LTC1479
PowerPath Controller
for Dual Battery Systems
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DESCRIPTION
FEATURES
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The LTC ®1479 is the “heart” of a total power management
solution for single and dual battery notebook computers
and other portable equipment. The LTC1479 directs power
from up to two battery packs and a DC power source to the
input of the main system switching regulator. It works in
concert with related LTC power management products
(e.g. LTC1435, LT ®1511, etc.) to create a total system
solution; starting from the batteries and the DC power
source, and ending at the input of each of the computer’s
complex loads. A system-provided power management
µP monitors and actively directs the LTC1479.
Complete Power Path Management for Two
Batteries, DC Power Source, Charger and Backup
Compatible with Li-Ion, NiCd, NiMH and Lead-Acid
Battery Chemistries
“3-Diode” Mode Ensures Powers is Available
under “Cold Start” Conditions
All N-Channel Switching Reduces Power Losses
Capacitor and Battery Inrush Current Limited
“Seamless” Switching Between Power Sources
Independent Charging and Monitoring of Two
Battery Packs
New, Small Footprint, 36-Lead SSOP Package
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APPLICATIONS
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The LTC1479 uses low loss N-channel MOSFET switches
to direct power from three main sources. An adaptive
current limiting scheme reduces capacitor and battery
inrush current by controlling the gates of the MOSFET
switches during transitions. The LTC1479 interfaces directly to the LT1510, LT1511 and LT1620/LTC1435 battery charging circuits.
Notebook Computer Power Management
Portable Instruments
Handheld Terminals
Portable Medical Equipment
Portable Industrial Control Equipment
, LTC and LT are registered trademarks of Linear Technology Corporation.
PowerPath is a trademark of Linear Technology Corporation.
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TYPICAL APPLICATION
Dual Battery PowerPathTM Controller System Block Diagram
AC
ADAPTER
SW A/B
DCIN
SW C/D
RSENSE
+
SW E/F
BAT1
SW G
CIN
HIGH EFFICIENCY
DC/DC SWITCHING
REGULATOR
(LTC1435/LTC1438
ETC.)
5V
SW H
BAT2
BATTERY CHARGER
(LT1510/LT1511/
LT1620/LTC1435)
BACKUP
REGULATOR
(LT1304)
LTC1479
PowerPath CONTROLLER
STATUS &
CONTROL
POWER
MANAGEMENT
µP
1479 TA01
1
LTC1479
U
W
U
U
W W
W
ABSOLUTE MAXIMUM RATINGS
PACKAGE/ORDER INFORMATION
DCIN, BAT1, BAT2 Supply Voltages .......... – 0.3V to 32V
SENSE +, SENSE –, VBAT, V + ..................... – 0.3V to 32V
GA, GB, GC, GD, GE, GF, GG, GH .............. – 0.3V to 42V
SAB, SCD, SEF, SG, SH ............................ – 0.3V to 32V
SW, VGG ................................................... – 0.3V to 42V
DCDIV, BDIV ............................................ – 0.3V to 5.5V
All Logic Inputs (Note 1).......................... – 0.3V to 7.5V
All Logic Outputs (Note 1) ....................... – 0.3V to 7.5V
VCC Regulator Output Current ................................ 1mA
VCCP Regulator Output Current .............................. 1mA
V + Output Current .................................................. 1mA
VGG Regulator Output Current ............................ 100µA
Operating Temperature
LTC1479CG ............................................. 0°C to 70°C
LTC1479IG ........................................ – 40°C to 85°C
Junction Temperature........................................... 125°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
TOP VIEW
DCIN
1
36 VBKUP
DCDIV
2
35 BAT1
LOBAT
3
34 BAT2
GA
4
33 BDIV
SAB
5
32 VBAT
GB
6
31 CHGMON
GC
7
30 BATSEL
SCD
8
29 GG
GD
9
28 SG
GE 10
27 GH
SEF 11
26 SH
GF 12
SENSE +
LTC1479CG
LTC1479IG
25 DCINGOOD
13
24 DCIN/BAT
SENSE – 14
23 BATDIS
VCC 15
22 3DM
VGG 16
21 CHGSEL
V+
ORDER PART
NUMBER
17
20 VCCP
SW 18
19 GND
G PACKAGE (209 mils)
36-LEAD PLASTIC SSOP
TJMAX = 100°C, θJA = 95°C/ W
Consult factory for Military grade parts.
DC ELECTRICAL CHARACTERISTICS
VDCIN = 25V, VBAT1 = 16V, VBAT2 = 12V, TA = 25°C unless otherwise noted. (Note 2)
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Power Supplies
VDCIN
DCIN Operating Range
(Mode 1) DCIN Selected
6
28
V
VBAT1
Battery 1 Operating Range
(Mode 5) Battery 1 Selected
6
28
V
VBAT2
Battery 2 Operating Range
(Mode 6) Battery 2 Selected
6
28
V
VBKUP
Backup Operating Range
(Mode 8) Backup Operation
6
28
V
IDCIN
DCIN Operating Current
(Mode 1) DCIN Selected
175
500
µA
IVBAT1
Battery 1 Operating Current
(Mode 5) Battery 1 Selected
150
500
µA
IVBAT2
Battery 2 Operating Current
(Mode 6) Battery 2 Selected
150
500
µA
IVBKUP
Backup Operating Current
(Mode 8) Backup Operation (VBKUP = 6V)
40
100
µA
VCCP
VCCP Regulator Output Voltage
(Modes 1, 5, 6) DCIN, Battery 1 or Battery 2 Selected
●
4.8
6.0
V
VCC
VCC Regulator Output Voltage
(Modes 1, 5, 6) DCIN, Battery 1 or Battery 2 Selected
●
3.3
3.6
3.9
V
VGG
VGG Gate Supply Voltage
(Modes 1, 5, 6) DCIN, Battery 1 or Battery 2 Selected
●
34.0
36.3
40.0
V
VUVLO
UV Lockout Threshold
(Mode 9) No Power, VBATX Falling from 12V
4.0
4.5
5.0
V
VUVLOHYS
UV Lockout Hysteresis
(Mode 9) No Power, VBATX Rising from 1V
0.2
0.5
1.0
V
2
4.0
LTC1479
DC ELECTRICAL CHARACTERISTICS
VDCIN = 25V, VBAT1 = 16V, VBAT2 = 12V, TA = 25°C unless otherwise noted. (Note 2)
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
1.190
1.215
1.240
10
35
50
UNITS
DCIN Good Monitor
VTHDCDIV
DCDIV Threshold Voltage
(Mode 1) VDCDIV Rising from 1V to 1.5V
VHYSDCDIV DCDIV Hysteresis Voltage
(Mode 1) VDCDIV Falling from 1.5V to 1V
IBIASDCDIV DCDIV Input Bias Current
(Mode 1) VDCDIV = 1.5V
VLODCGD
DCINGOOD Output Low Voltage
(Mode 1) VDCDIV = 1V, IDCINGOOD = 100µA
0
0.1
0.4
V
IPUDCGD
DCINGOOD Pull-Up Current
(Mode 1) VDCDIV = 1.5V, VDCINGOOD = 0V
1
2
6
µA
ILKGDCGD
DCINGOOD Leakage Current
(Mode 1) VDCDIV = 1.5V, VDCINGOOD = 7V
±1
µA
V
●
20
V
mV
nA
Battery Monitor
VTHLOBAT
Low-Battery Threshold Voltage
(Modes 5, 6) VBDIV Falling from 1.5V to 1V
VHYSLOBAT Low-Battery Hysteresis Voltage
(Modes 5, 6) VBDIV Rising from 1V to 1.5V
IBIASBDIV
BDIV Input Bias Current
(Modes 5, 6) VBDIV = 1.5V
VLOLOBAT
LOBAT Output Low Voltage
(Modes 5, 6) VBDIV = 1V, ILOBAT = 100µA
ILKGLOBAT
LOBAT Output Leakage Current
(Modes 5, 6) VBDIV = 1.5V, VLOBAT = 7V
RONBATSW Battery Switch ON Resistance
