LTC6101/LTC6101HV
High Voltage,
High-Side Current Sense
Amplifier in SOT-23
DESCRIPTION
FEATURES
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Supply Range:
5V to 100V, 105V Absolute Maximum (LTC6101HV)
4V to 60V, 70V Absolute Maximum (LTC6101)
Low Offset Voltage: 300μV Max
Fast Response: 1μs Response Time (0V to 2.5V on
a 5V Output Step)
Gain Configurable with 2 Resistors
Low Input Bias Current: 170nA Max
PSRR: 118dB Min
Output Current: 1mA Max
Low Supply Current: 250μA, VS = 12V
Specified Temperature Range: –40°C to 125°C
Operating Temperature Range: –55°C to 125°C
Low Profile (1mm) SOT-23 (ThinSOT™) Package
The LTC®6101/LTC6101HV are versatile, high voltage, high
side current sense amplifiers. Design flexibility is provided
by the excellent device characteristics; 300μV Max offset
and only 375μA (typical at 60V) of current consumption.
The LTC6101 operates on supplies from 4V to 60V and
LTC6101HV operates on supplies from 5V to 100V.
The LTC6101 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. Low DC
offset allows the use of a small shunt resistor and large
gain-setting resistors. As a result, power loss in the shunt
is reduced.
The wide operating supply range and high accuracy make
the LTC6101 ideal for a large array of applications from
automotive to industrial and power management. A maximum input sense voltage of 500mV allows a wide range
of currents to be monitored. The fast response makes the
LTC6101 the perfect choice for load current warnings and
shutoff protection control. With very low supply current,
the LTC6101 is suitable for power sensitive applications.
APPLICATIONS
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Current Shunt Measurement
Battery Monitoring
Remote Sensing
Power Management
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.
The LTC6101 is available in 5-lead SOT-23 and 8-lead
MSOP packages.
TYPICAL APPLICATION
16-Bit Resolution Unidirectional Output into LTC2433 ADC
ILOAD
VSENSE
–
Step Response
+
RIN
100Ω
+IN
VSENSE–
5V TO 105V
ΔVSENSE– = 100mV
–IN
L
O
A
D
+ –
V–
5.5V
5V
V+
5V
LTC6101HV
OUT
TA = 25°C
V+ = 12V
RIN = 100
ROUT = 5k
VSENSE+ = V+
1μF
VOUT
VOUT
IOUT = 100μA
ROUT
4.99k
LTC2433-1
TO μP
0.5V
0V
IOUT = 0
500ns/DIV
6101 TA01
VOUT =
6101 TA01b
ROUT
• VSENSE = 49.9VSENSE
RIN
6101fh
1
LTC6101/LTC6101HV
ABSOLUTE MAXIMUM RATINGS
(Note 1)
Total Supply Voltage (V+ to V–)
LTC6101............................................................... 70V
LTC6101HV ........................................................ 105V
Minimum Input Voltage (–IN Pin) .................... (V+ – 4V)
Maximum Output Voltage (Out Pin) ............................9V
Input Current....................................................... ±10mA
Output Short-Circuit Duration (to V–).............. Indefinite
Operating Temperature Range
LTC6101C/LTC6101HVC .......................– 40°C to 85°C
LTC6101I/LTC6101HVI ......................... –40°C to 85°C
LTC6101H/LTC6101HVH ................... –55°C to 125°C
Specified Temperature Range (Note 2)
