LM3524DN/NOPB National Semiconductor, LM3524DN/NOPB Datasheet - Page 13

• Manufacturer Part Number: LM3524DN/NOPB
• Description: IC REGULATOR PWM SWITCHER 16-DIP
• Manufacturer: National Semiconductor
• Type: Step-Down (Buck), Step-Up (Boost), Flybackr

Specifications of LM3524DN/NOPB

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 5V
• Current - Output: 200mA
• Frequency - Switching: 550kHz
• Voltage - Input: 8 ~ 40 V
• Operating Temperature: 0°C ~ 125°C
• Mounting Type: Through Hole
• Package / Case: 16-DIP (0.300", 7.62mm)
• Power - Output: 1W
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: *LM3524DN; LM3524DN

BASIC SWITCHING REGULATOR THEORY
AND APPLICATIONS
The basic circuit of a step-down switching regulator circuit is
shown in Figure 12, along with a practical circuit design using
the LM3524D in Figure 15.
Neglecting V
where T = Total Period
The above shows the relation between V
as Q1 only conducts during t
The efficiency, η, of the circuit is:
FIGURE 12. Basic Step-Down Switching Regulator
SAT
, V
D
, and settling ΔI
FIGURE 13. Relation of Switch Timing to Inductor Current in Step-Down Regulator
ON
.
L
+
= ΔI
IN
, V
L
−
;
o
and duty cycle.
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13
The circuit works as follows: Q1 is used as a switch, which
has ON and OFF times controlled by the pulse width modu-
lator. When Q1 is ON, power is drawn from V
to the load through L1; V
verse biased, and C
inductor L1 will force V
in it, D1 will start conducting and the load current will flow
through D1 and L1. The voltage at V
C
L1 is equal to the nominal DC load current plus some ΔI
which is due to the changing voltage across it. A good rule of
thumb is to set
ηMAX will be further decreased due to switching losses in Q1.
For this reason Q1 should be selected to have the maximum
possible f
CALCULATING INDUCTOR L1
Since ΔI
Solving the above for L1
where: L1 is in Henrys
o
f is switching frequency in Hz
filter giving a clean DC output. The current flowing through
L
+ = ΔI
T
, which implies very fast rise and fall times.
Δ I
L
−
LP-P
= 0.4I
o
is charging. When Q1 turns OFF the
A
40% × I
o
negative to keep the current flowing
A
is at approximately V
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o
.
A
is smoothed by the L1,
IN
and supplied
www.national.com
IN
, D1 is re-
L