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LT1787/LT1787HV Precision, High Side Current Sense Amplifiers
FEATURES

DESCRIPTIO
Input Offset Voltage: 75V (Max) 60V Supply Operation (LT1787HV) 12-Bit Dynamic Range Operating Current: 60A User-Selectable External Sense Resistor Bidirectional High Side Current Sensing Unidirectional or Bidirectional Output Input Noise Filtering -40C to 125C Operating Temperature Range Available in 8-Lead SO and MSOP Packages
APPLICATIO S

Battery Monitoring Power Monitoring Portable Phones Cellular Phones Portable Test/Measurement Systems Battery-Operated Systems
The LT (R)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 40V 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 60A and are available in 8-lead SO and MSOP packages.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners.
TYPICAL APPLICATIO
12-Bit Dynamic Resolution Unidirectional Output into LTC(R)1286 ADC
TO LOAD I = 100A 1 FIL- LT1787HV RSENSE 0.0016 FIL+ 8 2.5V TO 60V
INPUT OFFSET VOLTAGE (V)
50 40 30 20 10 0 -10 -20 -30 -40 -50 0 10 30 40 50 20 TOTAL SUPPLY VOLTAGE (V) 60
- 2 VS
VS+ 7
3 4
DNC VEE
VBIAS 6 ROUT 20k VOUT C2 0.1F 5
R1 15k
C1 1F VREF VCC CS +IN LTC1286 CLK -IN D GND OUT
5V
TO P
VOUT = VBIAS + (8 * ILOAD * RSENSE)
LT1634-1.25
1787 TA01
U
Input Offset Voltage vs Supply Voltage
1787 TA01b
U
U
1787fc
1
LT1787/LT1787HV
ABSOLUTE MAXIMUM RATINGS
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 ............................................. - 40C to 85C LT1787I .............................................. - 40C to 85C LT1787H .......................................... - 40C to 125C
PACKAGE/ORDER INFORMATION
TOP VIEW
TOP VIEW
FIL- V S- DNC* VEE FIL+ V S+ VBIAS VOUT
1 2 3 4
8 7 6 5
MS8 PACKAGE 8-LEAD PLASTIC MSOP
* DO NOT CONNECT TJMAX = 150C, JA = 250C/ W
ORDER PART NUMBER LT1787CMS8 LT1787IMS8 LT1787HVCMS8 LT1787HVIMS8
MS8 PART MARKING LTGM LTGN LTKJ LTKK
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.
(Note 5) The denotes the specifications which apply over the temperature range 0C TA 70C, otherwise specifications are at TA = 25C. Total supply = (VS- - VEE) = 2.5V to 36V (LT1787C), 2.5V to 60V (LT1787HVC) unless otherwise specified.
SYMBOL VS -, VS + VSENSE VOS PARAMETER CONDITIONS

ELECTRICAL CHARACTERISTICS
Sense Amplifier Supply Voltage Single Supply Operation (LT1787) Single Supply Operation (LT1787HV) Input Sense Voltage Full Scale Input Offset Voltage (S8) VSENSE = VS+ - VS-, VS = 10V, VBIAS = 5V, AV = 8 10% IOUT = 0, VS Supply = 5V 0C TA 70C IOUT = 0 (LT1787) 0C TA 70C IOUT = 0 (LT1787HV) 0C TA 70C
2
U
U
W
WW U
W
(Notes 1, 2)
Specified Temperature Range (Note 4) LT1787C ............................................. - 40C to 85C LT1787I .............................................. - 40C to 85C LT1787H .......................................... - 40C to 125C Storage Temperature Range ..................-65C to 150C Lead Temperature (Soldering, 10 sec).................. 300C
FIL- 1 VS-
2
8 7 6 5
FIL+ VS+ VBIAS VOUT
DNC* 3 VEE 4
S8 PACKAGE 8-LEAD PLASTIC SO
* DO NOT CONNECT TJMAX = 150C, JA = 190C/ W
ORDER PART NUMBER LT1787CS8 LT1787IS8 LT1787HS8 LT1787HVCS8 LT1787HVIS8 LT1787HVHS8
S8 PART MARKING 1787 1787I 1787H 1787HV 787HVI 787HVH
MIN 2.5 2.5 500 - 75 - 135 - 100 - 160 - 100 - 160
TYP
MAX 36 60
UNITS V V mV V V V V V V
1787fc
40
75 135 100 160 100 160
LT1787/LT1787HV
ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER Input Offset Voltage (MS8)
(Note 5) The denotes the specifications which apply over the temperature range 0C TA 70C, otherwise specifications are at TA = 25C. Total supply = (VS - - VEE) = 2.5V to 36V (LT1787C), 2.5V to 60V (LT1787HVC) unless otherwise specified.
CONDITIONS IOUT = 0, VS Supply = 5V 0C TA 70C IOUT = 0 (LT1787) 0C TA 70C IOUT = 0 (LT1787HV) 0C TA 70C MIN - 125 - 230 - 150 - 250 - 150 - 250 0.5 4

