ANP007 Datasheet, PDF (9/11 Pages) Anachip Corp – Dual Buck Converter

Application Note
AP2001 Dual Buck Converter
3. Design Procedure
ANP007
3.1 Introduction
The AP2001 integrated circuit is dual PWM controller, It operates over a wide input voltage range. This
together with its low cost makes it a very popular choice for use in PWM controller. This section will
describe the AP2001 to design procedure. The operation and the design of the dual-buck converter will
also be discussed in detail.
3.2 Operating Specifications
Specification
Min
Typ
Max Units
Input Voltage Range
Output Buck1 Voltage Range
Output Buck2 Voltage Range
Output Current (Buck1) Range
Output Current (Buck2) Range
Operating Frequency
Output Ripple
Efficiency
10.8
12
13.2
V
5
V
3.3
V
0.3
3
A
0.3
3
A
180
200
220
KHz
50
mV
86
%
Table 1. Operating Specifications
3.3 Design Procedures
This section describes the steps to design continuous-mode buck and boost converter, and
explains how to construct basic power conversion circuits including the design of the control chip
functions and the basic loop. A switching frequency of 200 kHz was chosen.
Example calculations accompany the design equations. Since this is a fixed output converter, all
example calculations apply to the converter with output voltage is 3.3V/5V and input voltage set to 12 V,
unless specified otherwise. The first quantity to be determined is the converter the duty cycle value.
Duty ratio D =
+ Vo
– Vin
Vd ₌
Vds(sat)
Ton
Ts
,
0≦D≦1
Assuming the commutating diode forward voltage Vd = 0.5 V and the power switch on voltage Vds(sat) =
0.1V, the duty cycle for Vo = 3.3V and Vin = 10.8, 12, 13.2 is 0.36, 0.32, 0.29 respectively; The duty cycle
for Vo = 5V and Vin = 10.8, 12, 13.2 is 0.51, 0.46 ,0.42 respectively.
3.3.1 Selection of the buck inductor (L)
A buck converter uses a single-stage LC filter. Choose an inductor to maintain continuous-mode
operation down to 10 percent (Io(min)) of the rated output load:
Anachip Corp.
www.anachip.com.tw
Rev. A.0 Feb. 20, 2003
9/11