AD8213

Rev. 0 | Page 11 of 16

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 versus 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.

This 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

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

differential inputs regardless of the common-mode voltage,

allows for 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

could 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 imple-

mented 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. This means the no gain or CMRR

errors are introduced by adding resistors at the input of the

AD8213. 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

The 3 dB frequency of this low-pass filter is calculated using the

following formula:

()

FILTER

dB

C

f

20000

2

1

3

π

=

−

It is recommended that in order to prevent output chatter due

to noise potentially entering through the filter pin and coupling

to the output, a capacitor is always placed from the filter pin to

GND. This can be a ≈20 pF capacitor in cases when all of the

bandwidth of the AD8213 is needed in the application.