AD8219BRMZ-RL【PDF 10/12 页】IC CURRENT MONITOR UNI-DIR 8MSOP

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Sheet目录39

6页 7页 8页 9页 [10页]11页 12页

AD8219

Rev. A | Page 10 of 12

THEORY OF OPERATION

AMPLIFIER CORE

In typical applications, the AD8219 amplifies a small differential

input voltage generated by the load current flowing through

a shunt resistor. The AD8219 rejects high common-mode vol-

tages (up to 80 V) and provides a ground referenced, buffered

output that interfaces with an analog-to-digital converter (ADC).

Figure 26 shows a simplified schematic of the AD8219.

LDO

AD8219

+IN

OUT

GND

LOAD

SHUNT

80V

GND

4V TO 80V

Figure 26. Simplified Schematic

The AD8219 is configured as a difference amplifier. The

transfer function is

OUT = (R4/R1) ?(V1 V2)

Resistors R4 and R1 are matched to within 0.01% and have

values of 1.5 M?and 25 k? respectively, meaning an input

to output total gain of 60 V/V for the AD8219, while the

difference at V1 and V2 is the voltage across the shunt resistor

or VIN. Therefore, the input-to-output transfer function for the

AD8219 is

OUT = (60) ?(VIN)

The AD8219 accurately amplifies the input differential signal,

rejecting high voltage common modes ranging from 4 V to 80 V.

The main amplifier uses a novel zero drift architecture, providing

the end user with breakthrough temperature stability. The offset

drift is typically less than ?00 nV/癈. This performance leads

to optimal accuracy and dynamic range.

SUPPLY CONNECTIONS

The AD8219 includes an internal LDO, which allows the user

to connect the VS pin to the inputs, or use a separate supply at

Pin 2 (VS) to power the device. The input range of the supply

pin is equivalent to the input common-mode range of 4 V to

80 V. The user must ensure that V

is always connected to the

+IN pin or a separate low impedance supply, which can range

from 4 V to 80 V. The V

pin should not be floating.

OUTPUT CLAMPING

When the input common-mode voltage in the application is

above 5.6 V, the internal LDO output of the AD8219 also

reaches its maximum value of 5.6 V, which is the maximum

output range of the AD8219. Because in typical applications

the output interfaces with a converter, clamping the AD8219

output voltage to 5.6 V ensures the ADC input is not damaged

due to excessive overvoltage.

OUTPUT LINEARITY

In all current sensing applications where the common-mode

voltage can vary significantly, it is important that the current

sensor maintain the specified output linearity, regardless of

the input differential or common-mode voltage. The AD8219

maintains a very high input-to-output linearity even when the

differential input voltage is very small.

0.7

0.1

0.2

0.3

0.4

0.5

0.6

DIFFERENTIAL INPUT VOLTAGE (mV)

Figure 27. Typical Gain Linearity at Small Differential Inputs

= 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.

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