LTC6101C/LTC6101HVC ........................... 0°C to 70°C
LTC6101I/LTC6101HVI ......................... –40°C to 85°C
LTC6101H/LTC6101HVH ................... –40°C to 125°C
Storage Temperature Range.................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec) ................. 300°C
PIN CONFIGURATION
TOP VIEW
TOP VIEW
–IN
NC
NC
OUT
1
2
3
4
8
7
6
5
+IN
V+
NC
V–
OUT 1
5 V+
V– 2
–IN 3
MS8 PACKAGE
8-LEAD PLASTIC MSOP
TJMAX = 150°C, θJA = 300°C/ W
4 +IN
S5 PACKAGE
5-LEAD PLASTIC TSOT-23
TJMAX = 150°C, θJA = 250°C/ W
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
SPECIFIED TEMPERATURE RANGE
LTC6101ACMS8#PBF
LTC6101ACMS8#TRPBF
LTBSB
8-Lead Plastic MSOP
0°C to 70°C
LTC6101AIMS8#PBF
LTC6101AIMS8#TRPBF
LTBSB
8-Lead Plastic MSOP
–40°C to 85°C
LTC6101AHMS8#PBF
LTC6101AHMS8#TRPBF
LTBSB
8-Lead Plastic MSOP
–40°C to 125°C
LTC6101HVACMS8#PBF
LTC6101HVACMS8#TRPBF
LTBSX
8-Lead Plastic MSOP
0°C to 70°C
LTC6101HVAIMS8#PBF
LTC6101HVAIMS8#TRPBF
LTBSX
8-Lead Plastic MSOP
–40°C to 85°C
LTC6101HVAHMS8#PBF
LTC6101HVAHMS8#TRPBF
LTBSX
8-Lead Plastic MSOP
–40°C to 125°C
6101fh
2
LTC6101/LTC6101HV
ORDER INFORMATION
Lead Free Finish
TAPE AND REEL (MINI)
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
SPECIFIED TEMPERATURE RANGE
LTC6101ACS5#TRMPBF
LTC6101ACS5#TRPBF
LTBND
5-Lead Plastic TSOT-23
0°C to 70°C
LTC6101AIS5#TRMPBF
LTC6101AIS5#TRPBF
LTBND
5-Lead Plastic TSOT-23
–40°C to 85°C
LTC6101AHS5#TRMPBF
LTC6101AHS5#TRPBF
LTBND
5-Lead Plastic TSOT-23
–40°C to 125°C
LTC6101BCS5#TRMPBF
LTC6101BCS5#TRPBF
LTBND
5-Lead Plastic TSOT-23
0°C to 70°C
LTC6101BIS5#TRMPBF
LTC6101BIS5#TRPBF
LTBND
5-Lead Plastic TSOT-23
–40°C to 85°C
LTC6101BHS5#TRMPBF
LTC6101BHS5#TRPBF
LTBND
5-Lead Plastic TSOT-23
–40°C to 125°C
LTC6101CCS5#TRMPBF
LTC6101CCS5#TRPBF
LTBND
5-Lead Plastic TSOT-23
0°C to 70°C
LTC6101CIS5#TRMPBF
LTC6101CIS5#TRPBF
LTBND
5-Lead Plastic TSOT-23
–40°C to 85°C
LTC6101CHS5#TRMPBF
LTC6101CHS5#TRPBF
LTBND
5-Lead Plastic TSOT-23
–40°C to 125°C
LTC6101HVACS5#TRMPBF
LTC6101HVACS5#TRPBF
LTBSZ
5-Lead Plastic TSOT-23
0°C to 70°C
LTC6101HVAIS5#TRMPBF
LTC6101HVAIS5#TRPBF
LTBSZ
5-Lead Plastic TSOT-23
–40°C to 85°C
LTC6101HVAHS5#TRMPBF
LTC6101HVAHS5#TRPBF
LTBSZ
5-Lead Plastic TSOT-23
–40°C to 125°C
LTC6101HVBCS5#TRMPBF
LTC6101HVBCS5#TRPBF
LTBSZ
5-Lead Plastic TSOT-23
0°C to 70°C
LTC6101HVBIS5#TRMPBF
LTC6101HVBIS5#TRPBF
LTBSZ
5-Lead Plastic TSOT-23
–40°C to 85°C
LTC6101HVBHS5#TRMPBF
LTC6101HVBHS5#TRPBF
LTBSZ
5-Lead Plastic TSOT-23
–40°C to 125°C
LTC6101HVCCS5#TRMPBF
LTC6101HVCCS5#TRPBF
LTBSZ
5-Lead Plastic TSOT-23
0°C to 70°C
LTC6101HVCIS5#TRMPBF
LTC6101HVCIS5#TRPBF
LTBSZ
5-Lead Plastic TSOT-23
–40°C to 85°C
LTC6101HVCHS5#TRMPBF LTC6101HVCHS5#TRPBF
LTBSZ
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/
–40°C to 125°C
6101fh
3
LTC6101/LTC6101HV
ELECTRICAL CHARACTERISTICS
(LTC6101) The ● denotes the specifications which apply over the full
specified temperature range, otherwise specifications are at TA = 25°C, RIN = 100Ω, ROUT = 10k, VSENSE+ = V+ (see Figure 1 for
details), 4V ≤ VS ≤ 60V unless otherwise noted.
