LTCWK [Linear]
36V Low Cost High Side Current Sense in a SOT-23; 36V低成本高端电流检测采用SOT- 23
| 型号： | LTCWK |
| 厂家： | 
Linear |
| 描述： | 36V Low Cost High Side Current Sense in a SOT-23 |
| 文件： | 总12页 (文件大小：240K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LT6106
36V Low Cost High Side
Current Sense in a SOT-23
FEATURES
DESCRIPTION
The LT®6106 is a versatile high side current sense ampli-
fier. Design flexibility is provided by the excellent device
characteristics: 250μV maximum offset and 40nA maxi-
mum input bias current. Gain for each device is set by two
resistors and allows for accuracy better than 1%.
■
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
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.
+
■
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
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.
■
Motor Control
■
Lamp Monitoring
■
Overcurrent and Fault Detection
, 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
LIMIT OVER TEMPERATURE
0.4
0.2
100Ω
0.02Ω
0
–0.2
–0.4
–0.6
–0.8
–1.0
TYPICAL PART AT T = 25°C
A
+IN
–IN
–
+
LOAD
LIMIT OVER TEMPERATURE
–
+
V
V
5A FULL SCALE
R
= 100Ω
= 1k
OUT
IN
R
V
= 0.02Ω
R
SENSE
+
A
= 10
V = 3V
–1.2
OUT
V
OUT
0
4
5
1
2
3
LT6106
200mV/A
LOAD CURRENT (A)
1k
6106 TA01b
6106 TA01a
6106fa
1
LT6106
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
+
–
–
–
Supply Voltage (V to V )..........................................44V
TOP VIEW
+
+
+
Input Voltage (+IN to V ) ............................................ V
OUT 1
–
5 V
(–IN to V ) ............................................ V
V
2
–IN 3
4 +IN
Input Current........................................................–10mA
Output Short-Circuit Duration .......................... Indefinite
Operating Temperature Range (Note 4)
S5 PACKAGE
5-LEAD PLASTIC TSOT-23
= 150°C, θ = 250°C/W
T
JMAX
JA
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
ORDER INFORMATION
Lead Free Finish
TAPE AND REEL (MINI)
LT6106CS5#TRMPBF
LT6106HS5#TRMPBF
TAPE AND REEL
PART MARKING*
LTCWK
LTCWK
PACKAGE DESCRIPTION
5-Lead Plastic TSOT-23
5-Lead Plastic TSOT-23
TEMPERATURE RANGE
LT6106CS5#TRPBF
LT6106HS5#TRPBF
0°C to 70°C
–40°C to 125°C
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/
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
CONDITIONS
MIN
TYP
MAX
UNITS
+
●
V
Supply Voltage Range
Input Offset Voltage
2.7
36
V
V
V
V
= 5mV
= 5mV
150
1
250
350
μV
μV
OS
SENSE
●
●
ΔV /ΔT
Input Offset Voltage Drift
Input Bias Current (+IN)
μV/°C
OS
SENSE
+
I
V = 12V, 36V
40
65
nA
nA
B
●
+
I
I
Input Offset Current
V = 12V, 36V
1
nA
mA
dB
V
OS
●
●
●
●
●
Maximum Output Current
Power Supply Rejection Ratio
Input Sense Voltage Full Scale
Gain Error (Note 3)
(Note 2)
1
OUT
+
PSRR
V = 2.7V to 36V, V
= 5mV
106
SENSE
V
R
IN
= 500Ω (Notes 2, 7)
0.5
SENSE(MAX)
+
A Error
V
SENSE
V
SENSE
V
SENSE
= 500mV, R = 500Ω, R
= 10k, V = 12.5V
–0.65
–0.45
–0.25
–0.14
0
%
V
IN
OUT
+
= 500mV, R = 500Ω, R
= 10k, V = 36V
0.1
%
IN
OUT
V
Output Swing High
= 120mV
1.2
1.4
V
V
OUT(HIGH)
+
●
(Referred to V )
6106fa
2
LT6106
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.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Minimum Output Voltage
(Note 5)
V
= 0mV, R = 100Ω, R
= 10k
12
45
65
mV
mV
SENSE
IN
OUT
●
●
+
V
= 0mV, R = 500Ω, R
= 10k, V = 12V, 36V
7
16
22
mV
mV
SENSE
IN
OUT
BW
Signal Bandwidth (–3dB)
I
= 1mA, R = 100Ω, R = 5k
OUT
200
3.5
kHz
μs
OUT
IN
t
r
Input Step Response (to 50% of ΔV
Output Step)
= 100mV Step, R = 100Ω, R
= 5k,
OUT
SENSE
IN
Rising Edge
+
I
S
Supply Current
V = 2.7V, I
= 0μA, (V
= –5mV)
60
65
70
85
μA
μA
μA
OUT
OUT
OUT
SENSE
SENSE
SENSE
●
●
●
115
+
V = 12V, I
= 0μA, (V
= 0μA, (V
= –5mV)
= –5mV)
95
120
+
V = 36V, I
100
130
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 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 5: The LT6106 output is an open collector current source. The
minimum output voltage scales directly with the ratio R /10k.
