DN1002 - Shrink Battery-Powered Products with a Combination Battery Charger and DC/DC Converter

advertisement
Shrink Battery-Powered Products with a Combination Battery
Charger and DC/DC Converter – Design Note 1002
Tom Hack
Introduction
Until now, power management in portable devices or
systems with battery backup have required a mix of
major components to fulfill the basic functions of battery
charging and generation of system supply voltages. A
typical solution requires at least one charger IC for
charging the battery, another IC to supply a regulated
system bus voltage from a constantly changing battery
voltage, PowerPath™ control and a low dropout regulator (Figure 1).
Space is at a premium in these ever shrinking portable
products, creating an imperative to shrink the power
circuitry as well. The LTC®1980 solves the space problem
by combining these functional blocks into a single IC. The
result is a substantial reduction in the complexity of
portable power systems (Figure 2).
How the LTC1980 Reduces Size and Cost
The LTC1980 manages both battery charging and
generaton of the regulated system bus voltage via a unique
bidirectional pulse-width modulator design (Figure 3).
When the wall adapter is present, power passes directly to
the system load DC/DC converters and to a pulse widthmodulated battery charger formed by M1, M2, T1 and the
LTC1980. With the wall adapter present, power flows into
CHARGE
TERMINATION
the battery. With the wall adapter removed, power flows
in the opposite direction, out of the battery, and is regulated through the DC/DC converter formed by the same
power components. In this way, a single bidirectional
supply replaces two traditional pulse width modulated
supplies producing a substantial parts savings. No additional power routing/management is needed, further
reducing the parts count and power losses that would be
incurred by the additional circuitry.
4.1V/1A Li-Ion Battery Charger and
3.3V DC/DC Converter
Figure 4 shows a 4.1V/1A Li-Ion battery charger and 3.3V
DC/DC converter. The LTC1980 includes a complete PWM
regulator controller, PowerPath management functions
and charge termination (including pre-trimmed 4.1V,
4.2V, 8.2V and 8.4V float voltages, under- and overvoltage protection, trickle-charge cell conditioning and charge
termination timing). Other battery chemistries may be
externally programmed.
This design is compatible with both regulated and
unregulated wall adapters (minimum output voltage 4.1V).
For higher voltage wall adapters, adjust R15 to increase
the wall-adapter detection threshold. D1 is optional and
provides protection against accidental wall-adapter connector shorts—a problem in some products that use
charging cradles with exposed connections.
, LTC and LT are registered trademarks of Linear Technology Corporation.
PowerPath is a trademark of Linear Technology Corporation.
FROM
WALL
ADAPTER
BATTERY
CHARGER
PowerPath
CONTROL
PWM
REGULATOR
LOW DROPOUT
REGULATOR
TO SYSTEM
LOAD DC/DC
CONVERTERS
DN1002 F01
FROM WALL ADAPTER
LTC1980-BASED
POWER DESIGN
DN1002 F02
Figure 1. Traditional Portable Power System
12/03/1002
TO SYSTEM LOAD
DC/DC CONVERTERS
Figure 2. An LTC1980-Based Portable Power System
•
T1
Li-Ion
BATTERY
WALL
ADAPTER
T1
Li-Ion
BATTERY
•
M1
M1
SYSTEM LOAD
DC/DC
CONVERTERS
RS
ISENSE
•
M2
•
M2
SYSTEM LOAD
DC/DC
CONVERTERS
RS
ISENSE
LTC1980
LTC1980
DN1002 F03a
DN1002 F03a
(3b) DC/DC Converter Mode (Wall Adapter Removed)
(3a) Battery Charger Mode
Figure 3. LTC1980 Bidirectional Power Conversion
VBAT
+
4.1V
Li-Ion
BATTERY
C1
68µF
D1*
5819
BH511-1014
+
VREG
+
•
5.1Ω
1nF
M1
1/2 FDC6401N
WALL
ADAPTER
C4
68µF
5.1Ω
OPTIONAL PASS
TRANSISTOR
FOR LDO FDC636P
1nF
M2
1/2 FDC6401N
•
50mΩ
RSENSE
14
BGTDR
18
VBAT
23
OVP
3
REGFB
22
CAOUT
PROG
1
R9
10k
12
R11
1M
21
GND ISENSE
11
7
6
5
PROGT
C11
1nF
VC
TIMER
4
17
C7
0.27µF
15
REG
16
MODE
9
BATT1
10
BATT2
C12
82pF
R13
806k
SS
24
C8
0.1µF
WA
VBIAS1
C9
1µF
200pF
ACIN
VLDO 3.1V
SYSTEM LOAD
DC/DC
CONVERTERS
C6
470µF
R5
154k
R6
100k
8
RGTDR VREG LDODRV LDOFB
LTC1980
2
R10
110k
M3
20
PGND
DCOUT
3.3V
VOUT
R15
221k
1%
R7
100k
1%
R8
169k
VBIAS2
13
C10
0.33µF
19
R14
100k
R12
100k
*OPTIONAL DIODE FOR
SHORTED WALL ADAPTER
TERMINAL PROTECTION.
DN1002 F04
Figure 4. 4.1V/4.2V Selectable 1A Li-Ion Battery Charger and 3.3V DC/DC Converter
Conclusion
The LTC1980 helps reduce size, complexity and lowers
the cost of portable products by integrating a DC/DC converter and battery charger circuitry into a single IC. It also
offers high efficiency, increasing battery run time and lowering power dissipation during battery charging.
90
85
EFFICIENCY (%)
High Efficiency Makes for Cool Running Products
and Extends Operating Time Between Charges
Peak DC/DC converter efficiency, excluding the optional,
low dropout regulator is over 88% (see Figure 5). In
addition, the LTC1980 uses pulse-width modulated charging. When compared to linear chargers, there is less power
dissipation keeping operating temperatures lower.
80
75
70
VBAT = 3.6V
TA = 25°C
FIGURE 4
65
60
10
100
LOAD CURRENT (mA)
1000
DN1002 F05
Figure 5. Regulator Efficiency vs Load Current
Data Sheet Download
http://www.linear.com
Linear Technology Corporation
For applications help,
call (408) 432-1900, Ext. 2593
dn1002 LT 1203 • PRINTED IN THE USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507 ● www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2003
Similar pages