(Modes 5, 6) Each Switch Tested Independently
ILKGBATSW Battery Switch OFF Leakage
(Modes 5, 6) Each Switch Tested Independently
●
1.190
1.215
1.240
10
35
50
0
0.1
20
200
mV
nA
0.4
V
±1
µA
800
Ω
±1
µA
5.5
5.2
7.0
7.0
V
V
0
0.4
V
400
Gate Drivers
VGS(ON)
Gate-to-Source ON Voltage (GA to GF) (Modes 1, 2, 4, 5, 6) IGS = –1µA
Gate-to-Source ON Voltage (GG, GH) (Modes 2, 4) IGS = –1µA
5.0
4.5
VGS(OFF)
Gate-to-Source OFF Voltage
(Modes 1, 2, 4, 5, 6) IGS = 100µA
IBSENSE+
SENSE +
Input Bias Current
(Modes 1, 5, 6)
5
15
30
µA
IBSENSE–
SENSE – Input Bias Current
(Modes 1, 5, 6)
5
15
30
µA
VSENSE
Inrush Current Limit Sense Voltage
(Modes 1, 5, 6)
0.15
0.20
0.25
V
IPDSAB
SAB Pull-Down Current
(Modes 5, 6) VSAB = 10V
30
100
300
µA
IPDSCD
SCD Pull-Down Current
(Mode 1) VSCD = 10V
30
100
300
µA
IPDSEF
SEF Pull-Down Current
(Mode 1) VSEF = 10V
30
100
300
µA
IPDSG
SG Pull-Down Current
(Mode 1) VSG = 10V
3
mA
IPDSH
SH Pull-Down Current
(Mode 1) VSH = 10V
3
mA
●
Charge Monitor
RONCMON
CHGMON Switch ON Resistance
(Modes 5, 6) Each Switch Tested Independently
ILKGCMON
CHGMON Switch OFF Leakage
(Modes 5, 6) Each Switch Tested Independently
50
150
250
Ω
±1
µA
Digital Inputs
VHIDIGIN
Input High Voltage
(Mode 1) All Digital Inputs
●
VLODIGIN
Input Low Voltage
(Mode 1) All Digital Inputs
●
IHIDIGIN
Input Leakage Current
(Mode 1) All Digital Inputs, VDIGINX = 7V
ILODIGIN
Input Leakage Current
(Mode 1) VDIGINX = 0V (Note 3)
IPUDIGIN
Input Pull-Up Current
(Mode 1) VDIGINX = 0V (Note 4)
2
1
V
2
0.8
V
±1
µA
±1
µA
6
µA
3
LTC1479
AC ELECTRICAL CHARACTERISTICS
VDCIN = 25V, VBAT1 = 16V, VBAT2 = 12V, TA = 25°C unless otherwise noted. (Note 2)
SYMBOL
tONGA/GB
tONGC/GD
tONGE/GF
tOFFGA/GB
tOFFGC/GD
tOFFGE/GF
tONGG/GH
tOFFGG/GH
fOVGG
tdLOBAT
tdDCINGOOD
PARAMETER
Gate A/B Turn-On Time
Gate C/D Turn-On Time
Gate E/F Turn-On Time
Gate A/B Turn-Off Time
Gate C/D Turn-Off Time
Gate E/F Turn-Off Time
Gate G/H Turn-On Time
Gate G/H Turn-Off Time
VGG Reg Operating Frequency
LOBAT Delay Times
DCINGOOD Delay Times
CONDITIONS
VGS > 3V (Note 5)
VGS > 3V (Note 5)
VGS > 3V (Note 5)
VGS < 1V (Note 5)
VGS < 1V (Note 5)
VGS < 1V (Note 5)
VGS > 3V (Note 5)
VGS < 1V (Note 5)
∆VBDIV = ±100mV, RPULLUP = 51k
∆VDCDIV = ±100mV, RPULLUP = 51k
The ● denotes specifications which apply over the full operating
temperature range.
Note 1: The logic inputs are high impedance CMOS gates with ESD
protection diodes to ground and therefore should not be forced below
ground. These inputs can however be driven above the VCCP or VCC supply
rails as there are no clamping diodes connected between the input pins
and the supply rails. This facilitates operation in mixed 5V/3V systems.
Note 2: The Selected Operating Mode Truth Table, which defines the
operating conditions and logical states associated with each “normal”
operating mode, should be used in conjunction with the Electrical
TRUTH TABLE
SELECTED MODES
MIN
MAX
UNITS
µs
µs
µs
µs
µs
µs
µs
µs
kHz
µs
µs
Characteristics table to establish test conditions. Actual production test
conditions may be more stringent.
Note 3: The following inputs are high impedance CMOS inputs:
3DM and DCIN/BAT and have no internal pull-up current.
Note 4: The following inputs have built-in 2µA pull-up current sources
(passed through series diodes): BATSEL, BATDIS and CHGSEL.
Note 5: Gate turn-on and turn-off times are measured with no inrush
current limiting, i. e., VSENSE = 0V, using Si4936DY MOSFETs in the typical
application circuit.
(Selected Operating Modes)
LOGIC INPUTS
SWITCH STATUS
SW SW SW
C/D E/F
G
Off Off Off
Off Off On
SW
H
Off
Off
CHGMON
Hi-Z
BAT1
Off
Off
Off
Hi-Z
BAT2
H
H
Off
Off
On
BAT2
BAT2
H
H
Off
On
Off
Off
Off
Off
Off
Off
Off
Hi-Z
Hi-Z
Hi-Z
BAT1
BAT2
BAT1
H
H
L
L
L
L
Off
Off
Off
Off
Off
Off
Hi-Z
Hi-Z
BAT1
BAT2
L
L
L
L
3DM* Off
Off Off
Off
Off
Hi-Z
Hi-Z
BAT1
BAT1
L
L
H
H
SW
NO. MODE
3DM DCIN/BAT BATSEL BATDIS CHGSEL A/B
1 DC Operation
H
H
H
L
H
On
2 DC Operation and
H
H
H
H
H
On
BAT1 Charging
3 DC Operation and
H
H
L
L
L
On
Off
BAT2 Disconnected
4 DC Operation and
H
H
L
H
L
On
Off
BAT2 Charging
5 BAT1 Operation
H
L
H
H
H
Off
On
6 BAT2 Operation
H
L
L
H
H
Off
Off
7 BAT1 Low and
H
L
H
L
H
Off
Off
Disconnected
8 Backup Operation
H
L
H
L
H
Off
Off
9 No Power
L
L
L
L
L
Off
Off
(No Backup)
10 DC Reconnected
L
L
H
L
H
3DM* 3DM*
11 DC Connected
H
H
H
L
H
On
Off
and Reset
* 3DM = Three Diode Mode. When this mode is invoked, only the first
MOSFET switch in each back-to-back switch pair, i. e., SW A, SW C and
SW E is turned on. Current may still pass through the inherent body
diode of the idled switches, i.e., SW B, SW D and SW F to help restart
4
TYP
30
30
30
3
3
3
300
5
30
5
5
OUTPUTS
VBAT LOBAT
BAT1
H
BAT1
H
DCINGOOD
H
H
the system after abnormal operating conditions have been encountered.
See the Timing Diagram and Applications Information sections for
further details.
LTC1479
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TYPICAL PERFORMANCE CHARACTERISTICS
MODE 1, DCDIV = 1.5V
NO OTHER POWER
TJ = 25°C
250
200
150
100
BAT2 Supply Current
350
MODE 5
NO OTHER POWER
TJ = 25°C
300
BAT1 SUPPLY CURRENT (µA)
300
250
200
150
100
20
30
15
25
10
DCIN SUPPLY VOLTAGE (V)
0
35
5
20
30
15
25
10
BAT1 SUPPLY VOLTAGE (V)
VBKUP Supply Current
70
150
100
35
0
0
VGG SUPPLY VOLTAGE (V)
42
50
40
30
20
35
1479 G03
MODE 1
VDCIN = 24V
40
38
36
34
30
50
100
25
75
– 50 – 25
0
JUNCTION TEMPERATURE (°C)
0
0
5
20
30
15
25
VBKUP SUPPLY VOLTAGE (V)
10
35
125
1479 G05
1479 G04
VCC Supply Voltage
3.9
20
30
15
25
10
BAT2 SUPPLY VOLTAGE (V)
32
10
4.0
5
VGG Supply Voltage
44
MODE 8
NO OTHER POWER
TJ = 25°C
60
200
1479 G02
1479 G01
VCCP Supply Voltage
6.5
MODE 1
VDCIN = 24V
6.0
VCCP SUPPLY VOLTAGE (V)
5
VBKUP SUPPLY CURRENT (µA)
0
250
50
0
0
MODE 6
NO OTHER POWER
TJ = 25°C
300
50
50
VCC SUPPLY VOLTAGE (V)
DCIN SUPPLY CURRENT (µA)
BAT1 Supply Current
350
BAT2 SUPPLY CURRENT (µA)
DCIN Supply Current
350
3.8
3.7
3.6
3.5
3.4
MODE 1
VDCIN = 24V
5.5
5.0
4.5
4.0
3.5
3.3
50
100
25
75
– 50 – 25
0
JUNCTION TEMPERATURE (°C)
125
1479 G06
3.0
50
100
25
75
– 50 – 25
0
JUNCTION TEMPERATURE (°C)
125
1479 G07
5
LTC1479
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PIN FUNCTIONS
External Power Supply Pins
DCIN (Pin 1): Supply Input. A 330Ω resistor should be
put in series with this pin and the external DC power
source. A 0.1µF bypass capacitor should be connected to
this pin as close as possible.