OUT
+
Note 6: V
is the voltage at the high side of the sense resistor,
SENSE
R . See Figure 1.
SENSE
Note 7: V
is the maximum sense voltage for which the Electrical
SENSE (MAX)
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.
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.
Note 4: The LT6106C is guaranteed functional over the operating
temperature range of –40°C to 85°C. The LT6106C is designed,
TYPICAL PERFORMANCE CHARACTERISTICS
Input Offset Voltage vs
Temperature
Input Offset Voltage vs
VOS Distribution
Supply Voltage
70
60
50
40
30
400
300
+
V
R
R
= 5mV
V
V
= 12V
= 5mV
V
V
= 5mV
= 12V
= 100Ω
R
= 10k
OUT
SENSE
IN
16
14
12
10
8
SENSE
+
= 100Ω
A
= 100
SENSE
V
= 10k
R
R
= 100Ω
R
TYPICAL UNITS
OUT
IN
IN
TYPICAL UNITS
= 10k
OUT
200
1068 UNITS
20
10
0
–10
–20
–30
–40
–50
–60
–70
100
0
–100
–200
–300
–400
6
4
2
0
–200
–120
–40
0
40
120
200
20 25
0
5
10 15
30 35 40
35
65
–55 –25
5
95
125
INPUT OFFSET VOLTAGE (μV)
SUPPLY VOLTAGE (V)
TEMPERATURE (°C)
6106 G23
6106 G02
6106 G03
6106fa
3
LT6106
TYPICAL PERFORMANCE CHARACTERISTICS
Power Supply Rejection Ratio
Power Supply Rejection Ratio
vs Frequency
Gain Error vs Temperature
vs Frequency
120
110
100
90
80
70
60
50
40
30
20
10
0
0
–0.05
–0.10
–0.15
–0.20
–0.25
–0.30
–0.35
–0.40
–0.45
–0.50
–0.55
–0.60
120
110
100
90
80
70
60
50
40
30
20
10
0
+
+
V
A
= 12.5V
V
A
= 12.5V
= 20
= 20
V
+
V
V
V
= 36V
R
R
= 500Ω
= 10k
R
R
= 100Ω
IN
OUT
IN
OUT
= 2k
+
= 12V
= 5V
+
V
+
V
= 2.7V
V
I
= 1V
= 1mA
= 1k
OUT
V
V
V
= 2.5V
= 5V
= 10V
V
V
V
= 0.5V
= 1V
= 2V
OUT
OUT
OUT
OUT
OUT
OUT
OUT
R
OUT
TYPICAL UNIT
100
1k
10k
FREQUENCY (Hz)
100k
1M
–45 –25 –5 15 35 55 75 95 115 130
100
1k
10k
FREQUENCY (Hz)
100k
1M
TEMPERATURE (°C)
6106 G06
6106 G08
6106 G04
Gain Error Distribution
Gain vs Frequency
Gain vs Frequency
45
40
35
30
25
20
15
10
5
24
45
40
35
30
25
20
15
10
5
+
+
+
V
V
= 12.5V
= 500mV
V
= 12.5V
= 20
V
V
A
= 12.5V
= 100
= 100Ω
= 10k
22
20
18
16
14
12
10
8
A
SENSE
V
V
= 10V
V
= 10V
OUT
OUT
R
R
= 500Ω
R
R
= 500Ω
IN
= 10k
OUT
R
R
IN
OUT
IN
OUT
V
= 2.5V
OUT
= 10k
11,072 UNITS
V
= 2.5V
OUT
T
= 25°C
A
0
–5
0
–5
–10
–15
–20
–25
–30
–10
–15
–20
–25
–30
6
4
2
0
1k
10k
100k
FREQUENCY (Hz)
1M
10M
–0.60 –0.48 –0.36 –0.24 –0.12
GAIN ERROR (%)
0
1k
10k
100k
FREQUENCY (Hz)
1M
10M
6106 G14
6106 G09
6106 G24
Input Bias Current vs Supply
Voltage
Step Response 0mV to 10mV
(RIN = 100Ω)
Step Response 10mV to 20mV
(RIN = 100Ω)
20
19
18
17
16
15
14
13
12
