Datasheet AD8219 (Analog Devices) - 10

link to page 10
AD8219 THEORY OF OPERATION AMPLIFIER CORE SUPPLY CONNECTIONS
In typical applications, the AD8219 amplifies a small differential The AD8219 includes an internal LDO, which allows the user input voltage generated by the load current flowing through to connect the VS pin to the inputs, or use a separate supply at a shunt resistor. The AD8219 rejects high common-mode vol- Pin 2 (VS) to power the device. The input range of the supply tages (up to 80 V) and provides a ground referenced, buffered pin is equivalent to the input common-mode range of 4 V to output that interfaces with an analog-to-digital converter (ADC). 80 V. The user must ensure that VS is always connected to the Figure 26 shows a simplified schematic of the AD8219. +IN pin or a separate low impedance supply, which can range from 4 V to 80 V. The VS pin should not be floating.
4V TO 80V OUTPUT CLAMPING V GND S
When the input common-mode voltage in the application is
R4 I
above 5.6 V, the internal LDO output of the AD8219 also
LOAD LDO R1 –IN
reaches its maximum value of 5.6 V, which is the maximum
V2 LOAD SHUNT OUT
output range of the AD8219. Because in typical applications
+IN V1 R2
the output interfaces with a converter, clamping the AD8219
4V R3 TO
output voltage to 5.6 V ensures the ADC input is not damaged
AD8219 80V
4 due to excessive overvoltage. 02
GND
5- 41 09
OUTPUT LINEARITY
Figure 26. Simplified Schematic In all current sensing applications where the common-mode The AD8219 is configured as a difference amplifier. The voltage can vary significantly, it is important that the current transfer function is sensor maintain the specified output linearity, regardless of OUT = (R4/R1) × (V1 − V2) the input differential or common-mode voltage. The AD8219 maintains a very high input-to-output linearity even when the Resistors R4 and R1 are matched to within 0.01% and have differential input voltage is very small. values of 1.5 MΩ and 25 kΩ, respectively, meaning an input to output total gain of 60 V/V for the AD8219, while the
0.7
difference at V1 and V2 is the voltage across the shunt resistor
0.6
or VIN. Therefore, the input-to-output transfer function for the AD8219 is
) 0.5 V ( E
OUT = (60) × (VIN)
G A 0.4 LT
The AD8219 accurately amplifies the input differential signal,
O V
rejecting high voltage common modes ranging from 4 V to 80 V.
T 0.3 U TP
The main amplifier uses a novel zero drift architecture, providing
OU 0.2
the end user with breakthrough temperature stability. The offset drift is typically less than ±100 nV/°C. This performance leads
0.1
to optimal accuracy and dynamic range.
0
7
0 1 2 3 4 5 6 7 8 9 1
12
0
5-
DIFFERENTIAL INPUT VOLTAGE (mV)
41 09 Figure 27. Typical Gain Linearity at Small Differential Inputs (V CM = 4 V to 80 V) Regardless of the common mode, the AD8219 provides a correct output voltage when the input differential is at least 1 mV. The ability of the AD8219 to work with very small differential inputs, regardless of the common-mode voltage, allows for optimal dynamic range, accuracy, and flexibility in any current sensing application. Rev. A | Page 10 of 12 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 AMPLIFIER CORE SUPPLY CONNECTIONS OUTPUT CLAMPING OUTPUT LINEARITY APPLICATIONS INFORMATION HIGH-SIDE CURRENT SENSING MOTOR CONTROL CURRENT SENSING OUTLINE DIMENSIONS ORDERING GUIDE