LT1787/LT1787HV
Precision, High Side
Current Sense Amplifiers
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DESCRIPTIO
FEATURES
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Input Offset Voltage: 75µV (Max)
60V Supply Operation (LT1787HV)
12-Bit Dynamic Range
Operating Current: 60µA
User-Selectable External Sense Resistor
Bidirectional High Side Current Sensing
Unidirectional or Bidirectional Output
Input Noise Filtering
–40°C to 125°C Operating Temperature Range
Available in 8-Lead SO and MSOP Packages
The LT ®1787 is a complete micropower precision high
side current sense amplifier. The LT1787 monitors bidirectional currents via the voltage across an external sense
resistor. A current or voltage output indicates the direction
and magnitude of the sense current. The LT1787 delivers
greater than a 12-bit dynamic range with ultralow 40µV
input offset voltage compared to a typical 250mV fullscale input voltage. A fixed gain of 8 is set by onboard
precision resistors. Input signal filtering is easily implemented with a capacitor between the FIL– and FIL+ pins.
The LT1787HV operates from 2.5V to 60V total supply
voltage and the LT1787 operates from 2.5V to 36V total
supply voltage. Both versions have a PSRR in excess of
120dB. The LT1787/LT1787HV draw only 60µA and are
available in 8-lead SO and MSOP packages.
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APPLICATIO S
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Battery Monitoring
Power Monitoring
Portable Phones
Cellular Phones
Portable Test/Measurement Systems
Battery-Operated Systems
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
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TYPICAL APPLICATIO
12-Bit Dynamic Resolution Unidirectional Output into LTC®1286 ADC
I = 100A
1
FIL–
–
2 VS
3
4
DNC
FIL+
LT1787HV
40
8
VS+ 7
VBIAS 6
ROUT
20k
VEE
50
RSENSE
0.0016Ω
5
VOUT
VOUT = VBIAS + (8 • ILOAD • RSENSE)
C2
0.1µF
2.5V TO 60V
R1
15k
C1
1µF
VREF VCC
CS
+IN
LTC1286 CLK
–IN
D
GND OUT
LT1634-1.25
5V
TO µP
1787 TA01
INPUT OFFSET VOLTAGE (µV)
TO
LOAD
Input Offset Voltage vs Supply Voltage
30
20
10
0
–10
–20
–30
–40
–50
0
10
30
40
50
20
TOTAL SUPPLY VOLTAGE (V)
60
1787 TA01b
1787fc
1
LT1787/LT1787HV
W W
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ABSOLUTE MAXIMUM RATINGS
(Notes 1, 2)
Differential Sense Voltage ...................................... ±10V
Total Supply Voltage (LT1787) ................................ 40V
Total Supply Voltage (LT1787HV) ........................... 65V
Output Voltage ..................... (VEE – 0.3V) to (VEE + 35V)
Output Bias Voltage ............. (VEE – 0.3V) to (VEE + 35V)
Operating Temperature Range (Note 3)
LT1787C ............................................. – 40°C to 85°C
LT1787I .............................................. – 40°C to 85°C
LT1787H .......................................... – 40°C to 125°C
Specified Temperature Range (Note 4)
LT1787C ............................................. – 40°C to 85°C
LT1787I .............................................. – 40°C to 85°C
LT1787H .......................................... – 40°C to 125°C
Storage Temperature Range ..................–65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
U
W
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PACKAGE/ORDER INFORMATION
TOP VIEW
TOP VIEW
FIL–
V S–
DNC*
VEE
1
2
3
4
8
7
6
5
FIL+
V S+
VBIAS
VOUT
FIL– 1
8
FIL+
VS–
2
7
VS+
DNC* 3
6
VBIAS
VEE 4
5
VOUT
MS8 PACKAGE
8-LEAD PLASTIC MSOP
S8 PACKAGE
8-LEAD PLASTIC SO
* DO NOT CONNECT
TJMAX = 150°C, θJA = 250°C/ W
ORDER PART NUMBER
LT1787CMS8
LT1787IMS8
LT1787HVCMS8
LT1787HVIMS8
* DO NOT CONNECT
TJMAX = 150°C, θJA = 190°C/ W
MS8 PART MARKING
LTGM
LTGN
LTKJ
LTKK
S8 PART MARKING
ORDER PART NUMBER
LT1787CS8
LT1787IS8
LT1787HS8
LT1787HVCS8
LT1787HVIS8
LT1787HVHS8
1787
1787I
1787H
1787HV
787HVI
787HVH
Order Options Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking: http://www.linear.com/leadfree/
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
(Note 5)
The ● denotes the specifications which apply over the temperature range 0°C ≤ TA ≤ 70°C, otherwise specifications are at TA = 25°C.
Total supply = (VS– – VEE) = 2.5V to 36V (LT1787C), 2.5V to 60V (LT1787HVC) unless otherwise specified.
SYMBOL
PARAMETER
VS –, VS +
CONDITIONS
MIN
Sense Amplifier Supply Voltage Single Supply Operation (LT1787)
Single Supply Operation (LT1787HV)
VSENSE
Input Sense Voltage Full Scale
VSENSE = VS+ – VS–, VS = 10V, VBIAS = 5V, AV = 8 ±10%
●
500
VOS
Input Offset Voltage (S8)
IOUT = 0, VS Supply = 5V
0°C ≤ TA ≤ 70°C
●
– 75
– 135
IOUT = 0 (LT1787)
0°C ≤ TA ≤ 70°C
●
IOUT = 0 (LT1787HV)
0°C ≤ TA ≤ 70°C
●
●
●
TYP
2.5
2.5
MAX
36
60
UNITS
V
V
mV
±40
75
135
µV
µV
– 100
– 160
100
160
µV
µV
– 100
– 160
100
160
µV
µV
1787fc
2
LT1787/LT1787HV
ELECTRICAL CHARACTERISTICS
(Note 5)
The ● denotes the specifications which apply over the temperature range 0°C ≤ TA ≤ 70°C, otherwise specifications are at TA = 25°C.