11
10
V
R
= 5mV
SENSE
IN
V
= 100Ω
SENSE
V
SENSE
20mV/DIV
20mV/DIV
V
OUT
500mV/DIV
V
OUT
500mV/DIV
0V
0V
T
T
T
T
= –40°C
= 25°C
= 70°C
= 125°C
A
A
A
A
6106 G1
6106 G1
A
V
= 100
5μs/DIV
V
A
V
= 100
5μs/DIV
V
= 0V TO 1V
= 10k
OUT
= 1V TO 2V
= 10k
OUT
R
OUT
R
OUT
+
+
V
= 12V
0
5
10 15 20 25 30 35 40 45 50
SUPPLY VOLTAGE (V)
6106 G05
V
= 12V
6106fa
4
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)
V
V
V
SENSE
SENSE
SENSE
200mV/DIV
200mV/DIV
100mV/DIV
V
V
OUT
OUT
V
OUT
500mV/DIV
2V/DIV
2V/DIV
0V
0V
0V
6106 G1
6106 G15
6106 G1
A
V
= 100
5μs/DIV
A
V
= 20
V
5μs/DIV
A
V
= 100
5μs/DIV
V
V
= 0V TO 10V
= 10k
= 1V TO 2V
= 10k
= 1V TO 10V
= 10k
OUT
OUT
OUT
OUT
OUT
R
R
OUT
R
+
+
+
V
= 12V
V = 12V
V
= 12V
Step Response 0mV to 50mV
(RIN = 500Ω)
Step Response 50mV to 500mV
(RIN = 500Ω)
Step Response 0mV to 500mV
(RIN = 500Ω)
V
V
V
SENSE
SENSE
SENSE
1V/DIV
100mV/DIV
1V/DIV
V
V
OUT
OUT
2V/DIV
2V/DIV
V
OUT
500mV/DIV
0V
0V
0V
6106 G17
6106 G16
6106 G18
A
V
= 20
5μs/DIV
A
V
= 20
5μs/DIV
A
V
= 20
5μs/DIV
V
V
V
= 1V TO 10V
= 10k
= 0V TO 1V
= 10k
= 0V TO 10V
= 10k
OUT
OUT
OUT
OUT
OUT
OUT
R
R
R
+
+
+
V
= 12V
V
= 12V
V
= 12V
Output Voltage vs Input Sense
Voltage (0mV ≤ VSENSE ≤ 10mV)
Output Voltage vs Input Sense
Voltage (0mV ≤ VSENSE ≤ 10mV)
Output Voltage Swing vs
Temperature
11.10
11.05
11.00
10.95
1100
1000
900
800
700
600
500
400
300
200
100
0
220
200
180
160
140
120
100
80
+
+
+
V
A
= 12V
= 100
V
A
= 12V
= 20
V
A
= 12V
= 100
V
V
V
R
R
= 100Ω
R
R
= 500Ω
IN
= 10k
OUT
R
R
= 100Ω
IN
OUT
IN
OUT
= 10k
= 10k
= 120mV
V
SENSE
10.90
10.85
10.80
60
40
20
0
50
TEMPERATURE (°C)
100 125
0
1
2
3
4
5
6
7
8
9
10
0
1
2
3
4
5
6
7
8
9
10
–50 –25
0
25
75
V
(mV)
V
(mV)
SENSE
SENSE
6106 G07
6106 G19
6106 G20
6106fa
5
LT6106
TYPICAL PERFORMANCE CHARACTERISTICS
Output Voltage vs Input Sense
Voltage (0mV ≤ VSENSE ≤ 200mV)
Output Voltage vs Input Sense
Voltage (0mV ≤ VSENSE ≤ 1V)
Supply Current vs Supply Voltage
12
10
12
10
120
100
+
+
V
A
= 12V
= 20
V
A
= 12V
= 100
V
V
R
R
= 500Ω
R
R
= 100Ω
IN
OUT
IN
OUT
= 10k
= 10k
80
8
6
8
6
60
40
4
2
0
4
2
0
T
T
T
T
= –40°C
= 25°C
= 70°C
= 125°C
A
A
A
A
20
0
0
100 200 300 400 500 600 700 800 900 1000
0
20 40 60 80 100 120 140 160 180 200
(mV)
0
5
10 15 20 25 30 35 40 45
SUPPLY VOLTAGE (V)
V
(mV)
V
SENSE
SENSE
6106 G22
6106 G21
6106 G01
PIN FUNCTIONS
OUT (Pin 1): Current Output. OUT will source a current
that is proportional to the sense voltage into an external
resistor.
