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LT1787/LT1787HV

1787fc

Precision, High Side

Current Sense Amplifiers

■

Input Offset Voltage: 75

V (Max)

■

60V Supply Operation (LT1787HV)

■

12-Bit Dynamic Range

■

Operating Current: 60µA

■

User-Selectable External Sense Resistor

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Bidirectional High Side Current Sensing

■

Unidirectional or Bidirectional Output

■

Input Noise Filtering

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–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.

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Battery Monitoring

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Power Monitoring

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Portable Phones

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Cellular Phones

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Portable Test/Measurement Systems

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Battery-Operated Systems

Input Offset Voltage vs Supply Voltage

12-Bit Dynamic Resolution Unidirectional Output into LTC

1286 ADC

TOTAL SUPPLY VOLTAGE (V)

INPUT OFFSET VOLTAGE (µV)

30 40

1787 TA01b

–10

–20

–30

–40

–50

LT1787HV

SENSE

0.0016Ω

1787 TA01

1µF

FIL

–

15k

0.1µF

OUT

= V

BIAS

+ (8 • I

LOAD

• R

SENSE

)

I = 100A

2.5V TO 60V

LOAD

LT1634-1.25

TO µP

REF

GND

LTC1286

CLK

OUT

+IN

–IN

BIAS

OUT

20k

–

DNC

APPLICATIO S

FEATURES

TYPICAL APPLICATIO

DESCRIPTIO

, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.

All other trademarks are the property of their respective owners.

Summary of content (16 pages)

PAGE 1
LT1787/LT1787HV Precision, High Side Current Sense Amplifiers U DESCRIPTIO FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ 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 se
PAGE 2
LT1787/LT1787HV W W U W 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 .
PAGE 3
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.
PAGE 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.
PAGE 5
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.
PAGE 6
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.
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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.
PAGE 8
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
PAGE 9
LT1787/LT1787HV U U U 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.
PAGE 10
LT1787/LT1787HV U W U U 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.
PAGE 11
LT1787/LT1787HV U U W U 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.
PAGE 12
LT1787/LT1787HV U W U U 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.
PAGE 13
LT1787/LT1787HV U W U U 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.
PAGE 14
LT1787/LT1787HV U 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 (.
PAGE 15
LT1787/LT1787HV U 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.
PAGE 16
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.