LINER LTC1980EGN

Final Electrical Specifications
LTC1980
Combination Battery
Charger and DC/DC Converter
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DESCRIPTIO
FEATURES
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The LTC®1980 integrates PWM power control for charging a battery and converting the battery voltage to a
regulated output or simultaneously charging the battery
while powering system load from an unregulated AC wall
adapter. Combining these features into a single IC produces a smaller area and lower cost solution compared to
presently available multi-IC solutions. The LTC1980 shares
the discrete components for both the battery charger and
the DC/DC converter thus minimizing size and cost relative
to dual controller solutions. Both the battery charger and
DC/DC converter use a current mode flyback topology for
high efficiency and excellent transient response. Optional
Burst Mode operation and power-down mode allow power
density, efficiency and output ripple to be tailored to the
application.
Single Controller IC Includes Battery Charger
Plus DC/DC Converter
Wall Adapter Voltage May be Above or Below
Battery Voltage
LDO Controller Allows Simultaneous Charging
and Regulating from Wall Adapter Input
Standalone Li-Ion Battery Charger Including Charge
Termination, Overvoltage Protection, Shorted-Cell
Detection and Battery Recharge
Selectable 4.1V, 4.2V, 8.2V and 8.4V Float Voltages
Simple NiMH and NiCd Battery Charger
Pin Programmable Regulator Burst Mode® Operation
and Shutdown for High Efficiency
High Efficiency Current Mode 300kHz PWM
Reduced Component Architecture
Undervoltage Protection and Soft-Start Insures
Start-Up with Current Limited Wall Adapter
Small 24-Pin SSOP Package
The LTC1980 provides a complete Li-Ion battery charger
with charge termination timer, preset Li-Ion battery voltages, overvoltage and undervoltage protection, and userprogrammable constant-current charging. Automatic battery recharging, shorted-cell detection, and open-drain
C/10 and wall plug detect outputs are also provided. User
programming allows NiMH and NiCd battery chemistries
to be charged as well.
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APPLICATIO S
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Digital Cameras
Handheld Computers
Personal Digital Assistants
1W to 10W Uninterruptable Power Supplies
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation.
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May 2003
TYPICAL APPLICATIO
Li-Ion Charger and DC/DC Converter Using One IC
3.3V Regulator Efficiency vs Load Current
POWER FLOW
90
CHARGING
BATTERY
OPERATION
Li-Ion
BATTERY
UNREGULATED
WALL ADAPTER
INPUT (3V TO 10V)
•
BAT-FET
•
EFFICIENCY (%)
SYSTEM
POWER
85
REG-FET
LDO/
SWITCH
SYSTEM LOAD
DC/DC
CONVERTERS
LTC1980
3.3V
80
75
70
VBAT = 3.6V
TA = 25°C
FIGURE 5
65
1.8V
1.5V
60
10
100
LOAD CURRENT (mA)
1980 TA01
1000
1980 G04
1980i
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.
1
LTC1980
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AXI U
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PACKAGE/ORDER I FOR ATIO
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ABSOLUTE
RATI GS
(Note 1)
VREG to GND ............................................. –0.5V to 12V
VBAT to GND ............................................. –0.5V to 12V
PROG, ISENSE .............................................. –0.5V to 5V
PROGT, REGFB, VC, BATT1, BATT2
TIMER, SS ............................................ –0.5V to VBIAS2
LDOFB, LDODRV .................................... –0.5V to VREG
WA, VBIAS1, REG ....................................... –0.5V to 12V
MODE ................................................... –0.5V to VBIAS1
VBIAS2 ......................................................... –0.5V to 5V
OVP ............................................................ –0.5V to 5V
PGND to GND .................................... Connect Together
Operating Ambient Temperature Range
(Note 2) ................................................. – 40°C to 85°C
Storage Temperature Range ................. – 65°C to 125°C
Lead Temperature (Soldering, 10 sec)................ 300°C
ORDER PART
NUMBER
TOP VIEW
PROG
1
24 SS
PROGT
2
23 OVP
REGFB
3
22 CAOUT
VC
4
21 ISENSE
LDOFB
5
20 GND
LDODRV
6
19 VBIAS2
VREG
7
18 VBAT
WA
8
17 TIMER
BATT1
9
16 MODE
BATT2 10
LTC1980EGN
15 REG
RGTDR 11
14 BGTDR
PGND 12
13 VBIAS1
GN PACKAGE
24-LEAD NARROW PLASTIC SSOP
