AD8209AWBRMZ Datasheet AD8209AWBRMZ-R7, AD8209AWBRMZ, AD8209AWBRMZ-RL | P10-P12

Data Sheet AD8209A

Rev. A | Page 9 of 15

Figure 20. Offset Distribution

Figure 21. Offset Drift Distribution

Figure 22. Gain Drift Distribution

–4

–3 –2

–1 0

2 3

COUNT

(mV)

+125°C

+25°C

–40°C

14511-020

–20 –15 –10 –5 0 5 10 15 20

COUNT

OFFSET DRIFT (µV/°C)

14511-021

–20 –15 –10 –5 0 5 10 15 20

COUNT

GAIN DRIFT (ppm /°C)

14511-022

AD8209A Data Sheet

Rev. A | Page 10 of 15

THEORY OF OPERATION

The AD8209A is a single-supply difference amplifier typically used

to amplify a small differential voltage in the presence of rapidly

changing, high common-mode voltages.

The AD8209A consists of two amplifiers (A1 and A2), a resistor

network, a small voltage reference, and a bias circuit (not shown);

see Figure 23.

The set of input attenuators preceding A1 consist of R

, R

, and

, which feature a combined series resistance of approximately

400 kΩ ± 20%. The purpose of these resistors is to attenuate the

input voltage to match the input voltage range of A1. This balanced

resistor network attenuates the common-mode signal by a ratio

of 1/14. The A1 amplifier inputs are held within the power supply

range, even as Pin 1 and Pin 8 exceed the supply or fall below the

common (ground). A reference voltage of 350 mV biases the

attenuator above ground, allowing Amplifier A1 to operate in

the presence of negative common-mode voltages.

The input resistor network also attenuates normal (differential)

mode voltages. Therefore, A1 features a gain of 97 V/V to provide

a total system gain, from ±IN to the output of A1, equal to 7 V / V,

as shown in the following equation:

Gain (A1) = 1/14 (V/V) × 97 (V/V) = 7 V/V

A precision trimmed, 100 kΩ resistor is placed in series with the

output of Amplifier A1. The user has access to this resistor via

an external pin (A1).

A low-pass filter can be easily implemented by connecting A1 to

A2 and placing a capacitor to ground (see Figure 32).

The value of R

and R

is 10 kΩ, providing a gain of 2 V/V for

Amplifier A2. When connecting Pin A1 and Pin A2 together, the

AD8209A provides a total system gain equal to

Total Gain of (A1 + A2) (V/V) = 7 (V/V) × 2 (V/V) = 14 V/V

at the output of A2 (the OUT pin).

The ratios of R

, R

, and R

are trimmed to a high level of

precision, allowing a typical CMRR value that exceeds 80 dB. This

performance is accomplished by laser trimming the resistor ratio

matching to better than 0.01%.

Figure 23. Simplified Schematic

OUT

GND

–IN

350mV

–

FILTER

+IN

–

145

1-025

Data Sheet AD8209A

Rev. A | Page 11 of 15

APPLICATIONS INFORMATION

HIGH-SIDE CURRENT SENSING

WITH A LOW-SIDE SWITCH

In load control configurations for high-side current sensing with a

low-side switch, the pulse-width modulation (PWM) controlled

switch is ground referenced. An inductive load (solenoid) connects

to a power supply/battery. A resistive shunt is placed between the

switch and the load (see Figure 24). An advantage of placing the

shunt on the high side is that the entire current, including the

recirculation current, is monitored because the shunt remains

in the loop when the switch is off. In addition, shorts to ground can

be detected with the shunt on the high side, enhancing the

diagnostics of the control loop. In this circuit configuration, when

the switch is closed, the common-mode voltage moves down to

near the negative rail. When the switch is opened, the voltage

reversal across the inductive load causes the common-mode

voltage to be held one diode drop above the battery by the

clamp diode.

Figure 24. Low-Side Switch

In cases where a high-side switch is used for PWM control of the

load current in an application, the AD8209A can be used as shown

in Figure 25. The recirculation current through the freewheeling

diode (clamp diode) is monitored through the shunt resistor. In

this configuration, the common-mode voltage in the application

drops below GND when the FET is switched off. The AD8209A

operates down to −2 V, providing an accurate current measurement.

Figure 25. High-Side Switch

HIGH RAIL CURRENT SENSING

In the high rail current sensing configuration, the shunt resistor is

referenced to the battery. High voltage is present at the inputs of

the current sense amplifier. When the shunt is battery referenced,

the AD8209A produces a linear ground-referenced analog output.

Additionally, the AD8214 can be used to provide an overcurrent

detection signal in as little as 100 ns (see Figure 26). This feature is

useful in high current systems where fast shutdown in overcurrent

conditions is essential.

Figure 26. Battery Referenced Shunt Resistor

LOW-SIDE CURRENT SENSING

In systems where low-side current sensing is preferable, the

AD8209A provides a simple, high accuracy, integrated solution. In

this configuration, the AD8209A rejects ground noise and offers

high input to output linearity, regardless of the differential input

voltage.

Figure 27. Ground Referenced Shunt Resistor

GND

DNC

–IN

+IN

OUT

AD8209A

INDUCTIVE

LOAD

SWITCH

SHUNT

CLAMP

DIODE

BATTERY

DNC = DO NOT CONNECT

OUTPUT

–

145

11-026

GND

DNC

–IN

+IN

OUT

AD8209A

INDUCTIVE

LOAD

SWITCH

SHUNT

CLAMP

DIODE

TTERY

DNC = DO NOT CONNECT

OUTPUT

–

14511-027

AD8214

INDUCTIVE

LOAD

SWITCH

CLAMP

DIODE

BATTERY

SHUNT

–IN

NCGND

OVERCURRENT

DETECTION (<100ns)

OUT

+IN

REG

–IN

GND

+IN

DNC

OUT

AD8209A

8765

–

14511-028

DNC = DO NOT CONNECT

GND

DNC

–IN

+IN

OUT

AD8209A

INDUCTIVE

LOAD

SWITCH

SHUNT

CLAMP

DIODE

BATTERY

DNC = DO NOT CONNECT

OUTPUT

14511-029

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P16

AD8209AWBRMZ

Mfr. #:

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Manufacturer:

Analog Devices Inc.

Description:

Current Sense Amplifiers Hgh Vltg Precision Diff Amp w/EMI Fltr

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AD8209AWBRMZ

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