Datasheet

A
3
50kW
50kW
50kW
50kW
V+
V-
V
OUT
V+
V-
REF
Q
2
V+
V-
Overvoltage
Protection
A
2
R
B
C
2
V
B
V-
R
2
24.7kW
A
1
R
B
C
1
R
1
24.7kW
R
(External)
G
V+
V-
V+
V-
V+
V-
Q
1
Overvoltage
Protection
-IN
V /2
D
V /2
D
V
CM
+IN
A Out=V +V +0.125V V /2 G
A Out=V +V +0.125V+V /2
OutputSwingRangeA ,A ,(V+) 0.1Vto(V )+0.1V
´
1 CM BE D
2 CM BE D
1 2
-
- -
G´
V =G (V V )+V
LinearInputRangeA =(V+) 0.9Vto(V )+0.1V
O IN+ IN REF
3
-
´ -
- -
INA826
SBOS562E –AUGUST 2011–REVISED APRIL 2013 www.ti.com
INSIDE THE INA826
See Figure 58 for a simplified representation of the INA826. A more detailed diagram (shown in Figure 60)
provides additional insight into the INA826 operation.
Each input is protected by two field-effect transistors (FETs) that provide a low series resistance under normal
signal conditions, and preserve excellent noise performance. When excessive voltage is applied, these
transistors limit input current to approximately 8 mA.
The differential input voltage is buffered by Q
1
and Q
2
and is impressed across R
G
, causing a signal current to
flow through R
G
, R
1
, and R
2
. The output difference amp, A
3
, removes the common-mode component of the input
signal and refers the output signal to the REF terminal.
The equations shown in Figure 60 describe the output voltages of A
1
and A
2
. The V
BE
and voltage drop across
R
1
and R
2
produce output voltages on A
1
and A
2
that are approximately 0.8 V higher than the input voltages.
Figure 60. INA826 Simplified Circuit Diagram
INPUT PROTECTION
The inputs of the INA826 are individually protected for voltages up to ±40 V. For example, a condition of –40 V
on one input and +40 V on the other input does not cause damage. However, if the input voltage exceeds (V–) –
2 V and the signal source current drive capability exceeds 3.5 mA, the output voltage switches to the opposite
polarity; see typical characteristic curve Input Overvoltage vs Input Current (Figure 17). This polarity reversal can
easily be avoided by adding resistance of 10 kΩ in series with both inputs.
Internal circuitry on each input provides low series impedance under normal signal conditions. If the input is
overloaded, the protection circuitry limits the input current to a safe value of approximately 8 mA. The typical
characteristic curves Input Current vs Input Overvoltage (Figure 17 and Figure 18) illustrate this input current limit
behavior. The inputs are protected even if the power supplies are disconnected or turned off.
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