TJMAX = 125°C, θJA = 85°C/W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VBAT = 2.4V, VREG = 5V, VBAT unloaded.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
VBAT
Positive Supply Voltage, VBAT
VREG
Positive Supply Voltage, VREG
VFB
Feedback Voltage
REGFB Tied to VC
VPROGT
Voltage on PROGT Pin
PROGT Tied to VC
IBURST
Burst Mode Operation
Supply Current, Quiescent, VREG
Regulator Mode, REGFB = 1.5V
IHIGH
Supply Current, Quiescent, VREG
Regulator Mode, REGFB = 0V
ISHDN
Supply Current in Shutdown Mode, VREG
Mode = 0V
VUVL
Positive-Going Undervoltage Lockout Voltage
From Either VBAT or VREG
VUVHYS
Undervoltage Lockout Hysteresis
From Either VBAT or VREG
ISS
Soft-Start Ramp Current
BATT1 = 0, BATT2 = 0, Charger Mode
VFLOAT0
Output Float Voltage in Constant Voltage Mode
BATT1 = 0, BATT2 = 0
●
4.059
4.1
4.141
V
VFLOAT1
Output Float Voltage in Constant Voltage Mode
BATT1 = 0, BATT2 = 0
●
4.158
4.2
4.242
V
VFLOAT2
Output Float Voltage in Constant Voltage Mode
BATT1 = 0, BATT2 = 1 (Note 3)
●
8.118
8.2
8.282
V
VFLOAT3
Output Float Voltage in Constant Voltage Mode
BATT1 = 0, BATT2 = 1 (Note 3)
●
8.316
8.4
8.484
V
VFLOAT4
Output Float Voltage in Constant Voltage Mode
BATT1 = Open, BATT2 = Don’t Care
Measured from OVP Input
●
1.207
1.225
1.243
V
VRCHG0
Recharge Threshold, Delta Voltage with Respect
to Float Voltage
BATT2 = 0, BATT1 = 0 or 1
200
mV
VRCHG1
Recharge Threshold, Delta Voltage with Respect
to Float Voltage
BATT2 = 1, BATT1 = 0 or 1
400
mV
2.85
10
2.85
●
MAX
UNITS
V
10
V
1.194
1.225
1.256
V
1.194
1.225
1.256
V
0.75
●
2.45
mA
2
4.3
mA
15
µA
2.7
2.85
V
100
mV
µA
10
1980i
2
LTC1980
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VBAT = 2.4V, VREG = 5V, VBAT unloaded.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
VRCHG2
Recharge Threshold, Delta Voltage with Respect
to Float Voltage, Measured at OVP
BATT 1 = Open
VLT0
Charger Shorted Cell Threshold
BATT2 = 0
2.55
2.7
2.8
V
VLT1
Charger Shorted Cell Threshold
BATT2 = 1
5.2
5.4
5.65
V
IBLDO
Input Bias Current, Low Dropout Regulator
Measured at LDOFB Pin
1.0
gmldo
Transconductance, Low Dropout Regulator
Measured from LDOFB to LDODRV
350
VOLLDO
Output Low Voltage, Low Dropout Regulator
VOHLDO
Output High Voltage, Low Dropout Regulator
IOUTLDO
Low Dropout Regulator Output Current, Source/Sink
AVOL
Error Amplifier Open-Loop Voltage Gain
IBEA
Error Amplifier Input Bias Current
VOLEA
Error Amplifier Output Low Voltage
VOHEA
Error Amplifier Output High Voltage
IOUT
Error Amplifier Output Source Current
Error Amplifier Output Sink Current
gmflt
Float Voltage Error Amplifier Transconductance
IBFLT
Float Voltage Error Amplifier Input Current
(Measured at OVP Input)
VOS1
Current Amplifier Offset Voltage
IBIS
Input Bias Current, ISENSE Input
AVCA
Current Amplifier Voltage Gain
RPROG
PROG Pin On Resistance
400
Ω
IPROG
PROG Pin Leakage Current
100
nA
fS
Switching Frequency
tr, tf
Driver Output Transition Times
tBREAK
fTIMER
ITIMER1
ITIMER2
60
mV
µA
µmhos
0.1
VREG – 0.1
From REGFB to VC
SS = Open
±20
µA
60
dB
µA
–0.1
0.1
0
0.5
V
1.4
2
V
Measured from OVP to SS,
Charger Mode, BATT1 = Open
mA
mA
µmhos
65
–0.1
0.1
µA
–6
6
mV
2.55
V/V
µA
–100
2.3
●
V
V
0.5
–1.2
Measured from ISENSE to
CAOUT Pin
UNITS
260
2.44
300
340
kHz
CL = 15pF
10
Driver Output Break Times
VBAT = VREG = 10V
100
ns
Timer Frequency
C = 1000pF
4.5
kHz
TIMER Pin Source Current
–4
µA
TIMER Pin Sink Current
4
µA
RREG
REG On Resistance
68
Ω
IREGPD
REG Pull-Down Current
IREGLK
REG Leakage Current
VVTHREG
REG Logic Threshold
VIL1
Digital Input Low Voltage,
Negative-Going, Wall Adapter (WA)
VREG = 5V
1.185
VIH1
Digital Input High Voltage,
Positive-Going, Wall Adapter (WA)
VREG = 5V
1.195
VIL2
Digital Input Low Voltage, BATT1
VIH2
Digital Input High Voltage, BATT1
2
5
ns
9
60
0.3
nA
1.3
V
1.221
1.247
V
1.226
1.257
V
100
VBIAS2 –
100mV
µA
mV
V
1980i
3
LTC1980
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C.VBAT = 2.4V, VREG = 5V, VBAT unloaded.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
VP2
Digital Input Pull-Up Voltage, BATT1
BATT1 Input Floating
VIL3
Digital Input Low Voltage, BATT2
0.3
V
VIH3
Digital Input High Voltage, BATT2
II1
Digital Input Current, WA
–5
5
µA
II2
Digital Input Current, BATT1
–10
10
µA
II3
Digital Input Current, BATT2
–1
1
µA
1.6
V
2
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: The LTC1980E is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C operating
V
temperature range are assured by design, characterization and correlation
with statistical process controls.
