Datasheet

MAX4380–MAX4384
Ultra-Small, Low-Cost, 210MHz, Single-Supply
Op Amps with Rail-to-Rail Outputs and Disable
12 ______________________________________________________________________________________
Output Capacitive Loading and Stability
The MAX4380–MAX4384 are optimized for AC perfor-
mance. They are not designed to drive highly reactive
loads, which decrease phase margin and may produce
excessive ringing and oscillation. Figure 2 shows a cir-
cuit that eliminates this problem. Figure 3 is a graph of
the Optimal Isolation Resistor (R
S
) vs. Capacitive Load.
Figure 4 shows how a capacitive load causes exces-
sive peaking of the amplifier’s frequency response if
the capacitor is not isolated from the amplifier by a
resistor. A small isolation resistor (usually 10Ω to 15Ω)
placed before the reactive load prevents ringing and
oscillation. At higher capacitive loads, AC performance
is controlled by the interaction of the load capacitance
and the isolation resistor. Figure 5 shows the effect of a
15Ω isolation resistor on closed-loop response.
Chip Information
MAX4380 TRANSISTOR COUNT: 66
MAX4381 TRANSISTOR COUNT: 132
MAX4382 TRANSISTOR COUNT: 196
MAX4383 TRANSISTOR COUNT: 264
MAX4384 TRANSISTOR COUNT: 264
6
-4
100k 10M 100M1M 1G
-2
FREQUENCY (Hz)
GAIN (dB)
0
2
4
5
-3
-1
1
3
C
L
= 10pF
C
L
= 15pF
C
L
= 5pF
Figure 4. Small-Signal Gain vs. Frequency with Load
Capacitance and No Isolation Resistor
3
-7
100k 10M 100M1M 1G
-5
FREQUENCY (Hz)
GAIN (dB)
-3
-1
1
2
-6
-4
-2
0
C
L
= 68pF
R
ISO
= 15Ω
C
L
= 120pF
C
L
= 47pF
Figure 5. Small-Signal Gain vs. Frequency with Load
Capacitance and 27Ω Isolation Resistor
R
G
R
F
R
ISO
C
L
V
OUT
V
IN
MAX438 _
Figure 2. Driving a Capacitive Load Through an Isolation Resistor
9
11
10
13
12
15
14
16
0 200100 300 40050 250150 350 450 500
ISOLATION RESISTANCE
vs. CAPACITIVE LOAD
MAX4380-84 toc23
C
LOAD
(pF)
R
ISO
(Ω)
Figure 3. Isolation Resistance vs. Capacitive Load