1
LT1787/LT1787HV
1787fc
Precision, High Side
Current Sense Amplifiers
■
Input Offset Voltage: 75
µ
V (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 bidi-
rectional 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 full-
scale input voltage. A fixed gain of 8 is set by onboard
precision resistors. Input signal filtering is easily imple-
mented 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.
■
Battery Monitoring
■
Power Monitoring
■
Portable Phones
■
Cellular Phones
■
Portable Test/Measurement Systems
■
Battery-Operated Systems
Input Offset Voltage vs Supply Voltage
12-Bit Dynamic Resolution Unidirectional Output into LTC
®
1286 ADC
TOTAL SUPPLY VOLTAGE (V)
0
INPUT OFFSET VOLTAGE (µV)
10 20 30 40
1787 TA01b
50
50
40
30
20
10
0
–10
–20
–30
–40
–50 60
18
27
36
45
LT1787HV
RSENSE
0.0016Ω
1787 TA01
C1
1µF5V
FIL+
FIL–
R1
15k
C2
0.1µF
VOUT = VBIAS + (8 • ILOAD • RSENSE)
I = 100A
2.5V TO 60V
TO
LOAD
LT1634-1.25
TO µP
VREF VCC
GND
LTC1286
CS
CLK
DOUT
+IN
–IN
VBIAS
VOUT
ROUT
20k
VS–VS+
DNC
VEE
APPLICATIO S
U
FEATURES
TYPICAL APPLICATIO
U
DESCRIPTIO
U
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
2
LT1787/LT1787HV
1787fc
ABSOLUTE MAXIMUM RATINGS
W
WW
U
Differential Sense Voltage ...................................... ±10V
Total Supply Voltage (LT1787) ................................ 40V
Total Supply Voltage (LT1787HV) ........................... 65V
Output Voltage ..................... (V
EE
– 0.3V) to (V
EE
+ 35V)
Output Bias Voltage ............. (V
EE
– 0.3V) to (V
EE
+ 35V)
Operating Temperature Range (Note 3)
LT1787C ............................................. –40°C to 85°C
LT1787I .............................................. –40°C to 85°C
LT1787H .......................................... –40°C to 125°C
(Notes 1, 2)
PACKAGE/ORDER INFORMATION
W
UU
ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
V
S–
, V
S+
Sense Amplifier Supply Voltage Single Supply Operation (LT1787) ●2.5 36 V
Single Supply Operation (LT1787HV) ●2.5 60 V
V
SENSE
Input Sense Voltage Full Scale V
SENSE
= V
S+
– V
S–
, V
S
= 10V, V
BIAS
= 5V, A
V
= 8 ±10% ●500 mV
V
OS
Input Offset Voltage (S8) I
OUT
= 0, V
S
Supply = 5V – 75 ±40 75 µV
0°C ≤ T
A
≤ 70°C●–135 135 µV
I
OUT
= 0 (LT1787) –100 100 µV
0°C ≤ T
A
≤ 70°C●–160 160 µV
I
OUT
= 0 (LT1787HV) –100 100 µV
0°C ≤ T
A
≤ 70°C●–160 160 µV
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.
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
(Note 5)
TOP VIEW
FIL
+
V
S+
V
BIAS
V
OUT
FIL
–
V
S–
DNC*
V
EE
S8 PACKAGE
8-LEAD PLASTIC SO
1
2
3
4
8
7
6
5
* DO NOT CONNECT
T
JMAX
= 150°C, θ
JA
= 190°C/ W
1
2
3
4
8
7
6
5
TOP VIEW
MS8 PACKAGE
8-LEAD PLASTIC MSOP
FIL+
VS+
VBIAS
VOUT
FIL–
VS–
DNC*
VEE
* DO NOT CONNECT
T
JMAX
= 150°C, θ
JA
= 250°C/ W
MS8 PART MARKING
Consult LTC Marketing for parts specified with wider operating temperature ranges.
