INPUT PROTECTION
The inputs of the INA2128 are individually protected for
voltages up to
±40V.
For example, a condition of –40V on
one input and +40V on the other input will not cause
damage. Internal circuitry on each input provides low series
impedance under normal signal conditions. To provide
equivalent protection, series input resistors would contribute
excessive noise. If the input is overloaded, the protection
circuitry limits the input current to a safe value of approxi-
mately 1.5 to 5mA. The typical performance curve “Input
Bias Current vs Common-Mode Input Voltage” shows this
input current limit behavior. The inputs are protected even if
the power supplies are disconnected or turned off.
CHANNEL CROSSTALK
The two channels of the INA2128 are completely indepen-
dent, including all bias circuitry. At DC and low frequency
there is virtually no signal coupling between channels.
Crosstalk increases with frequency and is dependent on
circuit gain, source impedance and signal characteristics.
As source impedance increases, careful circuit layout will
help achieve lowest channel crosstalk. Most crossstalk is
produced by capacitive coupling of signals from one channel
to the input section of the other channel. To minimize
coupling, separate the input traces as far as practical from
any signals associated with the opposite channel. A grounded
guard trace surrounding the inputs helps reduce stray cou-
pling between channels. Run the differential inputs of each
channel parallel to each other or directly adjacent on top and
bottom side of a circuit board. Stray coupling then tends to
produce a common-mode signal which is rejected by the
IA’s input.
V
EX
X-axis
1/2
INA2128
X-axis
V
O
V
1
R
GA
1/2
INA2128
Ref
V
2
V
O
= G
A
(V
2
– V
1
) + G
B
(V
4
– V
3
)
V
EX
Y-axis
1/2
INA2128
Y-axis
V
O
V
3
R
GB
V
4
1/2
INA2128
Ref
FIGURE 4. Two-Axis Bridge Amplifier.
FIGURE 5. Sum of Differences Amplifier.
R
G
= 5.6kΩ
2.8kΩ
LA
R
G
/2
2.8kΩ
390kΩ
RL
390kΩ
1/2
OPA2604
10kΩ
V
G
1/2
OPA2604
V
G
NOTE: Due to the INA2128’s current-feedback
topology, V
G
is approximately 0.7V less than
the common-mode input voltage. This DC offset
in this guard potential is satisfactory for many
guarding applications.
1/2
INA2128
Ref
G = 10
V
O
RA
FIGURE 6. ECG Amplifier With Right-Leg Drive.
®
INA2128
10
BURR-BROWN [ BURR-BROWN CORPORATION ]
