SOT23, Rail-to-Rail, Fixed-Gain
GainAmps/Open-Loop Op Amps
gain amplifiers of this GainAmp family are stable with
Supply Bypassing and Board Layout
All devices in the GainAmp family operate from a +2.5V
to +5.5V single supply or from 1.25V to 2.75V dual
supplies. For single-supply operation, bypass the
power supply with a 0.1µF capacitor to ground. For
dual supplies, bypass each supply to ground. Bypass
with capacitors as close to the device as possible, to min-
imize lead inductance and noise. A printed circuit board
with a low-inductance ground plane is recommended.
capacitive loads up to 470pF. Stability with higher
capacitive loads can be improved by adding an isolation
resistor in series with the op-amp output, as shown in
Figure 9. This resistor improves the circuit’s phase mar-
gin by isolating the load capacitor from the amplifier’s
output. In Figure 10, a 1000pF capacitor is driven with a
100Ω isolation resistor exhibiting some overshoot but no
oscillation. Figures 11 and 12 show the typical small-sig-
nal pulse responses of GainAmp fixed-gain amplifiers
with 250pF and 470pF capacitive loads and no isolation
resistor.
Capacitive-Load Stability
Driving large capacitive loads can cause instability in
most low-power, rail-to-rail output amplifiers. The fixed-
MAX4174
INPUT
V
CC
V
IN
R
R
F
V
OUT
= V 1+
IN
(
)
G
A = +5V/V
V
OUTPUT
OUTPUT
50mV/div
V
EE
R
F
A = +5V/V
V
500mV/div
R
G
Figure 8. Dual-Supply, DC-Coupled Noninverting Amplifier
Figure 10. Small-Signal/Large-Signal Transient Response with
Excessive Capacitive Load with Isolation Resistor
75,MAX812/4
MAX4174
R
R
F
G
V
CC
R
ISO
OUTPUT
INPUT
C
L
R
L
V
EE
Figure 9. Dual-Supply, Capacitive-Load Driving Circuit
14 ______________________________________________________________________________________
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
