Single/Dual/Quad, Micropower,

Single-Supply Rail-to-Rail Op Amps

the op amp in an inverting configuration (Figure 3a);

connect resistor R3 between the noninverting input and

the input signal when using the op amp in a noninvert-

ing configuration (Figure 3b). Select R3 to equal the

parallel combination of R1 and R2. High source resis-

tances will degrade noise performance, due to the ther-

mal noise of the resistor and the input current noise

(which is multiplied by the source resistance).

Input Stage Protection Circuitry

tion circuitry that prevents damage to the precision

input stage from large differential input voltages. This

protection circuitry consists of back-to-back diodes

between IN+ and IN- with two 1.7k

Ω resistors in series

(Figure 4). The diodes limit the differential voltage

applied to the amplifiers’ internal circuitry to no more

(about 0.7V at +25°C).

Input bias current for the ICs (±25nA typical) is speci-

fied for the small differential input voltages. For large

tion circuitry increases the input current at IN+ and IN-:

Input Current = ———————————

2 x 1.7k

Ω

For comparator applications requiring large differential

rent that flows through the diodes with external resistors

R1

R3

R2

MAX49_

Figure 3a. Reducing Offset Error Due to Bias Current:

Inverting Configuration

R3

R1

R2

MAX49_

MAX492

MAX494

MAX495

1.7k

Ω

1.7k

Ω

TO INTERNAL

CIRCUITRY

TO INTERNAL

CIRCUITRY

IN–

IN+

Figure 4. Input Stage Protection Circuitry

10,000

100

1

10

100

RESISTIVE LOAD (k

Ω)

1000

UNSTABLE REGION

Figure 5. Capacitive-Load Stable Region Sourcing Current

______________________________________________________________________________________

11

Figure 3b. Reducing Offset Error Due to Bias Current:

Noninverting Configuration