Datasheet AD8211 (Analog Devices) - 10

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AD8211 Data Sheet THEORY OF OPERATION
In typical applications, the AD8211 amplifies a smal differential A load current flowing through the external shunt resistor input voltage generated by the load current flowing through a produces a voltage at the input terminals of the AD8211. The shunt resistor. The AD8211 rejects high common-mode voltages input terminals connect to Amplifier A1 by Resistor R and (up to 65 V) and provides a ground referenced, buffered output Resistor R1. The inverting terminal, which has very high input that interfaces with an analog-to-digital converter (ADC). impedance, is held to the following because negligible current Figure 23 shows a simplified schematic of the AD8211. flows through Resistor R:
ISHUNT
(VCM) − (ISHUNT × RSHUNT)
R
Amplifier A1 forces the noninverting input to the same potential.
SHUNT
Therefore, the current that flows through Resistor R1 is equal to
IIN R1 R
IIN = (ISHUNT × RSHUNT)/R1 This current (IIN) is converted back to a voltage via ROUT. The
A1 V+
output buffer amplifier has a gain of 20 V/V and offers excellent
PROPRIETARY
accuracy because the internal gain setting resistors are precision
OFFSET CIRCUITRY
trimmed to within 0.01% matching. The resulting output voltage
Q1
is equal to
VOUT = (ISHUNT × RSHUNT) × 20
VOUT = (ISHUNT × RSHUNT) × 20
G = +20 ROUT AD8211
022
GND
06824- Figure 23. Simplified Schematic Rev. C | Page 10 of 13 Document Outline FEATURES APPLICATIONS FUNCTIONAL BLOCK DIAGRAM GENERAL DESCRIPTION REVISION HISTORY SPECIFICATIONS ABSOLUTE MAXIMUM RATINGS ESD CAUTION PIN CONFIGURATION AND FUNCTION DESCRIPTIONS TYPICAL PERFORMANCE CHARACTERISTICS THEORY OF OPERATION APPLICATION NOTES OUTPUT LINEARITY APPLICATIONS INFORMATION HIGH-SIDE CURRENT SENSE WITH A LOW-SIDE SWITCH HIGH-SIDE CURRENT SENSING LOW-SIDE CURRENT SENSING OUTLINE DIMENSIONS ORDERING GUIDE AUTOMOTIVE PRODUCTS