LINEAR TECHNOLOGY LTC4001 Technical data
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Handheld High Power Battery Charger
Design Note 393
Mark Gurries
Introduction
As the per formance of many handheld devices a pproaches
t h a t o f l a p t o p c o m p u t e r s , d e s i g n c o m p l e x i t y a l s o i n c r e a s es. Chief among them is thermal management—how do
you meet increasing p erformance demands while keeping
a compact and small product cool in the user’s hand?
For instance, as battery capacities inevitably increase,
cha rg e c ur re nt s w il l a ls o i ncr ea se to ma in tain or i mpr ov e
their charge times. Traditional linear regulator-based battery chargers will not be able to meet the charge current
and effi ciency demands necessary to allow a product to
run cool. What is needed is a switching-based charger
that takes just about the same amount of space as a linear
solution—but without the heat.
Small PCB Footprint
Figure 1 shows how simple a feature-laden LTC®4001based charger solution can be. This switching-based
charger only requires the IC, a small 1.5µH inductor, two
small 1206-size 10µF ceramic capacitors, and a few other
tiny components. Furthermore, even simpler confi gurations are possible (see Figure 2). This monolithic 2A,
1.5MHz synchronous PWM standalone battery charger
is packaged in a 4mm × 4mm 16-pin QFN package,
which contains the built-in switching MOSFETs and
charge termination controller. Figure 3 shows an actual
PCB solution.
Advanced Features and Functions
One of the more unique features of the LTC4001 is its
full remote voltage sense capability which permits faster
charge rates by bypassing voltage drops in narrow PCB
traces, EMI fi lters or current sense resistors for gas gauge
related support; this is placed on the system side of the
battery connector. Eliminating these losses in the sense
circuit can signifi cantly shorten the constant voltage
phase of the overall charge time.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
L1
1.5µH
07/06/393
V
4.5V TO 5.5V
IN
R1
10k
R3
10k
AT 25°C
L1: VISHAY DALE IHLP-2525AH-01
R3: NTC VISHAY DALE NTHS0603N02N1002J
R2
1k
C1
10µF
D1
LED
FROM µP
549Ω
V
PV
PGND
CHRG
NTC
FAULTTO µP
EN
PROG
R4
INSENSE
IN
SW SENSE
LTC4001
IDET TIMER
C2
0.22µF
R5
549Ω
SS
BATSENS
BAT
GNDSENS
C3
0.1µF
Figure 1. Li-Ion Battery Charger with 3-Hour Timer, Temperature
Qualifi cation, Soft-Start, Remote Sensing and C/10 Indication
C4
10µF
DN393 F01
2AHr
+
4.2V
Li-Ion
1.5µH
4.5V TO 5.5V
V
10µF
INSENSE
IN
274Ω
SW SENSE
LTC4001
IDET TIMER
0.1µF
IN
V
PV
PGND
CHRG
NTC
FAULT
EN
PROG
0.22µF
SS
BATSENS
BAT
GNDSENS
10µF
+
DN393 F02
4.2V
Li-Ion
Figure 2. Simple 2A Battery Charger
Another important feature is programmable soft-start,
which requires only a small ceramic capacitor on the SS
pin. S oft-s tar t saves design time and cos t by simplify ing
the power source requirements, precluding the need to
h a n d l e f a s t s t a r t - u p l o a d t r a n s i e n t s c o m m o n l y f o u n d w i t h
switching power supplies.
Other advanced features include: 50mA trickle charge
recovery of over-discharged batteries below 3V/cell;
adjustable charge timer via a single capacitor on the
TIMER pin; and automatic restart of a charge cycle when
the battery voltage falls below 100mV of the full charge
voltage.
Two signals provide status. First is the FAULT pin, which
in conjunction with the LTC4001 thermistor circuit,
reports an out-of-range temperature situation. When a
temperature fault occurs, the charge process is stopped
immediately. Charging a bat tery when it is out o f its normal
temp range can damage it. Second, the CHRG pin shows
three states relating to the charge state of the battery or
charger. In addition to the normal OFF indication, it also
indicates w hen the batter y is below its user programmable
threshold or when in bulk charge mode.
I
DET
The EN (Enable) pin allows for shutdown of the charger,
thus reducing its V
quiescent current below 50µA and
IN
the battery drain current to less than 3µA. Shutdown
also occurs automatically if V
falls to less than 250mV
IN
above the current battery voltage.
DN393 F03
Figure 3. Actual LTC4001 Demo Board Showing a
Compact Footprint (Height ≤ 1.8mm)
Flexible Options
The LTC4001 provides a number of fl exible options in its
small package. Bulk charge current is programmable via
the PROG pin and a simple resistor, from 2A and below.
A separate resistor on the I
pin is all that is required
DET
to set the full charge current termination or indication
threshold independently of the bulk charge current setting. Typically the I
threshold is set to 1/10 (C/10) of
DET
the bulk charge current, which equates to a battery being about 95% to 98% full. Raising the I
current trip
DET
threshold signifi cantly reduces charge time by having
a full charge indication occur sooner in exchange for a
slightly lower full state of charge. Likewise, increasing
the trip threshold extends the timer to approach a 100%
state of charge if there are no serious time constraints.
The type of charge termination is also fl exible. In addition
to timer-based termination, the charge can be terminated
when the I
thr es ho ld is re ach ed or c ha rg e t er mi na tio n
DET
can be defeated all together to allow an external power
manager to decide.
Conclusion
The LTC4001 is the charger of choice for the next generation of handheld devices with its tiny solution size,
unmatched power capability, high effi ciency, protection
features and fl exible options.
Data Sheet Download
www.linear.com
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507 ● www.linear.com
For applications help,
call (408) 432-1900, Ext. 2364
dn393f LT/TP 0706 305K • PRINTED IN THE USA
© LINEAR TECHNOLOGY CORPORATION 2006
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