AN004 Datasheet, PDF (1/7 Pages) Analog Intergrations Corporation – Using AIC1563

AN004
Universal Step-Down DC/DC Converter Design
Using AIC1563
Abstract
Voltage required in the modern electronic systems
are single or multiple regulated voltages such as
3.3 V, 5V, 12V, -5V, or –12V, etc. It can be supplied
by using DC/DC converters. The operations of
Step-Down DC/DC converter is introduced in the
application note. A practical constant voltage,
DC/DC step-down converter design based on the
AIC1563 is also illustrated to help the readers in
the circuit designs and applications.
Operations of Step-Down DC/DC
Converter
Figure 1 shows a basic circuit configuration of
step-down DC/DC Converter.
SW
V_G
V_IN
+ ^VL _-
L
+
D
C
V _OUT
I_OUT
LOAD
CONTROL
CIRCUIT
Fig. 1 Step-Down DC/DC Converter
The voltage and current waveforms in the circuit
are shown in Fig. 2. The control circuit is used to
detect the output voltage level and generates a
May 1997
driving signal to turn on or turn off on the power
switch (SW). The power switch can be controlled
by using different methods, such as pulse width
modulation (PWM), pulse frequency modulation
(PFM), or pulse skipping modulation (PSM),
depends on the applications. As for the output
voltage stability, it is maintained by controlling the
duty cycle without losing energy. This may be
illustrated by examining the energy stored in the
inductor.
V_G
t
Driving signal on SW
I_SW
t
SW current
I_L
t
Inductor current
V_OUT
Output voltage
t
Fig. 2 Voltage and Current Waveforms of
Converter
The input electric energy is delivered to the load
and partially stored in an inductor during the power
switch turned on. The stored energy will be also
transferred to the load through a free-wheel diode
1