Total supply = (VS – – VEE) = 2.5V to 36V (LT1787C), 2.5V to 60V (LT1787HVC) unless otherwise specified.
SYMBOL
PARAMETER
Input Offset Voltage (MS8)
CONDITIONS
IOUT = 0, VS Supply = 5V
0°C ≤ TA ≤ 70°C
●
MIN
– 125
– 230
IOUT = 0 (LT1787)
0°C ≤ TA ≤ 70°C
●
IOUT = 0 (LT1787HV)
0°C ≤ TA ≤ 70°C
●
●
TYP
±40
MAX
125
230
UNITS
µV
µV
– 150
– 250
150
250
µV
µV
– 150
– 250
150
250
µV
µV
Temperature Coefficient of VOS
VS Supply = 5V (Note 6)
IOUT(O)
No-Load Output Current Error
VSENSE = 0V
VOUT(O)
No-Load Output Voltage Error
(S8)
VSENSE = 0V, VS Supply = 5V
0°C ≤ TA ≤ 70°C
No-Load Output Voltage Error
(MS8)
VSENSE = 0V, VS Supply = 5V
0°C ≤ TA ≤ 70°C
gm
Tranconductance, IOUT/ VSENSE
±VSENSE = 10mV, 50mV, 100mV, 150mV, 250mV,
VS Supply = Total Supply + |VSENSE|
AV
Gain, VOUT/ VSENSE
±VSENSE = 100mV, VS Supply = 5V
●
7.76
8
8.24
V/V
Output Voltage Gain Error
±VSENSE = 100mV, VS Supply = 5V
●
–3
1
3
%
VS Supply Rejection Ratio
VSENSE = 0V, VS Supply = 2.5V to 36V (LT1787)
VSENSE = 0V, VS Supply = 2.5V to 60V (LT1787HV)
●
●
120
120
135
135
dB
dB
VEE PSRR Negative Supply Rejection Ratio VSENSE = 0V, VS Supply = 15V, VBIAS = 0V,
VEE = – 1V to – 15V (LT1787)
●
100
130
dB
VSENSE = 0V, VS Supply = 40V, VBIAS = 0V,
VEE = – 1V to – 15V (LT1787HV)
●
100
130
dB
100
100
130
130
dB
dB
VS PSRR
0.5
2
µV/°C
VOS TC
4
nA
●
–600
– 1080
600
1080
µV
µV
●
– 1000
– 1840
1000
1840
µV
µV
µA/V
400
∆VOS
∆VBIAS
Change in Input Offset Voltage
with Change in VBIAS Voltage
VSENSE = 0V, VS Supply = 36V, VBIAS = 0.5V to 25V (LT1787)
●
VSENSE = 0V, VS Supply = 60V, VBIAS = 0.5V to 25V (LT1787HV) ●
IS+(O)
Positive Input Sense Current
VSENSE = 0V
●
10
20
µA
IS–(O)
Negative Input Sense Current
VSENSE = 0V
●
50
100
µA
IEE(O)
Negative Supply Current
VSENSE = 0V
●
60
120
µA
IOUT
Output Current
VSENSE = ±128mV
VOUT
Output Voltage
VSENSE = ±128mV, VS+ ≥ 3.3V
Ripple Rejection
VS+ = VS– = 20V, ∆VS Supply = 1V, f = 1kHz
Minimum Output Voltage
VSENSE = 0V, VBIAS = 0V
VSENSE = VS+ – VS– = –128mV, VBIAS = 0V
VOMIN
VSENSE = 0V, VBIAS = 0V
VSENSE = VS+ – VS– = –128mV, VBIAS = 0V
Unipolar Output
Saturation Voltage
●
●
●
●
●
80
RG1A, RG2A Input Gain-Setting Resistor
Pin 1 to Pin 2, Pin 7 to Pin 8
ROUT
Pin 5 to Pin 6
µA
V
88
dB
30
10
45
mV
mV
30
10
49
mV
mV
32
38
43
49
50
55
60
65
mV
mV
mV
mV
32
38
43
49
54
59
64
69
mV
mV
mV
mV
VS + – 0.75
Maximum Output Voltage
Output Resistor
●
VSENSE = 2mV, VBIAS = 0V
VSENSE = 4mV, VBIAS = 0V
VSENSE = 5mV, VBIAS = 0V
VSENSE = 6mV, VBIAS = 0V
VSENSE = 2mV, VBIAS = 0V
VSENSE = 4mV, VBIAS = 0V
VSENSE = 5mV, VBIAS = 0V
VSENSE = 6mV, VBIAS = 0V
VOMAX
±50
VBIAS ±1.024
V
1.25
kΩ
20
kΩ
1787fc
3
LT1787/LT1787HV
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the temperature range –40°C ≤ TA ≤ 85°C, otherwise specifications are at
TA = 25°C. Total supply = (VS– – VEE) = 2.5V to 36V (LT1787I), 2.5V to 60V (LT1787HVI) unless otherwise specified. (Note 5)
SYMBOL
PARAMETER
VS –, VS +
Sense Amplifier Supply Voltage Single Supply Operation (LT1787)
Single Supply Operation (LT1787HV)
VSENSE
Input Sense Voltage Full Scale
VOS
Input Offset Voltage (S8)
Input Offset Voltage (MS8)
CONDITIONS
MIN
●
●
2.5
2.5
VSENSE = VS+ – VS–, VS = 10V, VBIAS = 5V, AV = 8 ±10%
●
500
IOUT = 0, VS Supply = 5V
– 40°C ≤ TA ≤ 85°C
●
– 75
– 200
IOUT = 0 (LT1787)
– 40°C ≤ TA ≤ 85°C
●
IOUT = 0 (LT1787HV)
– 40°C ≤ TA ≤ 85°C
TYP
MAX
36
60
UNITS
V
V
mV
±40
75
200
µV
µV
– 100
– 225
100
225
µV
µV
●
– 100
– 225
100
225
µV
µV