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/
ORDER PART NUMBER
LT1787CMS8
LT1787IMS8
LT1787HVCMS8
LT1787HVIMS8
S8 PART MARKING
1787
1787I
1787H
1787HV
787HVI
787HVH
ORDER PART NUMBER
LT1787CS8
LT1787IS8
LT1787HS8
LT1787HVCS8
LT1787HVIS8
LT1787HVHS8
3
LT1787/LT1787HV
1787fc
Input Offset Voltage (MS8) I
OUT
= 0, V
S
Supply = 5V –125 ±40 125 µV
0°C ≤ T
A
≤ 70°C●–230 230 µV
I
OUT
= 0 (LT1787) –150 150 µV
0°C ≤ T
A
≤ 70°C●–250 250 µV
I
OUT
= 0 (LT1787HV) –150 150 µV
0°C ≤ T
A
≤ 70°C●–250 250 µV
V
OS
TC Temperature Coefficient of V
OS
V
S
Supply = 5V (Note 6) ●0.5 2 µV/°C
I
OUT(O)
No-Load Output Current Error V
SENSE
= 0V 4 nA
V
OUT(O)
No-Load Output Voltage Error V
SENSE
= 0V, V
S
Supply = 5V –600 600 µV
(S8) 0°C ≤ T
A
≤ 70°C●–1080 1080 µV
No-Load Output Voltage Error V
SENSE
= 0V, V
S
Supply = 5V –1000 1000 µV
(MS8) 0°C ≤ T
A
≤ 70°C●–1840 1840 µV
g
m
Tranconductance, I
OUT
/V
SENSE
±V
SENSE
= 10mV, 50mV, 100mV, 150mV, 250mV, 400 µA/V
V
S
Supply = Total Supply + |V
SENSE
|
A
V
Gain, V
OUT
/V
SENSE
±V
SENSE
= 100mV, V
S
Supply = 5V ●7.76 8 8.24 V/V
Output Voltage Gain Error ±V
SENSE
= 100mV, V
S
Supply = 5V ●–3 1 3 %
V
S
PSRR V
S
Supply Rejection Ratio V
SENSE
= 0V, V
S
Supply = 2.5V to 36V (LT1787) ●120 135 dB
V
SENSE
= 0V, V
S
Supply = 2.5V to 60V (LT1787HV) ●120 135 dB
V
EE
PSRR Negative Supply Rejection Ratio V
SENSE
= 0V, V
S
Supply = 15V, V
BIAS
= 0V, ●100 130 dB
V
EE
= –1V to – 15V (LT1787)
V
SENSE
= 0V, V
S
Supply = 40V, V
BIAS
= 0V, ●100 130 dB
V
EE
= –1V to – 15V (LT1787HV)
∆V
OS
Change in Input Offset Voltage V
SENSE
= 0V, V
S
Supply = 36V, V
BIAS
= 0.5V to 25V (LT1787) ●100 130 dB
∆V
BIAS
with Change in V
BIAS
Voltage V
SENSE
= 0V, V
S
Supply = 60V, V
BIAS
= 0.5V to 25V (LT1787HV) ●100 130 dB
I
S+(O)
Positive Input Sense Current V
SENSE
= 0V ●10 20 µA
I
S–(O)
Negative Input Sense Current V
SENSE
= 0V ●50 100 µA
I
EE(O)
Negative Supply Current V
SENSE
= 0V ●60 120 µA
I
OUT
Output Current V
SENSE
= ±128mV ±50 µA
V
OUT
Output Voltage V
SENSE
= ±128mV, V
S+
≥ 3.3V V
BIAS
±1.024 V
Ripple Rejection V
S+
= V
S–
= 20V, ∆V
S
Supply = 1V, f = 1kHz ●80 88 dB
V
OMIN
Minimum Output Voltage V
SENSE
= 0V, V
BIAS
= 0V 30 45 mV
V
SENSE
= V
S+
– V
S–
= –128mV, V
BIAS
= 0V 10 mV
V
SENSE
= 0V, V
BIAS
= 0V ●30 49 mV
V
SENSE
= V
S+
– V
S–
= –128mV, V
BIAS
= 0V 10 mV
Unipolar Output V
SENSE
= 2mV, V
BIAS
= 0V 32 50 mV
Saturation Voltage V
SENSE
= 4mV, V
BIAS
= 0V 38 55 mV
V
SENSE
= 5mV, V
BIAS
= 0V 43 60 mV
V
SENSE
= 6mV, V
BIAS
= 0V 49 65 mV
V
SENSE
= 2mV, V
BIAS
= 0V ●32 54 mV
V
SENSE
= 4mV, V
BIAS
= 0V ●38 59 mV
V
SENSE
= 5mV, V
BIAS
= 0V ●43 64 mV
V
SENSE
= 6mV, V
BIAS
= 0V ●49 69 mV
V
OMAX
Maximum Output Voltage V
S+
– 0.75 V
R
G1A,
R
G2A
Input Gain-Setting Resistor Pin 1 to Pin 2, Pin 7 to Pin 8 1.25 kΩ
R
OUT
Output Resistor Pin 5 to Pin 6 20 kΩ
ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
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.
