DN395 - Universal Li-Ion Battery Charger Operates from USB and 6V to 36V Input in Just 2cm2

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Universal Li-Ion Battery Charger Operates from USB and
6V to 36V Input in Just 2cm2 – Design Note 395
Liu Yang
3mm × 6mm DFN package. The LTC4089’s buck regulator output voltage tracks the battery voltage to within
300mV. This Bat-TrackTM feature minimizes overall power
dissipation. The LTC4089-5 has a fixed 5V at OUT when
power is applied at HVIN. When power is supplied from
the USB port, the power manager maximizes the available
power to the system load; up to the full USB available
power of 2.5W. It automatically adjusts the Li-Ion battery
charge current with respect to the system load current
to maintain the total input current compliance within the
USB limits. The total solution size is less than 2cm2 with
all components on one side of the PCB.
Introduction
There are a number of advantages to offering USB and
high input voltage power and battery-charging capability in handheld devices such as GPS navigators, PDAs,
digital still cameras, photoviewers and MP3 players. For
instance, charging and operation from USB offers the
obvious convenience of not requiring a travel adapter. High
voltage sources, such as Firewire and 12V to 24V adapters
are even better, since they provide faster charging than
USB and allow charging in more places, such as in the car.
Nevertheless, there is an important design consideration
with high voltage power sources: the voltage difference
between the high voltage source and the battery in the
handheld is very large. Since a linear charger cannot handle
the power dissipation, a switching charger is required.
Adaptive High Voltage Buck Minimizes Total Power
Loss
The LTC4089’s buck converter output voltage VOUT tracks
the battery voltage VBAT. It is always 0.3V higher than
VBAT, so that the battery can be charged quickly while
The LTC® 4089 and LTC4089-5 (see Figure 1) conveniently integrate a high voltage and wide input range
(6V to 36V with 40V absolute maximum) monolithic
1.2A buck switching regulator and a USB power manager/charger into a compact thermally enhanced
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
Bat-Track is a trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
D2
C2
0.1µF
20
BOOST
SW
L1
10µH
19
C3
22µF
6.3V
D1
HVIN
6V TO 36V
21
C1
1µF
50V
HVIN
HVOUT
HVEN
HVOUT
3
18
22
7
HVPR
USB
4.35V TO 5.5V
12
C5
4.7µF
6.3V
15
C4
0.15µF
16
17
R3
2.1k 14
R4
71.5k
9
OUT
IN
HPWR
GATE
SUSP
BAT
CHRG
TIMER
VNTC
C10
10pF
GND
4
2
NTC
GND
1
(TO SYSTEM LOAD)
13
10
C6
4.7µF
6.3V
Q2
11
8
OUT
Li-ION+
(OPTIONAL)
6
CLPROG
PROG
VC
Q1
R6
10k
U1
LTC4089EDJC
5
R5
10k
1%
RNTC
10k
DN395 F01
Figure 1. The LTC4089 Schematic Illustrates Multiple Input Voltage Capability
08/06/395
minimizing overall power dissipation. Figure 2 shows the
overall efficiency at various input voltages, where the
total power dissipation is less than 1.1W. Furthermore,
if the battery is excessively discharged and VBAT falls
too low, the minimum VOUT is 3.6V to ensure continuous
system operation.
USB Power Manager Maximizes Power Available
to the System
In a traditional dual input device, the input charges the
battery and the system’s power is directly taken from
the battery. This creates a number of problems. One of
these is that the system’s available power is reduced
by the low-battery voltage when there is USB power
present. For example, when VBAT = 3.3V, the available
power to the system is only 1.65W while the USB itself
supplies 2.5W. The balance is dissipated as heat. The
LTC4089 successfully solves this problem by providing
an intermediate voltage VOUT to power the system load.
1.3
1.2
80
1.1
75
1.0
70
0.9
65
0.8
CHARGER EFFICIENCY
0.7
BUCK EFFICIENCY
TOTAL EFFICIENCY
0.6
TOTAL PLOSS
0.5
10 15 20 25 30 35 40
HIGH VOLTAGE INPUT (V)
0
5
The LTC4089 integrates a high voltage wide input monolithic switching regulator, USB power manager and Li-Ion
battery charger into a 3mm × 6mm DFN package and
improves the functionality of USB-based and multiple
power input portable devices.
1.4
85
55
Summary
TOTAL POWER LOSS (W)
EFFICIENCY (%)
VBAT = 3.5V
95 IBAT = 700mA
IOUT = 0
90
50
Small Footprint
With all the necessary components on the same side of
the PCB, the total solution size is less than 2cm2 (11.3mm
× 17.5mm) as shown in Figure 3.
1.5
100
60
This VOUT is independent of the battery voltage and equal
to the USB voltage, thus the full USB power is available
to the system load. Table 1 shows the advantages of the
LTC4089 power manager over the traditional dual input
configuration.
DN395 F02
Figure 2. The LTC4089 High Voltage Charger
Efficiency and Total Power Loss
DN395 F03
Figure 3. The LTC4089 Demo Circuit with Layout in
Bottom Right Corner
Table 1. Comparison of Traditional Dual Input Charger and Linear Technology’s LTC4089 Power Manager/Charger for USB
Charging
SCENARIO
Battery voltage is below trickle charging
voltage
Battery is not present
VBAT = 3.3V at USB input
System consuming close to the input
power limit
TRADITIONAL DUAL INPUT CHARGER
LTC4089 POWER MANAGER/CHARGER
Available current to system is only trickle charge
current (50mA to 100mA), which may not be
sufficient to start the system
Most chargers consider this as a fault. The
system cannot start
Available power to system is only 1.65W. The
system power cannot be greater than this
Cannot distinguish the available charging current.
Charger timer runs out before the battery is fully
charged
Full adapter/USB power is available to
system, although battery is in trickle charge
Full adapter/USB power is available to
system
Full 2.5W USB power is available to the
system
Charger time proportionally increases with
less available charge current. The battery is
always fully charged
Data Sheet Download
http://www.linear.com
For applications help,
call (408) 432-1900, Ext. 2364
Linear Technology Corporation
dn395f LT 0806 305K • PRINTED IN THE USA
FAX: (408) 434-0507 ● www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2006
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
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