Datasheet
Data Sheet AD8213
Rev. C | 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
012345678910
V
OUT
(mV)
V
IN
DIFFERENTIAL (mV)
IDEAL V
OUT
V
OUT
@ V
CM
= 0V
V
OUT
@ V
CM
= 65V
06639-029
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
R
SHUNT1
R
SHUNT2
I
SHUNT1
I
SHUNT2
PROPRIETARY
OFFSET
CIRCUITRY
V
+
AD8213
20kΩ20kΩ
R2
(1)
R2
(2)
R1
(1)
R1
(2)
GND
CAP2 CAP1
CF2 CF1
0
6639-030
Figure 27. Filter Capacitor Connections
The 3 dB frequency of this low-pass filter is calculated using the
following formula:
FILTER
dB
C
f
200002
1
3
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.