SYMBOL
PARAMETER
VS
Supply Voltage Range
VOS
Input Offset Voltage
CONDITIONS
MIN
●
VSENSE = 5mV, Gain = 100, LTC6101A
VSENSE = 5mV, Gain = 100, LTC6101AC, LTC6101AI
VSENSE = 5mV, Gain = 100, LTC6101AH
VSENSE = 5mV, Gain = 100, LTC6101B
VSENSE = 5mV, Gain = 100, LTC6101C
TYP
4
UNITS
60
V
±85
±300
±450
±535
μV
μV
μV
±150
±450
±810
μV
μV
±400
800
1200
μV
μV
●
●
●
●
●
●
●
MAX
μV/°C
μV/°C
μV/°C
ΔVOS/ΔT
Input Offset Voltage Drift
VSENSE = 5mV, LTC6101A
VSENSE = 5mV, LTC6101B
VSENSE = 5mV, LTC6101C
IB
Input Bias Current
RIN = 1M
IOS
Input Offset Current
RIN = 1M
●
VSENSE(MAX)
Input Sense Voltage Full Scale
VOS within Specification, RIN = 1k (Note 3)
●
500
PSRR
Power Supply Rejection Ratio
VS = 6V to 60V, VSENSE = 5mV, Gain = 100
118
115
140
●
dB
dB
110
105
133
●
dB
dB
8
3
1
VS = 4V to 60V, VSENSE = 5mV, Gain = 100
Maximum Output Voltage
12V ≤ VS ≤ 60V, VSENSE = 88mV
VS = 6V, VSENSE = 330mV, RIN = 1k, ROUT = 10k
VS = 4V, VSENSE = 550mV, RIN = 1k, ROUT = 2k
●
●
●
VOUT (0)
Minimum Output Voltage
VSENSE = 0V, Gain = 100, LTC6101A
VSENSE = 0V, Gain = 100, LTC6101AC, LTC6101AI
VSENSE = 0V, Gain = 100, LTC6101AH
●
●
VSENSE = 0V, Gain = 100, LTC6101C
100
170
245
nA
nA
±2
±15
nA
●
VOUT
VSENSE = 0V, Gain = 100, LTC6101B
±1
±3
±5
mV
V
V
V
0
30
45
53.5
mV
mV
mV
0
45
81
mV
mV
0
150
250
mV
mV
●
●
●
●
IOUT
Maximum Output Current
6V ≤ VS ≤ 60V, ROUT = 2k, VSENSE = 110mV, Gain = 20
VS = 4V, VSENSE = 550mV, Gain = 2, ROUT = 2k
tr
Input Step Response
(to 2.5V on a 5V Output Step)
ΔVSENSE = 100mV Transient, 6V ≤ VS ≤ 60V, Gain = 50
VS = 4V
1
1.5
μs
μs
BW
Signal Bandwidth
IOUT = 200μA, RIN = 100, ROUT = 5k
IOUT = 1mA, RIN = 100, ROUT = 5k
140
200
kHz
kHz
IS
Supply Current
VS = 4V, IOUT = 0, RIN = 1M
VS = 6V, IOUT = 0, RIN = 1M
VS = 12V, IOUT = 0, RIN = 1M
VS = 60V, IOUT = 0, RIN = 1M
LTC6101AI, LTC6101AC, LTC6101BI, LTC6101BC,
LTC6101CI, LTC6101CC
LTC6101AH, LTC6101BH, LTC6101CH
1
0.5
mA
mA
220
450
475
μA
μA
240
475
525
μA
μA
250
500
590
μA
μA
375
640
μA
690
720
μA
μA
●
●
●
●
●
6101fh
4
LTC6101/LTC6101HV
ELECTRICAL CHARACTERISTICS
(LTC6101HV) The ● denotes the specifications which apply over the full
specified temperature range, otherwise specifications are at TA = 25°C, RIN = 100Ω, ROUT = 10k, VSENSE+ = V+ (see Figure 1 for
details), 5V ≤ VS ≤ 100V unless otherwise noted.
