LM3478MM National Semiconductor, LM3478MM Datasheet - Page 11

• Manufacturer Part Number: LM3478MM
• Description: Pulse Width Modulation (PWM) Controller IC
• Manufacturer: National Semiconductor

Specifications of LM3478MM

• Peak Reflow Compatible (260 C): No
• Leaded Process Compatible: No
• Mounting Type: Surface Mount
• Features: High Efficiency
• Package / Case: 8-MSOP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Functional Description
The compensation ramp has been added internally in
LM3478. The slope of this compensation ramp has been
selected to satisfy most of the applications. The slope of the
internal compensation ramp depends on the frequency. This
slope can be calculated using the formula:
In the above equation, V
compensation ramp. Limits for V
the electrical characteristics.
In order to provide the user additional flexibility, a patented
scheme has been implemented inside the IC to increase the
slope of the compensation ramp externally, if the need
arises. Adding a single external resistor, R
Figure 4) increases the slope of the compensation ramp, M
by :
M
C
= V
SL
SL
.F
FIGURE 3. Compensation Ramp Avoids Sub-Harmonic Oscillation
S
is the amplitude of the internal
Volts/second
SL
have been specified in
(Continued)
SL
(as shown in
C
11
In this equation, ∆V
∆V
frequencies.
SL
versus R
SL
has been plotted in Figure 5 for different
SL
is equal to 40.10
-6
10135511
R
SL
. Hence,
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