MAX4256 Maxim, MAX4256 Datasheet - Page 12

• Manufacturer Part Number: MAX4256
• Description: The MAX4249–MAX4257 low-noise, low-distortion operational amplifiers offer rail-to-rail outputs and single-supply operation down to 2
• Manufacturer: Maxim

These devices maintain stability while driving loads up
to 400pF. To drive higher capacitive loads, place a
small isolation resistor in series between the output of
the amplifier and the capacitive load (Figure 5). This
resistor improves the amplifier’s phase margin by isolat-
ing the capacitor from the op amp’s output. Reference
Figure 6 to select a resistance value that will ensure a
load capacitance that limits peaking to <2dB (25%).
UCSP, Single-Supply, Low-Noise,
Low-Distortion, Rail-to-Rail Op Amps
Figure 6. Isolation Resistance vs. Capacitive Loading to
Minimize Peaking (<2dB)
12
Figure 7. Peaking vs. Capacitive Load
______________________________________________________________________________________
160
140
120
100
25
20
15
10
NOTE: USING AN ISOLATION RESISTOR REDUCES PEAKING.
80
60
40
20
5
0
0
10
10
MAX4250–MAX4254 (A
MAX4249/MAX4255–MAX4257 (A
R
SHADED AREA INDICATES
STABLE OPERATION
WITH NO NEED FOR
ISOLATION RESISTOR.
ISO
= 0
CAPACITIVE LOADING (pF)
CAPACITIVE LOAD (pF)
100
100
SHADED AREA INDICATES
STABLE OPERATION
WITH NO NEED FOR
ISOLATION RESISTOR.
V
= 1)
1000
1000
V
= 10)
10,000
10,000
For example, if the capacitive load is 1000pF, the corre-
sponding isolation resistor is 150Ω. Figure 7 shows that
peaking occurs without the isolation resistor. Figure 8
shows the unity-gain bandwidth vs. capacitive load for
the MAX4250–MAX4254.
The MAX4249–MAX4257 operate from a single 2.4V to
5.5V power supply or from dual supplies of ±1.20V to
±2.75V. For single-supply operation, bypass the power
supply with a 0.1µF ceramic capacitor placed close to
the V
each supply to ground.
Good layout improves performance by decreasing the
amount of stray capacitance and noise at the op amp’s
inputs and output. To decrease stray capacitance, min-
imize PC board trace lengths and resistor leads, and
place external components close to the op amp’s pins.
For the latest application details on UCSP construction,
dimensions, tape carrier information, PC board tech-
niques, bump-pad layout, and recommended reflow
temperature profile, as well as the latest information on
reliability testing results, refer to the Application Note:
UCSP—A Wafer-Level Chip-Scale Package on Maxim’s
web site at www.maxim-ic.com/ucsp.
Figure 8. MAX4250–MAX4254 Unity-Gain Bandwidth vs.
Capacitive Load
DD
UCSP Applications Information
pin. If operating from dual supplies, bypass
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
10
SHADED AREA INDICATES
STABLE OPERATION
WITH NO NEED FOR
ISOLATION RESISTOR.
NOTE: R
Power Supplies and Layout
CAPACITIVE LOAD (pF)
ISO
100
CHOSEN FOR PEAKING <2dB.
1000
V
DD
= 3V
10,000