Datasheet AD8418 (Analog Devices) - 10

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AD8418 Data Sheet THEORY OF OPERATION
The AD8418 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 smal resistors to the positive input of the main amplifier, which al ows differential current shunt voltages in the presence of rapidly the output offset to be adjusted anywhere in the output operating changing common-mode voltages. range. The gain is 1 V/V from the reference pins to the output when the reference pins are used in paral el. When the pins are In typical applications, the AD8418 is used to measure current used to divide the supply, the gain is 0.5 V/V. by amplifying the voltage across a shunt resistor connected to its inputs by a gain of 20 V/V (see Figure 26). The AD8418 offers breakthrough performance without compromising any of the robust application needs typical of The AD8418 is designed to provide excellent common-mode solenoid or motor control. The ability to reject PWM input rejection, even with PWM common-mode inputs that can change common-mode voltages and the zero drift architecture at very fast rates, for example, 1 V/ns. The AD8418 contains providing low offset and offset drift allows the AD8418 to patented technology to eliminate the negative effects of such deliver total accuracy for these demanding applications. fast changing external common-mode variations. The AD8418 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 bandwidth, which is typical y rated at 250 kHz.
VCM = –2V TO +70V VS = 2.7V TO 5.5V 70V V V S REF1 VOUT V V S CM AD8418 +IN EMI + I FILTER SHUNT 0V OUT G = 20 RSHUNT VS/2 –IN EMI – 50A FILTER ISHUNT 0V GND VREF2 –50A
225 1546- 1 Figure 26. Typical Application Rev. 0 | Page 10 of 16 Document Outline Features Applications General Description Functional Block Diagram Table of Contents Revision History Specifications Absolute Maximum Ratings ESD Caution Pin Configuration and Function Descriptions Typical Performance Characteristics Theory of Operation Output Offset Adjustment Unidirectional Operation Ground Referenced Output VS Referenced Output 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 High Rail Current Sensing Outline Dimensions Ordering Guide Automotive Products