Note 3: TA = 0°C to 70°C.
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TYPICAL PERFOR A CE CHARACTERISTICS
Switching Frequency Variance
vs Temperature
Regulator Load Regulation
1.2240
1.5
1.2235
1.0
–0.2
0.5
–0.4
1.2230
1.2225
1.2220
1.2215
1.2210
1.2205
–40
–15
10
35
TEMPERATURE (°C)
60
0
∆VREG (%)
FREQUENCY VARIANCE (%)
FEEDBACK REFERENCE VOLTAGE (V)
Feedback Reference Voltage
vs Temperature
0
–0.8
–1.0
–1.0
–15
60
10
35
TEMPERATURE (°C)
90
90
85
85
80
80
75
70
VBAT = 3.6V
TA = 25°C
FIGURE 5
10
100
LOAD CURRENT (mA)
–1.2
1000
1980 G04
0
100
200
300
400
LOAD CURRENT (mA)
500
1980 G03
5V Regulator Efficiency
vs Load Current
EFFICIENCY (%)
EFFICIENCY (%)
3.3V Regulator Efficiency
vs Load Current
60
85
1980 G02
1980 G01
65
–0.6
–0.5
–1.5
–40
85
VBAT = 4.2V
VREG ≅ 3.3V
TA = 25°C
FIGURE 5
Regulator Load Step Response
VREG
50mV/DIV
75
IL
500mA/DIV
70
VBAT = 3.6V
TA = 25°C
R8 = 309k
FIGURE 5
65
60
10
100
LOAD CURRENT (mA)
1000
VBAT = 3.6V
100µs/DIV
VREG ≅ 3.3V
IL = 100mA TO 500mA
TA = 25°C
FIGURE 5
1980 G06
1980 G05
1980i
4
LTC1980
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TYPICAL PERFOR A CE CHARACTERISTICS
Typical ISENSE Waveforms,
Regulator
Typical BGTDR and RGTDR
Waveforms
Typical Operation with Burst
Mode Operation Disabled
VREG
50mV/DIV
BGTDR
1V/DIV
ISENSE
20mV/DIV
PIN 21
FIGURE 5
ISENSE
50mV/DIV
RGTDR
1V/DIV
VBAT = 3.6V
VREG = 3.3V
TA = 25°C
IL = 500mA
1980 G07
1µs/DIV
VBAT = 3.6V
VREG = 3.3V
IL = 500mA
TA = 25°C
FIGURE 5
1µs/DIV
1980 G08
VREG
50mV/DIV
VLDO
0.1V/DIV
1980 G10
200µs/DIV
1980 G09
VREG
1V/DIV
VREG
1V/DIV
BGTDR
2V/DIV
1µs/DIV
Regulator Output Transient
Response—Wall Adapter “Hot
Plugged”
Regulator Output Transient
Response—Wall Adapter Removal
Burst Mode Circuit Operation
VBAT = 3.6V
VREG = 3.3V
IL = 10mA
TA = 25°C
FIGURE 5
VBAT = 3.6V
VREG ≅ 3.3V
IL = 500mA
MODE = VBIAS1
TA = 25°C
FIGURE 5
VLDO
0.5V/DIV
VBAT = 3.6V
500µs/DIV
VREG = 3.3V
VLDO = 3.1V
ILDO = 200mA
VWALL ADAPTER = 6V TO 0V
TA = 25°C
FIGURE 5
1980 G11
VBAT = 3.6V
500µs/DIV
VREG = 3.3V
VLDO = 3.1V
ILDO = 200mA
VWALL ADAPTER = 0V TO 6V
TA = 25°C
FIGURE 5
1980 G12
Typical CTIMER Waveform
Mode Pin Input Current vs VIN
MODE PIN INPUT CURRENT (µA)
1.5
VBAT = 2.4V
VREG = 5V
1.0 TA = 25°C
0.5
TIMER
100mV/DIV
PIN 17
0
–0.5
–1.0
–1.5
CTIMER = 0.24µF
TA = 25°C
0
0.5
1.0
1.5
2.0
MODE PIN VIN (V)
2.5
5ms/DIV
1980 G14
3.0
1980 G13
1980i
5
LTC1980
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PI FU CTIO S
PROG (Pin 1): Charge Current Ratio Programming Pin.
Programs the full charge current when the charger is in the
constant current mode. A resistor placed between the
PROG pin and the PROGT pin (Pin 2) determines the
charge current. The PROG pin connects to an open drain
MOSFET which turns on for full current and is off when
trickle charging.