IOUT = 0, VS Supply = 5V
– 40°C ≤ TA ≤ 85°C
●
– 125
– 250
125
250
µV
µV
IOUT = 0 (LT1787)
– 40°C ≤ TA ≤ 85°C
●
– 150
– 280
150
280
µV
µV
IOUT = 0 (LT1787HV)
– 40°C ≤ TA ≤ 85°C
●
– 150
– 280
150
280
µV
µV
●
±40
0.5
2
µV/°C
VOS TC
Temperature Coefficient of VOS
VS Supply = 5V (Note 6)
IOUT(O)
No-Load Output Current Error
VSENSE = 0V
VOUT(O)
No-Load Output Voltage Error
(S8)
VSENSE = 0V, VS Supply = 5V
– 40°C ≤ TA ≤ 85°C
●
–600
– 1600
600
1600
µV
µV
No-Load Output Voltage Error
(MS8)
VSENSE = 0V, VS Supply = 5V
– 40°C ≤ TA ≤ 85°C
●
– 1000
– 2000
1000
2000
µV
µV
gm
Tranconductance, IOUT/ VSENSE
±VSENSE = 10mV, 50mV, 100mV, 150mV, 250mV,
VS Supply = Total Supply + |VSENSE|
AV
Gain, VOUT/ VSENSE
±VSENSE = 100mV, VS Supply = 5V
●
Output Voltage Gain Error
±VSENSE = 100mV, VS Supply = 5V
●
VS PSRR
VS Supply Rejection Ratio
VSENSE = 0V, VS Supply = 2.5V to 36V (LT1787)
VSENSE = 0V, VS Supply = 2.5V to 60V (LT1787HV)
●
●
VEE PSRR Negative Supply Rejection Ratio VSENSE = 0V, VS Supply = 15V, VBIAS = 0V,
VEE = – 1V to – 15V (LT1787)
●
VSENSE = 0V, VS Supply = 40V, VBIAS = 0V,
VEE = – 1V to – 15V (LT1787HV)
4
nA
µA/V
400
7.76
8
8.24
V/V
–3
1
3
120
120
135
135
dB
dB
100
130
dB
●
100
130
dB
100
100
130
130
dB
dB
%
∆VOS
∆VBIAS
Change in Input Offset Voltage
with Change in VBIAS Voltage
VSENSE = 0V, VS Supply = 36V, VBIAS = 0.5V to 25V (LT1787)
●
VSENSE = 0V, VS Supply = 60V, VBIAS = 0.5V to 25V (LT1787HV) ●
IS+(O)
Positive Input Sense Current
VSENSE = 0V
●
10
20
µA
IS–(O)
Negative Input Sense Current
VSENSE = 0V
●
50
100
µA
IEE(O)
Negative Supply Current
VSENSE = 0V
●
60
120
µA
IOUT
Output Current
VSENSE = ±128mV
VOUT
VOMIN
±50
+ ≥ 3.3V
Output Voltage
VSENSE = ±128mV, VS
Ripple Rejection
VS+ = VS– = 20V, ∆VS Supply = 1V, f = 1kHz
Minimum Output Voltage
VSENSE = 0V, VBIAS = 0V
VSENSE = VS+ – VS– = –128mV, VBIAS = 0V
VSENSE = 0V, VBIAS = 0V
VSENSE = VS+ – VS– = –128mV, VBIAS = 0V
●
●
80
µA
VBIAS ±1.024
V
88
dB
30
10
45
mV
mV
30
10
51
mV
mV
1787fc
4
LT1787/LT1787HV
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the temperature range –40°C ≤ TA ≤ 85°C, otherwise specifications are at
TA = 25°C. Total supply = (VS– – VEE) = 2.5V to 36V (LT1787I), 2.5V to 60V (LT1787HVI) unless otherwise specified. (Note 5)
SYMBOL
PARAMETER
CONDITIONS
Unipolar Output
Saturation Voltage
VSENSE = 2mV, VBIAS = 0V
VSENSE = 4mV, VBIAS = 0V
VSENSE = 5mV, VBIAS = 0V
VSENSE = 6mV, VBIAS = 0V
MIN
VSENSE = 2mV, VBIAS = 0V
VSENSE = 4mV, VBIAS = 0V
VSENSE = 5mV, VBIAS = 0V
VSENSE = 6mV, VBIAS = 0V
VOMAX
●
●
●
●
MAX
32
38
43
49
50
55
60
65
mV
mV
mV
mV
32
38
43
49
56
61
66
71
mV
mV
mV
mV
VS + – 0.75
Maximum Output Voltage
RG1A, RG2A Input Gain-Setting Resistor
Pin 1 to Pin 2, Pin 7 to Pin 8
ROUT
Pin 5 to Pin 6
Output Resistor
TYP
UNITS
V
1.25
kΩ
20
kΩ
The ● denotes the specifications which apply over the temperature range –40°C ≤ TA ≤ 125°C, otherwise specifications are at
TA = 25°C. Total supply = (VS– – VEE) = 2.5V to 36V (LT1787H), 2.5V to 60V (LT1787HVH) unless otherwise specified. (Note 5)
VS –, VS +
Sense Amplifier Supply Voltage Single Supply Operation (LT1787H)
Single Supply Operation (LT1787HVH)
VSENSE
Input Sense Voltage Full Scale
VOS
Input Offset Voltage
●
●
2.5
2.5
VSENSE = VS+ – VS–, VS = 10V, VBIAS = 5V, AV = 8 ±10%
●
500
IOUT = 0, VS Supply = 5V
– 40°C ≤ TA ≤ 125°C
●
– 75
– 400
IOUT = 0 (LT1787H)
– 40°C ≤ TA ≤ 125°C
●
IOUT = 0 (LT1787HVH)
– 40°C ≤ TA ≤ 125°C
●
●
VOS TC
