Datasheet AD8207 (Analog Devices) - 10

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AD8207 THEORY OF OPERATION
The AD8207 is a single-supply, zero drift, difference amplifier The reference inputs, VREF1 and VREF2, are tied through 100 kΩ that uses a unique architecture to accurately amplify small resistors to the positive input of the main amplifier, which differential current shunt voltages in the presence of rapidly allows the output offset to be adjusted anywhere in the output changing common-mode voltage. operating range. The gain is 1 V/V from the reference pins to In typical applications, the AD8207 is used to measure current the output when the reference pins are used in parallel. When by amplifying the voltage across a shunt resistor connected to the pins are used to divide the supply, the gain is 0.5 V/V. its inputs. The AD8207 offers breakthrough performance without The AD8207 includes a zero-drift amplifier, a precision resistor compromising any of the robust application needs typical network, a common-mode control amplifier, and a precision of solenoid or motor control. The part rejects PWM input reference (see Figure 25). common-mode voltages, while the zero-drift architecture yields the lowest offset and offset drift performance on the market. A set of precision-trimmed resistors make up the network
SHUNT
that attenuates the input common-mode voltage to within the
+IN –IN
supply range of the amplifier, in this case with a ratio of 20/1. This attenuation ensures that when the input pins are externally
120kΩ 120kΩ ZERO-DRIFT
at the common-mode extremes of −4 V and +65 V, the actual
AMPLIFIER
voltage at the inputs of the main amplifier is still within the
100kΩ 9kΩ OUT
supply range.
60kΩ 60kΩ 100kΩ
The input resistor network also attenuates normal (differential)
6kΩ 6kΩ 50kΩ 100kΩ
mode voltages. Therefore, the total internal gain of the AD8207 is set to 400 V/V to provide a total system gain of 20 V/V.
VREF1 100kΩ
Total Gain (V/V) = 1/20 (V/V) × 400 (V/V) = 20 V/V
COMMON-MODE VREF2 CONTROL AMPLIFIER 100kΩ
The AD8207 is designed to provide excellent common-mode
3.5V/2.2V AD8207
rejection, even with PWM common-mode inputs that can
REF
change at very fast rates, for example, 1 V/ns. An internal 25 0
GND
0- common-mode control amplifier is used to maintain the input 16 09 common mode of the main amplifier at 3.5 V (with 5 V supply), Figure 25. Simplified Schematic and therefore eliminates the negative effects of such fast- changing external common-mode variations. The AD8207 features an input offset drift of less than 500 nV/°C. This performance is achieved through a novel zero-drift architecture that does not compromise band- width, which is typically rated at 150 kHz. Rev. 0 | Page 10 of 16 Document Outline FEATURES APPLICATIONS FUNCTIONAL BLOCK DIAGRAM GENERAL DESCRIPTION TABLE OF CONTENTS REVISION HISTORY SPECIFICATIONS ABSOLUTE MAXIMUM RATINGS ESD CAUTION PIN CONFIGURATION AND FUNCTION DESCRIPTIONS TYPICAL PERFORMANCE CHARACTERISTICS THEORY OF OPERATION POWER SUPPLY ADJUSTMENT 3.3 V TO 4.5 V SUPPLY OPERATION 4.5 V TO 5.5 V SUPPLY OPERATION OUTPUT OFFSET ADJUSTMENT UNIDIRECTIONAL OPERATION Ground Referenced Output Mode V+ Referenced Output Mode BIDIRECTIONAL OPERATION EXTERNAL REFERENCED OUTPUT SPLITTING THE SUPPLY SPLITTING AN EXTERNAL REFERENCE APPLICATIONS INFORMATION MOTOR CONTROL 3-Phase Motor Control H-Bridge Motor Control SOLENOID CONTROL High-Side Current Sense with a Low-Side Switch High-Side Current Sense with a High-Side Switch OUTLINE DIMENSIONS ORDERING GUIDE AUTOMOTIVE PRODUCTS