Data Sheet

AD8213

Rev. D | Page 11 of 14

APPLICATION NOTES

OUTPUT LINEARITY

In all current sensing applications, and especially in automotive

and industrial environments 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 AD8213 contains

specific circuitry on the input stage, which ensures that even

when the differential input voltage is very small, and the common-

mode voltage is also low (below the 5 V supply), the input to

output linearity is maintained. Figure 26 displays the input

differential voltage vs. the corresponding output voltage at

different common modes.

220

200

180

160

140

120

100

80

60

40

20

0

0123456789

10

Figure 26. Gain Linearity due to Differential and Common-Mode Voltage

The AD8213 provides a correct output voltage, regardless of the

common mode, when the input differential is at least 2 mV,

which is due to the voltage range of the output amplifier that

can go as low as 33 mV typical. The specified minimum output

amplifier voltage is 100 mV in order to provide sufficient guard

bands. The ability of the AD8213 to work with very small

differential inputs regardless of the common-mode voltage,

allows more dynamic range, accuracy, and flexibility in any

current sensing application.

LOW-PASS FILTERING

In typical applications, such as motor and solenoid current

sensing, filtering the differential input signal of the AD8213 can

be beneficial in reducing differential common-mode noise as

well as transients and current ripples flowing through the input

shunt resistor. Typically, such a filter can be implemented by

adding a resistor in series with each input and a capacitor directly

between the input pins. However, the AD8213 features a filter pin

available after the input stage but before the final amplification

stage. The user can connect a capacitor to ground, making a

low-pass filter with the internal precision trimmed, 20 kΩ

resistor. Connecting this capacitor to ground, results in no gain

or CMRR errors. Figure 27 shows the typical connection.

A2

G = +20

PROPRIETARY

OFFSET

CIRCUITRY

A1

G = +20

PROPRIETARY

OFFSET

CIRCUITRY

V+

AD8213

20kΩ

20kΩ

GND

CAP2

CAP1

CF2

CF1

Figure 27. Filter Capacitor Connections

Use the following formula to calculate the 3 dB frequency of

this low-pass filter:



FILTER

dB

C

f

20000

2

1

3







It is recommended to always place a capacitor from the filter

pin to GND to prevent the output chatter due to noise

potentially entering through the filter pin and coupling to the

output. This capacitor can be a ≈20 pF capacitor in cases when

all of the bandwidth of the AD8213 is needed in the application.