A

3

50kW

50kW

50kW

50kW

V+

V-

V

OUT

V+

V-

REF

Q

2

V+

V-

Overvoltage

Protection

A

2

R

B

C

2

V

B

V-

R

2

24.7kW

A

1

R

B

C

1

R

1

24.7kW

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

+0.125V

V /2

G

A Out=V

+V

+0.125V+V /2

OutputSwingRangeA ,A ,(V+)

0.1Vto(V )+0.1V

´

1

CM

BE

D

2

CM

BE

D

1

2

-

-

-

G

´

V =G

(V

V

)+V

LinearInputRangeA =(V+)

0.9Vto(V )+0.1V

O

IN+

IN

REF

3

-

´

-

-

-

INA826

SBOS562B

– AUGUST 2011 – REVISED DECEMBER 2011

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.

signal and refers the output signal to the REF terminal.

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 k

Ω 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.

20

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© 2011, Texas Instruments Incorporated

Product Folder Link(s): INA826