+
+
V (Pin 5): Positive Supply Pin. The V pin should be con-
nected directly to either side of the sense resistor, R
.
SENSE
Supply current is drawn through this pin. The circuit may
be configured so that the LT6106 supply current is or is
–
V (Pin 2): Normally Connected to Ground.
not monitored along with the system load current. To
+
–IN (Pin 3): The internal sense amplifier will drive –IN to
the same potential as +IN. A resistor (R ) tied from V
to –IN sets the output current I
is the voltage developed across R
monitor only the system load current, connect
V
to the
+
more positive side of the sense resistor. To monitor the
IN
+
= V
SENSE
/R . V
total current, including that of the LT6106, connect
the more negative side of the sense resistor.
V
to
OUT
SENSE IN SENSE
.
+IN (Pin 4): Must be tied to the system load end of the
sense resistor, either directly or through a resistor.
BLOCK DIAGRAM
I
LOAD
V
SENSE
+
–
V
BATTERY
R
SENSE
5
L
O
A
D
R
+
IN
V
14k
14k
–IN
+IN
–
+
3
4
I
OUT
R
R
R
OUT
OUT
V
= V
•
SENSE
1
–
OUT
V
IN
2
OUT
6106 F01
Figure 1. LT6106 Block Diagram and Typical Connection
6106fa
6
LT6106
APPLICATIONS INFORMATION
Introduction
must be small enough that V
does not exceed the
SENSE
maximum input voltage specified by the LT6106, even un-
der 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,
TheLT6106highsidecurrentsenseamplifier(Figure1)pro-
videsaccuratemonitoringofcurrentthroughauser-selected
sense resistor. The sense voltage is amplified by a user-
selected gain and level shifted from the positive power sup-
ply to a ground-referred output. The output signal is analog
and may be used as is, or processed with an output filter.
R
should be no more than 50mΩ.
SENSE
Once the maximum R
value is determined, the mini-
SENSE
mum sense resistor value will be set by the resolution or
dynamic range required. The minimum signal that can be
accuratelyrepresentedbythissenseamplifierislimitedby
the input offset. As an example, the LT6106 has a typical
input offset of 150μV. If the minimum current is 20mA, a
Theory of Operation
An internal sense amplifier loop forces –IN to have the
same potential as +IN. Connecting an external resistor,
+
R , between –IN and V forces a potential across R
IN
IN
. A
sense resistor of 7.5mΩ will set V
to 150μV. This is
SENSE
that is the same as the sense voltage across R
SENSE
the same value as the input offset. A larger sense resis-
tor will reduce the error due to offset by increasing the
sense voltage for a given load current. Choosing a 50mΩ
corresponding current, V
/R , will flow through R .
SENSE IN
IN
The high impedance inputs of the sense amplifier will not
conduct this current, so it will flow through an internal
R
will maximize the dynamic range and provide a
SENSE
PNP to the output pin as I
.
OUT
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
5mΩsenseresistorisemployed,thentheeffectivecurrent
error is 30mA, while the peak sense voltage is reduced to
10mV at 2A, dissipating only 20mW.
The output current can be transformed into a voltage by
–
adding a resistor from OUT to V . The output voltage is
–
then V = V + I
• R
.
O
OUT
OUT
Table 1. Useful Gain Configurations
GAIN
20
50
100
GAIN
20
R
R
V
at V
= 5V
I
at V = 5V
OUT
IN
OUT
SENSE
OUT
OUT
499Ω
200Ω
100Ω
10k
10k
10k
250mV
100mV
50mV
500μA
500μA
500μA
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 dy-
namic 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.