Temperature Coefficient of VOS
VS Supply = 5V (Note 6)
IOUT(O)
No-Load Output Current Error
VSENSE = 0V
VOUT(O)
No-Load Output Voltage Error
VSENSE = 0V, VS Supply = 5V
– 40°C ≤ TA ≤ 125°C
36
60
mV
±40
75
400
µV
µV
– 100
– 550
100
550
µV
µV
– 100
– 550
100
550
µV
µV
0.5
4
4
●
V
V
–600
– 3200
µV/°C
nA
600
3200
µV
µV
gm
Tranconductance, IOUT/ VSENSE
±VSENSE = 10mV, 50mV, 100mV, 150mV, 250mV,
VS Supply = Total Supply + |VSENSE|
AV
Gain, VOUT/ VSENSE
±VSENSE = 100mV, VS Supply = 5V
●
7.76
8
8.24
V/V
Output Voltage Gain Error
±VSENSE = 100mV, VS Supply = 5V
●
–3
1
3
%
VS Supply Rejection Ratio
VSENSE = 0V, VS Supply = 2.5V to 36V (LT1787H)
VSENSE = 0V, VS Supply = 2.5V to 60V (LT1787HVH)
●
●
100
100
130
130
dB
dB
VEE PSRR Negative Supply Rejection Ratio VSENSE = 0V, VS Supply = 15V, VBIAS = 0V,
VEE = – 1V to – 15V (LT1787H)
●
100
130
dB
VSENSE = 0V, VS Supply = 40V, VBIAS = 0V,
VEE = – 1V to – 15V (LT1787HVH)
●
100
130
dB
100
100
130
130
dB
dB
VS PSRR
µA/V
400
∆VOS
∆VBIAS
Change in Input Offset Voltage
with Change in VBIAS Voltage
VSENSE = 0V, VS Supply = 36V, VBIAS = 0.5V to 25V (LT1787H)
●
VSENSE = 0V, VS Supply = 60V, VBIAS = 0.5V to 25V (LT1787HVH) ●
IS+(O)
Positive Input Sense Current
VSENSE = 0V
●
10
25
µA
IS–(O)
Negative Input Sense Current
VSENSE = 0V
●
50
115
µA
IEE(O)
Negative Supply Current
VSENSE = 0V
●
60
140
µA
IOUT
Output Current
VSENSE = ±128mV
VOUT
Output Voltage
VSENSE = ±128mV, VS
Ripple Rejection
VS+
+ ≥ 3.3V
= VS = 20V, ∆VS Supply = 1V, f = 1kHz
–
●
80
±50
µA
VBIAS ±1.024
V
88
dB
1787fc
5
LT1787/LT1787HV
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the temperature range –40°C ≤ TA ≤ 125°C, otherwise specifications are at
TA = 25°C. Total supply = (VS– – VEE) = 2.5V to 36V (LT1787H), 2.5V to 60V (LT1787HVH) unless otherwise specified. (Note 5)
SYMBOL
PARAMETER
CONDITIONS
MIN
VOMIN
Minimum Output Voltage
VSENSE = 0V, VBIAS = 0V
VSENSE = VS+ – VS– = –128mV, VBIAS = 0V
●
VSENSE = 0V, VBIAS = 0V
VSENSE = VS+ – VS– = –128mV, VBIAS = 0V
Unipolar Output
Saturation Voltage
VSENSE = 2mV, VBIAS = 0V
VSENSE = 4mV, VBIAS = 0V
VSENSE = 5mV, VBIAS = 0V
VSENSE = 6mV, VBIAS = 0V
●
●
●
●
VSENSE = 2mV, VBIAS = 0V
VSENSE = 4mV, VBIAS = 0V
VSENSE = 5mV, VBIAS = 0V
VSENSE = 6mV, VBIAS = 0V
VOMAX
MAX
UNITS
30
10
45
mV
mV
30
10
55
mV
mV
32
38
43
49
50
55
60
65
mV
mV
mV
mV
32
38
43
49
60
65
70
75
mV
mV
mV
mV
VS + – 0.75
Maximum Output Voltage
RG1A, RG2A Input Gain-Setting Resistor
Pin 1 to Pin 2, Pin 7 to Pin 8
ROUT
Pin 5 to Pin 6
Output Resistor
TYP
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: ESD (Electrostatic Discharge) sensitive devices. Extensive use of
ESD protection devices are used internal to the LT1787/LT1787HV,
however, high electrostatic discharge can damage or degrade the device.
Use proper ESD handling precautions.
Note 3: The LT1787C/LT1787I are guaranteed functional over the
operating temperature range of –40°C to 85°C. The LT1787H is
V
1.25
kΩ
20
kΩ
guaranteed functional over the operating temperature range of –40°C to
125°C.
Note 4: The LT1787C is guaranteed to meet specified performance from
0°C to 70°C. The LT1787C 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 LT1787I is guaranteed to meet
specified performance from – 40°C to 85°C. The LT1787H is guaranteed to
meet specified performance from –40°C to 125°C.
Note 5: Testing done at VBIAS = 1.25V, VEE = 0V unless otherwise
specified.
Note 6: This parameter is not 100% tested.