SYMBOL
PARAMETER
VS
Supply Voltage Range
VOS
Input Offset Voltage
CONDITIONS
MIN
●
VSENSE = 5mV, Gain = 100, LTC6101HVA
VSENSE = 5mV, Gain = 100, LTC6101HVAC, LTC6101HVAI
VSENSE = 5mV, Gain = 100, LTC6101HVAH
VSENSE = 5mV, Gain = 100, LTC6101HVB
VSENSE = 5mV, Gain = 100, LTC6101HVC
TYP
MAX
UNITS
100
V
±85
±300
±450
±535
μV
μV
μV
±150
±450
±810
μV
μV
±400
800
1200
μV
μV
5
●
●
●
●
●
●
●
ΔVOS/ΔT
Input Offset Voltage Drift
VSENSE = 5mV, LTC6101HVA
VSENSE = 5mV, LTC6101HVB
VSENSE = 5mV, LTC6101HVC
IB
Input Bias Current
RIN = 1M
IOS
Input Offset Current
RIN = 1M
●
VSENSE(MAX)
Input Sense Voltage Full Scale
VOS within Specification, RIN = 1k (Note 3)
●
500
PSRR
Power Supply Rejection Ratio
VS = 6V to 100V, VSENSE = 5mV, Gain = 100
118
115
140
●
dB
dB
110
105
133
●
dB
dB
8
3
VS = 5V to 100V, VSENSE = 5mV, Gain = 100
Maximum Output Voltage
12V ≤ VS ≤ 100V, VSENSE = 88mV
VS = 5V, VSENSE = 330mV, RIN = 1k, ROUT = 10k
●
●
VOUT (0)
Minimum Output Voltage
VSENSE = 0V, Gain = 100, LTC6101HVA
VSENSE = 0V, Gain = 100, LTC6101HVAC, LTC6101HVAI
VSENSE = 0V, Gain = 100, LTC6101HVAH
●
●
VSENSE = 0V, Gain = 100, LTC6101HVC
170
245
nA
nA
±2
±15
nA
mV
V
V
0
30
45
53.5
mV
mV
mV
0
45
81
mV
mV
0
150
250
mV
mV
●
●
●
μV/°C
μV/°C
μV/°C
100
●
VOUT
VSENSE = 0V, Gain = 100, LTC6101HVB
±1
±3
±5
IOUT
Maximum Output Current
5V ≤ VS ≤ 100V, ROUT = 2k, VSENSE = 110mV, Gain = 20
tr
Input Step Response
(to 2.5V on a 5V Output Step)
ΔVSENSE = 100mV Transient, 6V ≤ VS ≤ 100V, Gain = 50
VS = 5V
1
1.5
μs
μs
BW
Signal Bandwidth
IOUT = 200μA, RIN = 100, ROUT = 5k
IOUT = 1mA, RIN = 100, ROUT = 5k
140
200
kHz
kHz
IS
Supply Current
VS = 5V, IOUT = 0, RIN = 1M
VS = 6V, IOUT = 0, RIN = 1M
VS = 12V, IOUT = 0, RIN = 1M
VS = 60V, IOUT = 0, RIN = 1M
LTC6101HVI, LTC6101HVC
LTC6101HVH
VS = 100V, IOUT = 0, RIN = 1M
LTC6101HVAI, LTC6101HVAC, LTC6101HVBI,
LTC6101HVBC, LTC6101HVCI, LTC6101HVCC
LTC6101HVAH, LTC6101HVBH, LTC6101HVCH
1
mA
200
450
475
μA
μA
220
475
525
μA
μA
230
500
590
μA
μA
350
640
690
720
μA
μA
μA
350
640
μA
690
720
μA
μA
●
●
●
●
●
●
●
6101fh
5
LTC6101/LTC6101HV
ELECTRICAL CHARACTERISTICS
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.
Note 2: The LTC6101C/LTC6101HVC are guaranteed to meet specified
performance from 0°C to 70°C. The LTC6101C/LTC6101HVC are designed,
characterized and expected to meet specified performance from –40°C to
85°C but are not tested or QA sampled at these temperatures. LTC6101I/
LTC6101HVI are guaranteed to meet specified performance from –40°C
to 85°C. The LTC6101H/LTC6101HVH are guaranteed to meet specified
performance from –40°C to 125°C.
Note 3: ROUT = 10k for 6V ≤ VS ≤ 100V, ROUT = 2k for VS = 4V.
