LMV321 Просмотр технического описания (PDF) - Fairchild Semiconductor
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LMV321 Datasheet PDF : 16 Pages
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LMV321/LMV358/LMV324
Application Information
General Description
The LMV3XX family are single supply, general purpose,
voltage-feedback amplifiers that are pin-for-pin compatible
and drop in replacements with other industry standard
LMV321, LMV358, and LMV324 amplifiers. The LMV3XX
family is fabricated on a CMOS process, features a rail-to-rail
output, and is unity gain stable.
The typical non-inverting circuit schematic is shown in
+Vs
6.8µF
+
+In
0.01µF
+
Out
LMV3XX
-
Rf
Rg
DATA SHEET
+
LMV3XX
Rs
-
10kΩ
CL 2kΩ
10kΩ
Figure 2: Typical Topology for driving a
capacitive load
3
2
1
0
-1
CL = 50pF
Rs = 0
-2
-3
CL = 100pF
Rs = 400Ω
-4
-5
CL = 200pF
Rs = 450Ω
-6
-7
-8
-9
0.01
0.1
1
10
Frequency (M H z )
Figure 1.
Figure 1: Typical Non-inverting configuration
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
degradation will occur. If the maximum junction temperature
exceeds 175°C for an extended time, device failure may occur.
Driving Capacitive Loads
The Frequency Response vs CL plot on page 4, illustrates the
response of the LMV3XX family. A small series resistance (Rs)
at the output of the amplifier, illustrated in Figure 2, will improve
stability and settling performance. Rs values in the Frequency
Response vs CL plot were chosen to achieve maximum band-
width with less than 1dB of peaking. For maximum flatness,
use a larger Rs. As the plot indicates, the LMV3XX family
can easily drive a 200pF capacitive load without a series
resistance. For comparison, the plot also shows the LMV321
driving a 200pF load with a 225Ω series resistance.
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 LMV3XX family
requires a 450Ω series resistor to drive a 200pF load. The
response is illustrated in Figure 3.
Rev. 1 November 2002
Figure 3: Frequency Response vs CL for unity
gain configuration
Layout Considerations
General layout and supply bypassing play major roles in high
frequency performance. Fairchild has evaluation boards to
use as a guide for high frequency layout and as aid in device
testing and characterization. Follow the steps below as a
basis for high frequency layout:
• Include 6.8µF and 0.01µF ceramic capacitors
• Place the 6.8µF capacitor within 0.75 inches of
the power pin
• Place the 0.01µF capacitor within 0.1 inches of
the power pin
• Remove the ground plane under and around the part,
especially near the input and output pins to reduce
parasitic capacitance
• Minimize all trace lengths to reduce series inductances
Refer to the evaluation board layouts shown in Figure 5 on
page 8 for more information.
7
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