IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS—I: REGULAR PAPERS, VOL. 54, NO. 4, APRIL 2007705
New Compact CMOS Li-Ion Battery Charger Using
Charge-Pump Technique for Portable Applications
Yuh-Shyan Hwang, Member, IEEE, Shu-Chen Wang, Fong-Cheng Yang, and Jiann-Jong Chen, Member, IEEE
Abstract—This paper presents a new compact CMOS Li-Ion
battery charger for portable applications that uses a charge-pump
technique. The proposed charger features a small chip size and
a simple circuit structure. Additionally, it provides basic func-
tions with voltage/current detection, end-of-charge detection,
and charging speed control. The charger operates in dual-mode
and is supported in the trickle/large constant-current mode to
constant-voltage mode with different charging rates. This charger
is implemented using a TSMC 0.35- m CMOS process with
a 5-V power supply. The output voltage is almost 4.2 V, and
the maximum charging current reaches 700 mA. It has 67.89%
power efficiency, 837-mW chip power dissipation, and only
? ???? ??? mm?in chip area including pads.
Index Terms—Charge pump, charger circuit, Li-Ion battery.
cations systems . The demand for smaller, sleeker portable
communications devices is pushing the wireless industry to re-
duce rechargeable battery size. Essential parameters that a de-
signer has to consider include voltage, energy density, tempera-
ture performance, and battery’s life , . A rechargeable bat-
tery’s life depends not only on charging time, but also on over-
charging control and charging method . A charger controller
is supplied a suitable electro-power for a rechargeable battery,
and it must detect overcharging to prevent explosions. High-en-
Li-Ion’s success on the market. Over the past few years, several
Li-Ion battery chargers based upon BJT and BiCMOS –
have been proposed. There are also charger systems built with
a microcontroller –, a low dropout (LDO) voltage reg-
ulator , two PNP transistors to switch between a current
and a voltage loop , and other chargers of various structures
that include power switch  or control using continuous and
switched loops to regulate the different charging process phases
sition between two high-gain linear feedback loops has been
OWADAYS, design engineers can choose from many en-
ergy solution options for portable and wireless communi-
Manuscript received August 18, 2006. This work was supported by the Na-
tional Science Council, Taiwan, R.O.C., under Grant NSC94-2213-E-027-049
Editor T. B. Tarim.
Y.-S. Hwang, F.-C. Yang and J.-J. Chen are with Department of Electronic
Engineering, National Taipei University of Technology, Taipei 106, Taiwan,
R.O.C. (e-mail: firstname.lastname@example.org).
S.-C. Wang is with Department of Electronic Engineering, National Taipei
University of Technology, Taipei 106, Taiwan, R.O.C. and also with the Busi-
ness Customer Service Laborator, Chunghwa Telecom Laboratory, Taoyuan
326, Taiwan, R.O.C.
Digital Object Identifier 10.1109/TCSI.2007.890605
Fig. 1. Li-Ion battery better charging mode.
proposed , . Most of these elements are complex, gen-
erating great circuits and increased costs. On the other hand,
using charge-pump techniques to translate voltages merely re-
quires two extra capacitors, with no need for any additional in-
ductors. Therefore, it is smaller in size, features lower electro-
magnetic interference (EMI) and noise, and can operate at a
higher switching frequency. The proposed charger has a simple
speed can be controlled by the charge-pump through the current
sensor feedback signal, thereby balancing the charging rate and
reducing battery damage at the same time.
II. DESIGN CONCEPT
A. Charging Control Algorithm
The charging control algorithm is a set of rules that follows
the specifications of the Li-Ion battery, as this charge-pump
based charger designed. The following four steps are recom-
mended for the Li-Ion battery charger.
1) Start charging and detect voltage across the Li-Ion battery.
2) Select a suitable charging mode, according to the Li-Ion
battery voltage determined in step 1.
battery at the same time. Observe the charging current
of the Li-Ion battery whether it exceeds
charging current is defined as the constant
Therefore, a battery with 1000-mAh capacity will be fully
charged with a constant charging current of 1000 mA in
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