TYPICAL PERFORMANCE CHARACTERISTICS
Input VOS vs Temperature
Input VOS vs Supply Voltage
600
INPUT OFFSET (μV)
INPUT OFFSET (μV)
TA = 0°C
0
0
–200
–400
A GRADE
B GRADE
C GRADE
–800
–1000
–40 –20
0
RIN = 100
ROUT = 5k
VIN = 5mV
–40
TA = 25°C
–60
–80
TA = 85°C
RIN = 100
ROUT = 5k
VIN = 5mV
–120
4
11
18
25 32 39
VSUPPLY (V)
46
12
60
10
7
6
MAXIMUM IOUT (mA)
MAXIMUM OUTPUT (V)
VS = 4V
2
VS = 12V
8
6
VS = 6V
VS = 5V
4
VS = 4V
20 40 60 80
TEMPERATURE (°C)
100 120
6101 G06
0
–40 –20
5
VS = 12V
VS = 60V
4
3
VS = 6V
2
VS = 4V
2
0
RIN = 3k
ROUT = 3k
LTC6101: IOUT Maximum
vs Temperature
10
4
LTC6101
LTC6101HV
6101 G05
VS = 100V
VS = 6V
TA = 125°C
4 10 20 30 40 50 60 70 80 90 100
VSUPPLY (V)
12
VS = 60V
MAXIMUM OUTPUT (V)
53
0
LTC6101HV: VOUT Maximum
vs Temperature
6
TA = 85°C
1
6101 G02
LTC6101: VOUT Maximum
vs Temperature
0
–40 –20
TA = 70°C
0.5
6101 G01
VS = 12V
TA = –40°C
1.5
TA = 125°C
–140
20 40 60 80 100 120
TEMPERATURE (°C)
8
TA = 0°C
2
TA = –40°C
–20
–100
–600
TA = 25°C
20
400
200
Input Sense Range
2.5
40
REPRESENTATIVE
UNITS
MAXIMUM VSENSE (V)
800
1
0
20 40 60 80
TEMPERATURE (°C)
100 120
6101 G20
0
–40 –20
0
20 40 60 80
TEMPERATURE (°C)
100 120
6101 G07
6101fh
6
LTC6101/LTC6101HV
TYPICAL PERFORMANCE CHARACTERISTICS
LTC6101HV: IOUT Maximum
vs Temperature
Output Error Due to Input Offset
vs Input Voltage
100
7
4
VS = 6V
VS = 5V
2
25
1
B GRADE
0.01
20 40 60 80
TEMPERATURE (°C)
100 120
6101 G21
140
400
VS = 6V TO 100V
IB (nA)
VS = 4V
60
40
70°C
125°C
500
350
300
250
25°C
200
0°C
150
–40°C
0
20 40 60 80
TEMPERATURE (°C)
100 120
–40°C
0°C
125°C
300
25°C
200
VIN = 0
RIN = 1M
0
10 20 30 40 50 60 70 80 90 100
SUPPLY VOLTAGE (V)
6101 G11
Step Response 0mV to 10mV
6101 G22
Step Response 10mV to 20mV
–
VSENSE
V+-10mV
VSENSE–
+
V -20mV
+
0.5V
1V
TA = 25°C
V+ = 12V
RIN = 100
ROUT = 5k
VSENSE+ = V+
TA = 25°C
V+ = 12V
RIN = 100
ROUT = 5k
VSENSE+ = V+
0V
70°C
0
0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60
SUPPLY VOLTAGE (V)
6101 G10
V+
V -10mV
400
85°C
100
VIN = 0
RIN = 1M
50
0
6101 G09
600
85°C
100
20
0
–40 –20
1M
LTC6101HV: Supply Current
vs Supply Voltage
SUPPLY CURRENT (μA)
SUPPLY CURRENT (μA)
450
100
10k
100k
FREQUENCY (Hz)
1k
6101 G08
LTC6101: Supply Current
vs Supply Voltage
160
80
–10
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5
INPUT VOLTAGE (V)
Input Bias Current
vs Temperature
120
IOUT = 200μA
10
–5
A GRADE
0
15
0
VS = 4V
0
–40 –20
20
5
C GRADE
0.1
IOUT = 1mA
TA = 25°C
RIN = 100
ROUT = 4.99k
30
GAIN (dB)
VS = 100V
1
35
10
5
3
TA = 25°C
GAIN =10
VS = 12V
OUTPUT ERROR (%)
MAXIMUM IOUT (mA)
6
Gain vs Frequency
40
0.5V
VOUT
TIME (10μs/DIV)
VOUT
TIME (10μs/DIV)
6101 G12
6101 G13
6101fh
7
LTC6101/LTC6101HV
TYPICAL PERFORMANCE CHARACTERISTICS
Step Response 100mV
V+
V+-100mV
5V
Step Response Rising Edge
Step Response 100mV
VSENSE–
V+
V+-100mV
CLOAD = 10pF
VSENSE–
TA = 25°C
V+ = 12V
CLOAD = 2200pF
RIN = 100
ROUT = 5k
VSENSE+ = V+
5V
TA = 25°C
V+ = 12V
RIN = 100
ROUT = 5k
VSENSE+ = V+
CLOAD = 1000pF
VSENSE–
ΔVSENSE– =100mV
5.5V
5V
TA = 25°C
V+ = 12V
RIN = 100
ROUT = 5k
VSENSE+ = V+
VOUT
IOUT = 100μA