(Note 5)
4
LT1787/LT1787HV
1787fc
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 MIN TYP MAX UNITS
V
S–
, V
S+
Sense Amplifier Supply Voltage Single Supply Operation (LT1787) ●2.5 36 V
Single Supply Operation (LT1787HV) ●2.5 60 V
V
SENSE
Input Sense Voltage Full Scale V
SENSE
= V
S+
– V
S–
, V
S
= 10V, V
BIAS
= 5V, A
V
= 8 ±10% ●500 mV
V
OS
Input Offset Voltage (S8) I
OUT
= 0, V
S
Supply = 5V – 75 ±40 75 µV
–40°C ≤ T
A
≤ 85°C●–200 200 µV
I
OUT
= 0 (LT1787) –100 100 µV
–40°C ≤ T
A
≤ 85°C●–225 225 µV
I
OUT
= 0 (LT1787HV) –100 100 µV
–40°C ≤ T
A
≤ 85°C●–225 225 µV
Input Offset Voltage (MS8) I
OUT
= 0, V
S
Supply = 5V –125 ±40 125 µV
–40°C ≤ T
A
≤ 85°C●–250 250 µV
I
OUT
= 0 (LT1787) –150 150 µV
–40°C ≤ T
A
≤ 85°C●–280 280 µV
I
OUT
= 0 (LT1787HV) –150 150 µV
–40°C ≤ T
A
≤ 85°C●–280 280 µV
V
OS
TC Temperature Coefficient of V
OS
V
S
Supply = 5V (Note 6) ●0.5 2 µV/°C
I
OUT(O)
No-Load Output Current Error V
SENSE
= 0V 4 nA
V
OUT(O)
No-Load Output Voltage Error V
SENSE
= 0V, V
S
Supply = 5V –600 600 µV
(S8) –40°C ≤ T
A
≤ 85°C●–1600 1600 µV
No-Load Output Voltage Error V
SENSE
= 0V, V
S
Supply = 5V –1000 1000 µV
(MS8) –40°C ≤ T
A
≤ 85°C●–2000 2000 µV
g
m
Tranconductance, I
OUT
/V
SENSE
±V
SENSE
= 10mV, 50mV, 100mV, 150mV, 250mV, 400 µA/V
V
S
Supply = Total Supply + |V
SENSE
|
A
V
Gain, V
OUT
/V
SENSE
±V
SENSE
= 100mV, V
S
Supply = 5V ●7.76 8 8.24 V/V
Output Voltage Gain Error ±V
SENSE
= 100mV, V
S
Supply = 5V ●–3 1 3 %
V
S
PSRR V
S
Supply Rejection Ratio V
SENSE
= 0V, V
S
Supply = 2.5V to 36V (LT1787) ●120 135 dB
V
SENSE
= 0V, V
S
Supply = 2.5V to 60V (LT1787HV) ●120 135 dB
V
EE
PSRR Negative Supply Rejection Ratio V
SENSE
= 0V, V
S
Supply = 15V, V
BIAS
= 0V, ●100 130 dB
V
EE
= –1V to – 15V (LT1787)
V
SENSE
= 0V, V
S
Supply = 40V, V
BIAS
= 0V, ●100 130 dB
V
EE
= –1V to – 15V (LT1787HV)
∆V
OS
Change in Input Offset Voltage V
SENSE
= 0V, V
S
Supply = 36V, V
BIAS
= 0.5V to 25V (LT1787) ●100 130 dB
∆V
BIAS
with Change in V
BIAS
Voltage V
SENSE
= 0V, V
S
Supply = 60V, V
BIAS
= 0.5V to 25V (LT1787HV) ●100 130 dB
I
S+(O)
Positive Input Sense Current V
SENSE
= 0V ●10 20 µA
I
S–(O)
Negative Input Sense Current V
SENSE
= 0V ●50 100 µA
I
EE(O)
Negative Supply Current V
SENSE
= 0V ●60 120 µA
I
OUT
Output Current V
SENSE
= ±128mV ±50 µA
V
OUT
Output Voltage V
SENSE
= ±128mV, V
S+
≥ 3.3V V
BIAS
±1.024 V
Ripple Rejection V
S+
= V
S–
= 20V, ∆V
S
Supply = 1V, f = 1kHz ●80 88 dB
V
OMIN
Minimum Output Voltage V
SENSE
= 0V, V
BIAS
= 0V 30 45 mV
V
SENSE
= V
S+
– V
S–
= –128mV, V
BIAS
= 0V 10 mV
V
SENSE
= 0V, V
BIAS
= 0V ●30 51 mV
V
SENSE
= V
S+
– V
S–
= –128mV, V
BIAS
= 0V 10 mV
5
LT1787/LT1787HV
1787fc
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 MIN TYP MAX UNITS
Unipolar Output V