PROGT (Pin 2): Trickle Charge Programming Pin. Programs the trickle charge current for a deeply discharged
battery. Two resistors are used, one between the PROGT
pin and CAOUT (Pin 22) and another from PROGT to
ground. A capacitor between the PROGT pin and VC (Pin
4) provides compensation for the constant current feedback loop.
REGFB (Pin 3): DC/DC Converter Feedback Pin. This pin is
used to program the DC/DC converter output voltage when
the LTC1980 is in the DC/DC (regulator) converter mode.
An external resistor divider from VREG to REGFB to ground
programs the output voltage. The virtual reference voltage
(VREF) on this pin is 1.225V. A series RC from the REGFB
pin to VC (Pin 4) provides pole-zero compensation for the
regulator outer loop.
VC (Pin 4): Control Signal of the Inner Loop of the Current
Mode PWM. A common current mode loop is used by the
battery charger and voltage regulator functions. Minimum
duty factor (measured on BGTDR (Pin 14) in regulator
mode and RGTDR (Pin 11) in charger mode) occurs at
approximately 1V. Duty factor increases as VC increases.
This part includes slope compensation, so there is some
variation in VC for minimum and maximum duty factor as
VREG or VBAT is varied.
LDOFB (Pin 5): Low Dropout Regulator Feedback Pin.
This pin is used to program the low dropout linear regulator output voltage. An external resistor divider from the
output of the LDO regulator (drain of the external MOSFET)
to LDOFB to ground programs the output voltage. The
virtual reference voltage on this pin is 1.225V.
LDODRV (Pin 6): Low Dropout Error Amplifier Output.
This pin drives the gate of an external PMOS pass transistor. This pin is pulled up to VREG (shutting off the pass
transistor) if MODE (Pin 16) is grounded or if undervoltage
occurs.
VREG (Pin 7): Connection Point to the DC/DC Converter
Side of the Combo Charger/Converter Circuit.
WA (Pin 8): Wall Adapter Comparator Input. An external
resistor divider from the wall adapter output to WA to
ground sets the threshold which determines if charging
can occur. If the wall adapter is below this threshold, the
LTC1980 assumes the wall adapter is not present and the
charger shuts down. Wall adapter sense threshold is set
higher than the DC/DC converter output voltage to insure
correct operation.
BATT1 (Pin 9): Logic Input Pin for Selecting
Preprogrammed Li-Ion Charge Voltage. See Truth Table
logic settings.
BATT2 (Pin 10): Logic Input Pin for Selecting
Preprogrammed Li-Ion Charge Voltage. The following
combinations of BATT1 and BATT2 select the correct LiIon charge voltage. See Truth Table.
BATT2
BATT1
FLOAT VOLTAGE
0
0
4.1V
0
1
4.2V
1
0
8.2V
1
1
8.4V
Don’t Care
Open
Externally Set Via OVP
Logic 1 = VBIAS2 (Pin 19), Logic 0 = GND
RGTDR (Pin 11): DC/DC Converter (Regulator) Side Gate
Drive Pin. This pin provides gate drive to the external
MOSFET (REG-FET) that connects to VREG via the transformer.
PGND (Pin 12): Power Ground. Refer to the Applications
Information section for proper use of ground and power
ground connections.
VBIAS1 (Pin 13): Internally Generated Power Bus. Bypass
this pin with a 1µF or larger ceramic capacitor (or other low
ESR capacitor) to PGND (Pin 12). Do not connect any load
to this pin.
BGTDR (Pin 14): DC/DC Converter (Battery) Side Gate
Drive Pin. This pin provides gate drive to the external
MOSFET (BAT-FET) that connects to VBAT via the transformer.
1980i
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LTC1980
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PI FU CTIO S
REG (Pin 15): Bidirectional Regulator Mode Control Pin. A
pull-up resistor is required between this pin and VBIAS2.
This pin is open when charging normally, has a weak pulldown (approximately 5µA) when conditioning the battery
and a strong pull-down when in regulator mode. Pulling
this pin low forces the IC into regulator mode.
MODE (Pin 16): Selects different operating modes in both
charger and DC/DC converter configurations. Also enables and disables Burst Mode operation. See Mode Pin
Operation table in Application section.
TIMER (Pin 17): A timing capacitor on this pin determines
the normal charge time for charge termination.
C(µF) = 0.25 • Time (Hours)
VBAT (Pin 18): This pin connects to the positive terminal of
the battery and the battery side of the power converter.
VBIAS2 (Pin 19): Internally Generated Voltage. Bypass this
pin with a 1µF or larger ceramic capacitor (or other low
ESR capacitor). Do not connect any load to this pin.
GND (Pin 20): Signal Ground. This pin should Kelvinconnect to the current sense resistor (RSENSE).
ISENSE (Pin 21): Current Sense Input Pin. Connects internally to a current amplifier and zero current comparator.
This pin should Kelvin-connect to the current sense resistor (RSENSE) .