U W
TYPICAL PERFORMANCE CHARACTERISTICS
No Load Output Voltage
vs Supply Voltage
50
INPUT OFFSET VOLTAGE (µV)
40
30
20
TA = 85°C
TA = 25°C
–10
–20
–30
VS+ = VS–
VBIAS = 0V
VEE = –1.25V
300
10
0
10
400
OUTPUT VOLTAGE (µV)
VS + = V S –
VBIAS = 0V
VEE = –1.25V
TA = –40°C
No Load Output Current vs
Supply Voltage
200
6
TA = 85°C
100
0
TA = 25°C
–100
–200
–50
0
10
30
40
50
20
TOTAL SUPPLY VOLTAGE (V)
60
1787 G01
–400
TA = 25°C
4
2
0
–2
TA = 85°C
–4
–6
TA = –40°C
–300
–40
TA = –40°C
8
OUTPUT CURRENT (nA)
Input Offset Voltage vs
Supply Voltage
VBIAS = 1V
VEE = 0V
VS + = V S –
–8
–10
0
50
10
20
30
40
TOTAL SUPPLY VOLTAGE (V)
60
1787 G02
0
10
30
40
50
20
TOTAL SUPPLY VOLTAGE (V)
60
1787 G03
1787fc
6
LT1787/LT1787HV
U W
TYPICAL PERFORMANCE CHARACTERISTICS
Input Offset Voltage vs
Temperature
Input Offset Voltage vs
Negative Supply Voltage
50
20
10
0
VS+ = VS–
VBIAS = 0V
VEE = –1.25V
40
TA = 85°C
30
TA = 25°C
–10
TA = –40°C
–20
2.5
2.0
1.5
OUTPUT VOLTAGE (V)
VS+ = VS– = 2.5V
VBIAS = 1V
INPUT OFFSET VOLTAGE (µV)
20
10
0
–10
–20
0
–5
–10
–15
–20
–25
NEGATIVE SUPPLY VOLTAGE (V)
0
20
40
TEMPERATURE (°C)
60
80
85
–250
Gain vs Temperature
1.4
Gain vs Frequency
30
VS = (2.5V + |VSENSE|)TO 60V
VS = 2.5V TO 60V
TA = –40°C TO 85°C
VBIAS = VEE
VSENSE = 10mV
20
8.185
VS+ > VS–
1.0
250
1787 G06
8.195
1.2
–150
50
150
–50
SENSE VOLTAGE (VS+ – VS–) (mV)
1787 G05
Output Voltage vs Sense Voltage
(Unidirectional Mode)
10
0.8
0.6
GAIN (dB)
8.175
GAIN (V/V)
OUPUT VOLTAGE (V)
–1.0
–2.5
–20
1787 G04
8.165
8.155
0.4
0
–10
–20
VS+ < VS–
–30
8.145
0.2
–40
0
0
30
60
90
120
SENSE VOLTAGE (VS+ – VS–) (mV)
150
8.135
–40
–20
0
20
40
TEMPERATURE (°C)
–50
0.1k
80
85
60
NEGATIVE INPUT SENSE CURRENT (µA)
65
TA = 25°C
60
TA = –40°C
55
50
45
VS+ = VS–
40
0
20
30
40
50
10
TOTAL SUPPLY VOLTAGE (V)
60
1787 G10
110
90
80
60
TA = 85°C
TA = 25°C
50
40
100M
60
VS = (2.5V + |VSENSE |) TO 60V
100
70
10M
Positive Input Sense Current vs
Sense Voltage
120
75
TA = 85°C
10k 100k
1M
FREQUENCY (Hz)
1787 G09
Negative Input Sense Current vs
Sense Voltage
Supply Current vs Supply Voltage
70
1k
1787 G08
1787 G07
SUPPLY CURRENT (µA)
–0.5
–2.0
–50
–40
–30
0.5
VBIAS
–1.5
–30
–40
–30
VS = 5.5V TO 60V
VBIAS = 2.5V
VEE = 0V
1.0
TA = –40°C
30
–128 –96 –64 –32 0
32 64 96
SENSE VOLTAGE (VS+ – VS–) (mV)
128
1787 G11
POSITIVE INPUT SENSE CURRENT (µA)
INPUT OFFSET VOLTAGE (µV)
30
Output Voltage vs Sense Voltage
(Bidirectional Mode)
VS = (2.5V + |VSENSE |) TO 60V
50
40
TA = 85°C
30
20
TA = 25°C
TA = –40°C
10
0
–128 –96 –64 –32 0
32 64 96
SENSE VOLTAGE (VS+ – VS–) (mV)
128
1787 G17
1787fc
7
LT1787/LT1787HV
U W
TYPICAL PERFORMANCE CHARACTERISTICS
Step Response at
VSENSE = 0V to 10mV
Step Response at
VSENSE = 0V to 128mV
Step Response at
VSENSE = 0V to 128mV
10mV
100mV
100mV
0V
0V
0V
80mV
1V
1V
500mV
500mV
0V
0V
0V
COUT = 0pF
COUT = 0pF
1787 G12
Step Response at
VSENSE = 0V to –128mV
COUT = 1000pF
1787 G18
Step Response at
VSENSE = 0V to –128mV
Step Response at
VSENSE = – 128mV to 128mV
0V
0V
– 100mV
–100mV
100mV
0V
– 100mV
1V
0V
0V
– 500mV
–500mV
0V
– 1V
–1V
–1V
COUT = 1000pF
1787 G19
Step Response at
VSENSE = 128mV to –128mV
VOUT Error vs Supply Ripple
Voltage (VSENSE = ±128mV)
16
900
14
1V
0V
–1V
1787 G15
SUPPLY RIPPLE VOLTAGE (mV)
–100mV
12
800
700
600
500
0.5%
400
5%
1%
300
200
VOUT ERROR
LESS THAN 0.1%
2%
10
VS– = 18V
VBIAS = 0V
VEE = –18V
8
6
4
2
0
–2
–4
100
0
100
1787 G20
Output Voltage vs Sense Voltage
1000
100mV
COUT = 2200pF
COUT = 0
1787 G14
OUTPUT VOLTAGE (V)
COUT = 0
1787 G13
–6
–8
1k
10k
100k
FREQUENCY (Hz)
1M
1787 G16
0.4 0.8 1.2 1.6
0
–0.8 –0.4
SENSE VOLTAGE (VS+ – VS–) (V)
2.0
1787 G21
1787fc
8
LT1787/LT1787HV
U
U
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PIN FUNCTIONS
FIL–, FIL+ (Pins 1, 8): Negative and Positive Filter Terminals. Differential mode noise can be filtered by connecting
a capacitor across FIL– and FIL+ . Pole frequency
f– 3dB = 1/(2πRC), R = 1.25kΩ.
where:
VOUT > VBIAS for VS+ > VS–
VOUT < VBIAS for VS+ < VS–
VOUT(O) is the no load output voltage at VSENSE = 0V.