SENSE
= 2mV, V
BIAS
= 0V 32 50 mV
Saturation Voltage V
SENSE
= 4mV, V
BIAS
= 0V 38 55 mV
V
SENSE
= 5mV, V
BIAS
= 0V 43 60 mV
V
SENSE
= 6mV, V
BIAS
= 0V 49 65 mV
V
SENSE
= 2mV, V
BIAS
= 0V ●32 56 mV
V
SENSE
= 4mV, V
BIAS
= 0V ●38 61 mV
V
SENSE
= 5mV, V
BIAS
= 0V ●43 66 mV
V
SENSE
= 6mV, V
BIAS
= 0V ●49 71 mV
V
OMAX
Maximum Output Voltage V
S+
– 0.75 V
R
G1A,
R
G2A
Input Gain-Setting Resistor Pin 1 to Pin 2, Pin 7 to Pin 8 1.25 kΩ
R
OUT
Output Resistor Pin 5 to Pin 6 20 kΩ
V
S–
, V
S+
Sense Amplifier Supply Voltage Single Supply Operation (LT1787H) ●2.5 36 V
Single Supply Operation (LT1787HVH) ●2.5 60 V
V
SENSE
Input Sense Voltage Full Scale V
SENSE
= V
S+
– V
S–
, V
S
= 10V, V
BIAS
= 5V, A
V
= 8 ±10% ●500 mV
V
OS
Input Offset Voltage I
OUT
= 0, V
S
Supply = 5V – 75 ±40 75 µV
–40°C ≤ T
A
≤ 125°C●–400 400 µV
I
OUT
= 0 (LT1787H) –100 100 µV
–40°C ≤ T
A
≤ 125°C●–550 550 µV
I
OUT
= 0 (LT1787HVH) –100 100 µV
–40°C ≤ T
A
≤ 125°C●–550 550 µV
V
OS
TC Temperature Coefficient of V
OS
V
S
Supply = 5V (Note 6) ●0.5 4 µV/°C
I
OUT(O)
No-Load Output Current Error V
SENSE
= 0V 4 nA
V
OUT(O)
No-Load Output Voltage Error V
SENSE
= 0V, V
S
Supply = 5V –600 600 µV
–40°C ≤ T
A
≤ 125°C●–3200 3200 µV
g
m
Tranconductance, I
OUT
/V
SENSE
±V
SENSE
= 10mV, 50mV, 100mV, 150mV, 250mV, 400 µA/V
V
S
Supply = Total Supply + |V
SENSE
|
A
V
Gain, V
OUT
/V
SENSE
±V
SENSE
= 100mV, V
S
Supply = 5V ●7.76 8 8.24 V/V
Output Voltage Gain Error ±V
SENSE
= 100mV, V
S
Supply = 5V ●–3 1 3 %
V
S
PSRR V
S
Supply Rejection Ratio V
SENSE
= 0V, V
S
Supply = 2.5V to 36V (LT1787H) ●100 130 dB
V
SENSE
= 0V, V
S
Supply = 2.5V to 60V (LT1787HVH) ●100 130 dB
V
EE
PSRR Negative Supply Rejection Ratio V
SENSE
= 0V, V
S
Supply = 15V, V
BIAS
= 0V, ●100 130 dB
V
EE
= –1V to – 15V (LT1787H)
V
SENSE
= 0V, V
S
Supply = 40V, V
BIAS
= 0V, ●100 130 dB
V
EE
= –1V to – 15V (LT1787HVH)
∆V
OS
Change in Input Offset Voltage V
SENSE
= 0V, V
S
Supply = 36V, V
BIAS
= 0.5V to 25V (LT1787H) ●100 130 dB
∆V
BIAS
with Change in V
BIAS
Voltage V
SENSE
= 0V, V
S
Supply = 60V, V
BIAS
= 0.5V to 25V (LT1787HVH) ●100 130 dB
I
S+(O)
Positive Input Sense Current V
SENSE
= 0V ●10 25 µA
I
S–(O)
Negative Input Sense Current V
SENSE
= 0V ●50 115 µA
I
EE(O)
Negative Supply Current V
SENSE
= 0V ●60 140 µA
I
OUT
Output Current V
SENSE
= ±128mV ±50 µA
V
OUT
Output Voltage V
SENSE
= ±128mV, V
S+
≥ 3.3V V
BIAS
±1.024 V
Ripple Rejection V
S+
= V
S–
= 20V, ∆V
S
Supply = 1V, f = 1kHz ●80 88 dB
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)
6
LT1787/LT1787HV
1787fc
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
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 V
BIAS
= 1.25V, V
EE
= 0V unless otherwise
specified.
Note 6: This parameter is not 100% tested.