DCDIV (Pin 2): Supply Divider Input. This is a high
impedance comparator input with a 1.215V threshold
(rising edge) and approximately – 35mV hysteresis.
BAT1, BAT2 (Pins 35, 34): Supply Input. These two pins
are the inputs from the two batteries. A 1µF bypass
capacitor should be connected to each pin as close as
possible if there is no larger battery supply capacitor
within 2".
VBAT (Pin 32): Battery Voltage Sense. This pin connects
the top of the battery resistor ladder to either BAT1 or
BAT2.
BDIV (Pin 33): Battery Divider Input. A high impedance
comparator input with a 1.215V threshold (falling edge)
and approximately 35mV hysteresis.
VBKUP (Pin 36): Supply Input. This input supplies power to
the LTC1479 when in the backup mode of operation. A 1µF
bypass capacitor should be connected to the VBKUP pin as
close as possible if there is no larger backup supply
capacitor within 2".
micropower gate drive circuitry. Do not load this pin with
any external circuitry. Bypass this pin with a 1µF/50V
capacitor.
SW (Pin 18): Output. This pin drives the “bottom” of the
VGG switching regulator inductor which is connected
between this pin and the V + pin.
GND (Pin 19): Ground. The VGG and V + bypass capacitors
should be returned to this ground which is connected
directly to the source of the N-channel switch in the VGG
regulator.
Input Power Switches
GA, GB (Pins 4, 6): DCIN Switch Gate Drive. These two
pins drive the gates of the back-to-back N-channel switches
in series with the DCIN input.
SAB (Pin 5): Source Return. The SAB pin is connected to
the sources of SW A and SW B. A small pull-down current
source returns this node to 0V when the switches are
turned off.
GC, GD (Pins 7, 9): BAT1 Switch Gate Drive. These two
pins drive the gates of the back-to-back N-channel
switches in series with the BAT1 input.
Internal Power Supply Pins
SCD (Pin 8): Source Return. The SCD pin is connected to
the sources of SW C and SW D. A small pull-down current
source returns this node to 0V when the switches are
turned off.
VCCP (Pin 20): Power Supply Output. Bypass this output
with at least a 0.1µF capacitor. The VCCP power supply is
used primarily to power internal logic circuitry.
GE, GF (Pins 10, 12): BAT2 Switch Gate Drive. These two
pins drive the gates of the back-to-back N-channel
switches in series with the BAT2 input.
VCC (Pin 15): Power Supply Output. This is a nominal
3.60V output. Bypass this regulator output with a 2.2µF
tantalum capacitor. This capacitor is required for stability.
SEF (Pin 11): Source Return. The SEF pin is connected to
the sources of SW E and SW F. A small pull-down current
source returns this node to 0V potential when the switches
are turned off.
V + (Pin 17): Supply. The V + pin is connected via three
internal diodes to the DCIN, BAT1 and BAT2 pins and
powers the top of the VGG switching regulator inductor.
Bypass this pin with a 1µF/35V capacitor.
VGG (Pin 16): Gate Supply. This high voltage (36.5V)
switching regulator is intended only for driving the internal
6
SENSE + (Pin 13): Inrush Current Input. This pin should
be connected directly to the “top” (switch side) of the low
valued resistor in series with the three input power
selector switch pairs, SW A/B, SW C/D and SW E/F, for
detecting and controlling the inrush current into and out
of the power supply sources and the output capacitor.
LTC1479
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PIN FUNCTIONS
SENSE – (Pin 14): Inrush Current Input. This pin should
be connected directly to the “bottom” (output side) of the
low valued resistor in series with the three input power
selector switch pairs, SW A/B, SW C/D and SW E/F, for
detecting and controlling the inrush current into and out
of the power supply sources and the output capacitor.
Battery Charging Switches
GG, GH (Pins 29, 27): Charger Switch Gate Drive. These
two pins drive the gates of the back-to-back N-channel
switch pairs, SW G and SW H, between the charger output
and the two batteries.
SG, SH (Pin 28, 26): Source Returns. These two pins are
connected to the sources of SW G and SW H respectively.
A small pull-down current source returns these nodes to
0V when the switches are turned off.
CHGMON (Pin 31): Battery Selector Output. This pin is
the output of an internal switch which is connected to
BAT1 and BAT2 and connects the positive terminal of the
selected battery to the voltage feedback resistors in the
charger circuit.
Microprocessor Interface
DCINGOOD (Pin 25): Comparator Output. This open-drain
output has an internal 2µA pull-up current source connected through a diode to the VCCP power supply. An
external pull-up resistor can be added if more pull-up
current is required. This output is active high when the DC
supply rises above the programmed voltage.
LOBAT (Pin 3): Comparator Output. This open-drain output does not have an internal pull-up current source and
is active low when the selected battery voltage drops
below the programmed voltage.
DCIN/BAT (Pin 24): Selector Input. This high impedance
logic input allows the µP to make the ultimate decision on
the connection of the DC power source, based upon the
DCINGOOD pin information. In some minimized systems,
the DCIN/BAT pin may be connected directly to the
DCINGOOD pin.
BATDIS (Pin 23): Battery Disconnect Input. This highimpedance logic input has a built-in 2µA pull-up current
source and allows the µP to disconnect the battery from
the system.
3DM (Pin 22): Three Diode Mode Input. This high impedance logic input has no built-in pull-up current source.
Connect a 100k resistor from this pin to ground to ensure
three diode mode operation from a “cold start.”
CHGSEL (Pin 21): Battery Charger Selector Input. This
high impedance logic input has a built-in 2µA pull-up
current source and allows the µP to determine which
battery is being charged by connecting the selected
battery to the charger output via one of the switch pairs,
SW G or SW H. (The charger voltage feedback ladder is
simultaneously switched to the selected battery.)
BATSEL (Pin 30): Battery Selector Input. This high impedance logic input has a built-in 2µA pull-up current source
and allows the µP to select which battery is connected to
the system and the battery monitor comparator input.
Battery 1 is selected with a logic high on this input and
battery 2 is selected with a logic low.
7
LTC1479
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BLOCK DIAGRAM
DCIN
GA
SAB
GB
GC
SCD
GD
GE
SEF
GF
VSENSE +
DCIN
MONITOR
DCDIV
SW A/B
GATE
DRIVERS
BAT1 BAT2
SW C/D
GATE
DRIVERS
BAT2
INRUSH
SENSE
SW E/F
GATE
DRIVERS
BAT1
INRUSH
SENSE
DCIN
DCIN
INRUSH
SENSE
V+
VCC
VSENSE –
VCC
REGULATOR
& BIAS
GENERATOR
VCCP
VCCP
VCCP
2µA
2µA
2µA
VCCP
VGG
SWITCH
CONTROL
LOGIC
SW
3DM
BATDIS
DCIN/BAT
DCINGOOD
VGG
SWITCHING
REGULATOR
BAT1 BAT2 DCIN
VCCP
VBKUP
2µA
LOBAT
BATTERY
MONITOR
VCCP
BAT2
SW G
GATE
DRIVER
GND
SW H
GATE
DRIVER
BAT1
BATSEL
8
VBAT
CHGSEL
CHGMON
BDIV
SG
GG
SH
GH
1479 BD
LTC1479
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TI I G DIAGRA S
DC and Battery Operation Timing
MODE 1
DC OPERATION
BAT1 DISCONNECTED
MODE 2
DC OPERATION
BAT1 CHARGING
MODE 3
DC OPERATION
BAT2 DISCONNECTED
MODE 4
DC OPERATION
BAT2 CHARGING
MODE 5
BAT1 OPERATION
MODE 6
BAT2 OPERATION
25V
DCIN
0V
25V
(16V)
OUTPUT
(12V)
0V
DCINGOOD
DCIN/BAT
BATDIS
BATSEL
CHGSEL
1479 TD01
NOTE: FOR MODES 1 TO 6, 3DM = H, BAT1 = 16V, BAT2 = 12V
Backup and DC Restoration Timing
MODE 7
BAT1 LOW &
DISCONNECTED
MODE 8
BACKUP
OPERATION
MODE 9
NO POWER
(NO BACKUP)
MODE 10
DC RESTORED
(THREE DIODE MODE)
MODE 11
DC RECONNECTED
(SW A/B ON)
MODE 12
THREE DIODE MODE
25V
DCIN
0V
(25V)
25V
OUTPUT
0V
BAT1
DISCHARGING
(24.3V)
(24.3V)
(VBKUP = 6V)
(0V)
LOBAT
BATDIS
DCIN/BAT
3DM
1479 TD02
NOTE: FOR MODES 7 TO 12, BATSEL = H, BAT1 = 16V AND DISCHARGING, BAT2 = 0V
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OPERATION
The LTC1479 is responsible for low-loss switching at the
“front end” of the power management system, where up
to two battery packs and a DC power source can be
indiscriminately connected and disconnected. Smooth
switching between input power sources is accomplished
with the help of low-loss N-channel switches driven by
special gate drive circuitry which limits the inrush current
in and out of the battery packs and the system power
supply capacitors.
