AN002 Datasheet, PDF (1/5 Pages) Analog Intergrations Corporation – Portable Applications

AN002
Two-Cell, Step-Up Converter Design for
Portable Applications
Introduction
In recent years, the markets for portable electrical
devices, such as the electronic dictionary, palmtop
computers, notebook PCs, PDAs and cellular
phones has grown rapidly. All of these devices use
batteries as the source of power. Due to their
limitations of small size and light weight and due to
increasingly stringent environmental requirements
in product development, the use of small numbers,
small size, long-lasting batteries has become a
trend.
The AIC1630/1631/1633 are very suitable for the
application of using 2~4 batteries. This article will
focus on the application of AIC1631-5 for 2
batteries in the following description.
A set of two alkaline, NiMH, or NiCd battery cells
accompanied by a switching converter with 3V,
3.3V, or 5V output voltage is frequently used as
the power supply source for portable electronic
products. Using two battery cells is usually a result
of compromise between size and battery
operating life. Besides the batteries’ own stored
energy, two other factors also influence batteries’
operating life: the product’s power consumption
and conversion efficiency of the converter. In
order to choose the appropriate switching
converter for an electronic product, therefore, 5
key factors need to be considered:
(1) The current capacity and regulation of the
output should meet the product’s demands.
(2) High conversion efficiency.
(3) Low power consumption.
May 1997
(4) Squeeze out as much of the battery energy
as possible.
(5) Small size and light weight.
The first factor is absolutely necessary, and the
importance of the other four differs in priority
depending on the character of the product. For
products, which operate relatively high current
for extended time periods, conversion efficiency
is paramount. For products operate with low
current for most of the time, the current
consumption of the converter itself must also be
low. With regards to size and weight, an 8-pin IC,
which does not need a heatsink, with a small
inductor, and minimum number of external parts,
would be an ideal choice. In the following, we use
the AIC1631 DC/DC converter as an example for
several different special products using two
battery cells to demonstrate how the AIC1631
can be used to make an ideal power source.
+V_IN
+V_OUT
1K
33K
(+5V)
ILIM/SD
VOUT
R1
R2
VIN
LBI
+
100µF
C1
+
10µF
C2
SW
SGND
LBO
CGND
+
C3
100µF
AIC1631-5
47µH*
1N5819
*Sumida RCH-108
D1
Fig. 1 A High-Efficiency 2-Cell to 5V Converter
1