TYP 40

MAX 125 230 150 250 150 250 2 600 1080 1000 1840
UNITS V V V V V V V/C nA V V V V A/V
VOS TC IOUT(O) VOUT(O)
Temperature Coefficient of VOS No-Load Output Current Error No-Load Output Voltage Error (S8) No-Load Output Voltage Error (MS8)
VS Supply = 5V (Note 6) VSENSE = 0V VSENSE = 0V, VS Supply = 5V 0C TA 70C VSENSE = 0V, VS Supply = 5V 0C TA 70C VSENSE = 10mV, 50mV, 100mV, 150mV, 250mV, VS Supply = Total Supply + |VSENSE| VSENSE = 100mV, VS Supply = 5V VSENSE = 100mV, VS Supply = 5V VSENSE = 0V, VS Supply = 2.5V to 36V (LT1787) VSENSE = 0V, VS Supply = 2.5V to 60V (LT1787HV)
-600 - 1080 - 1000 - 1840 400
gm AV VS PSRR
Tranconductance, IOUT/ VSENSE Gain, VOUT/ VSENSE Output Voltage Gain Error VS Supply Rejection Ratio

7.76 -3 120 120 100 100 100 100
8 1 135 135 130 130 130 130 10 50 60 50 VBIAS 1.024
8.24 3
V/V % dB dB dB dB dB dB
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) VOS VBIAS IS+(O) IS-(O) IEE(O) IOUT VOUT VOMIN Change in Input Offset Voltage with Change in VBIAS Voltage Positive Input Sense Current Negative Input Sense Current Negative Supply Current Output Current Output Voltage Ripple Rejection Minimum Output Voltage
VSENSE = 0V, VS Supply = 36V, VBIAS = 0.5V to 25V (LT1787) VSENSE = 0V, VS Supply = 60V, VBIAS = 0.5V to 25V (LT1787HV) VSENSE = 0V VSENSE = 0V VSENSE = 0V VSENSE = 128mV VSENSE = 128mV, VS+ 3.3V VS+ = VS- = 20V, VS Supply = 1V, f = 1kHz VSENSE = 0V, VBIAS = 0V VSENSE = VS+ - VS- = -128mV, VBIAS = 0V VSENSE = 0V, VBIAS = 0V VSENSE = VS+ - VS- = -128mV, VBIAS = 0V

20 100 120
A A A A V dB
80
88 30 10 30 10 32 38 43 49 45 49 50 55 60 65 54 59 64 69
mV mV mV mV mV mV mV mV mV mV mV mV V k k
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

32 38 43 49 VS + - 0.75 1.25 20
VOMAX ROUT
Maximum Output Voltage Pin 1 to Pin 2, Pin 7 to Pin 8 Pin 5 to Pin 6 Output Resistor
RG1A, RG2A Input Gain-Setting Resistor
1787fc
3
LT1787/LT1787HV
ELECTRICAL CHARACTERISTICS
SYMBOL VS -, VS + VSENSE VOS PARAMETER CONDITIONS

The denotes the specifications which apply over the temperature range -40C TA 85C, otherwise specifications are at TA = 25C. Total supply = (VS- - VEE) = 2.5V to 36V (LT1787I), 2.5V to 60V (LT1787HVI) unless otherwise specified. (Note 5)
MIN 2.5 2.5 500 - 75 - 200 - 100 - 225 - 100 - 225 - 125 - 250 - 150 - 280 - 150 - 280 0.5 4