All N-Channel Switching
The LTC1479 drives external back-to-back N-channel
MOSFET switches to direct power from the three main
power sources: the external DC power source, the primary battery and the secondary battery connected to the
main supply pins—DCIN, BAT1 and BAT2 respectively.
(N-channel MOSFET switches are more cost effective
and provide lower voltage drops than their P-channel
counterparts.)
Gate Drive (VGG) Power Supply
The gate drive for the low-loss N-channel switches is
supplied by a micropower boost regulator which is regulated at approximately 36.5V. The VGG supply provides
sufficient headroom above the maximum 28V operating
voltage of the three main power sources to ensure that the
MOSFET switches are fully enhanced.
The power for this inductor based regulator is taken from
three internal diodes as shown in Figure 1. The three
diodes are connected to each of the three main power
sources, DCIN, BAT1 and BAT2. The highest voltage
potential is directed to the top of the boost regulator
inductor to maximize regulator efficiency. C1 provides
filtering at the top of the 1mH switched inductor, L1, which
is housed in a small surface mount package.
A fourth internal diode directs the current from the 1mH
inductor to the VGG output capacitor, C2, further reducing
the external parts count. In fact, as demonstrated in Figure
1, only three external components are required by the VGG
regulator, L1, C1 and C2.
Inrush Current Limiting
The LTC1479 uses an adaptive inrush current limiting
scheme to reduce current flowing in and out of the three
main power sources and the DC/DC converter input capacitor during switch-over transitions. The voltage across
a single small-valued resistor, RSENSE, is measured to
ascertain the instantaneous current flowing through the
three main switch pairs, SW A/B, SW C/D, and SW E/F
during the transitions.
Figure 2 is a block diagram showing only the DCIN switch
pair, SW A/B. (The gate drive circuits for switch pairs SW
C/D and SW E/F are identical). A bidirectional current
sensing and limiting circuit determines when the voltage
drop across RSENSE reaches plus or minus 200mV. The
gate-to-source voltage, VGS, of the appropriate switch is
limited during the transition period until the inrush current
subsides, generally within a few milliseconds, depending
upon the value of the DC/DC converter input capacitor.
DCIN BAT1 BAT2
LTC1479
SW A
V+
TO GATE
DRIVERS
(36.5V)
VGG
SW
SW B
RSENSE
DCIN
+
L1
1mH
GA
LTC1479
+
VGG
SWITCHING
REGULATOR
C2
1µF
50V
+
6V
SAB
GB
VSENSE +
VSENSE –
6V
±200mV
THRESHOLD
C1
1µF
35V
VGG
SW A/B
GATE
DRIVERS
BIDIRECTIONAL
INRUSH CURRENT
SENSING AND
LIMITING
GND
1479 F01
Figure 1. VGG Switching Regulator
10
1479 F02
Figure 2. SW A/B Inrush Current Limiting
OUTPUT
TO DC/DC
CONVERTER
COUT
LTC1479
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OPERATION
This scheme allows capacitors and MOSFET switches of
differing sizes and current ratings to be used in the same
system without circuit modifications.
After the transition period has passed, the VGS of both
MOSFETs in the selected switch pair rises to approximately 6V. The gate drive is set at 6V to provide ample
overdrive for logic level MOSFET switches without exceeding their maximum VGS rating.
Internal Power Supplies
Two internal supplies provide power for the control logic
and power source monitoring functions. The VCCP logic
supply is approximately 5V and provides power for the
majority of the internal logic circuitry. The VCC supply is
approximately 3.60V and provides power for the VGG
switching regulator control circuitry and the gate drivers.
The VCC supply has an undervoltage lockout circuit which
minimizes power consumption in the event of a total loss
of system power; i.e., when all available power sources fall
below approximately 4.5V.
DCIN Voltage Monitoring
The DCIN input is continuously monitored via a two
resistor ladder connected between the DCIN pin and the
DCDIV input. The input threshold is 1.215V (rising edge)
with approximately – 35mV hysteresis. The use of a definitive voltage threshold ensures that the DC supply is not
only connected but “healthy” before being attached to the
DC/DC converter input.
Battery Charging Management Functions
The LTC1479 directly interfaces with LT1510/LT1511
battery charger circuits. Two gate drive circuits control
the two back-to-back N-channel switch pairs, SW G and
SW H, under logic (CHGSEL) control to connect the
output of the charger to the selected battery pack. Breakbefore-make action ensures that current does not pass
from one battery pack to the other during switch-over of
the charger output. The CHGSEL input also simultaneously switches the positive terminal of the selected
battery pack to the top of the voltage feedback resistor
ladder in the charger system through the CHGMON pin.
Backup Supply Interface
Power for the LTC1479 is obtained from the backup
supply when power is unavailable from the three main
sources of power.
Interface to Companion Microprocessor
A companion µP must be used in conjunction with the
LTC1479 to provide overall control of the power management system. The LTC1479 communicates with the µP by
means of five logic inputs and two logic outputs as
described in Table 1.
Table 1. LTC1479 µP Interface Inputs and Outputs
INPUT
ACTION
DCIN/BAT
Logic High Required to Connect a Good DC Supply
BATDIS
Logic Low Disconnects the Battery from the System
BATSEL
Selects Which Battery is Connected to the System
(Logic High Selects BAT1; Logic Low Selects BAT2)
Battery Voltage Monitoring
CHGSEL
The LTC1479 has the ability to independently monitor both
battery packs. (Because of this, one battery pack may be
discharged as the other is being charged.)
Selects Which Battery is Charged and Monitored
(Logic High Selects BAT1; Logic Low Selects BAT2)
3DM
Forces the Main Three Power Path Switches Into
“3-Diode Mode.” See Applications Information Section
OUTPUT
ACTION
A low-battery detector signals when the selected battery
pack has dropped to the level where a shutdown sequence
should be initiated or the other battery pack engaged.
DCINGOOD
Logic High When a Good DC Supply is Present
LOBAT
Logic Low When Selected Battery Voltage is Low
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POWER PATH SWITCHING CONCEPTS
Power Source Selection
The LTC1479 drives low-loss switches to direct power in
the main power path of a dual rechargeable battery system
— the type found in most notebook computers and other
portable equipment.
Figure 3 is a conceptual block diagram which illustrates
the main features of an LTC1479 dual battery power
management system, starting with the three main power
sources and ending at the system DC/DC regulator.
Switches SW A/B, SW C/D and SW E/F direct power from
either the AC adapter (DCIN) or one of the two battery
packs (BAT1 and BAT2) to the input of the DC/DC switching regulator. Switches SW G and SW H connect the
desired battery pack to the battery charger.
Note: The capacitor manufacturer should be consulted for
specific inrush current specifications and limitations and
some experimentation may be required to ensure compliance with these limitations under all possible operating
conditions.
Back-to-Back Switch Topology
The simple SPST switches shown in Figure 3 actually
consist of two back-to-back N-channel switches. These
low-loss, N-channel switch pairs are housed in 8-pin SO
and SSOP packaging and are available from a number of
manufacturers. The back-to-back topology eliminates the
problems associated with the inherent body diodes in
power MOSFET switches and allows each switch pair to
block current flow in either direction when the two switches
are turned off.
Each of the five switches is intelligently controlled by the
LTC1479 which interfaces directly with a power management system µP.
