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High Common-Mode Voltage, Programmable Gain Difference Amplifier
AD628
02992-001
FEATURES
High common-mode input voltage range ±120 V at VS = ±15 V
Gain range 0.1 to 100 Operating temperature range: −40°C to +85°C Supply voltage range
Dual supply: ±2.25 V to ±18 V Single supply: 4.5 V to 36 V Excellent ac and dc performance Offset temperature stability RTI: 10 μV/°C maximum Offset: ±1.5 V mV maximum CMRR RTI: 75 dB minimum, dc to 500 Hz, G = +1
APPLICATIONS
High voltage current shunt sensing Programmable logic controllers Analog input front end signal conditioning
+5 V, +10 V, ±5 V, ±10 V, and 4 to 20 mA Isolation Sensor signal conditioning Power supply monitoring Electrohydraulic controls Motor controls
GENERAL DESCRIPTION
The AD628 is a precision difference amplifier that combines excellent dc performance with high common-mode rejection over a wide range of frequencies. When used to scale high voltages, it allows simple conversion of standard control voltages or currents for use with single-supply ADCs. A wideband feedback loop minimizes distortion effects due to capacitor charging of Σ-Δ ADCs.
A reference pin (VREF) provides a dc offset for converting bipolar to single-sided signals. The AD628 converts +5 V, +10 V, ±5 V, ±10 V, and 4 to 20 mA input signals to a single-ended output within the input range of single-supply ADCs.
The AD628 has an input common mode and differential mode operating range of ±120 V. The high common mode, input impedance makes the device well suited for high voltage measurements across a shunt resistor. The inverting input of the buffer amplifier is available for making a remote Kelvin connection.
FUNCTIONAL BLOCK DIAGRAM
REXT2
REXT1
+VS 7
6 RG
100kΩ –IN 8
100kΩ +IN 1
10kΩ
G = +0.1 –IN
A1 +IN
10kΩ
2 –VS
3 VREF
10kΩ
4 CFILT
–IN A2
+IN
OUT 5
AD628
Figure 1.
CMRR (dB)
130 120 110 100
90 80 70 60 50 40 30
10
VS = ±15V
VS = ±2.5V
100 1k 10k FREQUENCY (Hz)
Figure 2. CMRR vs. Frequency of the AD628
100k
02992-002
A precision 10 kΩ resistor connected to an external pin is provided for either a low-pass filter or to attenuate large differential input signals. A single capacitor implements a lowpass filter. The AD628 operates from single and dual supplies and is available in an 8-lead SOIC_N or an 8-lead MSOP. It operates over the standard industrial temperature range of −40°C to +85°C.
Rev. G
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AD628
TABLE OF CONTENTS
Features .............................................................................................. 1
Applications....................................................................................... 1
General Description ......................................................................... 1
Functional Block Diagram .............................................................. 1
Revision History ............................................................................... 2
Specifications..................................................................................... 3
Absolute Maximum Ratings............................................................ 7
Thermal Characteristics .............................................................. 7
ESD Caution.................................................................................. 7
Pin Configuration and Function Descriptions............................. 8
Typical Performance Characteristics ............................................. 9
Test Circuits..................................................................................... 13
REVISION HISTORY
4/07—Rev. F to Rev. G Changes to Features.......................................................................... 1 Changes to Figure 22...................................................................... 11 Changes to Figure 25...................................................................... 13 Changes to Voltage Level Conversion Section............................ 17 Changes to Monitoring Battery Voltages Section ...................... 18 Changes to Figure 34...................................................................... 18 Changes to Figure 35...................................................................... 19 Updated Outline Dimensions ....................................................... 20
3/06—Rev. E to Rev. F Changes to Table 1.......................................