Datasheet

MAX4321
Low-Cost, Low-Voltage, Rail-to-Rail,
Input/Output, SOT23 5MHz Op Amp
8 _______________________________________________________________________________________
Rail-to-Rail Output Stage
The minimum output voltage will be within millivolts of
ground for single-supply operation where the load is
referenced to ground (V
EE
). Figure 3 shows the input
voltage range and output voltage swing of a MAX4321
connected as a voltage follower. With a +3V supply
and the 100kΩ load tied to ground, the output swings
from 0.02V to 2.97V. The maximum output voltage
swing depends on the load but will be within 300mV of
a +5V supply, even with the maximum load (250Ω to
ground).
Driving a capacitive load can cause instability in most
high-speed op amps, especially those with low quies-
cent current. The MAX4321 has a high tolerance for
capacitive loads. It is stable with capacitive loads up to
500pF. Figure 4 gives the stable operating region for
capacitive loads. Figures 5 and 6 show the response
with capacitive loads and the results of adding an isola-
tion resistor in series with the output (Figure 7). The
resistor improves the circuit’s phase margin by isolating
the load capacitor from the op amp’s output.
Figure 3. Rail-to-Rail Input /Output Voltage Range Figure 4. Capacitive-Load Stability
Figure 5. Small-Signal Transient Response with Capacitive
Load
Figure 6. Transient Response to Capacitive Load with Isolation
Resistor
IN
400ns/div
VOLTAGE
50mV/div
OUT
A
V
= +1
C
L
= 500pF
IN
400ns/div
VOLTAGE
50mV/div
OUT
A
V
= +1
C
L
= 1000pF
R
S
= 39Ω
IN
2μs/div
VOLTAGE
1V/div
OUT
V
CC
= 3V
A
V
= +1
R
L
= 100kΩ
10,000
100
100 1k 100k10k
RESISTIVE LOAD (Ω)
LOAD CAPACITIVE (pF)
1000
UNSTABLE
REGION
R
L
TO V
EE
V
OUT
= V
CC
/ 2