TYP
MAX 36 60
UNITS V V mV V V V V V V V V V V V V V/C nA V V V V A/V
Sense Amplifier Supply Voltage Single Supply Operation (LT1787) Single Supply Operation (LT1787HV) Input Sense Voltage Full Scale Input Offset Voltage (S8) VSENSE = VS+ - VS-, VS = 10V, VBIAS = 5V, AV = 8 10% IOUT = 0, VS Supply = 5V - 40C TA 85C IOUT = 0 (LT1787) - 40C TA 85C IOUT = 0 (LT1787HV) - 40C TA 85C Input Offset Voltage (MS8) IOUT = 0, VS Supply = 5V - 40C TA 85C IOUT = 0 (LT1787) - 40C TA 85C IOUT = 0 (LT1787HV) - 40C TA 85C
40
75 200 100 225 100 225
40
125 250 150 280 150 280 2 600 1600 1000 2000
VOS TC IOUT(O) VOUT(O)
Temperature Coefficient of VOS No-Load Output Current Error No-Load Output Voltage Error (S8) No-Load Output Voltage Error (MS8)
VS Supply = 5V (Note 6) VSENSE = 0V VSENSE = 0V, VS Supply = 5V - 40C TA 85C VSENSE = 0V, VS Supply = 5V - 40C TA 85C VSENSE = 10mV, 50mV, 100mV, 150mV, 250mV, VS Supply = Total Supply + |VSENSE| VSENSE = 100mV, VS Supply = 5V VSENSE = 100mV, VS Supply = 5V VSENSE = 0V, VS Supply = 2.5V to 36V (LT1787) VSENSE = 0V, VS Supply = 2.5V to 60V (LT1787HV)
-600 - 1600 - 1000 - 2000 400
gm AV VS PSRR
Tranconductance, IOUT/ VSENSE Gain, VOUT/ VSENSE Output Voltage Gain Error VS Supply Rejection Ratio

7.76 -3 120 120 100 100 100 100
8 1 135 135 130 130 130 130 10 50 60 50 VBIAS 1.024
8.24 3
V/V % dB dB dB dB dB dB
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) VOS VBIAS IS+(O) IS-(O) IEE(O) IOUT VOUT VOMIN Change in Input Offset Voltage with Change in VBIAS Voltage Positive Input Sense Current Negative Input Sense Current Negative Supply Current Output Current Output Voltage Ripple Rejection Minimum Output Voltage
VSENSE = 0V, VS Supply = 36V, VBIAS = 0.5V to 25V (LT1787) VSENSE = 0V, VS Supply = 60V, VBIAS = 0.5V to 25V (LT1787HV) VSENSE = 0V VSENSE = 0V VSENSE = 0V VSENSE = 128mV VSENSE = 128mV, VS
+ 3.3V

20 100 120
A A A A V dB
VS+ = VS- = 20V, VS Supply = 1V, f = 1kHz VSENSE = 0V, VBIAS = 0V VSENSE = VS+ - VS- = -128mV, VBIAS = 0V VSENSE = 0V, VBIAS = 0V VSENSE = VS+ - VS- = -128mV, VBIAS = 0V
80
88 30 10 45 51
mV mV mV mV
30 10
1787fc
4
LT1787/LT1787HV
The denotes the specifications which apply over the temperature range -40C TA 85C, otherwise specifications are at TA = 25C. Total supply = (VS- - VEE) = 2.5V to 36V (LT1787I), 2.5V to 60V (LT1787HVI) unless otherwise specified. (Note 5)
SYMBOL PARAMETER Unipolar Output Saturation Voltage CONDITIONS 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 ROUT Maximum Output Voltage Pin 1 to Pin 2, Pin 7 to Pin 8 Pin 5 to Pin 6 Output Resistor RG1A, RG2A Input Gain-Setting Resistor

ELECTRICAL CHARACTERISTICS
MIN
TYP 32 38 43 49 32 38 43 49 VS + - 0.75 1.25 20
MAX 50 55 60 65 56 61 66 71
UNITS mV mV mV mV mV mV mV mV V k k
The denotes the specifications which apply over the temperature range -40C TA 125C, otherwise specifications are at TA = 25C. Total supply = (VS- - VEE) = 2.5V to 36V (LT1787H), 2.5V to 60V (LT1787HVH) unless otherwise specified. (Note 5)
VS -, VS + VSENSE VOS Sense Amplifier Supply Voltage Single Supply Operation (LT1787H) Single Supply Operation (LT1787HVH) Input Sense Voltage Full Scale Input Offset Voltage VSENSE = VS+ - VS-, VS = 10V, VBIAS = 5V, AV = 8 10% IOUT = 0, VS Supply = 5V - 40C TA 125C IOUT = 0 (LT1787H) - 40C TA 125C IOUT = 0 (LT1787HVH) - 40C TA 125C VOS TC IOUT(O) VOUT(O) gm AV VS PSRR Temperature Coefficient of VOS No-Load Output Current Error No-Load Output Voltage Error Tranconductance, IOUT/ VSENSE Gain, VOUT/ VSENSE Output Voltage Gain Error VS Supply Rejection Ratio VS Supply = 5V (Note 6) VSENSE = 0V VSENSE = 0V, VS Supply = 5V - 40C TA 125C VSENSE = 10mV, 50mV, 100mV, 150mV, 250mV, VS Supply = Total Supply + |VSENSE| VSENSE = 100mV, VS Supply = 5V VSENSE = 100mV, VS Supply = 5V VSENSE = 0V, VS Supply = 2.5V to 36V (LT1787H) VSENSE = 0V, VS Supply = 2.5V to 60V (LT1787HVH)

