FAN4272 Datasheet, PDF (7/11 Pages) Fairchild Semiconductor – Dual, Low Cost, +2.7V & +5V, Rail-to-Rail I/O Amplifier

FAN4272
DATA SHEET
Application Information
General Description
The FAN4272 is single supply, general purpose, voltage-feed-
back amplifier. The FAN4272 is fabricated on a complementary
bipolar process, features a rail-to-rail input and output, and is
unity gain stable.
The typical non-inverting circuit schematic is shown in Figure 1.
+V_s
6.8µF
+
degradation will occur. It the maximum junction temperature
exceeds 175°C for an extended time, device failure may occur.
Overdrive Recovery
Overdrive of an amplifier occurs when the output and/or
input ranges are exceeded. The recovery time varies based on
whether the input or output is overdriven and by how much
the ranges are exceeded. The FAN4272 will typically recover
in less than 50ns from an overdrive condition. Figure 3
shows the FAN4272 in an overdriven condition.
5.5
G=5
4.5
Output
In
0.01µF
+
Out
FAN4272
-
R_f
R_g
Figure 1: Typical Non-inverting Configuration
Input Common Mode Voltage
The common mode input range extends to 250mV below
ground and to 250mV above V_s, in single supply operation.
Exceeding these values will not cause phase reversal. However,
if the input voltage exceeds the rails by more than 0.5V, the
input ESD devices will begin to conduct. The output will
stay at the rail during this overdrive condition. If the absolute
maximum input voltage (700mV beyond either rail) is
exceeded, externally limit the input current to ±5mA as shown
in Figure 2.
-
FAN4272
V_o
V_in
+
10kΩ
Figure 2: Circuit for Input Current Protection
Power Dissipation
The maximum internal power dissipation allowed is directly
related to the maximum junction temperature. If the maximum
junction temperature exceeds 150°C, some performance
3.5
2.5
1.5
Input
0.5
-0.5
0
10 20 30 40 50 60 70 80
Time (µs)
Figure 3: Overdrive Recovery
Driving Capacitive Loads
The Frequency Response vs. C_L plot, illustrates the response
of the FAN4272. A small series resistance (R_s) at the output
of the amplifier, illustrated in Figure 4, will improve stability
and settling performance. R_s values in the Frequency Response
vs. C_L plot were chosen to achieve maximum bandwidth with
less than 2dB of peaking. For maximum flatness, use a larger
R_s. Capacitive loads larger than 200pF require the use of R_s.
+
-
R_f
R_g
R_s
C_L R_L
Figure 4: Typical Topology for driving
a capacitive load
Driving a capacitive load introduces phase-lag into the output
signal, which reduces phase margin in the amplifier. The
unity gain follower is the most sensitive configuration. In a
unity gain follower configuration, the FAN4272 requires a
75Ω series resistor to drive a 100pF load.
Rev. 2 December 2002
7