Rainbow Electronics MAX4074_MAX4078 User Manual
Page 12
MAX4074–MAX4078
Micropower, SOT23, Rail-to-Rail,
Fixed-Gain, GainAmp/Open-Loop Op Amps
12
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GainAmp Signal Coupling
and Configurations
Common op amp configurations include both noninvert-
ing and inverting amplifiers. Figures 3–6 show various
single- and dual-supply circuit configurations. In single-
supply systems, use a resistor-divider to bias the nonin-
verting input. A lowpass filter capacitor from the op amp
input to ground (Figure 5) prevents high-frequency
power-supply noise from coupling into the op amp input.
Dual-supply systems can have ground-referenced sig-
nals DC-coupled into the inverting or noninverting inputs.
Supply Bypassing and Board Layout
All devices in this 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 sup-
plies, bypass each supply to ground. Bypass with
capacitors as close to the device as possible to mini-
mize lead inductance and noise. A printed circuit board
with a low-inductance ground plane is recommended.
Capacitive-Load Stability
Driving large capacitive loads can cause instability in
most low-power, rail-to-rail output amplifiers. The fixed-
gain amplifiers of this GainAmp family are stable with
capacitive loads up to 100pF. Stability with higher
capacitive loads can be improved by adding an isola-
tion resistor in series with the op amp output, as shown
in Figure 7. This resistor improves the circuit’s phase
margin by isolating the load capacitor from the amplifi-
er’s output. In Figure 8, a 220pF capacitor is driven with
a 100
Ω isolation resistor exhibiting some overshoot but
no oscillation. Figures 9 and 10 show the typical small-
signal pulse responses of GainAmp fixed-gain ampli-
fiers with 47pF and 100pF capacitive loads and no
isolation resistor
MAX4074
V
CC
V
CC
R
G
R
F
V
IN
V
OUT
=
-R
F
(V
IN
)
R
G
Figure 3. Single-Supply, DC-Coupled Inverting Amplifier with
Negative Input Voltage
MAX4074
V
EE
V
CC
R
G
R
F
V
IN
V
OUT
= - V
IN
(
R
F
)
R
G
Figure 4. Dual-Supply, DC-Coupled Inverting Amplifier
MAX4074
V
CC
V
CC
R
G
R
F
V
IN
0.1
µF
V
OUT
=
V
CC
- V
IN
(
R
F
)
2 R
G
Figure 5. Single-Supply, AC-Coupled Inverting Amplifier
MAX4074
V
EE
V
CC
R
G
R
F
V
IN
V
OUT
= V
IN
(
1+
R
F
)
R
G
Figure 6. Dual-Supply, DC-Coupled Noninverting Amplifier