The back-to-back topology also allows for independent
control of each half of the switch pair which facilitates
bidirectional inrush current limiting and the so called “3diode” mode described in the following section.
Using Tantalum Capacitors
The “3-Diode” Mode
The inrush and “outrush” current of the system DC/DC
regulator input capacitor is limited by the LTC1479. i.e.,
the current flowing both in and out of the capacitor during
transitions from one input power source to another is
limited. In many applications, this inrush current limiting
makes it feasible to use lower cost/size tantalum surface
mount capacitors in place of more expensive/larger aluminum electrolytics at the input of the DC/DC converter.
Under normal operating conditions, both halves of each
switch pair are turned on and off simultaneously. For
example, when the input power source is switched from a
good DC input (AC adapter) to a good battery pack, BAT1,
both gates of switch pair SW A/B are turned off and both
gates of switch pair SW C/D are turned on. The back-toback body diodes in switch pair, SW A/B, block current
flow in or out of the DC input connector.
SW A/B
DCIN
SW C/D
RSENSE
12V
BAT1
+
SW E/F
CIN
BAT2
SW G
SW H
HIGH
EFFICIENCY
DC/DC
SWITCHING
REGULATOR
5V
3.3V
BATTERY
CHARGER
LTC1479
PowerPath CONTROLLER
Figure 3. LTC1479 PowerPath Conceptual Diagram
12
POWER
MANAGEMENT
µP
1479 F03
LTC1479
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APPLICATIONS INFORMATION
In the “3-diode” mode, only the first half of each power
path switch pair, i.e., SW A, SW C and SW E, is turned on;
and the second half, i.e., SW B, SW D and SW F, is turned
off. These three switch pairs now act simply as three
diodes connected to the three main input power sources
as illustrated in Figure 4. The power ‘diode’ with the
highest input voltage passes current through to the input
of the DC/DC converter to ensure that the power management µP is powered at start-up or under abnormal operating conditions. (An undervoltage lockout circuit defeats
this mode when the V + pin drops below approximately
4.5V).
“Cold Start” Initial Condition
The LTC1479 is designed to start in the “3- diode” mode
when all five logic inputs are low— when no power is
available (including the backup system). A 100k resistor
from the 3DM input to ground ensures that this input is low
during a “cold start.” This will cause the main PowerPath
switches to pass the highest voltage available to the input
of the DC/DC converter. Normal operation will then
resume after a good power source is identified.
Recovery from Uncertain Power Conditions
The “3-diode” mode can also be asserted (by applying an
active low to the 3DM input) when abnormal conditions
exist in the system, i.e., when all power sources are
deemed not “good” or are depleted, or the management
system µP is being reset or not functioning properly. (See
the Power Management µP Interface section for additional
information on when to invoke “3-diode” mode.)
COMPONENT SELECTION
N-Channel Switches
The LTC1479 adaptive inrush limiting circuitry permits the
use of a wide range of logic-level N-channel MOSFET
switches. A number of dual low RDS(ON) N-channel switches
in 8-lead surface mount packages are available that are
well suited for LTC1479 applications.
The maximum allowable drain source voltage, VDS(MAX),
of the three main switch pairs, SW A/B, SW C/D and SW
E/F, must be high enough to withstand the maximum DC
supply voltage. If the DC supply is in the 20V to 28V range,
use 30V MOSFET switches. If the DC supply is in the 10V
to 18V range, and is well regulated, then use 20V MOSFET
switches.
As a general rule, select the switch with the lowest RDS(ON)
at the maximum allowable VDS. This will minimize the heat
dissipated in the switches while increasing the overall
system efficiency. Higher switch resistances can be tolerated in some systems with lower current requirements,
but care should be taken to ensure that the power dissipated in the switches is never allowed to rise above the
manufacturer’s recommended levels.
The maximum allowable drain-source voltage, VDS(MAX),
of the two charger switch pairs, SW G and SW H, need only
SW B
SW A
DCIN
SW D
ON
OFF
SW C
RSENSE
12V
BAT1
+
SW F
ON
OFF
CIN
SW E
BAT2
ON
OFF
HIGH
EFFICIENCY
DC/DC
SWITCHING
REGULATOR
5V
3.3V
LTC1479
PowerPath CONTROLLER
POWER
MANAGEMENT
µP
1479 F04
Figure 4. LTC1479 PowerPath Switches in “3-Diode” Mode
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be high enough to withstand the maximum battery or
charger output voltage. In most cases, this will allow the
use of 20V MOSFET switches in the charger path, while
30V switches are used in the main power path.
DC
SUPPLY
TO SW A/B
LTC1479
DCIN
DCINGOOD
+
1.215V
RDC2
1%
DCDIV
Inrush Current Sense Resistor, RSENSE
A small valued sense resistor (current shunt) is used by
the three main switch pair drivers to measure and limit the
inrush current flowing through the conducting switch
pair.
It should be noted that the inrush limiting circuit is not
intended to provide short-circuit protection ; but rather, is
designed to limit the large peak currents which flow into or
out of the large power supply capacitors and the battery
packs during power supply switch-over transitions. The
inrush current limit should be set at approximately 2× or
3× the maximum required DC/DC input current.
For example, if the maximum current required by the
DC/DC converter is 2A, an inrush current limit of 6A is set
by selecting a 0.033Ω sense resistor, RSENSE, using the
following formula:
RSENSE = (200mV)/IINRUSH
Note that the voltage drop across the resistor in this
example is only 66mV under normal operating conditions.
Therefore, the power dissipated in the resistor is extremely
small (132mW), and a small 1/4W surface mount resistor
can be used in this application. A number of small valued,
surface mount resistors are available that have been
specifically designed for high efficiency current sensing
applications.
DC Input Monitor Resistor Divider
The DCDIV input continuously monitors the DC power
supply voltage via a two resistor divider network, RDC1 and
RDC2, as shown in Figure 5. The threshold voltage of the
DC good comparator is 1.215V when the power supply
input voltage is rising. Approximately – 35mV of hysteresis is provided to ensure clean switching of the comparator when the DC supply voltage is falling.
To minimize errors due to the input bias current of the DC
good comparator, set RDC1 = 12.1k so that approximately
100µA flows through the resistor divider when the desired
14
–
RDC1
12.1k
1%
1479 F05
Figure 5. DC Monitor Resistor Divider
BATSEL
BAT1
SWITCH
CONTROL
LOGIC
BAT2
VBAT
RB2
1%
1.215V
BDIV
RB1
121k
1%
LOBAT
+
–
LTC1479
1479 F06
Figure 6. Battery Monitor Resistor Divider
threshold is reached. RDC2 is then selected according to
the following formula:
RDC2 = 12.1k
)
)
VGOOD
–1
1.215V
Battery Monitor Resistor Divider
A switch controlled by the BATSEL input connects one of
the two batteries to the VBAT pin and therefore to the top
of the battery resistor divider as shown in Figure 6. The
threshold voltage of the low-battery comparator is 1.215V
when the battery voltage is falling. Approximately +35mV
of hysteresis is provided to ensure clean switching of the
comparator when the battery voltage rises again.
To minimize errors due to the input bias current of the low
battery comparator, assume RB1 = 121k so that approximately 10µA flows through the resistor divider when the
threshold is reached. RB2 is selected according to the
following formula:
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)
)
The VCC supply is approximately 3.60V and provides
power for the VGG switching regulator control circuitry and
the gate drivers. Bypass this output with a 2.2µF tantalum
capacitor. This capacitor is required for stability of the VCC
regulator output.
V
RB2 = 121k LOBAT – 1
1.215V
VGG Regulator Inductor and Capacitors
The VGG regulator provides a power supply voltage significantly higher than any of the three main power source
voltages to allow the control of N-channel MOSFET
switches. This 36.5V micropower, step-up voltage regulator is powered by the highest potential available from the
three main power sources for maximum regulator efficiency.
Because the three input supply diodes and regulator
output diode are built into the LTC1479, only three external
components are required by the VGG regulator: L1, C1 and
C2 as shown in Figure 7.
L1 is a small, low current 1mH surface mount inductor. C1
provides filtering at the top of the 1mH switched inductor
and should be 1µF to filter switching transients. The VGG
output capacitor, C2, provides storage and filtering for the
VGG output and should be 1µF and rated for 50V operation.
C1 and C2 can be either tantalum or ceramic capacitors.
VCC and VCCP Regulator Capacitors
The VCCP logic supply is approximately 5V and provides
power for the majority of the internal logic circuitry.
Bypass this output with a 0.1µF capacitor.