2.5 2.5 500 - 75 - 400 - 100 - 550 - 100 - 550 0.5 4 -600 - 3200 400 7.76 -3 100 100 100 100 100 100 8 1 130 130 130 130 130 130 10 50 60 50 VBIAS 1.024 40
36 60 75 400 100 550 100 550 4 600 3200
V V mV V V V V V V V/C nA V V A/V
8.24 3
V/V % dB dB dB dB dB dB
VEE PSRR Negative Supply Rejection Ratio VSENSE = 0V, VS Supply = 15V, VBIAS = 0V, VEE = - 1V to - 15V (LT1787H) VSENSE = 0V, VS Supply = 40V, VBIAS = 0V, VEE = - 1V to - 15V (LT1787HVH) VOS VBIAS IS+(O) IS-(O) IEE(O) IOUT VOUT Change in Input Offset Voltage with Change in VBIAS Voltage Positive Input Sense Current Negative Input Sense Current Negative Supply Current Output Current Output Voltage Ripple Rejection
VSENSE = 0V, VS Supply = 36V, VBIAS = 0.5V to 25V (LT1787H) VSENSE = 0V, VS Supply = 60V, VBIAS = 0.5V to 25V (LT1787HVH) VSENSE = 0V VSENSE = 0V VSENSE = 0V VSENSE = 128mV VSENSE = 128mV, VS VS+
- + 3.3V

25 115 140
A A A A V dB
1787fc
= VS = 20V, VS Supply = 1V, f = 1kHz
80
88
5
LT1787/LT1787HV
The denotes the specifications which apply over the temperature range -40C TA 125C, otherwise specifications are at TA = 25C. Total supply = (VS- - VEE) = 2.5V to 36V (LT1787H), 2.5V to 60V (LT1787HVH) unless otherwise specified. (Note 5)
SYMBOL VOMIN PARAMETER Minimum Output Voltage CONDITIONS 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 ROUT Maximum Output Voltage Pin 1 to Pin 2, Pin 7 to Pin 8 Pin 5 to Pin 6 Output Resistor RG1A, RG2A Input Gain-Setting Resistor