0V
0V
VOUT
0.5V
0V
VOUT
TIME (100μs/DIV)
TIME (10μs/DIV)
IOUT = 0
TIME (500ns/DIV)
6101 G15
6101 G14
Step Response Falling Edge
6101 G16
PSRR vs Frequency
160
140
ΔVSENSE– =100mV
120
VOUT
TA = 25°C
V+ = 12V
RIN = 100
ROUT = 5k
VSENSE+ = V+
IOUT = 100μ
0.5V
0V
IOUT = 0
TIME (500ns/DIV)
6101 G17
PSRR (dB)
5.5V
5V
LTC6101,
V+ = 4V
100
80
LTC6101,
LTC6101HV,
V+ = 12V
60 R = 100
IN
ROUT = 10k
40 C
OUT = 5pF
GAIN = 100
LTC6101HV,
20 I
V+ = 5V
OUTDC = 100μA
VINAC = 50mVp
0
0.1
1
10 100 1k
10k 100k
FREQUENCY (Hz)
1M
6101 G19
6101fh
8
LTC6101/LTC6101HV
PIN FUNCTIONS
V+: Positive Supply Pin. Supply current is drawn through
this pin. The circuit may be configured so that the
LTC6101 supply current is or is not monitored along
with the system load current. To monitor only system
load current, connect V+ to the more positive side of the
sense resistor. To monitor the total current, including the
LTC6101 current, connect V+ to the more negative side
of the sense resistor.
OUT: Current Output. OUT will source a current that is
proportional to the sense voltage into an external resistor.
V – : Negative Supply (or Ground for Single-Supply
Operation).
–IN: 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 the external RSENSE (Figure 1).
+IN: Must be tied to the system load end of the sense
resistor, either directly or through a resistor.
BLOCK DIAGRAM
ILOAD
–
VSENSE
+
V+
RSENSE
VBATTERY
RIN
10V
L
O
A
D
–IN
5k
–
+IN
5k
+
IOUT
10V
OUT
LTC6101/LTC6101HV
V–
6101 BD
VOUT = VSENSE x
ROUT
RIN
ROUT
Figure 1. LTC6101/LTC6101HV Block Diagram and Typical Connection
APPLICATIONS INFORMATION
The LTC6101 high side current sense amplifier (Figure 1)
provides accurate monitoring of current through a userselected sense resistor. The sense voltage is amplified by
a user-selected 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 resis-
tor, 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 input current,
so it will flow through an internal MOSFET to the output pin.
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.
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LTC6101/LTC6101HV
APPLICATIONS INFORMATION
Useful Gain Configurations
Gain
RIN
ROUT
VSENSE at VOUT = 5V
IOUT at VOUT = 5V
20
499
10k
250mV
500μA
50
200
10k
100mV
500μA
100
100
10k
50mV
500μA
Selection of External Current Sense Resistor
The external sense resistor, RSENSE, has a significant effect
on the function of a current sensing system and must be
chosen with care.
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
reproduced signal, and is limited primarily by input DC
offset of the internal amplifier of the LTC6101. In addition,
RSENSE must be small enough that VSENSE does not exceed
the maximum input voltage specified by the LTC6101, 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 amp is limited by the
input offset. As an example, the LTC6101B 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 LTC6101 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
max, and over 70dB of dynamic range if the rated input
maximum of 500mV is allowed.
