Rainbow Electronics MAX4249_MAX4257 - Manual (Page 12)

MAX4249–MAX4257
UCSP, Single-Supply, Low-Noise,
Low-Distortion, Rail-to-Rail Op Amps
12 ______________________________________________________________________________________
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%).
For example, if the capacitive load is 1000pF, the corre-
sponding isolation resistor is 150
Ω. Figure 7 shows that
peaking occurs without the isolation resistor. Figure 8
shows the unity-gain bandwidth vs. capacitive load for
the MAX4250–MAX4254.
Power Supplies and Layout
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
DD pin. If operating from dual supplies, bypass
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.
UCSP Package Consideration
For general UCSP package information and PC layout
considerations, please refer to the Maxim Application
Note (Wafer-Level Ultra-Chip-Board-Scale-Package).
UCSP Reliability
The UCSP represents a unique packaging form factor
that may not perform equally to a packaged product
through traditional mechanical reliability tests. UCSP
reliability is integrally linked to the user’s assembly
methods, circuit board material, and usage environ-
ment. The user should closely review these areas when
considering use of a UCSP. Performance through oper-
ating life test and moisture resistance remains uncom-
promised as it is primarily determined by the
wafer-fabrication process. Mechanical stress perfor-
mance is a greater consideration for a UCSP. UCSPs
are attached through direct solder contact to the user’s
PC board, foregoing the inherent stress relief of a pack-
aged product lead frame. Solder-joint contact integrity
must be considered. Table 1 shows the testing done to
characterize the UCSP reliability performance. In con-
clusion, the UCSP is capable of performing reliably
through environmental stresses as indicated by the
results in the table. Additional usage data and recom-
mendations are detailed in the UCSP application note,
which can be found on Maxim’s website at
www.maxim-ic.com.
160
140
0
10 10,000
60
20
40
120
100
80
CAPACITIVE LOADING (pF)
1000 100
SHADED AREA INDICATES
STABLE OPERATION
WITH NO NEED FOR
ISOLATION RESISTOR.
NOTE: USING AN ISOLATION RESISTOR REDUCES PEAKING.
R
ISO
(Ω
)
4.5
3.5
4.0
0
10 10,000
2.0
3.0
2.5
1.0
0.5
1.5
CAPACITIVE LOAD (pF)
UNITY-GAIN BANDWIDTH (MHz)
1000 100
V DD = 3V
SHADED AREA INDICATES
STABLE OPERATION
WITH NO NEED FOR
ISOLATION RESISTOR.
NOTE: R ISO CHOSEN FOR PEAKING <2dB.
25
20
0
10 10,000
15
5
10
CAPACITIVE LOAD (pF)
PEAKING (dB)
1000 100
MAX4250–MAX4254 (A V = 1)
MAX4249/MAX4255–MAX4257 (A V = 10)
R ISO = 0
SHADED AREA INDICATES
STABLE OPERATION
WITH NO NEED FOR
ISOLATION RESISTOR.
Figure 6. Isolation Resistance vs. Capacitive Loading to
Minimize Peaking (<2dB)
Figure 7. Peaking vs. Capacitive Load
Figure 8. MAX4250-4254 Unity-Gain Bandwidth vs. Capacitive
Load