MAX4078 Maxim, MAX4078 Datasheet - Page 12

• Manufacturer Part Number: MAX4078
• Description: The MAX4074–MAX4078 GainAmp™ op amp family combines low-cost rail-to-rail op amps with precision internal gain-setting resistors
• Manufacturer: Maxim

Micropower, SOT23, Rail-to-Rail,
Fixed-Gain, GainAmp/Open-Loop Op Amps
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.
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.
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 100Ω 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
Figure 3. Single-Supply, DC-Coupled Inverting Amplifier with
Negative Input Voltage
12
______________________________________________________________________________________
V
IN
Supply Bypassing and Board Layout
R
G
GainAmp Signal Coupling
Capacitive-Load Stability
R
V
F
CC
and Configurations
MAX4074
V
V
CC
OUT
=
-R
R
F
G
(V
IN
)
Figure 4. Dual-Supply, DC-Coupled Inverting Amplifier
Figure 5. Single-Supply, AC-Coupled Inverting Amplifier
Figure 6. Dual-Supply, DC-Coupled Noninverting Amplifier
0.1µF
V
IN
V
IN
V
IN
V
CC
R
G
R
G
R
G
R
V
V
F
CC
EE
MAX4074
R
R
V
MAX4074
V
MAX4074
F
F
CC
EE
V
CC
V
V
OUT
OUT
V
OUT
= V
=
= - V
V
IN
CC
2
(
IN
1+
- V
(
R
R
IN
R
R
F
G
F
G
(
)
)
R
R
F
G
)