ELECTRICAL CHARACTERISTICS
No Load Output Voltage
vs Supply Voltage
TOTAL SUPPLY VOLTAGE (V)
010
OUTPUT VOLTAGE (µV)
20 4030 50 60
1787 G02
400
300
200
100
0
–100
–200
–300
–400
TA
= 85°C
TA
= 25°C
TA
= –40°C
VS+ = VS–
VBIAS = 0V
VEE = –1.25V
TOTAL SUPPLY VOLTAGE (V)
0
OUTPUT CURRENT (nA)
10 20 30 40
1787 G03
50
10
8
6
4
2
0
–2
–4
–6
–8
–10 60
V
BIAS
= 1V
V
EE
= 0V
V
S+
= V
S–
T
A
= 25°C
T
A
= 85°C
T
A
= –40°C
No Load Output Current vs
Supply Voltage
TOTAL SUPPLY VOLTAGE (V)
0
INPUT OFFSET VOLTAGE (µV)
10 20 30 40
1787 G01
50
50
40
30
20
10
0
–10
–20
–30
–40
–50 60
VS+ = VS–
VBIAS = 0V
VEE = –1.25V
TA = 25°C
TA = 85°C
TA = –40°C
Input Offset Voltage vs
Supply Voltage
TYPICAL PERFORMANCE CHARACTERISTICS
UW
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
V
OMIN
Minimum Output Voltage V
SENSE
= 0V, V
BIAS
= 0V 30 45 mV
V
SENSE
= V
S+
– V
S–
= –128mV, V
BIAS
= 0V 10 mV
V
SENSE
= 0V, V
BIAS
= 0V ●30 55 mV
V
SENSE
= V
S+
– V
S–
= –128mV, V
BIAS
= 0V 10 mV
Unipolar Output V
SENSE
= 2mV, V
BIAS
= 0V 32 50 mV
Saturation Voltage V
SENSE
= 4mV, V
BIAS
= 0V 38 55 mV
V
SENSE
= 5mV, V
BIAS
= 0V 43 60 mV
V
SENSE
= 6mV, V
BIAS
= 0V 49 65 mV
V
SENSE
= 2mV, V
BIAS
= 0V ●32 60 mV
V
SENSE
= 4mV, V
BIAS
= 0V ●38 65 mV
V
SENSE
= 5mV, V
BIAS
= 0V ●43 70 mV
V
SENSE
= 6mV, V
BIAS
= 0V ●49 75 mV
V
OMAX
Maximum Output Voltage V
S+
– 0.75 V
R
G1A,
R
G2A
Input Gain-Setting Resistor Pin 1 to Pin 2, Pin 7 to Pin 8 1.25 kΩ
R
OUT
Output Resistor Pin 5 to Pin 6 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)
7
LT1787/LT1787HV
1787fc
Output Voltage vs Sense Voltage
(Unidirectional Mode) Gain vs FrequencyGain vs Temperature
TYPICAL PERFORMANCE CHARACTERISTICS
UW
SENSE VOLTAGE (V
S+
– V
S–
) (mV)
0
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
120
1787 G07
30 60 90 150
OUPUT VOLTAGE (V)
V
S
= 2.5V TO 60V
T
A
= –40°C TO 85°C
V
BIAS
= V
EE
TEMPERATURE (°C)
–40
GAIN (V/V)
8.195
8.185
8.175
8.165
8.155
8.145
8.135 –20 0 20 40 60
1787 G08
80
85
V
S
= (2.5V + |V
SENSE
|)TO 60V
V
S+
> V
S–
V
S+
< V
S–
FREQUENCY (Hz)
0.1k 1k
GAIN (dB)
10k 1M100k 10M 100M
1787 G09
30
20
10
0
–10
–20
–30
–40
–50
V
SENSE
= 10mV
Input Offset Voltage vs
Negative Supply Voltage
Output Voltage vs Sense Voltage
(Bidirectional Mode)
Input Offset Voltage vs
Temperature
NEGATIVE SUPPLY VOLTAGE (V)
0
INPUT OFFSET VOLTAGE (µV)
30
20
10
0
–10
–20
–30 –5 –10 –15 –20 –25
1787 G04
–30
T
A
= 25°C
T
A
= 85°C
V
S+
= V
S–
= 2.5V
V
BIAS
= 1V
T
A
= –40°C
TEMPERATURE (°C)
–40
INPUT OFFSET VOLTAGE (µV)
50
40
30
20
10
0
–10
–20
–30
–40
–50 –20 0 20 40 60
1787 G05
80
85
V
S+
= V
S–
V
BIAS
= 0V
V
EE
= –1.25V
SENSE VOLTAGE (V
S+
– V
S–
) (mV)
–250
OUTPUT VOLTAGE (V)
2.5
2.0
1.5
1.0
0.5
V
BIAS
–0.5
–1.0
–1.5
–2.0
–2.5
150
1787 G06
–150 –50 50 250
V
S
= 5.5V TO 60V
V
BIAS
= 2.5V
V
EE
= 0V
Supply Current vs Supply Voltage
Negative Input Sense Current vs
Sense Voltage
TOTAL SUPPLY VOLTAGE (V)
SUPPLY CURRENT (µA)
75
70
65
60
55
50
45
40
1787 G10
010 20 30 40 50 60
TA = 85°C
TA = 25°C
TA = –40°C
VS+ = VS–
SENSE VOLTAGE (VS+ – VS–) (mV)
–128
NEGATIVE INPUT SENSE CURRENT (µA)
120
110
100
90
80
70
60
50
40
30 –64 032
1787 G11
–96 –32 64 96 128
VS = (2.5V + |VSENSE|) TO 60V
TA = 25°C
TA = 85°C
TA = –40°C
SENSE VOLTAGE (VS+ – VS–) (mV)
–128
POSITIVE INPUT SENSE CURRENT (µA)
60
50
40
30
20
10
0–64 032
1787 G17
–96 –32 64 96 128
VS = (2.5V + |VSENSE|) TO 60V
TA = 85°C
TA = –40°C
TA = 25°C
Positive Input Sense Current vs
Sense Voltage
8
LT1787/LT1787HV
1787fc
0V
–100mV
0V
–500mV
–1V
COUT = 1000pF 1787 G14
