MAX492 Maxim, MAX492 Datasheet - Page 12

• Manufacturer Part Number: MAX492
• Description: The dual MAX492, quad MAX494, and single MAX495 operational amplifiers combine excellent DC accuracy with rail-to-rail operation at the input and output
• Manufacturer: Maxim

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).
T
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
Figure 3a. Reducing Offset Error Due to Bias Current:
Inverting Configuration
Figure 3b. Reducing Offset Error Due to Bias Current:
Noninverting Configuration
he MAX492/MAX494/MAX495 include internal protec-
V
IN
R3 = R2
V
IN
II
R1
Input Stage Protection Circuitry
R1
R3
______________________________________________________________________________________
R3
MAX49_
MAX49_
R2
R3 = R2
Single-Supply Rail-to-Rail Op Amps
II
R1
resistors in series
R2
R1
V
V
Single/Dual/Quad, Micropower,
OUT
OUT
(Figure 4). The diodes limit the differential voltage
applied to the amplifiers’ internal circuitry to no more
than V
(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
differential input voltages (exceeding V
tion circuitry increases the input current at IN+ and IN-:
For comparator applications requiring large differential
voltages (greater than V
rent that flows through the diodes with external resistors
Figure 4. Input Stage Protection Circuitry
Figure 5. Capacitive-Load Stable Region Sourcing Current
IN+
IN–
Input Current = ———————————
F
10,000
, where V
1000
100
1
1.7k
1.7k
F
is the diodes’ forward-voltage drop
RESISTIVE LOAD (k )
UNSTABLE REGION
(V
F
), you can limit the input cur-
IN
10
+ - V
2 x 1.7k
TO INTERNAL
CIRCUITRY
TO INTERNAL
CIRCUITRY
IN
V
V
R
A
CC
OUT
V
- ) - V
L
TO V
= +1
= +5V
= V
EE
CC
F
F
/2
), this protec-
100
MAX492
MAX494
MAX495
11