R
R
OUT
V
at V
= 2.5V
I
at V
= 2.5V
IN
SENSE
OUT
OUT
OUT
500μA
500μA
500μA
249Ω
100Ω
50Ω
5k
5k
5k
125mV
50mV
25mV
50
100
Selection of External Current Sense Resistor
The external sense resistor, R , has a significant ef-
Sense Resistor Connection
Kelvin connection of the –IN and +IN inputs to the sense
resistor should be used in all but the lowest power appli-
cations. Solder connections and PC board interconnec-
tions 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 cur-
rent in the same interconnect will cause a 5% error for the
same100mVsignal. Byisolatingthesensetracesfromthe
high current paths, this error can be reduced by orders of
SENSE
fect on the function of a current sensing system and must
be chosen with care.
First, the power dissipation in the resistor should be con-
sidered. The system load current will cause both heat and
voltage loss in R
. As a result, the sense resistor
SENSE
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 mea-
sured signal, and is limited primarily by input DC offset of
the internal amplifier of the LT6106. In addition, R
SENSE
6106fa
7
LT6106
APPLICATIONS INFORMATION
magnitude. A sense resistor with integrated Kelvin sense
terminals will give the best results. Figure 2 illustrates the
recommended method.
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
R , especially for small R values. All trace and inter-
+
V
IN
IN
connect resistances will increase the effective R value,
IN
R
IN
causing a gain error.
R
SENSE
+IN
–IN
–
Selection of External Output Resistor, R
+
OUT
LOAD
–
+
V
V
The output resistor, R , determines how the output cur-
OUT
rent is converted to voltage. V
is simply I
• R
.
OUT
OUT
OUT
In choosing an output resistor, the maximum output volt-
age must first be considered. If the following circuit is a
OUT
V
LT6106
OUT
R
OUT
buffer or ADC with limited input range, then R
must be
OUT
6106 F02
chosen so that I
• R
is less than the allowed
OUT(MAX)
OUT
Figure 2. Kelvin Input Connection Preserves Accuracy with
Large Load Currents
maximum input range of this circuit.
In addition, the output impedance is determined by R . If
OUT
the circuit to be driven has high enough input impedance,
then almost any useful output impedance will be accept-
able. However, if the driven circuit has relatively low input
impedance, or draws spikes of current such as an ADC
Selection of External Input Resistor, R
IN
R
should be chosen to allow the required resolution
IN
while limiting the output current to 1mA. In addition, the
maximum value for R is 500Ω. By setting R such that
the largest expected sense voltage gives I
IN
IN
might do, then a lower R
value may be required in order
OUT
= 1mA, then
OUT
to preserve the accuracy of the output. As an example, if
the input impedance of the driven circuit is 100 times R
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
,
OUT
then the accuracy of V
will be reduced by 1% since:
OUT
ROUT •RIN(DRIVEN)
VOUT = IOUT
•
R
OUT +RIN(DRIVEN)
dynamic range is required, then R can be increased
IN
accordingly, reducing the maximum output current and
power dissipation. If low sense currents must be resolved
accuratelyinasystemthathasaverywidedynamicrange,
100
101
= IOUT •ROUT
•
= 0.99 •IOUT •ROUT
a smaller R than the maximum current spec allows may
IN
Error Sources
be used if the maximum current is limited in another way,
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.
such as with a Schottky diode across R
(Figure 3).
SENSE
This will reduce the high current measurement accuracy
by limiting the result, while increasing the low current
measurement resolution.
Ideally, the circuit output is:
+
V
R
RIN
VOUT = VSENSE
•
OUT ; VSENSE = RSENSE •ISENSE
R
SENSE
D
SENSE
6106 F03
LOAD
In this case, the only error is due to resistor mismatch,
which provides an error in gain only. However, offset volt-
Figure 3. Shunt Diode Limits Maximum Input Voltage to Allow
Better Low Input Resolution Without Overranging
age and bias current cause additional errors.
6106fa
8
LT6106
APPLICATIONS INFORMATION
+
V
Output Error Due to the Amplifier DC Offset
Voltage, V
OS
–
+
R
IN
R
IN
R
SENSE
ROUT
RIN
+IN
–IN
E
OUT(VOS) = VOS •
–
+
LOAD
–
+
V
V
The DC offset voltage of the amplifier adds directly to the
value of the sense voltage, V . This is the dominant
error of the system and it limits the low end of the dynamic
range.Theparagraph“SelectionofExternalCurrentSense
Resistor” provides details.