Step Response at
VSENSE = 0V to –128mV
TYPICAL PERFORMANCE CHARACTERISTICS
UW
Step Response at
VSENSE = 0V to 10mV
Step Response at
VSENSE = 0V to 128mV
10mV
0V
80mV
0V
COUT = 0pF 1787 G12
100mV
0V
1V
500mV
0V
COUT = 1000pF 1787 G13
Step Response at
VSENSE = 0V to 128mV
100mV
0V
1V
500mV
0V
COUT = 0pF 1787 G18
Step Response at
VSENSE = 0V to –128mV
0V
–100mV
0V
–500mV
–1V
COUT = 0 1787 G19
Step Response at
VSENSE = –128mV to 128mV
0V
–100mV
1V
100mV
0V
–1V
COUT = 0 1787 G20
Step Response at
VSENSE = 128mV to –128mV
100mV
–100mV
1V
0V
–1V
COUT = 2200pF 1787 G15
FREQUENCY (Hz)
SUPPLY RIPPLE VOLTAGE (mV)
1000
900
800
700
600
500
400
300
200
100
0
100 10k 100k 1M
1787 G16
1k
V
OUT
ERROR
LESS THAN 0.1%
0.5% 5%
2%
1%
VOUT Error vs Supply Ripple
Voltage (VSENSE = ±128mV)
SENSE VOLTAGE (V
S+
– V
S–
) (V)
OUTPUT VOLTAGE (V)
16
14
12
10
8
6
4
2
0
–2
–4
–6
–8 0 0.8 2.0
1787 G21
–0.8 –0.4 0.4 1.2 1.6
V
S–
= 18V
V
BIAS
= 0V
V
EE
= –18V
Output Voltage vs Sense Voltage
9
LT1787/LT1787HV
1787fc
PIN FUNCTIONS
UUU
FIL
–
, FIL
+
(Pins 1, 8): Negative and Positive Filter Termi-
nals. Differential mode noise can be filtered by connecting
a capacitor across FIL
–
and FIL
+
. Pole frequency
f
–3dB
= 1/(2πRC), R = 1.25kΩ.
V
S–
(Pin 2): Negative Input Sense Terminal. Negative
sense voltage will result in an output sinking current
proportional to the sense current. V
S–
is connected to an
internal gain-setting resistor R
G1A
and supplies bias cur-
rent to the internal amplifier.
DNC (Pin 3): Do Not Connect. Connected internally. Do not
connect external circuitry to this pin.
V
EE
(Pin 4): Negative Supply or Ground for Single Supply
Operation.
V
OUT
(Pin 5): Voltage Output or Current Output propor-
tional to the magnitude of the sense current flowing
through R
SENSE
. For bidirectional current sensing opera-
tion, V
OUT
= A
V
• V
SENSE
+ V
OUT(O)
+ V
BIAS
,
where:
V
OUT
> V
BIAS
for V
S+
> V
S–
V
OUT
< V
BIAS
for V
S+
< V
S–
V
OUT(O)
is the no load output voltage at V
SENSE
= 0V.
V
BIAS
(Pin 6): Output Bias Pin. For single supply, bidirec-
tional current sensing operation, V
BIAS
is connected to an
external bias voltage, so that at V
SENSE
= 0V, V
OUT
=
V
OUT(O)
+ V
BIAS
. For dual supply, bidirectional current
sensing operation, V
BIAS
is connected to ground. Thus,
V
OUT
= V
OUT(O)
at V
SENSE
= 0V.
V
S+
(Pin 7): Positive Input Sense Terminal. Positive sense
voltage will result in an output sourcing current propor-
tional to the sense current. V
S+
is connected to an internal
gain-setting resistor R
G2A
. Connecting a supply to V
S+
and
a load to V
S–
will allow the LT1787 to measure its own
supply current.
BLOCK DIAGRAM
W
RSENSE
1787 F 01
RG2A
1.25k
RG2B
1.25k
RG1A
1.25k
RG1B
1.25k
VOUT
IOUT
VBIAS
ROUT
20k
VS–
–+
A1
Q1 Q2
CURRENT MIRROR
VEE
FIL–
VS+
FIL+
ISENSE
Figure 1. LT1787 Functional Diagram
10
LT1787/LT1787HV
1787fc
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 elimi-
nate aliasing errors.
Theory of Operation
Inputs V
S+
and V
S–
apply the sense voltage to matched
resistors R
G1
and R
G2
. The opposite ends of resistors R
G1
and R
G2
are forced to be at equal potentials by the voltage
gain of amplifier A1. The currents through R
G1
and R
G2
are
forced to flow through transistors Q1 and Q2 and are
summed at node V
OUT
by the 1:1 current mirror. The net
current from R
G1
and R
G2
flowing through resistor R
OUT
gives a voltage gain of eight. Positive sense voltages result
in V
OUT
being positive with respect to pin V
BIAS
.