ELECTRICAL CHARACTERISTICS
MIN
TYP 30 10 30 10 32 38 43 49 32 38 43 49 VS + - 0.75 1.25 20
MAX 45 55 50 55 60 65 60 65 70 75
UNITS mV mV mV mV mV mV mV mV mV mV mV mV V k k
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 -40C to 85C. The LT1787H is
guaranteed functional over the operating temperature range of -40C to 125C. Note 4: The LT1787C is guaranteed to meet specified performance from 0C to 70C. The LT1787C is designed, characterized and expected to meet specified performance from -40C to 85C but is not tested or QA sampled at these temperatures. The LT1787I is guaranteed to meet specified performance from - 40C to 85C. The LT1787H is guaranteed to meet specified performance from -40C to 125C. Note 5: Testing done at VBIAS = 1.25V, VEE = 0V unless otherwise specified. Note 6: This parameter is not 100% tested.
TYPICAL PERFORMANCE CHARACTERISTICS
Input Offset Voltage vs Supply Voltage
50 40 INPUT OFFSET VOLTAGE (V) 30 20 10 0 -10 -20 -30 -40 -50 0 10 30 40 50 20 TOTAL SUPPLY VOLTAGE (V) 60
1787 G01
VS + = V S - VBIAS = 0V VEE = -1.25V
OUTPUT VOLTAGE (V)
OUTPUT CURRENT (nA)
TA = 85C
TA = 25C
TA = -40C
6
UW
No Load Output Voltage vs Supply Voltage
400 300 200 100 0 -100 -200 TA = -40C -300 -400 0 50 10 20 30 40 TOTAL SUPPLY VOLTAGE (V) 60
1787 G02
No Load Output Current vs Supply Voltage
10 8 TA = -40C TA = 25C
VS+ = VS- VBIAS = 0V VEE = -1.25V
TA = 85C
6 4 2 0 -2 -4 -6 -8 -10 0 10 30 40 50 20 TOTAL SUPPLY VOLTAGE (V) 60
1787 G03
TA = 25C
TA = 85C VBIAS = 1V VEE = 0V VS + = V S -
1787fc
LT1787/LT1787HV TYPICAL PERFORMANCE CHARACTERISTICS
Input Offset Voltage vs Negative Supply Voltage
30 20 10 0 -10 TA = -40C -20 -30 VS+ = VS- = 2.5V VBIAS = 1V TA = 85C
INPUT OFFSET VOLTAGE (V)
INPUT OFFSET VOLTAGE (V)
20 10 0 -10 -20 -30 -40
OUTPUT VOLTAGE (V)
TA = 25C
0
-5 -10 -15 -20 -25 NEGATIVE SUPPLY VOLTAGE (V)
Output Voltage vs Sense Voltage (Unidirectional Mode)
1.4 1.2
OUPUT VOLTAGE (V)
VS = 2.5V TO 60V TA = -40C TO 85C VBIAS = VEE
1.0
GAIN (V/V)
0.8 0.6 0.4 0.2 0 0 120 SENSE VOLTAGE (VS+ - VS-) (mV) 30 60 90 150
8.165 8.155 8.145 VS+ < VS-
GAIN (dB)
Supply Current vs Supply Voltage
75
120
NEGATIVE INPUT SENSE CURRENT (A)
70 SUPPLY CURRENT (A) 65 60 55 50 45 VS+ = VS- 40 0
TA = 85C
110 100 90 80 70 60 50 40
POSITIVE INPUT SENSE CURRENT (A)
TA = 25C TA = -40C
20 30 40 50 10 TOTAL SUPPLY VOLTAGE (V)
UW
1787 G04
1787 G07
Input Offset Voltage vs Temperature
50 40 30 VS+ = VS- VBIAS = 0V VEE = -1.25V
2.5 2.0 1.5 1.0 0.5 VBIAS -0.5 -1.0 -1.5 -2.0 -2.5
Output Voltage vs Sense Voltage (Bidirectional Mode)
VS = 5.5V TO 60V VBIAS = 2.5V VEE = 0V
-30
-50 -40
-20
0 20 40 TEMPERATURE (C)
60
80 85
1787 G05
-250
-150 50 150 -50 SENSE VOLTAGE (VS+ - VS-) (mV)
250
1787 G06
Gain vs Temperature
8.195 VS = (2.5V + |VSENSE|)TO 60V 8.185 VS+ > VS- 8.175
0 -10 -20 -30 -40 20 10 30
Gain vs Frequency
VSENSE = 10mV
8.135 -40
-20
0 20 40 TEMPERATURE (C)
60
80 85
1787 G08
-50 0.1k
1k
10k 100k 1M FREQUENCY (Hz)
10M
100M
1787 G09
Negative Input Sense Current vs Sense Voltage
60 VS = (2.5V + |VSENSE |) TO 60V
Positive Input Sense Current vs Sense Voltage
VS = (2.5V + |VSENSE |) TO 60V 50 40 30 20 TA = 25C 10 0 -128 -96 -64 -32 0 32 64 96 SENSE VOLTAGE (VS+ - VS-) (mV) TA = -40C TA = 85C
TA = 85C TA = 25C TA = -40C
60
1787 G10
30 -128 -96 -64 -32 0 32 64 96 SENSE VOLTAGE (VS+ - VS-) (mV)
128
128
1787 G11
1787 G17
1787fc
7
LT1787/LT1787HV TYPICAL PERFORMANCE CHARACTERISTICS
Step Response at VSENSE = 0V to 10mV
10mV 0V 80mV 1V 500mV 0V 0V COUT = 0pF
1787 G12
Step Response at VSENSE = 0V to -128mV
0V - 100mV 0V -100mV
0V - 500mV - 1V
COUT = 0
