OPA705, 2705, 4705

8

SBOS182A

APPLICATIONS INFORMATION

OPA705 series op amps can operate on 160

µA quiescent

current from a single (or split) supply in the range of 4V to

12V (

±2V to ±6V), making them highly versatile and easy

to use. The OPA705 is unity-gain stable and offers 1MHz

bandwidth and 0.6V/

µs slew rate.

Rail-to-rail input and output swing helps maintain dynamic

range, especially in low supply applications. Figure 1 shows

the input and output waveforms for the OPA705 in unity-

gain configuration. Operation is from a

±5V supply with a

100k

Ω load connected to V

S/ 2. The input is a 10Vp-p

sinusoid. Output voltage is approximately 10Vp-p.

Power-supply pins should be bypassed with 1000pF ceramic

capacitors in parallel with 1

µF tantalum capacitors.

OPERATING VOLTAGE

OPA705 series op amps are fully specified and guaranteed

from +4V to +12V over a temperature range of –40ºC to

+85ºC. Parameters that vary significantly with operating volt-

ages or temperature are shown in the Typical Characteristics.

RAIL-TO-RAIL INPUT

The input common-mode voltage range of the OPA705 series

extends 300mV beyond the supply rails at room temperature.

This is achieved with a complementary input stage—an N-

channel input differential pair in parallel with a P-channel

differential pair, as shown in Figure 2. The N-channel pair is

active for input voltages close to the positive rail, typically

(V+) – 2.0V to 300mV above the positive supply, while the P-

channel pair is on for inputs from 300mV below the negative

supply to approximately (V+) – 1.5V. There is a small

transition region, typically (V+) – 2.0V to (V+) – 1.5V, in

which both pairs are on. This 500mV transition region can

vary

±100mV with process variation. Thus, the transition

region (both stages on) can range from (V+) – 2.1V to (V+)

– 1.4V on the low end, up to (V+) – 1.9V to (V+) – 1.6V on

the high end. Within the 500mV transition region PSRR,

CMRR, offset voltage, and offset drift, and THD may vary

compared to operation outside this region.

FIGURE 2. Simplified Schematic.

FIGURE 1. Rail-to-Rail Input and Output.

Input

Output (inverted on scope)

G = +1, V

S = ±5V

200

µs/div

V

O

V–

V+

V

IN+

V

IN–