Pins V
EE
, V
BIAS
and V
OUT
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 V
S–
pin.
The user may choose to include this current in the moni-
tored current through R
SENSE
by careful choice of connec-
tion polarity.
Selection of External Current Sense Resistor
External R
SENSE
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 maxi-
mum 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.
APPLICATIONS INFORMATION
WUUU
Kelvin connection of the LT1787’s V
S+
and V
S–
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 R
G1
and R
G2
. 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 R
G1
and R
G2
into output resistor
R
OUT
. The pins V
OUT
and V
BIAS
may be connected in
numerous configurations to interface with following cir-
cuitry 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 V
OUT
are imposed by the negative supply, V
EE
, and the
input voltage V
S+
. In the negative direction, internal circuit
saturation with loss of accuracy occurs for V
OUT
< 70mV
11
LT1787/LT1787HV
1787fc
APPLICATIONS INFORMATION
WUUU
with absolute minimum swing at 30mV above V
EE
. V
OUT
may swing positive to within 0.75V of V
S+
or a maximum
of 35V, a limit set by internal junction breakdown. Within
these contraints, an amplified, level shifted representation
of the R
SENSE
voltage is developed across R
OUT
.
Split Supply Bipolar Output Swing
Figure 2 shows the LT1787 used with split power supplies.
The V
BIAS
pin is connected to ground, and the output
signal appears at the V
OUT
pin. Bidirectional input currents
can be monitored with the output swinging positive for
current flow from V
S+
and V
S–
. Input currents in the
opposite direction cause V
OUT
to swing below ground.
Figure 2 shows an optional output capacitor connected
from V
OUT
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 V
BIAS
Figure 4 shows the LT1787 used in a single supply mode
with the V
BIAS
pin shifted positive using an external
LT1634 voltage reference. The V
OUT
output signal can
swing above and below V
BIAS
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 V
OUT
to swing without saturating the
internal circuitry. The component values shown in Figure 4
allow operation with V
S
supplies as low as 3.1V.
Figure 2. Split Supply Operation
*OPTIONAL
C2
1µF
–5V
1787 F02
OUTPUT
C3*
1000pF
C1
1µF
R
SENSE
15V
TO
CHARGER/
LOAD
1
2
3
4
8
7
6
5
LT1787
FIL
+
FIL
–
V
BIAS
V
OUT
V
S–
V
S+
DNC
V
EE
R
OUT
Figure 3. Split Supply Output Voltage
SENSE VOLTAGE (V
S+
– V
S–
) (mV)
OUTPUT VOLTAGE – OUTPUT BIAS VOLTAGE (V)
1787 F05
1.5
1.0
0.5
0
–0.5
–1.0
–1.5
–128 –64 032
–96 –32 64 96 128
V
S
= 3.3V TO 60V
T
A
= –40°C TO 85°C
Figure 5. Single Supply Output Voltage
with VBIAS = 1.25V
Figure 4. Charge/Discharge Current Monitor on
Single Supply with VBIAS = 1.25V
C2
1µF
20k
5%
1787 F04
3.3V
LT1634-1.25
*OPTIONAL OUTPUT
C1
1µF
R
SENSE
3.3V
TO
60V
TO
CHARGER/
LOAD
1
2
3
4
8
7
6
5
LT1787HV
FIL
+
FIL
–
V
BIAS
V
OUT
V
S–
V
S+
DNC
V
EE
C3*
1000pF
R
OUT
SENSE VOLTAGE (VS+ – VS–) (mV)
OUTPUT VOLTAGE (V)
1787 F03
1.5
1.0
0.5
0
–0.5
–1.0
–1.5
–128 –64 032
–96 –32 64 96 128
VS = 3.3V TO 60V
TA = –40°C TO 85°C
12
LT1787/LT1787HV
1787fc
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 con-
verters –IN and +IN terminals. The front page of the data
sheet shows a similar circuit which uses a voltage refer-
ence 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 V
BIAS
to V
OUT
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 V
OUT
pin is held equal to the
reference voltage appearing at the op amp’s noninverting
input. This allows monitoring V
S
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 configu-
ration 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 V
BIAS
pin is connected to
ground, and the V
OUT
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 V
BIAS
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 V
BIAS
and V
OUT
.