VS – (Pin 2): Negative Input Sense Terminal. Negative
sense voltage will result in an output sinking current
proportional to the sense current. VS – is connected to an
internal gain-setting resistor RG1A and supplies bias current to the internal amplifier.
VBIAS (Pin 6): Output Bias Pin. For single supply, bidirectional current sensing operation, VBIAS is connected to an
external bias voltage, so that at VSENSE = 0V, VOUT =
VOUT(O) + VBIAS. For dual supply, bidirectional current
sensing operation, VBIAS is connected to ground. Thus,
VOUT = VOUT(O) at VSENSE = 0V.
DNC (Pin 3): Do Not Connect. Connected internally. Do not
connect external circuitry to this pin.
VS+ (Pin 7): Positive Input Sense Terminal. Positive sense
voltage will result in an output sourcing current proportional to the sense current. VS+ is connected to an internal
gain-setting resistor RG2A. Connecting a supply to VS+ and
a load to VS– will allow the LT1787 to measure its own
supply current.
VEE (Pin 4): Negative Supply or Ground for Single Supply
Operation.
VOUT (Pin 5): Voltage Output or Current Output proportional to the magnitude of the sense current flowing
through RSENSE. For bidirectional current sensing operation, VOUT = AV • VSENSE + VOUT(O) + VBIAS,
W
BLOCK DIAGRAM
RSENSE
VS –
ISENSE
RG1A
1.25k
VS+
RG2A
1.25k
FIL–
FIL+
RG2B
1.25k
RG1B
1.25k
–
+
A1
IOUT
VBIAS
Q1
Q2
ROUT
20k
VOUT
VEE
CURRENT MIRROR
1787 F 01
Figure 1. LT1787 Functional Diagram
1787fc
9
LT1787/LT1787HV
U
W
U
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APPLICATIONS INFORMATION
The LT1787 high side current sense amplifier (Figure 1)
provides accurate bidirectional monitoring of current
through a user-selected sense resistor. The sense voltage
is amplified by a fixed gain of 8 and level shifted from the
positive power supply to the ground referenced outputs.
The output signal may be used in a variety of ways to
interface with subsequent signal processing circuitry.
Input and output filtering are easily implemented to eliminate aliasing errors.
Theory of Operation
Inputs VS+ and VS– apply the sense voltage to matched
resistors RG1 and RG2. The opposite ends of resistors RG1
and RG2 are forced to be at equal potentials by the voltage
gain of amplifier A1. The currents through RG1 and RG2 are
forced to flow through transistors Q1 and Q2 and are
summed at node VOUT by the 1:1 current mirror. The net
current from RG1 and RG2 flowing through resistor ROUT
gives a voltage gain of eight. Positive sense voltages result
in VOUT being positive with respect to pin VBIAS.
Pins VEE, VBIAS and VOUT may be connected in a variety of
ways to interface with subsequent circuitry. Split supply
and single supply output configurations are shown in the
following sections.
Supply current for amplifier A1 is drawn from the VS– pin.
The user may choose to include this current in the monitored current through RSENSE by careful choice of connection polarity.
Selection of External Current Sense Resistor
External RSENSE resistor selection is a delicate trade-off
between power dissipation in the resistor and current
measurement accuracy. The LT1787 makes this decision
less difficult than with competitors’ products. The maximum sense voltage may be as large as ±500mV to get
maximum resolution, however, high current applications
will not want to suffer this much power dissipation in the
sense resistor. The LT1787’s input offset voltage of 40µV
gives high resolution for low sense voltages. This wide
operating dynamic range gives the user wide latitude in
tailoring the range and resolution of his supply monitoring
function.
Kelvin connection of the LT1787’s VS+ and VS– inputs to
the sense resistor should be used in all but the lowest
power applications. Solder connections and PC board
interconnect resistance (approximately 0.5mΩ per square)
can be a large error in high current systems. A 5-Amp
application might choose a 20mΩ sense resistor to give a
100mV full-scale input to the LT1787. Input offset voltage
will limit resolution to 2mA. Neglecting contact resistance
at solder joints, even one square of PC board copper at
each resistor end will cause an error of 5%. This error will
grow proportionately higher as monitored current levels
rise to tens or hundreds of amperes.
Input Noise Filtering
The LT1787 provides input signal filtering pins FIL+ and
FIL– that are internally connected to the midpoint taps of
resistors RG1 and RG2. These pins may be used to filter the
input signal entering the LT1787’s internal amplifier, and
should be used when fast current ripple or transients may
flow through the sense resistor. High frequency signals
above the 300kHz bandwidth of the LT1787’s internal
amplifier will cause errors. A capacitor connected between
FIL+ and FIL– creates a single pole low pass filter with
corner frequency:
f –3dB = 1/(2πRC)
where R = 1.25k. A 0.01µF capacitor creates a pole at
12.7kHz, a good choice for many applications.
Common mode filtering from the FIL+ and FIL– pins should
not be attempted, as mismatch in the capacitors from FIL+
and FIL– will create AC common mode errors. Common
mode filtering must be done at the power supply output.
Output Signal Range
The LT1787’s output signal is developed by summing the
net currents through RG1 and RG2 into output resistor
ROUT. The pins VOUT and VBIAS may be connected in
numerous configurations to interface with following circuitry in either single supply or split supply applications.