SENSE
OUT
V
LT6106
+
OUT
R
OUT
6106 F04
–
R
= R – R
IN
IN
SENSE
Figure 4. Second Input R Minimizes Error Due to Input Bias Current
+
–
Output Error Due to the Bias Currents, I and I
B
B
+
–
The bias current I flows into the positive input of the
Minimum Output Voltage
B
internal op amp. I flows into the negative input.
B
The curves of the Output Voltage vs Input Sense Voltage
showthebehavioroftheLT6106withlowinputsensevolt-
⎛
⎜
⎝
⎞
RSENSE
RIN
+
–
EOUT(IBIAS) = ROUT IB
•
–IB
⎟
ages. When V
= 0V, the output voltage will always
SENSE
⎠
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.
+
–
Assuming I ≅ I = I
, and R
BIAS
<< R then:
SENSE IN
B
B
E
≅ –R
• I
OUT(IBIAS)
OUT BIAS
It is convenient to refer the error to the input:
≅ –R • I
E
IN(IBIAS)
IN BIAS
Power Dissipation Considerations
ForinstanceifI
is60nAandR is1k,theinputreferred
IN
BIAS
The power dissipated by the LT6106 will cause a small
increase in the die temperature. This rise in junction tem-
perature can be calculated if the output current and the
supply current are known.
error is 60μV. Note that in applications where R
≅
SENSE
+
R , I causes a voltage offset in R
that cancels the
IN
B
SENSE
–
error due to I and E
tions,R
reduced if an external resistor R = (R – R
connected as shown in Figure 4. Under both conditions:
≅ 0mV. In most applica-
B
OUT(IBIAS)
<<R ,thebiascurrenterrorcanbesimilarly
SENSE
IN
The power dissipated in the LT6106 due to the output
signal is:
+
) is
IN
IN
SENSE
–
P
= (V – V ) • I
+
–
OUT
IN
OUT
OUT
+
E
= R • I ; where I = I – I
IN OS OS B B
IN(IBIAS)
–
+
Since V ≅ V , P
≅ (V – V ) • I
IN
OUT
OUT
OUT
If the offset current, I , of the LT6106 amplifier is 6nA,
the 60μV error above is reduced to 6μV.
OS
The power dissipated due to the quiescent supply current is:
+
+
–
Adding R
as described will maximize the dynamic
P = I • (V – V )
IN
Q
S
+
range of the circuit. For less sensitive designs, R is
not necessary.
IN
The total power dissipated is the output dissipation plus
the quiescent dissipation:
Output Error Due to Gain Error
P
TOTAL
= P + P
OUT Q
The LT6106 exhibits a typical gain error of –0.25% at 1mA
output current. The primary source of gain error is due to
thefinitegaintothePNPoutputtransistor, whichresultsin
The junction temperature is given by:
T = T + θ • P
J
A
JA
TOTAL
At the maximum operating supply voltage of 36V and the
maximum guaranteed output current of 1mA, the total
asmallpercentageofthecurrentinR notappearinginthe
IN
outputloadR
.
OUT
6106fa
9
LT6106
APPLICATIONS INFORMATION
power dissipation is 41mW. This amount of power dis-
sipation will result in a 10°C rise in junction temperature
above the ambient temperature.
normal operation, V
SENSE(MAX)
should not exceed 500mV (see
SENSE
V
under Electrical Characteristics). This ad-
+
ditional constraint can be stated as V – (+IN) ≤ 500mV.
Referring to Figure 5, feedback will force the voltages
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
at the inputs –IN and +IN to be equal to (V – V
).
SENSE
S
+
Connecting V to the load side of the shunt results in equal
+
+
voltages at +IN, –IN and V . Connecting V to the supply
be taken to limit the maximum output current by proper
–
end of the shunt results in the voltages at +IN and –IN to
choice of sense resistor and R and, if input fault con-
IN
+
be V
below V .
SENSE
+
ditions exist, external clamps.
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 con-
Output Filtering
+
The output voltage, V , is simply I
• Z . This makes
OUT OUT
OUT
filtering straightforward. Any circuit may be used which
generates the required Z to get the desired filter re-
nected 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
OUT
sponse. For example, a capacitor in parallel with R
OUT
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 switch-
ing 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:
be monitored since it is drawn through the R resistor
IN
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.