APPLICATIONS INFORMATION
WUUU
Figure 8. Unidirectional Current Sensing Mode
1787 F08
C
0.1µF
R
SENSE
2.5V TO
60V
V
OUT
TO
LOAD
1
2
3
4
8
7
6
5
LT1787HV
FIL
+
FIL
–
V
BIAS
V
OUT
V
S–
V
S+
DNC
V
EE
R
OUT
Figure 7. Single Supply 2.5V Bidirectional Operation
with External Voltage Reference and I/V Converter
2.5V
C1
1µF
RSENSE
ISENSE
2.5V + VSENSE(MAX)
TO
CHARGER/
LOAD
VOUT A
1M
5%
1787 F07
LT1495
C3
1000pF
LT1389-1.25
2.5V +
–
A1
1
2
3
4
8
7
6
5
LT1787
FIL+
FIL–
VBIAS
VOUT
VS–VS+
DNC
VEE
ROUT
Figure 6. Unidirectional Output into A/D
with Fixed Supply at VS+
R2
5k
5%
1787 F06
I
OUT
C1
1µF5V
V
REF
V
CC
GND
LTC1286
CS
CLK
D
OUT
+IN
–IN TO µP
R
SENSE
5V
1
2
3
4
8
7
6
5
LT1787
FIL
+
FIL
–
V
BIAS
V
OUT
V
S–
V
S+
DNC
V
EE
R1
20k
5%
R
OUT
13
LT1787/LT1787HV
1787fc
APPLICATIONS INFORMATION
WUUU
Adjusting Gain Setting
The LT1787 may be used in all operating modes with an
external resistor used in place of the internal 20k R
OUT
V
S+
– V
S–
(V)
0
OUTPUT VOLTAGE (V)
0.30
0.25
0.20
0.15
0.10
0.05
00.005 0.010
IDEAL
0.015 0.020
1787 F09
0.025 0.030
Figure 9. Expanded Scale of Unidirectional Output
resistor. When an external resistor is used, leave the V
BIAS
pin floating or connected to the V
OUT
pin. This will remove
the internal R
OUT
from the circuit.
The voltage gain will be gm • R
OUT
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 R
OUT
:
A
V
= gm • R
OUT
= 400µA/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 accu-
racy. 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 V
OMAX
specification of V
S
+ –0.75V.
14
LT1787/LT1787HV
1787fc
MS8 Package
8-Lead Plastic MSOP
(LTC DWG # 05-08-1660)
PACKAGE DESCRIPTION
U
MSOP (MS8) 0204
0.53 ± 0.152
(.021 ± .006)
SEATING
PLANE
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
0.18
(.007)
0.254
(.010)
1.10
(.043)
MAX
0.22 – 0.38
(.009 – .015)
TYP
0.127 ± 0.076
(.005 ± .003)
0.86
(.034)
REF
0.65
(.0256)
BSC
0° – 6° TYP
DETAIL “A”
DETAIL “A”
GAUGE PLANE
12
34
4.90 ± 0.152
(.193 ± .006)
8765
3.00 ± 0.102
(.118 ± .004)
(NOTE 3)
3.00 ± 0.102
(.118 ± .004)
(NOTE 4)
0.52
(.0205)
REF
5.23
(.206)
MIN
3.20 – 3.45
(.126 – .136)
0.889 ± 0.127
(.035 ± .005)
RECOMMENDED SOLDER PAD LAYOUT
0.42 ± 0.038
(.0165 ± .0015)
TYP
0.65
(.0256)
BSC
15
LT1787/LT1787HV
1787fc
PACKAGE DESCRIPTION
U
S8 Package
8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
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 represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
.016 – .050
(0.406 – 1.270)
.010 – .020
(0.254 – 0.508)× 45°
0°– 8° TYP
.008 – .010
(0.203 – 0.254)
SO8 0303
.053 – .069
(1.346 – 1.752)
.014 – .019
(0.355 – 0.483)
TYP
.004 – .010
(0.101 – 0.254)
.050
(1.270)
BSC
1234
.150 – .157
(3.810 – 3.988)
NOTE 3
8765
.189 – .197
(4.801 – 5.004)
NOTE 3
.228 – .244
(5.791 – 6.197)
.245
MIN .160 ±.005
RECOMMENDED SOLDER PAD LAYOUT
.045 ±.005
.050 BSC
.030 ±.005
TYP
INCHES
(MILLIMETERS)
NOTE:
1. DIMENSIONS IN
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)
16
LT1787/LT1787HV
1787fc
LT 0606 REV C • PRINTED IN USA
© LINEAR TECHNOLOGY CORPORATION 1999
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507
●
www.linear.com
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.
TYPICAL APPLICATION
U
Split or Single Supply Operation, Bidirectional Output into A/D
1Ω
1%
VEE
–5V
VOUT (±1V)
VSRCE
≈4.75V
IS = ±125mA
1
2
3
4
8
7
6
5
LT1787
FIL+
FIL–
VBIAS
VOUT
VS–VS+
DNC
VEE
20k
1787 TA02
10µF
16V
7
6
8
5
4
3
2
1
VREF
GND
LTC1404
CONV
CLK
DOUT
AIN
VCC
5V
VEE
–5V
DOUT
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
10µF
16V
10µF
16V
CLOCKING
CIRCUITRY
