LM3524DN National Semiconductor, LM3524DN Datasheet - Page 19

• 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

Typical Applications
In calculating the output capacitor C
supplies I
time will be some ∆V
regulator. Calculation of C
where: C
Calculation of inductor L1 is as follows:
V
where: L1 is in henrys, f is the switching frequency in Hz
To apply the above theory, a complete step-up switching
regulator is shown in Figure 20. Since V
to V
amplifier’s inverting input. The output voltage is:
IN
∆V
is applied across L1
IN
o
. The input voltage is divided by 2 to bias the error
is the p-p output ripple
o
o
is in farads, f is the switching frequency,
during t
ON
. The voltage change on C
c
= ∆V
o
is:
o
or the output ripple of the
o
(Continued)
it can be seen that C
IN
is 5V, V
o
during this
REF
is tied
o
19
The network D1, C1 forms a slow start circuit.
This holds the output of the error amplifier initially low thus
reducing the duty-cycle to a minimum. Without the slow start
circuit the inductor may saturate at turn-on because it has to
supply high peak currents to charge the output capacitor
from 0V. It should also be noted that this circuit has no
supply rejection. By adding a reference voltage at the non-
inverting input to the error amplifier, see Figure 21, the input
voltage variations are rejected.
The LM3524D can also be used in inductorless switching
regulators. Figure 22 shows a polarity inverter which if con-
nected to Figure 20 provides a −15V unregulated output.
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