Sense Resistor Connection
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 x 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 magnitude. A sense resistor with integrated
Kelvin sense terminals will give the best results. Figure 2
illustrates the recommended method.
V+
RIN
RSENSE
+IN
–IN
+
–
LOAD
V–
V+
LTC6101
OUT
VOUT
ROUT
6101 F02
Figure 2. Kelvin Input Connection Preserves
Accuracy Despite Large Load Current
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LTC6101/LTC6101HV
APPLICATIONS INFORMATION
Selection of External Input Resistor, RIN
V+
The external input resistor, RIN, controls the transconductance of the current sense circuit. Since IOUT = VSENSE/RIN,
transconductance gm = 1/RIN. For example, if RIN = 100,
then IOUT = VSENSE /100 or IOUT = 1mA for VSENSE = 100mV.
6101 F03a
LOAD
RIN should be chosen to allow the required resolution
while limiting the output current. At low supply voltage,
IOUT may be as much as 1mA. 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 max output current and power dissipation.
If low sense currents must be resolved accurately in a
system that has very wide dynamic range, a smaller RIN
than the max current spec allows may be used if the max
current is limited in another way, such as with a Schottky
diode across RSENSE (Figure 3a). This will reduce the high
current measurement accuracy by limiting the result, while
increasing the low current measurement resolution.
Figure 3a. Shunt Diode Limits Maximum Input Voltage to Allow
Better Low Input Resolution Without Overranging
This approach can be helpful in cases where occasional
large burst currents may be ignored. It can also be used
in a multirange configuration where a low current circuit
is added to a high current circuit (Figure 3b). Note that
a comparator (LTC1540) is used to select the range, and
transistor M1 limits the voltage across RSENSE LO.
Care should be taken when designing the board layout
for RIN, especially for small RIN values. All trace and interconnect impedances will increase the effective RIN value,
causing a gain error. In addition, internal device resistance
will add approximately 0.2Ω to RIN.
VLOGIC
(3.3V TO 5V)
CMPZ4697
7
10k
3
M1
Si4465
VIN
RSENSE HI
10m
ILOAD
VOUT
301
RSENSE LO
100m
+IN
V–
DSENSE
RSENSE
+ –
LTC6101
4
+
–
8
5
Q1
CMPT5551
40.2k 6
301
301
301
–IN
+IN
–IN
V+
V–
VIN
OUT
+ –
4.7k
1.74M
2
V+
LTC1540
1
619k
OUT
LTC6101
HIGH
RANGE
INDICATOR
(ILOAD > 1.2A)
HIGH CURRENT RANGE OUT
250mV/A
7.5k
VLOGIC
BAT54C
R5
7.5k
(VLOGIC +5V) ≤ VIN ≤ 60V
LOW CURRENT RANGE OUT
2.5V/A
0 ≤ ILOAD ≤ 10A
6101 F03b
Figure 3b. Dual LTC6101s Allow High-Low Current Ranging
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LTC6101/LTC6101HV
APPLICATIONS INFORMATION
Selection of External Output Resistor, ROUT
The output resistor, ROUT, determines how the output current is converted to voltage. VOUT is simply IOUT • ROUT.
Output Error, EOUT, Due to the Amplifier DC Offset
Voltage, VOS
EOUT(VOS) = VOS • (ROUT/RIN)
In choosing an output resistor, the max output voltage
must first be considered. If the circuit that is driven by
the output does not limit the output voltage, then ROUT
must be chosen such that the max output voltage does
not exceed the LTC6101 max output voltage rating. 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.
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 available dynamic
range. The paragraph “Selection of External Current Sense
Resistor” provides details.
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:
•R
R
VOUT =IOUT • OUT IN(DRIVEN)
ROUT +RIN(DRIVEN)
The bias current IB(+) flows into the positive input of the
internal op amp. IB(–) flows into the negative input.
=IOUT • ROUT •
100
= 0.99 •IOUT • ROUT
101
Error Sources
Output Error, EOUT, Due to the Bias Currents,
IB(+) and IB(–)
EOUT(IBIAS) = ROUT((IB(+) • (RSENSE/RIN) – IB(–))
Since IB(+) ≈ IB(–) = IBIAS, if RSENSE
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