DCIN BAT1 BAT2
LTC1479
V+
TO GATE
DRIVERS
(36.5V)
VGG
SW
VGG
SWITCHING
REGULATOR
L1*
1mH
+
C2
1µF
50V
+
C1
1µF
35V
SYSTEM LEVEL CONSIDERATIONS
The Complete Power Management System
The LTC1479 is the “heart” of a complete power management system and is responsible for the main power path
and charger switching. A companion power management
µP provides overall control of the power management
system in concert with the LTC1479 and the auxiliary
power management systems.
A typical dual Li-Ion battery power management system is
illustrated in Figure 8. If “good” power is available at the
DCIN input (from the AC adapter), switch pair SW A/B are
turned on—providing a low-loss path for current flow to
the input of the LTC1538-AUX DC/DC converter. Switch
pairs, SW C/D and SW E/F are turned off to block current
from flowing back into the two battery packs from the DC
input.
In this case, an LT1510 constant-voltage/constant-current (CC/CV) battery charger circuit is used to alternately
charge the two Li-Ion battery packs. The µP “decides”
which battery is in need of recharging by either querying
the “smart” battery directly or by more indirect means.
After the determination is made, either switch pair, SW G
or SW H, is turned on to pass charger output current to one
of the batteries. Simultaneously, the selected battery voltage is returned to the voltage feedback input of the LT1510
CV/CC battery charger via the CHGMON output of the
LTC1479. After the first battery has been charged, it is
disconnected from the charger circuit and the second
battery is connected through the other switch pair and the
second battery charged.
Backup power is provided by the LT1304 circuit which
ensures that the DC/DC input voltage does not drop
below 6V.
GND
1479 F07
*COILCRAFT 1812LS-105 XKBC (708) 639-6400
OR EQUIVALENT
Figure 7. VGG Step-Up Switch Regulator
Backup System Interface
The LTC1479 is designed to work in concert with related
power management products including the LT1304 mi-
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SW A
DCIN
RSENSE
0.033Ω
SW B
12V AUX
SW C
LTC1538-AUX
TRIPLE, HIGH EFFICIENCY,
SWITCHING REGULATOR
SW D
SW E
RDC2
3.3V
SW F
0.1µF
330Ω
Li-ION
BATTERY
PACK #1
5V
BACKUP
NiCD
GA SAB GB
DCIN
GE SEF GF SENSE + SENSE –
GC SCD GD
DCDIV
BACKUP
REGULATOR
VBKUP
RDC1
BAT1
BAT2
Li-ION
BATTERY
PACK #2
LTC1479
2
VBAT
RB2
BDIV
5
POWER
MANAGEMENT
µP
RB1
CHGMON
VCC
2.2µF
16V
V+
VCCP
+
SW VGG
GG SG
GH SH
DCIN
1mH*
+
0.1µF
1µF
50V
+
1µF
50V
+
SW H
LT1510
Li-ION BATTERY
CHARGER
SW G
1479 F08
*COILCRAFT 1812LS-105 XKBC (708) 639-1469
Figure 8. Simplified Dual Li-Ion Battery Power Management System
FROM
PowerPath
CONTROLLER
5VCC
FROM
DC/DC
(BOLD LINES INDICATE HIGH CURRENT PATHS)
ROHM
DTA144E
R1
10k
+
NiCD
CELL
R4
390k
1%
4
Q1
2N7002
R5
100k
1%
SW
2
D2
BAS16LT1
1
LBO
FB
LT1304
ILIM
C2
0.1µF
SHDN
LBI
6
R3
22k
GND
VIN
8
Charger System Interface
The LTC1479 is designed to work directly with constantvoltage (CV), constant-current (CC) battery chargers such
as the LT1510 and LT1511.
7
5VCC
FROM
DC/DC
3
5
C3
0.1µF
LT1510 Battery Charger Interface
1479 F09
Figure 9. LT1304 Micropower Backup Converter Circuit
16
cropower DC/DC converter. As shown in Figure 9, the
LT1304 monitors the input supply voltage and activates
when it drops below 6V.
Power for the DCIN and battery monitors and the logic
supply in the LTC1479 is then obtained from the output of
the LT1304 step-up regulator.
C1
0.1µF
BACKUP
R2
470k
D1
MBR0530
L1*
10µH
TO INPUT
OF DC/DC
CONVERTER
As illustrated in Figure 10, the LT1510 CV/CC battery
charger, takes power from the DC adapter input through
Schottky diode D1. The output of the charger is directed to
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LT1511 Battery Charger Interface
the charging battery through one of the N-channel switch
pairs, SW G or SW H. The charging battery voltage is
simultaneously connected through the CHGMON switch
in the LTC1479 to the top of the charger voltage resistor
divider, R4 and R5, for constant voltage charging. (See the
LT1510 data sheet for further detail.)
The LT1511, 3A CC/CV battery charger with input current
limiting, is connected in a slightly different manner than
the LT1510 as illustrated in Figure 11.
CHGMON
POWER
MANAGEMENT
µP
LTC1479
D1
MBRS140T
0.1µF
TO SW C/D
+
BAT1
4 Li-ION
BATTERY
PACK
BAT2
4 Li-ION
BATTERY
PACK
TO
SW A/B
TO SW E/F
+C
BAT1
RPROG
11k
1%
47µF
–
SW G
Si9926DY
+
–
C6
10µF
CERAMIC
D2
MBRS140T
VCC SW
C3
0.22µF
PROG
VC
BOOST
R1
100k
1%
R3
1k
R2
300Ω
C1
1µF
C2
0.1µF
L1*
33µH
D3
1N4148
LT1510
R4
649k
0.25%
SENSE
Q1
2N7002
+ CBAT2
47µF
DC INPUT
(FROM AC
ADAPTOR)
330Ω
BAT2 GG SG GH SH DCIN
BAT1
GND
OVP
BAT
R5
115k
0.25%
SW H
Si9926DY
(CHARGER OUTPUT)
+
CCHG
22µF
TANT
CURRENT CONTROL
FROM POWER
MANAGEMENT µP
*COILTRONICS CTX33-2
1479 F10
Figure 10. Interfacing to the LT1510 Constant-Voltage/Constant-Current Battery Charger
CHGMON
POWER
MANAGEMENT
µP
LTC1479
BAT1
RS4
0.05Ω
330Ω
BAT2 GG SG GH SH
C4
10µF
CERAMIC
0.1µF
+
TO
SW A/B
CBAT1
47µF
RPROG
4.93k
1%
C1
1µF
SW G
Si9926DY
–
R1
500Ω
+
R2
1k
C2
0.33µF
COMP1 BOOST
C3
200pF
LT1511
SPIN
GND
BAT
CBAT2
47µF
SW H
Si9926DY
Q1
2N7002
–
RS2
200Ω
1%
(CHARGER OUTPUT)
+
CURRENT CONTROL
FROM POWER
MANAGEMENT µP
R3
500Ω
CLN VCC CLP
UV
PROG
SW
VC
+
BAT2
4 Li-ION
BATTERY
PACK
C12
1µF
C5
10µF
+
+
DC INPUT
(FROM AC
ADAPTOR)
DCIN
TO SW C/D
TO SW E/F
BAT1
4 Li-ION
BATTERY
PACK
D1
MBRS340T
OVP
SENSE
RS1
0.033Ω
RS3
200Ω
1%
R4
5k
R5
6.8k
D2
MBRS340T
C6
0.47µF L1
20µH
D3
MBR0540T
C7
50pF
R6
649k
0.25%
R7
115k
0.25%
1479 F11
CCHG
22µF
TANT
Figure 11. Interfacing to the LT1511 Constant-Voltage/Constant-Current Battery Charger with Input Current Limiting
17
LTC1479
U
W
U
U
APPLICATIONS INFORMATION
The LT1511 has a third control loop that regulates the
current drawn from the AC adapter. Therefore, the DC
input to the LTC1479 and the input to the host system
through SW A/B, is obtained from the “output” of the
LT1511 adapter sense resistor, RS4, and not directly from
the DC input connector as with the LT1510. This allows
simultaneous operation of the host system while charging
a battery without overloading the AC adapter. Charging
current is reduced to keep the adapter current within
specified levels.
capacitance to ground on the CHGMON output to less than
100pF. If more capacitance is required, it may become
necessary to “mask” the LOBAT output when the charge
monitor is switched between batteries. (Internal resistance between the BAT1 and BAT2 inputs and the charge
monitor switch may create a transient voltage drop at the
VBAT output during transitions which could be falsely
interpreted by the µP as a low battery condition.)