CAOUT (Pin 22): Current Amplifier Output. A program
resistor connects between this pin and PROGT (Pin 2) to
set the charge current (in constant-current mode).
OVP (Pin 23): Overvoltage Protection. This pin connects
to the tap on an optional external voltage divider connected across the battery. This allows nonstandard float
voltages to be used for the battery charger. Overvoltage,
restart and undervoltage thresholds will also be affected
by the external voltage division ratio. To use this pin,
BATT1 (Pin 9) must float.
SS (Pin 24): Soft-Start. A capacitor between this pin and
ground sets the battery charge ramp rate. Battery charge
current is very low the moment after the converter switches
from DC/DC converter (regulator) mode to battery charger
mode then ramps up to final battery charge current from
there. This insures that the wall adapter is not loaded down
with a large inrush current that could prevent correct
battery charger operation.
The same capacitor, which sets the soft-start ramp rate,
also sets the compensation for the battery float voltage
control loop.
1980i
7
LTC1980
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BLOCK DIAGRA
VBIAS1
BATT1
LDOFB
LDODRV
CAOUT
13
9
5
6
22
REF_UVL
21 ISENSE
+
–
GM
VREF
VMAX
VREF
+
VREF
–
VBIAS2 19
+
I=O
COMP
–
UVL
VDD REG
7
+
–
+
–
VBAT 18
VREG
REFERENCE
+
–
VREF
VREF
SR_EN
DIS
MODE 16
L
H
MODE
VM
S
H = BURST MODE OPERATION OFF
OPEN = BURST MODE OPERATION ON
L = DISABLE
VC
DUMP
XFMR
VREF
OSC
+
VREG
VBAT
4
AC
11 RGTDR
Q
RAMP
R
PWM
COMP
14 BGTDR
12 PGND
–
PROGT
2
REGFB
3
BATT1
9
VREF
+
VREF
–
AC
SLEEP
EA
WAKE
+
–
BURST
VREF
+
CONDITION BATTERY
OVP 23
–
BATT2 10
VBAT 18
VREF
+
VCELL <3.8V
TIMEOUT
TIMER
SHORT CYCLE
START
–
VREF
17 TIMER
+
–
WA 8
5µA
REG 15
VREF
1 PROG
+
GM
–
GND 20
REG
24
SS
1980 BD
1980i
8
LTC1980
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OPERATIO
The LTC1980 is an IC designed to provide a regulated
voltage to a system load from an unregulated or regulated
wall adapter, or from a battery and also charge a battery,
thereby providing an uninterruptable power source for the
system. When the wall adapter is present it provides
power to the system load and, if needed, a portion of the
power can be used to simultaneously charge the battery.
If the wall adapter is removed, the LTC1980 uses the
battery as a power source to continue providing a regulated output voltage to power the system.
Combining these two functions into a single IC reduces
circuit area compared to presently available solutions
(Figure 1). The unique bidirectional power converter topology (Figure 2) accounts for much of the area savings.
A transformer based design allows the wall adapter voltage to be less than or greater than the battery voltage.
The LTC1980 includes a 300kHz DC/DC PWM converter
that operates in two modes. The first mode is when the wall
adapter is present and the LTC1980 is used to charge the
battery using a constant-current/constant-voltage charge
scheme. The second mode is when the wall adapter is
removed and the battery powers the LTC1980 and the
DC/DC converter generates a regulated output voltage.
Existing Methods
CHARGE
TERMINATION
Using the LTC1980
BATTERY
CHARGER
FROM
WALL ADAPTER
FROM WALL ADAPTER
LTC1980-BASED
POWER DESIGN
POWER ROUTING
LOW DROPOUT
REGULATOR
PWM
REGULATOR
TO SYSTEM LOAD
DC/DC CONVERTERS
1980 F01
TO SYSTEM LOAD
DC/DC CONVERTERS
Figure 1. Portable Power Systems
WALL
ADAPTER
T1
Li-Ion
BATTERY
•
BAT-FET
ISENSE
•
REG-FET
T1
Li-Ion
BATTERY
•
BAT-FET
SYSTEM LOAD
DC/DC
CONVERTERS
RS
ISENSE
LTC1980
•
REG-FET
SYSTEM LOAD
DC/DC
CONVERTERS
RS
LTC1980
1980 F02a
1980 F02a
(a) Battery Charger Mode
(b) DC/DC Converter Mode (Wall Adapter Removed)
Figure 2. LTC1980 Bidirectional Power Conversion
1980i
9
LTC1980
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OPERATIO
Lithium-Ion Battery Charger Operation
With the wall adapter power applied, the LTC1980 operates as a constant-current/constant-voltage PWM battery
charger, with a portion of the adapter current used for
charging and the rest flowing to the system load through
an optional low dropout regulator.
A charge cycle begins when the voltage at VREG exceeds
the undervoltage lockout threshold level and the IC is
enabled via the MODE pin. If the battery has been deeply
discharged and the battery voltage is less than 2.7V, the
charger will begin with the programmed trickle charge
current.