Care must be used in connecting the output pins to
preserve signal accuracy. Limitations on the signal swing
at VOUT are imposed by the negative supply, VEE, and the
input voltage VS+. In the negative direction, internal circuit
saturation with loss of accuracy occurs for VOUT < 70mV
1787fc
10
LT1787/LT1787HV
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APPLICATIONS INFORMATION
with absolute minimum swing at 30mV above VEE. VOUT
may swing positive to within 0.75V of VS+ or a maximum
of 35V, a limit set by internal junction breakdown. Within
these contraints, an amplified, level shifted representation
of the RSENSE voltage is developed across ROUT.
1.5
OUTPUT VOLTAGE (V)
1.0
Split Supply Bipolar Output Swing
Figure 2 shows the LT1787 used with split power supplies.
The VBIAS pin is connected to ground, and the output
signal appears at the VOUT pin. Bidirectional input currents
can be monitored with the output swinging positive for
current flow from VS+ and VS–. Input currents in the
opposite direction cause VOUT to swing below ground.
Figure 2 shows an optional output capacitor connected
from VOUT to ground. This capacitor may be used to filter
the output signal before it is processed by other
circuitry.Figure 3 shows the voltage transfer function of
the LT1787 used in this configuration.
VS = 3.3V TO 60V
TA = – 40°C TO 85°C
0.5
0
–0.5
–1.0
–1.5
–128 –96 –64 –32 0
32 64 96
SENSE VOLTAGE (VS+ – VS–) (mV)
1787 F03
Figure 3. Split Supply Output Voltage
RSENSE
TO
CHARGER/
LOAD
1
FIL–
–
2 VS
Single Supply with Shifted VBIAS
3
RSENSE
TO
CHARGER/
LOAD
1
FIL–
2
VS–
3
DNC
FIL+
LT1787
C1
1µF
8
15V
VS+ 7
VBIAS 6
ROUT
4
C2
1µF
–5V
VEE
5
VOUT
OUTPUT
C3*
1000pF
1787 F02
*OPTIONAL
Figure 2. Split Supply Operation
DNC
FIL+
LT1787HV
+
VS
VEE
*OPTIONAL
3.3V
TO
60V
C1
1µF
8
3.3V
7
20k
5%
VBIAS 6
ROUT
4
C2
1µF
5
VOUT
LT1634-1.25
C3*
1000pF
OUTPUT
1787 F04
Figure 4. Charge/Discharge Current Monitor on
Single Supply with VBIAS = 1.25V
OUTPUT VOLTAGE – OUTPUT BIAS VOLTAGE (V)
Figure 4 shows the LT1787 used in a single supply mode
with the VBIAS pin shifted positive using an external
LT1634 voltage reference. The VOUT output signal can
swing above and below VBIAS to allow monitoring of
positive or negative currents through the sense resistor,
as shown in Figure 5. The choice of reference voltage is not
critical except for the precaution that adequate headroom
must be provided for VOUT to swing without saturating the
internal circuitry. The component values shown in Figure 4
allow operation with VS supplies as low as 3.1V.
128
1.5
1.0
VS = 3.3V TO 60V
TA = – 40°C TO 85°C
0.5
0
–0.5
–1.0
–1.5
–128 –96 –64 –32 0
32 64 96
SENSE VOLTAGE (VS+ – VS–) (mV)
128
1787 F05
Figure 5. Single Supply Output Voltage
with VBIAS = 1.25V
1787fc
11
LT1787/LT1787HV
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APPLICATIONS INFORMATION
RSENSE
Operation with A/D Converter
Figure 6 shows the LT1787 operating with the LTC1286
A/D converter. This low cost circuit is capable of 12-bit
resolution of unipolar currents. The – IN pin of the A/D
converter is biased at 1V by the resistor divider R1 and R2.
This voltage increases as sense current increases, with the
amplified sense voltage appearing between the A/D converters –IN and +IN terminals. The front page of the data
sheet shows a similar circuit which uses a voltage reference for improved accuracy and signal range. The LTC1286
converter uses sequential sampling of its –IN and +IN
inputs. Accuracy is degraded if the inputs move between
sampling intervals. A filter capacitor from FIL+ to FIL– as
well as a filter capacitor from VBIAS to VOUT may be
necessary if the sensed current changes more than 1LSB
within a conversion cycle.
Buffered Output Operation
Figure 7 shows the LT1787’s outputs buffered by an
operational amplifier configured as an I/V converter. This
configuration is ideal for monitoring very low voltage
supplies. The LT1787’s VOUT pin is held equal to the
reference voltage appearing at the op amp’s noninverting
input. This allows monitoring VS supplies as low as 2.5V.
The op amp’s output may swing from ground to its positive
supply voltage. The low impedance output of the op amp
may drive following circuitry more effectively than the high
output impedance of the LT1787. The I/V converter configuration also works well with split supply voltages.
5V
1
FIL
–
2 VS
3
4
LT1787
VS+ 7
ROUT
VEE
5V
R1
20k
5%
VBIAS 6 IOUT
DNC
VCC
CS
LTC1286 CLK
–IN
D
VREF GND OUT
5
+IN
VOUT
R2
5k
5%
TO µP
1787 F06
Figure 6. Unidirectional Output into A/D
with Fixed Supply at VS+
ISENSE
RSENSE
TO
CHARGER/
LOAD
1
FIL–
–
2 VS
3
4
C1
1µF
8
FIL+
LT1787
2.5V + VSENSE(MAX)
VS+ 7
2.5V
VBIAS 6
DNC
ROUT
VEE
C3
1000pF
5
VOUT
–
VOUT A
A1
+
2.5V
1M
5%
LT1495
LT1389-1.25
1787 F07
Figure 7. Single Supply 2.5V Bidirectional Operation
with External Voltage Reference and I/V Converter
Single Supply Unidirectional Operation
Figure 8 shows the simplest connection in which the
LT1787 may be used. The VBIAS pin is connected to
ground, and the VOUT pin swings positive with increasing
sense current. The LT1787’s outputs can swing as low as
30mV as shown in Figure 9. Accuracy is sacrificed at small
output levels, but this is not a limitation in protection
circuit applications or where sensed currents do not vary
greatly. Increased low level accuracy can be obtained by
level shifting VBIAS above ground. The level shifting may be
done with resistor dividers, voltage references or a simple
diode. Accuracy is ensured if the output signal is sensed
differentially between VBIAS and VOUT.
