LM3524DN National Semiconductor, LM3524DN Datasheet - Page 14

• Manufacturer Part Number: LM3524DN
• Description: ENHANCED PWM CONTROLLER, 3524, DIP
• Manufacturer: National Semiconductor

Specifications of LM3524DN

• Frequency: 350kHz
• Power Dissipation Pd: 1W
• Digital Ic Case Style: DIP
• No. Of Pins: 16
• Operating Temperature Range: 0°C To +125°C
• Svhc: No SVHC (15-Dec-2010)
• Operating Temperature Max: 125°C
• Base Number: 3524
• Controller Type: PWM
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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Typical Applications
where: L1 is in Henrys
Also, see LM1578 data sheet for graphical methods of in-
ductor selection.
CALCULATING OUTPUT FILTER CAPACITOR C
Figure 13 shows L1’s current with respect to Q1’s t
t
flow to the load and C
ence between I
From Figure 13 it can be seen that current will be flowing into
C
a time, t
∆I
For best regulation, the inductor’s current cannot be allowed
to fall to zero. Some minimum load current I
inductor current, is required as shown below:
OFF
o
L
f is switching frequency in Hz
/4. The resulting ∆V
for the second half of t
times (V
ON
/2 + t
A
L
is at the collector of Q1). This curent must
, and I
OFF
/2. The current flowing for this time is
o
o
c
. C
.
Ic
or ∆V
ON
o
o
’s current will then be the differ-
= I
through the first half of t
o
L
− I
is described by:
o
(Continued)
o
, and thus
o
:
ON
OFF
and
, or
14
A complete step-down switching regulator schematic, using
the LM3524D, is illustrated in Figure 15. Transistors Q1 and
Q2 have been added to boost the output to 1A. The 5V
regulator of the LM3524D has been divided in half to bias the
error amplifier’s non-inverting input to within its common-
mode range. Since each output transistor is on for half the
period, actually 45%, they have been paralleled to allow
longer possible duty cycle, up to 90%. This makes a lower
possible input voltage. The output voltage is set by:
where V
input.
Resistor R3 sets the current limit to:
Figures 16, 17 and show a PC board layout and stuffing
diagram for the 5V, 1A regulator of Figure 15. The regulator’s
performance is listed in Table 1.
FIGURE 14. Inductor Current Slope in Step-Down
NI
is the voltage at the error amplifier’s non-inverting
Regulator
00865019