However, as with the LT1510 , the output of the LT1511 is
directed to the charging battery through either SW G or SW
H, and the charging battery voltage is connected to the top
of the voltage resistor divider, R6 and R7, for constant
voltage charging. (See the LT1511 data sheet for further
detail on battery charging techniques and applications
hints.)
Interfacing to the LTC1479
LT1620/LTC1435 Battery Charger Interface
The LTC1479 also interfaces with the LT1620/LTC1435
synchronous high efficiency low dropout battery charger.
The circuit shown in Figure 12 is a constant-current/
constant-voltage battery charger specifically designed for
lithium-ion applications having thermal, output current, or
input voltage headroom constraints which preclude the
use of other high performance chargers such as the
LT1510 or LT1511.
This circuit can charge batteries at up to 4A. The precision
current sensing of the LT1620 combined with the high
efficiency and low dropout characteristics of the LTC1435
provide a battery charger with over 96% efficiency requiring only 0.5V input-to-output differential at 3A charging
current.
Charge current programming is achieved by applying a
0µA to 100µA current from the LT1620 PROG pin to
ground, which can be derived from a resistor or DAC
output controlled by the power management µP. (See the
LT1620 data sheet for further details on this circuit.)
Capacitive Loading on the CHGMON Output
In most applications, there is virtually no capacitive loading on the CHGMON output—just a simple resistor
divider. Care should be taken to restrict the amount of
18
THE POWER MANAGEMENT MICROPROCESSOR
The LTC1479 can be thought as a “real world” interface to
the power management µP. It takes logic level commands
directly from the µP, and makes changes at high current
and high voltage levels in the power path. Further, it
provides information directly to the µP on the status of the
AC adapter, the batteries and the charging system.
The LTC1479 logic inputs are TTL level compatible and
therefore interface directly with standard power management µPs. Further, because of the direct interface via the
five logic inputs and the two logic outputs, there is virtually
no latency (i.e. time delay) between the µP and the LTC1479.
In this way, time critical decisions can be made by the µP
without the inherent delays associated with bus protocols,
etc. These delays are acceptable in certain portions of the
power management system, but it is vital that the power
path switching control be made through a direct connection to the power management µP. The remainder of the
power management system can be easily interfaced to the
µP through a serial interface.
Selecting a Power Management Microprocessor
The power management µP provides intelligence for the
entire power system, is programmed to accommodate the
custom requirements of each individual system and allow
performance updates without resorting to costly hardware changes.
The power management µP must meet the requirements
of the total power management system, including the
LTC1479 controller, the batteries (and interface), the
backup system, the charging system and the host processor. A number of inexpensive processors are available
which can easily fulfill these requirements.
LTC1479
U
U
W
U
APPLICATIONS INFORMATION
CHGMON
POWER
MANAGEMENT
µP
LTC1479
DC INPUT
(FROM AC
ADAPTER)
330Ω
BAT2 GG SG GH SH DCIN
BAT1
0.1µF
TO SW C/D
TO SW E/F
TO
W A/B
+
+
BAT1
4 Li-ION
BATTERY
PACK
SW G
Si9926DY
–
R2
76.8k
0.1%
+
BAT2
4 Li-ION
BATTERY
PACK
+
CBAT2
10µF
SW H
Si9926DY
–
+
C11
56pF
SHDN
R5
1.5M
C3
0.1µF
C2
100pF
1
COSC
TG
2 RUN/SS BOOST
3
SW
ITH
LTC1435
4
VIN
SFB
5
INTV
SGND
CC
6
VOSENSE
BG
C9, 100pF 7
SENSE – PGND
C10
8
VCC
SENSE +
100pF
C4
0.033µF
R5, 1k
1
2
SENSE
AVG
8
7
PROG
LT1620
3
6
GND
VCC
4
5
NIN
PIN
IPROG
R1
1M
0.1%
C1
100pF
CBAT1
10µF
IOUT
16
15
L1
27µH
14
13
Q1
Si4412DY
C13
D2*
CMDSH-3 0.33µF
12
+
D1*
CMDSH-3
11
R4
0.025Ω
C16
22µF
35V
Q2
Si4412DY
10
9
C14
4.7µF
C6
0.1µF
C7
0.33µF
C5
0.01µF
C12
0.1µF
C15
22µF
35V
×2
C8
0.1µF
+
R3
10k
1%
1479 F12
*CENTRAL SEMICONDUCTOR CO. (516) 435-1110
Figure 12. Interfacing to an LT1620/LTC1435 High Efficiency Constant-Voltage/Constant-Current Battery Charger
19
LTC1479
U
W
U
U
APPLICATIONS INFORMATION
Interfacing to the Battery Pack
The LTC1479 is designed to work with virtually any
battery pack chemistry or cell count, as long as the
battery pack operating voltage range is somewhere
between 6V and 28V. This permits great flexibility in
system design. The low-battery threshold is adjustable
and can be set anywhere between 6V and 28V.
Conventional Battery Packs
Conventional battery packs do not include a “smart”
battery interface between the battery pack and the host
system. Thus, these battery packs generally have only
three terminals to connect the battery and a temperature
sensor (thermistor) to the host system. The NTC thermistor typically has a nominal resistance of 10k at room
temperature and is used to monitor the battery pack
temperature.
LOBAT and DCINGOOD Blanking/Filtering
It is good practice to include some delay in accepting low
battery and DCIN good information during transitional
periods, e.g., when switching the charger from one battery
20
to another or when switching from batteries to DC power.
This technique will eliminate false triggering at the associated µP I/O. (Remember that the “3-diode” mode may be
used during periods of uncertainty to eliminate the need
for “instantaneous” DCIN and battery status information.)
Smart Battery Packs
Smart battery packs, compliant with the Smart Battery
System specification, have a five-terminal connector. Two
of the terminals are the minus and plus connections to the
battery. A third terminal is connected to the top of a
thermistor in NiCd and NiMH battery packs and to a
resistor in Li-Ion battery packs. A fourth and fifth terminal
are connected to the Smart Management Bus (SMBus)
SMBDATA and SMBCLK lines from an integrated circuit
inside the battery pack.
Applications Assistance
Linear Technology applications engineers have developed
a smart battery charger around the LT1511 charger IC.
Contact the factory for applications assistance in developing a complete smart battery system with intelligent
PowerPath control using the LTC1479.
