANGER! Lethal Potentials Present — Use Caution
ISENSE

VSENSE

–

400V

RSENSE
+IN
L
O
A
D

V–

–IN

+ –

RIN
100Ω

DANGER!!
HIGH VOLTAGE!!

V+

OUT

LT6106

12V
CMPZ12L
M1

VOUT
M1 AND M2 ARE FQD3P50
ROUT
VOUT =
• VSENSE = 49.9 VSENSE
RIN

M2
ROUT
4.99k

BAT46

6106 TA02

RELATED PARTS
PART NUMBER

DESCRIPTION

COMMENTS

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Gain-Selectable High Side Current Sense Ampliﬁer

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6106fa

12 Linear Technology Corporation

LT 0807 REV A • PRINTED IN USA

1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507

●

www.linear.com

www.s-manuals.com

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