C1
1µF
8
FIL+
–
RSENSE
TO
LOAD
2.5V TO
60V
C
0.1µF
8
FIL+
LT1787HV
–
VS+ 7
2 VS
1
3
4
FIL–
DNC
VBIAS 6
ROUT
VEE
VOUT
5
VOUT
1787 F08
Figure 8. Unidirectional Current Sensing Mode
1787fc
12
LT1787/LT1787HV
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APPLICATIONS INFORMATION
resistor. When an external resistor is used, leave the VBIAS
pin floating or connected to the VOUT pin. This will remove
the internal ROUT from the circuit.
0.30
OUTPUT VOLTAGE (V)
0.25
0.20
The voltage gain will be gm • ROUT where gm is the
LT1787’s transconductance, 400µA/V typical. A nominal
gain of 40 may be obtained with an external 100k resistor
used in place of the internal 20k ROUT:
0.15
0.10
AV = gm • ROUT = 400µA/V • 100k = 40
0.05
0
IDEAL
0
0.005 0.010 0.015 0.020
VS+ – VS– (V)
0.025 0.030
1787 F09
Figure 9. Expanded Scale of Unidirectional Output
Adjusting Gain Setting
The LT1787 may be used in all operating modes with an
external resistor used in place of the internal 20k ROUT
The transconductance gm is set by on-chip resistors on
the LT1787. These resistors match well but have loose
absolute tolerance. This will normally require that the
external gain setting resistor be trimmed for initial accuracy. After trimming, the temperature stability of the gm
and therefore gain will be –200ppm/°C.
The only limitations placed upon the resistor choice is care
must be taken not to saturate the internal circuitry by
violating the VOMAX specification of VS + –0.75V.
1787fc
13
LT1787/LT1787HV
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PACKAGE DESCRIPTION
MS8 Package
8-Lead Plastic MSOP
(LTC DWG # 05-08-1660)
0.889 ± 0.127
(.035 ± .005)
5.23
(.206)
MIN
3.20 – 3.45
(.126 – .136)
0.42 ± 0.038
(.0165 ± .0015)
TYP
3.00 ± 0.102
(.118 ± .004)
(NOTE 3)
0.65
(.0256)
BSC
8
7 6 5
0.52
(.0205)
REF
RECOMMENDED SOLDER PAD LAYOUT
0.254
(.010)
3.00 ± 0.102
(.118 ± .004)
(NOTE 4)
4.90 ± 0.152
(.193 ± .006)
DETAIL “A”
0° – 6° TYP
GAUGE PLANE
0.53 ± 0.152
(.021 ± .006)
DETAIL “A”
1
2 3
4
1.10
(.043)
MAX
0.86
(.034)
REF
0.18
(.007)
SEATING
PLANE
0.22 – 0.38
(.009 – .015)
TYP
0.65
(.0256)
BSC
0.127 ± 0.076
(.005 ± .003)
MSOP (MS8) 0204
NOTE:
1. DIMENSIONS IN MILLIMETER/(INCH)
2. DRAWING NOT TO SCALE
3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.
MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
1787fc
14
LT1787/LT1787HV
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PACKAGE DESCRIPTION
S8 Package
8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
.189 – .197
(4.801 – 5.004)
NOTE 3
.045 ±.005
.050 BSC
8
.245
MIN
7
6
5
.160 ±.005
.150 – .157
(3.810 – 3.988)
NOTE 3
.228 – .244
(5.791 – 6.197)
.030 ±.005
TYP
1
RECOMMENDED SOLDER PAD LAYOUT
.010 – .020
× 45°
(0.254 – 0.508)
.008 – .010
(0.203 – 0.254)
3
4
.053 – .069
(1.346 – 1.752)
.004 – .010
(0.101 – 0.254)
0°– 8° TYP
.016 – .050
(0.406 – 1.270)
NOTE:
1. DIMENSIONS IN
2
.014 – .019
(0.355 – 0.483)
TYP
INCHES
(MILLIMETERS)
2. DRAWING NOT TO SCALE
3. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .006" (0.15mm)
.050
(1.270)
BSC
SO8 0303
1787fc
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.
15
LT1787/LT1787HV
U
TYPICAL APPLICATION
Split or Single Supply Operation, Bidirectional Output into A/D
1Ω
1%
IS = ±125mA
VSRCE
≈4.75V
1
–
2 VS
3
VCC
5V
8
FIL+
FIL–
LT1787
VS+ 7
10µF
16V
VBIAS 6
DNC
20k
VEE 4
VEE
–5V
VOUT
1
VOUT (±1V)
5
OPTIONAL SINGLE
SUPPLY OPERATION:
DISCONNECT VBIAS
FROM GROUND
AND CONNECT IT TO VREF.
REPLACE –5V SUPPLY
WITH GROUND.
OUTPUT CODE FOR ZERO
CURRENT WILL BE ~2430
CONV
7
2
6
AIN LTC1404 CLK
VREF
5
DOUT
GND
10µF
16V
4
8
3
10µF
16V
VEE
–5V
CLOCKING
CIRCUITRY
DOUT
1787 TA02
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC1043
Dual Precision Instrumentation Switched Capacitor Building Block
120dB CMRR, 3V to 18V Operation
LT1490/LT1491
Dual and Quad Micropower Rail-to-Rail Input and Output Op Amps
50µA Amplifier, 2.7V to 40V Operation,
Over-The-TopTM Inputs
LT1620/LT1621
Rail-to-Rail Current Sense Amplifiers
Accurate Output Current Programming, Battery
Charging to 32V
Over-The-Top is a trademark of Linear Technology Corporation.
1787fc
16
Linear Technology Corporation
LT 0606 REV C • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
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