Step Response at VSENSE = 128mV to -128mV
1000
100mV -100mV
SUPPLY RIPPLE VOLTAGE (mV)
700 600 500 400 300 200 100 0 100 1k 10k 100k FREQUENCY (Hz) 1M
1787 G16
OUTPUT VOLTAGE (V)
1V 0V -1V
COUT = 2200pF
8
UW
1787 G19 1787 G15
Step Response at VSENSE = 0V to 128mV
100mV 0V 100mV 0V
Step Response at VSENSE = 0V to 128mV
1V 500mV 0V
COUT = 0pF
1787 G18
COUT = 1000pF
1787 G13
Step Response at VSENSE = 0V to -128mV
100mV 0V - 100mV
Step Response at VSENSE = - 128mV to 128mV
0V -500mV -1V
1V 0V -1V
COUT = 1000pF
1787 G14
COUT = 0
1787 G20
VOUT Error vs Supply Ripple Voltage (VSENSE = 128mV)
16 14 12 10 8 6 4 2 0 -2 -4 -6 -8
900 800
Output Voltage vs Sense Voltage
VS- = 18V VBIAS = 0V VEE = -18V
0.5%
5% 1%
VOUT ERROR LESS THAN 0.1%
2%
0.4 0.8 1.2 1.6 0 -0.8 -0.4 SENSE VOLTAGE (VS+ - VS-) (V)
2.0
1787 G21
1787fc
LT1787/LT1787HV
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/(2RC), R = 1.25k. 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. DNC (Pin 3): Do Not Connect. Connected internally. Do not connect external circuitry to this pin. 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, where: VOUT > VBIAS for VS+ > VS- VOUT < VBIAS for VS+ < VS- VOUT(O) is the no load output voltage at VSENSE = 0V. 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. 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.
BLOCK DIAGRAM
W
U
U
U
VS - RG1A 1.25k FIL- RG1B 1.25k
RSENSE
ISENSE
VS+
RG2A 1.25k FIL+ RG2B 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
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 40V 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 0.5m per square) can be a large error in high current systems. A 5-Amp application might choose a 20m 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/(2RC) where R = 1.25k. A 0.01F 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
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1787fc
LT1787/LT1787HV
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. 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. Single Supply with Shifted VBIAS 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.
TO CHARGER/ LOAD 1 2 3 4 -5V C2 1F FIL- VS- DNC VEE LT1787 RSENSE C1 1F 15V
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE - OUTPUT BIAS VOLTAGE (V)
FIL+
8
VS+ 7 VBIAS 6 ROUT 5 VOUT C3* 1000pF
1787 F02
*OPTIONAL
Figure 2. Split Supply Operation
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1.5 1.0 0.5 0 -0.5 -1.0 -1.5 -128 -96 -64 -32 0 32 64 96 SENSE VOLTAGE (VS+ - VS-) (mV) VS = 3.3V TO 60V TA = - 40C TO 85C
128
1787 F03
Figure 3. Split Supply Output Voltage
TO CHARGER/ LOAD 1 FIL-
-
RSENSE C1 1F 3.3V TO 60V 3.3V 20k 5% C2 1F C3* 1000pF OUTPUT
1787 F04
FIL+ LT1787HV VS
+
8 7
2 VS 3 4
DNC VEE
VBIAS 6 ROUT VOUT 5
LT1634-1.25
*OPTIONAL
Figure 4. Charge/Discharge Current Monitor on Single Supply with VBIAS = 1.25V
1.5 1.0 0.5 0 -0.5 -1.0 -1.5 -128 -96 -64 -32 0 32 64 96 SENSE VOLTAGE (VS+ - VS-) (mV) VS = 3.3V TO 60V TA = - 40C TO 85C
OUTPUT
128
1787 F05
Figure 5. Single Supply Output Voltage with VBIAS = 1.25V
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LT1787/LT1787HV
APPLICATIONS INFORMATION
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. 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.
TO LOAD
1 FIL
-
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RSENSE 5V 8 FIL+ LT1787 VS+ 7 VBIAS 6 IOUT ROUT VEE VOUT R2 5k 5% 5 R1 20k 5% C1 1F 5V
- 2 VS
3 4
DNC
VCC CS LTC1286 CLK -IN D VREF GND OUT +IN
TO P
1787 F06
Figure 6. Unidirectional Output into A/D with Fixed Supply at VS+
ISENSE
TO CHARGER/ LOAD 1 FIL-
RSENSE