LTC1479
U
TYPICAL APPLICATIONS N
Dual NiMH Battery Power Management System (Using an LT1510, 1A Charger)
RSENSE
0.033Ω
Si4936DY
SW A
SW B
Si4936DY
SW C
SW D
330Ω
RDC2
205k
1%
GA SAB GB
DCIN
GC SCD GD
GE SEF GF
SENSE +
D1
L2**
10µH MBR0530
R8
10k
NiCD
CELL
+
VBKUP
R2
390k
1%
Q2
2N7002
LTC1479
R7
470k
BDIV
RB1
121k
1%
VCC
GND V + SW
C1
0.1µF
VGG
GG SG GH SH BATDIS DCIN/BAT CHGMON LOBAT
+
C3
1µF
50V
+
POWER
MANAGEMENT
µP
C4
1µF
50V
SMBUS
RTH1
RTH2
BAT2
12-CELL
NiMH
BATTERY
PACK
RTH1
C6
10µF
CERAMIC
CBAT1
10µF
SW G
Si9926DY
RPROG
11k
1%
Q1
2N7002
+
RTH1
CBAT2
10µF
R4
100k
1%
C11
0.1µF
100k
D2
MBRS140T
+
5
6
R1
22k
VCC
RCM1
100k
1%
BAT1
12-CELL
NiMH
BATTERY
PACK
5VCC
FROM
DC/DC
(BACKUP)
RCM2
909k
1%
L1*
1mH
C2
2.2µF
16V
C10
0.1µF
BATSEL
CHGSEL
DCINGOOD
3DM
VCCP
+
8
LBO
FB
LT1304
7
SHDN
1
3
LBI
VIN
ILIM GND
D5
BAS16LT1
BAT2
VBAT
R3
100k
1%
4
SW
2
BAT1
RB2
909k
1%
C5
0.1µF
SENSE –
DCDIV
RDC1
12.1k
1%
ROHM
DTA144E
5VCC
FROM
DC/DC
Si4936DY
SW E
SW F
0.1µF
TO INPUT
OF DC/DC
CONVERTER
(BOLD LINES INDICATE HIGH CURRENT PATHS)
R5
300Ω
C8
1µF
8
VCC SW 1
7
PROG
2
6
VC
BOOST
R6
1k
C9
0.1µF
3
+
CDCIN
10µF
35V
ALUM
C7
0.22µF
LT1510
GND
SW H
Si9926DY
SENSE
BAT
4
DC INPUT
(FROM AC
ADAPTOR)
D3
1N4148
D4
MBRS140T
L3***
33µH
5
*1812LS-105 XKBC, COILCRAFT
**CD43, SUMIDA
***CTX33-2, COILTRONICS
(CHARGER OUTPUT)
+
CCHG
22µF
TANT
1479 TA02
21
LTC1479
U
TYPICAL APPLICATIONS N
Dual Li-Ion Battery Power Management System
RSENSE
0.033Ω
Si4936DY
SW A
SW B
Si4936DY
SW C
SW D
330Ω
RDC2
205k
1%
GA SAB GB
DCIN
GC SCD GD
GE SEF GF
SENSE +
R2
390k
1%
Q2
2N7002
LTC1479
RB1
121k
1%
R7
470k
VCC
GND V + SW
C1
0.1µF
+
C10
0.1µF
BATSEL
CHGSEL
DCINGOOD
3DM
VCCP
VGG
GG SG GH SH BATDIS DCIN/BAT CHGMON LOBAT
+
C3
1µF
50V
+
6
R1
22k
5VCC
FROM
DC/DC
5
C11
0.1µF
(BACKUP)
VCC
100k
L1*
1mH
C2
2.2µF
16V
SW
8
LBO
FB
LT1304
7
SHDN
1
3
LBI
VIN
ILIM GND
D5
BAS16LT1
BDIV
R3
100k
1%
4
2
BAT2
VBAT
TO INPUT
OF DC/DC
CONVERTER
C5
0.1µF
SENSE –
BAT1
RB2
909k
1%
D1
L2**
10µH MBR0530
R8
10k
NiCD +
CELL
VBKUP
DCDIV
RDC1
12.1k
1%
ROHM
DTA144E
5VCC
FROM
DC/DC
Si4936DY
SW E
SW F
0.1µF
(BOLD LINES INDICATE HIGH CURRENT PATHS)
POWER
MANAGEMENT
µP
C4
1µF
50V
SMBUS
RBAT1
RBAT2
D2
MBRS140T
BAT1
4 Li-ION
SMART
BATTERY
PACK
+
RBAT1
C6
10µF
CERAMIC
CBAT1
10µF
SW G
Si9926DY
BAT2
4 Li-ION
SMART
BATTERY
PACK
RPROG
3.83k
1%
Q1
2N7002
+
RBAT2
R5
300Ω
C8
1µF
14, 15
VCC SW 2
7
PROG
3
6
VC
BOOST
R6
1k
C9
0.1µF
1, 7-10, 16
LT1510
SENSE
GND
OVP
6
5
BAT
CBAT2
10µF
SW H
Si9926DY
+
CDCIN
10µF
35V
ALUM
DC INPUT
(FROM AC
ADAPTOR)
D4
MBRS140T
C7
0.22µF
D3
1N4148
L3***
33µH
R7
649k
0.25%
R8
115k
0.25%
11
(CHARGER OUTPUT)
+
CCHG
22µF
TANT
*1812LS-105 XKBC, COILCRAFT
**DT1608-223, COILCRAFT
***CTX33-2, COILTRONICS
1479 TA03
22
LTC1479
U
TYPICAL APPLICATIONS N
Dual Li-Ion Battery Power Management System (Using an LT1511, 3A Charger)
RSENSE
0.033Ω
Si4936DY
SW A
SW B
Si4936DY
SW C
SW D
330Ω
RDC2
205k
1%
RDC1
12.1k
1%
GA SAB GB
DCIN
GC SCD GD
GE SEF GF
ROHM
DTA144E
5VCC
FROM
DC/DC
Si4936DY
SW E
SW F
0.1µF
(BOLD LINES INDICATE HIGH CURRENT PATHS)
SENSE +
+
R2
390k
1%
Q2
2N7002
BAT1
LTC1479
R11
470k
BDIV
RB1
121k
1%
VCC
GND V + SW
C1
0.1µF
+
C14
0.1µF
BATSEL
CHGSEL
DCINGOOD
3DM
VCCP
VGG
+
C3
1µF
50V
+
6
R1
22k
5VCC
FROM
DC/DC
5
C15
0.1µF
(BACKUP)
VCC
100k
GG SG GH SH BATDIS DCIN/BAT CHGMON LOBAT
L1*
1mH
C2
2.2µF
16V
8
LBO
FB
LT1304
7
SHDN
1
3
LBI
VIN
ILIM GND
D5
BAS16LT1
BAT2
VBAT
R3
100k
1%
4
SW
2
RB2
1.05M
1%
C5
0.1µF
SENSE –
VBKUP
DCDIV
D1
L2**
10µH MBR0530
R12
10k
NiCD
CELL
TO INPUT
OF DC/DC
CONVERTER
POWER
MANAGEMENT
µP
C4
1µF
50V
SMBUS
RBAT1
RBAT2
D1
MBRS340T
RS4
0.05Ω
BAT1
4 Li-ION
SMART
BATTERY
PACK
C6
10µF
CERAMIC
+
RBAT1
C8
1µF
RBAT2
CBAT2
10µF
R4
500Ω
SW H
Si9926DY
9
19 CLN VCC CLP 6
UV
PROG
18
2
SW
VC
R6
3
11
COMP1 BOOST
1k
R5
C10
500Ω
200pF
LT1511
18
C9
SPIN
1,
4, 5, 7,
0.33µF
16, 23, 24
8
GND
OVP
BAT
SENSE
Q1
2N7002
RS2
200Ω
1%
(CHARGER OUTPUT)
+
14 12
RS1
0.033Ω
RS3
200Ω
1%
CCHG
22µF
TANT
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
R10
5k
+
CDCIN
10µF
35V
ALUM
R9
6.8k
20 TO 22
10
RPROG
4.93k
1%
+
C12
1µF
C7
10µF
CBAT1
10µF
SW G
Si9926DY
BAT2
4 Li-ION
SMART
BATTERY
PACK
+
DC INPUT
(FROM AC
ADAPTOR)
D2
MBRS340T
C13
0.47µF
D3
MBR0540T
L3***
20µH
C11
50pF
*1812LS-105 XKBC, COILCRAFT
**DT1608-223, COILCRAFT
***CTX20-4, COILTRONICS
R7
649k
0.25%
R8
115k
0.25%
1479 TA04
23
LTC1479
U
PACKAGE DESCRIPTION
Dimensions in inches (millimeters) unless otherwise noted.
G Package
36-Lead Plastic SSOP (0.209)
(LTC DWG # 05-08-1640)
0.499 – 0.509*
(12.67 – 12.93)
36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 20 19
0.301 – 0.311
(7.65 – 7.90)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
0.205 – 0.212**
(5.20 – 5.38)
0.068 – 0.078
(1.73 – 1.99)
0° – 8°
0.005 – 0.009
(0.13 – 0.22)
0.022 – 0.037
(0.55 – 0.95)
0.0256
(0.65)
BSC
*DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
**DIMENSIONS DO NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
0.002 – 0.008
(0.05 – 0.21)
0.010 – 0.015
(0.25 – 0.38)
G36 SSOP 1196
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LT1304
Micropower DC/DC Step-Up Converter
5V at 200mA from 2 Cells, IQ = 10µA in Shutdown
LTC1435
High Efficiency Synchronous Step-Down Converter
Fixed Frequency, Ultrahigh Efficiency
LTC1438
Dual High Efficiency Synchronous Step-Down Converter
Fixed Frequency, PLL Lockable, Ultrahigh Efficiency
LTC1473
Dual PowerPath Switch Driver
Protected Power Management Building Block
LT1510
Constant-Voltage/Constant-Current Battery Charger
1.5A Internal Switch, Precision 0.5% Reference
LT1511
Constant-Voltage/Constant-Current 3A Battery Charger
Adapter Current Limit Loop
LTC1538-AUX
Dual, Synchronous Controller with Aux Regulator
5V Standby in Shutdown
LT1620
Battery Charger Current Controller
96% Efficiency When Used with LTC1435
LT1621
Dual Battery Charger Current Controller
For Dual Loop Applications
24
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417 ● (408) 432-1900
FAX: (408) 434-0507● TELEX: 499-3977 ● www.linear-tech.com
1479f LT/TP 0697 7K • PRINTED IN USA
LINEAR TECHNOLOGY CORPORATION 1996
工商网监
湘ICP备2023018690号