V
S
R
IN
1
f–3dB
=
R
SENSE
2 • π •ROUT •COUT
+IN
–IN
–
+
LOAD
–
+
V
V
Useful Equations
Input Voltage: VSENSE = ISENSE •RSENSE
OUT
VOUT
VSENSE
ROUT
RIN
V
LT6106
OUT
Voltage Gain:
Current Gain:
=
R
OUT
6106 F05
IOUT
ISENSE
RSENSE
RIN
=
Figure 5. LT6106 Supply Current Monitored with the Load
Reverse Supply Protection
IOUT
VSENSE RIN
1
Transconductance:
Transimpedance:
=
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 ex-
ternal reversal of supply polarity. To prevent damage that
may occur during this condition, a Schottky diode should
VOUT
ISENSE
ROUT
RIN
= RSENSE
•
–
Power Supply Connection
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
For normal operation, the V pin should be connected to
either side of the sense resistor. Either connection will
+
+
effectively reducing the supply voltage to the part by V .
meet the constraint that +IN ≤ V and –IN ≤ V . During
D
6106fa
10
LT6106
APPLICATIONS INFORMATION
In addition, if the output of the LT6106 is wired to a de-
vice that will effectively short it to high voltage (such as
through an ESD protection clamp) during a reverse sup-
ply condition, the LT6106’s output should be connected
through a resistor or Schottky diode (Figure 7).
Response Time
ThephotosintheTypicalPerformanceCharacteristicsshow
the response of the LT6106 to a variety of input conditions
and values of R . The photos show that if the output cur-
IN
rentisveryloworzeroandaninputtransientoccurs, there
willbeanincreaseddelaybeforetheoutputvoltagebegins
changing while internal nodes are being charged.
Demo Board
Demo board DC1240 is available for evaluation of the
LT6106.
R
SENSE
R
SENSE
R1
V
BATT
100Ω
+IN
–IN
R1
100Ω
+IN
–IN
–
+
+
L
O
A
D
–
V
V
–
+
+
L
O
A
D
–
V
V
R3
1k
V
OUT
BATT
LT6106
ADC
R2
4.99k
D1
OUT
D1
LT6106
R2
4.99k
6106 F07
6106 F06
Figure 7. Additional Resistor R3 Protects Output
During Supply Reversal
Figure6.SchottkyDiodePreventsDamageDuringSupplyReversal
PACKAGE DESCRIPTION
S5 Package
5-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1635)
0.62
MAX
0.95
REF
2.90 BSC
(NOTE 4)
1.22 REF
1.50 – 1.75
(NOTE 4)
2.80 BSC
1.4 MIN
3.85 MAX 2.62 REF
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
DATUM ‘A’
0.01 – 0.10
1.00 MAX
0.30 – 0.50 REF
1.90 BSC
0.09 – 0.20
(NOTE 3)
S5 TSOT-23 0302 REV B
NOTE:
1. DIMENSIONS ARE IN MILLIMETERS
2. DRAWING NOT TO SCALE
3. DIMENSIONS ARE INCLUSIVE OF PLATING
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 representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
11
LT6106
TYPICAL APPLICATION
Simple 400V Current Monitor
DANGER! Lethal Potentials Present — Use Caution
I
V
SENSE
400V
SENSE
SENSE
+
–
R
R
IN
100Ω
+IN
–IN
L
O
A
D
–
+
DANGER!!
HIGH VOLTAGE!!
+
–
V
V
OUT
12V
CMPZ12L
LT6106
M1
BAT46
V
OUT
M2
OUT
4.99k
R
2M
M1 AND M2 ARE FQD3P50
R
R
OUT
V
=
• V
= 49.9 V
SENSE SENSE
OUT
6106 TA02
IN
RELATED PARTS
PART NUMBER
LT1787
DESCRIPTION
COMMENTS
Precision Bidirectional, High Side Current Sense Amplifier
75μV V , 60V, 60μA Operation
OS
LT6100
Gain-Selectable High Side Current Sense Amplifier
4.1V to 48V, Pin-Selectable Gain: 10, 12.5, 20, 25, 40, 50V/V
LTC®6101/LTC6101HV High Voltage, High Side, Precision Current Sense Amplifiers 4V to 60V/5V to 100V, Gain Configurable, SOT-23
LTC6103
LTC6104
Dual High Side, Precision Current Sense Amplifier
4V to 60V, Gain Configurable 8-Pin MSOP
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Bidirectional High Side, Precision Current Sense Amplifier
6106fa
LT 0807 REV A • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
12
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