ncp1536 ON Semiconductor, ncp1536 Datasheet - Page 6

• Manufacturer Part Number: ncp1536
• Description: 3.0 A, Step-down Switching Regulator
• Manufacturer: ON Semiconductor

Buck Converter Basics
which is the most elementary forward−mode converter. Its
basic schematic can be seen in Figure 3.
time periods. The first one occurs when the series switch is
on, the input voltage is connected to the input of the inductor.
rectifier (or catch diode) is reverse biased. During this
period, since there is a constant voltage source connected
across the inductor, the inductor current begins to linearly
ramp upwards, as described by the following equation:
material in the form of magnetic flux. If the inductor is
properly designed, there is sufficient energy stored to carry
the requirements of the load during the “off” period.
When the power switch turns off, the voltage across the
inductor reverses its polarity and is clamped at one diode
voltage drop below ground by the catch diode. The current
now flows through the catch diode thus maintaining the load
current loop. This removes the stored energy from the
inductor. The inductor current during this time is:
The NCP1536 is a “Buck” or Step−Down Converter
The operation of this regulator topology has two distinct
The output of the inductor is the output voltage, and the
During this “on” period, energy is stored within the core
The next period is the “off” period of the power switch.
V
in
Switch
Power
Figure 3. Basic Buck Converter
I
I
L(on)
L(off)
+
+
D
V
V out – V
in
– V out t on
L
L
L
D
t
off
C
out
DESIGN PROCEDURE
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R
Load
NCP1536
6
turned on. Regulation of the converter is accomplished by
varying the duty cycle of the power switch. It is possible to
describe the duty cycle as follows:
cycle can also be described as:
of the catch diode voltage and the inductor current.
This period ends when the power switch is once again
For the buck converter with ideal components, the duty
Figure 4 shows the buck converter, idealized waveforms
d +
Figure 4. Buck Converter Idealized Waveforms
t on
I
Power
Switch
V
min
Diode
T
D
Off
(FWD)
, where T is the period of switching.
V
on(SW)
Switch
Power
Switch
Power
On
d +
Switch
Power
Diode
Off
V out
V
I
pk
in
Switch
Power
Switch
Power
On
I
Load
Time
Time
(AV)