When the battery exceeds 2.7V, the charger begins the
constant-current portion of the charge cycle with the
charge current equal to the programmed level. As the
battery accepts charge, the voltage increases. When the
battery voltage reaches 3.8V, the programmable timer
begins. Constant-current charging continues until the
battery approaches the programmed charge voltage of
4.1V or 4.2V/cell at which time the charge current will
begin to drop, signaling the beginning of the constantvoltage portion of the charge cycle. The charger will
maintain the programmed preset float voltage across the
battery until the timer terminates the charge cycle. During
trickle charging, if the battery voltage remains below 2.7V
for 1/4 of the total programmed charge time, the battery
may be defective and the charge cycle ends. Also, if a
battery open circuit is detected, the charge cycle ends
immediately. The charger can be shut down by pulling the
REG pin low, although the timer will continue until it times
out.
Power Converter Operation from Battery
When the AC adapter is removed, the LTC1980 operates as
a DC/DC PWM converter using the battery for input power
to provide a regulated output voltage for the system load.
The LTC1980 is a current mode switcher. This means that
the switch duty cycle is directly controlled by switch
current rather than by output voltage or current. Battery
charger operation will be described for the simplified
diagram (Figure 3). At the start of the oscillator cycle, latch
U9 is set causing M2 to turn on. When switch current
reaches a predetermined level M2 turns off and M1 turns
on. This level is set by the control voltage at the output of
error amplifier U10.
U1 VOLTAGE
SELECTION
B1
VREG
T1
C1 SN1 SNUBBER
NETWORK
BDRIVE
U4
DRIVERS
R1
–
U2
R2
RDRIVE
M1 M2
WALL
ADAPTER
C2
SN2 SNUBBER
NETWORK
+
+
+
C6
R12
–
VBAT
TO SYSTEM
LOAD
DIRECTION
SENSE
TYPICAL
WAVEFORM
–
U5
+
R4
+
ZC
VREF
CURRENT
AMPLIFIER
VREF
U7
OSC
R5
S
R
+
+
U6
–
R13
U9
Q
U8
–
–
R6
SW1
PWM
C3
R7
–
R8
SW2
SW3
+
C4
U10
R10
–
R9
EA
R11
U12
C5
+
U11
REFERENCE
VREF
1980 F03
Figure 3. Simplified Diagram—Power Converter
1980i
10
LTC1980
U
OPERATIO
Transformer current is sensed across RS, gained up via U6
and sampled through switch SW1. The current in R7 is a
scaled-down replica of the battery charging current pulses
from the transformer. During battery charging, switch
SW2 is in the down position connecting R7, R8, R9 and C4
to the inverting input of amplifier U10 forming an integrator which closes the outer loop of the converter and
establishes constant current charging. U12 is a gm amplifier that clamps U10 as the battery float voltage is reached.
R10 and R11 set the float voltage and C5 compensates this
loop and provides a soft-start function.
DC/DC Converter Operation
When the LTC1980 is operating as a DC/DC converter, M1
turns on at the start of the oscillator cycle. When transformer current reaches a predetermined level set by U10’s
output voltage, M1 turns off and M2 turns on. SW2 is in the
up position forming an integrator with zero, which compares the output voltage (via R1 and R2 to reference U11
establishing the output voltage.
U
W
U U
APPLICATIO S I FOR ATIO
Setting Battery Charge Current
Referring to the simplified schematic in Figure 4, the
average current through R7 must equal the current through
RTRKL with switch SW3 open. This leads to the equation
for setting the trickle charge current:
RTRKL =
VREF • R7
ITRICKLE • RS • A V
where AV = 2.44 and VREF = 1.225V. The suggested value
for R7 is 10k.
Setting the Float Voltage
Pin selectable 4.1V, 4.2V, 8.2V, and 8.4V Li-Ion float
voltages are available. Other float voltages may be set via
external resistors. The following combinations of logic
inputs BATT1 and BATT2 determine the float voltage.
Normal charge current is set via the parallel combination
of RTRKL and RCHRG which leads to the following equation
for RCHRG
BATT2
BATT1
FLOAT VOLTAGE
0
0
4.1V
0
1
4.2V
1
0
8.2V
VREF • R7
1
1
8.4V
Don’t Care
Open
Externally Set via OVP
RCHRG =
(INORMAL – ITRICKLE) • RS • A V
where logic 0 = GND and logic 1 = VBIAS2 (Pin 19)
VREF
1.218V
ISENSE
21
I
+
U6
AV = 2.5
RS
20
–
R7
10k
SW1
2
VC
U10
PROGT
22
CAOUT
C4
+
22
–
RCHRG
RTRKL
GND
PROG
1
SW3
20
1980 F04
Figure 4. Battery Charger Current Control Loop
1980i
11
LTC1980
U
W
U U
APPLICATIO S I FOR ATIO
An external resistor divider (Figure 3) can be used to
program other float voltages. Resistor values are found
using the following equation:
R10 = R11 • (VFLOAT – VREF)/VREF
where VREF = 1.225V. The suggested value for R11 is
100k. Use 1% or better resistors.
