AD8270

Rev. 0 | Page 14 of 20

INPUT VOLTAGE RANGE

The AD8270 has a true rail-to-rail input range for the majority

of applications. Because most AD8270 configurations divide down

the voltage before they reach the internal op amp, the op amp sees

only a fraction of the input voltage. Figure 41 shows an example

of how the voltage division works in the difference amplifier

configuration.

R4

R3

R1

R2

R2

R1 + R2

R2

R1 + R2

Figure 41. Voltage Division in the Difference Amplifier Configuration

The internal op amp voltage range may be relevant in the

following applications, and calculating the voltage at the

internal op amp is advised.

•

Difference amplifier configurations using supply voltages

of less than ±4.5 V

•

Difference amplifier configurations with a reference

voltage near the rail

•

Single-ended amplifier configurations

For correct operation, the input voltages at the internal op amp

must stay within 1.5 V of either supply rail.

Voltages beyond the supply rails should not be applied to the

part. The part contains ESD diodes at the input pins, which

conduct if voltages beyond the rails are applied. Currents greater

than 5 mA can damage these diodes and the part. For a similar

part that can operate with voltages beyond the rails, see the

AD8273 data sheet.