MAX4091 Maxim, MAX4091 Datasheet - Page 9

• Manufacturer Part Number: MAX4091
• Description: The single MAX4091, dual MAX4092, and quad MAX4094 operational amplifiers combine excellent DC accuracy with rail-to-rail operation at the input and output
• Manufacturer: Maxim

tance. If the output sources either more or less current,
stability is increased. These devices perform well with a
1000pF pure capacitive load (Figure 5). Figures 6a, 6b,
and 6c show the performance with a 500pF load in par-
allel with various load resistors.
To increase stability while driving large-capacitive
loads, connect a pullup resistor to V
decrease the current the amplifier must source. If the
amplifier is made to sink current rather than source,
stability is further increased.
Frequency stability can be improved by adding an out-
put isolation resistor (R
(Figure 7). This resistor improves the phase margin of
the circuit by isolating the load capacitor from the op
amp’s output. Figure 8a shows the MAX4092 driving
5000pF (R
lation resistor.
Because the MAX4091/MAX4092/MAX4094 have excel-
lent stability, no isolation resistor is required, except in
the most demanding applications. This is beneficial
because an isolation resistor would degrade the low-
frequency performance of the circuit.
The MAX4091/MAX4092/MAX4094 have a typical sup-
ply current of 130µA per op amp. Although supply cur-
rent is already low, it is sometimes desirable to reduce
it further by powering down the op amp and associated
ICs for periods of time. For example, when using a
MAX4092 to buffer the inputs of a multi-channel analog-
to-digital converter (ADC), much of the circuitry could
be powered down between data samples to increase
battery life. If samples are taken infrequently, the op
amps, along with the ADC, may be powered down
most of the time.
When power is reapplied to the MAX4091/MAX4092/
Single/Dual/Quad, Micropower, Single-Supply,
L
≥ 100kΩ), while Figure 8b adds a 47Ω iso-
_______________________________________________________________________________________
S
) to the voltage-follower circuit
Power-Up Settling Time
CC
at the output to
MAX4094, it takes some time for the voltages on the
supply pin and the output pin of the op amp to settle.
Supply settling time depends on the supply voltage, the
value of the bypass capacitor, the output impedance of
the incoming supply, and any lead resistance or induc-
tance between components. Op amp settling time
depends primarily on the output voltage and is slew-
rate limited. With the noninverting input to a voltage fol-
lower held at midsupply (Figure 9), when the supply
steps from 0 to V
2µs for V
(Figure 10b).
The MAX4091/MAX4092/MAX4094 operate from a sin-
gle 2.7V to 6V power supply, or from dual supplies of
±1.35V to ±3V. For single-supply operation, bypass the
power supply with a 0.1µF capacitor. If operating from
dual supplies, bypass each supply to ground.
Good layout improves performance by decreasing the
amount of stray capacitance at the op amp’s inputs
and output. To decrease stray capacitance, minimize
both trace lengths and resistor leads and place exter-
nal components close to the op amp’s pins.
MAX4091 TRANSISTOR COUNT: 168
MAX4092 TRANSISTOR COUNT: 336
MAX4094 TRANSISTOR COUNT: 670
PROCESS: Bipolar
Rail-to-Rail Op Amps
CC
= 3V (Figure 10a) and 8µs for V
CC
, the output settles in approximately
Power Supplies and Layout
Chip Information
CC
= 5V
9