Setting DC/DC Converter Output Voltage
From Figure 5, select the following resistors based on
output voltage VREG:
R8 = R14 • (VREG – VREF)/VREF
where VREF = 1.225V, suggested value for R14 is 100k, 1%.
LDO Operation
The LTC1980 provides an uninterrupted power supply for
the system load. When a wall adapter is connected and
operating, power is taken from the wall adapter to charge
the batteries and supply power to the system. In applications where an unregulated wall adapter is used but a
regulated voltage is needed by the system, an external Pchannel MOSFET pass transistor may be added to the
LTC1980 to create a low dropout linear regulator.
From Figure 5, select the following resistors based on the
output voltage VLDO:
R5 = R6 • (VLDO – VREF)/VREF
where VREF = 1.225V, suggested value for R6 is 100k, 1%.
This is the voltage that will be seen when operating from
a higher voltage wall adapter. When operating from the
batteries (as a regulator), the load will see either this
voltage or the voltage set by the PWM regulator, whichever is less, minus any drops in the pass transistor.
Placing a large-valued capacitor from the drain of this
MOSFET to ground creates output compensation.
Wall Adapter Comparator Threshold
From Figure 5, select the following resistors based on the
wall adapter comparator threshold VWATH:
R15 = R7(VWATH – VIH1)/VIH1
where VIH1= 1.222V, suggested value for R7 is 100k. Use
1% resistors.
MODE Pin Operation
The following truth table describes MODE pin operation.
Burst Mode operation is disabled during battery charging
to reduce broadband noise inherent in Burst Mode operation. (Refer to the LT1307 data sheet for details).
POWER FLOW
MODE PIN
Battery Charger
0
Battery Charger
Open
OPERATING MODE
Disabled
Enabled Continuous
Battery Charger
1
Enabled Continuous
DC/DC converter
0
Disabled
DC/DC converter
Open
DC/DC converter
1
Enabled Burst Mode Operation
Enabled Continuous
Logic 1 = VBIAS1 (Pin 13) Logic 0 = GND
The MODE pin should be decoupled with 200pF to ground
when left open.
Snubber Design
The values given in the applications schematics have been
found to work quite well for most applications. Care
should be taken in selecting other values for your application since efficiency may be impacted by a poor choice. For
a detailed look at snubber design, several very helpful
notes are available in Application Note 19.
Frequency Compensation
Load step testing can be used to empirically determine
compensation. Application Note 25 provides information
on the technique. To adjust the compensation for the DC/
DC converter, adjust C12 and R13 (in Figure 5). Battery
charger current loop compensation is set by C11 and
battery charger float voltage compensation is set by C8.
Component Selection Basics
The application circuits work well for most 1- and 2-cell
Li-Ion, 0.5A to 1A output current designs. The next section
highlights the component selection process. More information is available in Application Note 19.
1980i
12
LTC1980
U
W
U
U
APPLICATIO S I FOR ATIO
Current Sense Resistor
Voltage drop in the current sense resistor should be
limited to approximately ±100mV with respect to ground
at max load currents in all modes. This value strikes a
reasonable balance between providing an adequate low
current signal, while keeping the losses from this resistor
low. For applications where the inputs and output voltages
may be low, a somewhat lower drop can be used (in order
to reduce conduction losses slightly).
The LTC1980 has several features, such as leading-edge
blanking, which make application of this part easier to use.
However for best charge current accuracy, the current
sense resistor should be Kelvin sensed.
MOSFETs
The LTC1980 uses low side MOSFET switches. There are
two very important advantages. First, N-channel MOSFETs
are used—this generally means that efficiency will be
higher than a comparable on-resistance P-channel device
(because less gate charge is required). Second, low VT
(‘logic-level’) MOSFETs with relatively low absolute maximum VGS ratings can be used, even in higher voltage
applications. Refer to Application Note 19 for information
on determining MOSFET voltage and current ratings.
Transformer
Turns ratio affects the duty factor of the power converter
which impacts current and voltage stress on the power
MOSFETs, input and output capacitor RMS currents and
transformer utilization (size vs power). Using a 50% duty
factor under nominal operating conditions usually gives
reasonable results. For a 50% duty factor, the turns ratio
is:
N = VREG/VBAT
N should be calculated for the design operating as a DC/DC
converter and as a battery charger. The final turns ratio
should be chosen so that it is approximately equal to the
average of the two calculated values for N. In addition
choose a turns ratio which can be made from the ratio of
small integers. This allows bifilar windings to be used in
the transformer which can reduce the leakage inductance,
reduce the need for aggressive snubber design and for this
reason improve efficiency.
Avoid transformer saturation under all operating conditions and combinations (usually the biggest problems
occur at high output currents and extreme duty cycles.
Also check these conditions for battery charging and
regulation modes.
Finally, in low voltage applications, select a transformer
with low winding resistance. This will improve efficiency at
heavier loads.
Capacitors
Check the RMS current rating on your capacitors on both
sides of your circuit. Low ESR and ESL is recommended
for lowest ripple. OS-CON capacitors (from Sanyo) work
very well in this application.