8 FIL+ LT1787 VS+ 7 VBIAS 6 ROUT 5
C1 1F
2.5V + VSENSE(MAX)
- 2 VS
3 4
2.5V C3 1000pF
DNC VEE
VOUT 2.5V 1M 5%
-
A1
+
LT1389-1.25
VOUT A LT1495
1787 F07
Figure 7. Single Supply 2.5V Bidirectional Operation with External Voltage Reference and I/V Converter
RSENSE C 0.1F 2.5V TO 60V
8 FIL+ LT1787HV + - VS 7 2 VS 1 FIL- 3 4 DNC VEE VBIAS 6 ROUT VOUT
1787 F08
5
VOUT
Figure 8. Unidirectional Current Sensing Mode
1787fc
LT1787/LT1787HV
APPLICATIONS INFORMATION
0.30 0.25
OUTPUT VOLTAGE (V)
0.20 0.15 0.10 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
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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. The voltage gain will be gm * ROUT where gm is the LT1787's transconductance, 400A/V typical. A nominal gain of 40 may be obtained with an external 100k resistor used in place of the internal 20k ROUT: AV = gm * ROUT = 400A/V * 100k = 40 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.
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LT1787/LT1787HV
PACKAGE DESCRIPTION
5.23 (.206) MIN
0.42 0.038 (.0165 .0015) TYP
RECOMMENDED SOLDER PAD LAYOUT
DETAIL "A" 0 - 6 TYP
4.90 0.152 (.193 .006)
0.254 (.010) GAUGE PLANE
0.18 (.007) SEATING PLANE 0.22 - 0.38 (.009 - .015) TYP 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
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MS8 Package 8-Lead Plastic MSOP
(LTC DWG # 05-08-1660)
0.889 0.127 (.035 .005)
3.20 - 3.45 (.126 - .136)
0.65 (.0256) BSC
3.00 0.102 (.118 .004) (NOTE 3)
8
7 65
0.52 (.0205) REF
3.00 0.102 (.118 .004) (NOTE 4)
0.53 0.152 (.021 .006) DETAIL "A"
1
23
4
1.10 (.043) MAX
0.86 (.034) REF
0.65 (.0256) BSC
1787fc
LT1787/LT1787HV
PACKAGE DESCRIPTION
.050 BSC
8
.245 MIN
.030 .005 TYP RECOMMENDED SOLDER PAD LAYOUT
.010 - .020 x 45 (0.254 - 0.508) .008 - .010 (0.203 - 0.254) 0- 8 TYP
.016 - .050 (0.406 - 1.270) NOTE: 1. DIMENSIONS IN
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)
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.
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S8 Package 8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
.189 - .197 (4.801 - 5.004) NOTE 3 7 6 5
.045 .005
.160 .005
.228 - .244 (5.791 - 6.197)
.150 - .157 (3.810 - 3.988) NOTE 3
1
2
3
4
.053 - .069 (1.346 - 1.752)
.004 - .010 (0.101 - 0.254)
.014 - .019 (0.355 - 0.483) TYP
.050 (1.270) BSC
SO8 0303
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LT1787/LT1787HV
TYPICAL APPLICATION
Split or Single Supply Operation, Bidirectional Output into A/D
1 1% 1 FIL- LT1787 8 FIL+ VS+ 7 VBIAS 6 20k VOUT 5 VOUT (1V) 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 1 CONV 2 3 7 CLOCKING CIRCUITRY VCC 5V 10F 16V
IS = 125mA VSRCE 4.75V
- 2 VS
3
DNC
VEE 4 VEE -5V
RELATED PARTS
PART NUMBER LTC1043 LT1490/LT1491 LT1620/LT1621 DESCRIPTION Dual Precision Instrumentation Switched Capacitor Building Block Dual and Quad Micropower Rail-to-Rail Input and Output Op Amps Rail-to-Rail Current Sense Amplifiers COMMENTS 120dB CMRR, 3V to 18V Operation 50A Amplifier, 2.7V to 40V Operation, Over-The-TopTM Inputs Accurate Output Current Programming, Battery Charging to 32V
Over-The-Top is a trademark of Linear Technology Corporation.
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Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 FAX: (408) 434-0507
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6 AIN LTC1404 CLK VREF 5 DOUT GND 10F 16V 4 8 10F 16V VEE -5V
DOUT
1787 TA02
1787fc LT 0606 REV C * PRINTED IN USA
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 1999

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