LM3524DM National Semiconductor, LM3524DM Datasheet - Page 18

• Manufacturer Part Number: LM3524DM
• Description: IC, REGULATING PWM, 16-SOIC
• Manufacturer: National Semiconductor

Specifications of LM3524DM

• Primary Input Voltage: 40V
• No. Of Outputs: 1
• Output Voltage: 18V
• Output Current: 200mA
• No. Of Pins: 16
• Operating Temperature Range: 0°C To +125°C
• Power Dissipation Pd: 1W
• Termination Type: SMD
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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In calculating the output capacitor C
supplies I
time will be some ΔV
lator. Calculation of C
where: C
ΔV
Calculation of inductor L1 is as follows:
V
IN
is applied across L1
o
is the p-p output ripple
o
o
is in farads, f is the switching frequency,
during t
ON
c
. The voltage change on C
o
= ΔV
is:
o
or the output ripple of the regu-
o
it can be seen that C
o
during this
o
18
where: L1 is in henrys, f is the switching frequency in Hz
To apply the above theory, a complete step-up switching reg-
ulator is shown in Figure 20. Since V
V
amplifier's inverting input. The output voltage is:
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 re-
jection. 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.
IN
. The input voltage is divided by 2 to bias the error
IN
is 5V, V
REF
is tied to