Diodes
In low voltage applications, Schottky diodes should be
placed in parallel with the drain and source of the MOSFETs
in the PWM supply. This prevents body diode turn on and
improves efficiency by eliminating loss from reverse recovery in these diodes. It also reduces conduction loss
during the RGTDR/BGTDR break interval.
The LTC1980 can operate to voltages as low as 2.8V.
Suitable Schottky diodes include the ZHCS1000 (VF =
420mV at IF = 1A) and SL22/23 (VF = 440mV at IF = 2A) for
most 500mA to 1A output current applications.
Vendor List
VENDOR
COMPONENTS
TELEPHONE
BH Electronics
Transformers
952-894-9590
Coiltronics/Cooper Electronic
Transformers
561-752-5000
Fairchild Semiconductor
MOSFETs
Schottky Rectifiers
800-341-0392
Vishay (General Semiconductor) MOSFETs
Schottky Rectifiers
631-847-3000
Sanyo
OS-CON Capacitors
408-749-9714
Sumida Electric USA
Transformers
847-956-0666
Vishay (Siliconix)
MOSFETs
408-988-8000
1980i
13
LTC1980
U
TYPICAL APPLICATIO
VBAT
+
4.1V
Li-Ion
BATTERY
C1
68µF
D1*
5819
BH511-1014
+
VREG
+
•
5.1Ω
5.1Ω
•
1nF
WALL
ADAPTER
C4
68µF
OPTIONAL PASS
TRANSISTOR
FOR LDO FDC636P
1nF
1/2 FDC6401N
1/2 FDC6401N
BGTDR
18
VBAT
23
OVP
3
REGFB
22
CAOUT
PROG
1
R9
10k
12
PGND
R11
1M
21
GND ISENSE
11
7
6
5
PROGT
C11
1nF
VC
TIMER
4
17
C7
0.27µF
WA
15
REG
16
MODE
9
BATT1
10
BATT2
SS
24
C8
0.1µF
R6
100k
8
RGTDR VREG LDODRV LDOFB
LTC1980
2
R10
110k
20
VBIAS1
C9
1µF
200pF
R8
169k
ACIN
VLDO 3.1V
SYSTEM LOAD
DC/DC
CONVERTERS
C6
470µF
R5
154k
50mΩ
RSENSE
14
DCOUT
3.3V
VOUT
R15
300k
R7
100k
VBIAS2
13
C10
0.33µF
19
R14
100k
R12
100k
*OPTIONAL DIODE FOR
SHORTED WALL ADAPTER
TERMINAL PROTECTION.
C12
82pF
R13
806k
1980 TA02
Figure 5. 4.1V/1A Li-Ion Battery Charger and 3.3V DC/DC Converter
1980i
14
LTC1980
U
PACKAGE DESCRIPTIO
GN Package
24-Lead Plastic SSOP (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1641)
.337 – .344*
(8.560 – 8.738)
24 23 22 21 20 19 18 17 16 15 1413
.033
(0.838)
REF
.045 ±.005
.229 – .244
(5.817 – 6.198)
.254 MIN
.150 – .157**
(3.810 – 3.988)
.150 – .165
1
.0165 ± .0015
2 3
4
5 6
7
8
9 10 11 12
.0250 TYP
RECOMMENDED SOLDER PAD LAYOUT
.015 ± .004
× 45°
(0.38 ± 0.10)
.007 – .0098
(0.178 – 0.249)
.053 – .068
(1.351 – 1.727)
.004 – .0098
(0.102 – 0.249)
0° – 8° TYP
.016 – .050
(0.406 – 1.270)
NOTE:
1. CONTROLLING DIMENSION: INCHES
INCHES
2. DIMENSIONS ARE IN
(MILLIMETERS)
3. DRAWING NOT TO SCALE
*DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
**DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
.008 – .012
(0.203 – 0.305)
.0250
(0.635)
BSC
GN24 (SSOP) 0502
1980i
15
LTC1980
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PART NUMBER
DESCRIPTION
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Complete Dual-Battery Charger/Selector System, Easy Interface with
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LTC4007
4A Standalone Multiple Cell Li-Ion Battery Charger
6V ≤ VIN ≤ 28V, 3- or 4-Cell, Up to 96% Efficiency
LTC4050
Lithium-Ion Linear Battery Charger Controller
Simple Charger uses External FET, Thermistor Input for
Battery Temperature Sensing
LTC4052
Lithium-Ion Linear Battery Pulse Charger
Fully Integrated, Standalone Pulse Charger, Minimal Heat Dissipation,
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Ideal Diode or PowerPathTM
Very Low Loss Replacement for Power Supply, ORing Diodes,
3V ≤ VIN ≤ 28V, ThinSOT Package.
ThinSOT and PowerPath are trademarks of Linear Technology Corporation.
1980i
16
Linear Technology Corporation
LT/TP 0503 1.5K • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507 ● www.linear.com
 LINEAR TECHNOLOGY CORPORATION 2003