FEATURES
LT1308A/LT1308B
High Current, Micropower
Single Cell, 600kHz
DC/DC Converters
U
DESCRIPTIO
■
5V at 1A from a Single Li-Ion Cell
■
5V at 800mA in SEPIC Mode from Four NiCd Cells
■
Fixed Frequency Operation: 600kHz
■
Boost Converter Outputs up to 34V
■
Starts into Heavy Loads
■
Automatic Burst ModeTM Operation at
Light Load (LT1308A)
■
Continuous Switching at Light Loads (LT1308B)
■
Low V
■
Pin-for-Pin Upgrade Compatible with LT1308
■
Lower Quiescent Current in Shutdown: 1μA (Max)
■
Improved Accuracy Low-Battery Detector
Switch: 300mV at 2A
CESAT
Reference: 200mV ± 2%
■
Available in 8-Lead SO and 14-Lead TSSOP Packages
U
APPLICATIO S
■
GSM/CDMA Phones
■
Digital Cameras
■
LCD Bias Supplies
■
Answer-Back Pagers
■
GPS Receivers
■
Battery Backup Supplies
■
Handheld Computers
The LT®1308A/LT1308B are micropower, fixed frequency
step-up DC/DC converters that operate over a 1V to 10V
input voltage range. They are improved versions of the
LT1308 and are recommended for use in new designs. The
LT1308A features automatic shifting to power saving
Burst Mode operation at light loads and consumes just
140μA at no load. The LT1308B features continuous
switching at light loads and operates at a quiescent current
of 2.5mA. Both devices consume less than 1μA in
shutdown.
Low-battery detector accuracy is significantly tighter than
the LT1308. The 200mV reference is specified at ± 2% at
room and ± 3% over temperature. The shutdown pin
enables the device when it is tied to a 1V or higher source
and does not need to be tied to VIN as on the LT1308. An
internal VC clamp results in improved transient response
and the switch voltage rating has been increased to 36V,
enabling higher output voltage applications.
The LT1308A/LT1308B are available in the 8-lead SO and
the 14-lead TSSOP packages.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. Burst
Mode is a registered trademark of Linear Technology Corporation. All other trademarks are
the property of their respective owners.
U
TYPICAL APPLICATIO
L1
4.7μH
V
+
C1
47μF
Li-Ion
CELL
C1: AVX TAJC476M010
C2: AVX TPSD227M006
D1: IR 10BQ015
IN
LBI
LT1308B
SHDNSHUTDOWN
V
C
47k
100pF
L1: MURATA LQH6C4R7
*R1: 887k FOR V
Figure 1. LT1308B Single Li-Ion Cell to 5V/1A DC/DC Converter
SW
LBO
GND
OUT
FB
D1
= 12V
R1*
309k
R2
100k
5V
1A
+
C2
220μF
1308A/B F01a
95
90
85
80
75
70
EFFICIENCY (%)
65
60
55
50
1
Converter Efficiency
VIN = 3.6V
VIN = 1.5V
10 100 1000
LOAD CURRENT (mA)
VIN = 4.2V
VIN = 2.5V
1308A/B F01b
1308abfa
1
LT1308A/LT1308B
A
W
O
LUTEXI TIS
S
A
WUW
U
(Note 1)
ARB
G
VIN, SHDN, LBO Voltage ......................................... 10V
SW Voltage ............................................... –0.4V to 36V
FB Voltage ....................................................... VIN + 1V
VC Voltage ................................................................ 2V
LBI Voltage ................................................. –0.1V to 1V
Current into FB Pin .............................................. ±1mA
UUU
PI CO FIGURATIO
TOP VIEW
LBO
8
LBI
7
V
6
IN
SW
5
SHDN
GND
V
C
FB
T
JMAX
1
2
3
4
S8 PACKAGE
8-LEAD PLASTIC SO
= 125°C, θJA = 190°C/W
Operating Temperature Range
Commercial ............................................ 0°C to 70°C
Extended Commerial (Note 2) ........... – 40°C to 85°C
Industrial ........................................... –40°C to 85°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
TOP VIEW
1
V
C
2
FB
3
SHDN
4
GND
5
GND
6
GND
7
GND
F PACKAGE
14-LEAD PLASTIC TSSOP
= 125°C, θJA = 80°C/W
T
JMAX
(Note 6)
LBO
14
LBI
13
V
12
IN
V
11
IN
SW
10
SW
9
SW
8
NOT RECOMMENDED FOR NEW DESIGNS
Contact Linear Technology for Potential Replacement
UUW
ORDER I FOR ATIO
LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE
LT1308ACS8#PBF LT1308ACS8#TRPBF 1308A 8-Lead Plastic SO 0°C to 70°C
LT1308AIS8#PBF LT1308AIS8#TRPBF 1308AI 8-Lead Plastic SO –40°C to 85°C
LT1308BCS8#PBF LT1308BCS8#TRPBF 1308B 8-Lead Plastic SO 0°C to 70°C
LT1308BIS8#PBF LT1308BIS8#TRPBF 1308BI 8-Lead Plastic SO –40°C to 85°C
LT1308ACF#PBF LT1308ACF#TRPBF LT1308ACF 14-Lead Plastic TSSOP 0°C to 70°C
LT1308BCF#PBF LT1308BCF#TRPBF LT1308BCF 14-Lead Plastic TSSOP 0°C to 70°C
LEAD BASED FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE
LT1308ACS8 LT1308ACS8#TR 1308A 8-Lead Plastic SO 0°C to 70°C
LT1308AIS8 LT1308AIS8#TR 1308AI 8-Lead Plastic SO –40°C to 85°C
LT1308BCS8 LT1308BCS8#TR 1308B 8-Lead Plastic SO 0°C to 70°C
LT1308BIS8 LT1308BIS8#TR 1308BI 8-Lead Plastic SO –40°C to 85°C
LT1308ACF LT1308ACF#TR LT1308ACF 14-Lead Plastic TSSOP 0°C to 70°C
LT1308BCF LT1308BCF#TR LT1308BCF 14-Lead Plastic TSSOP 0°C to 70°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
2
1308abfa
LT1308A/LT1308B
ELECTRICAL CHARACTERISTICS
range, otherwise specifications are TA = 25°C. Commercial Grade 0°C to 70°C. VIN = 1.1V, V
The ● denotes specifications which apply over the full operating temperature
= VIN, unless otherwise noted.
SHDN
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
I
Q
Quiescent Current Not Switching, LT1308A 140 240 μA
Switching, LT1308B 2.5 4 mA
= 0V (LT1308A/LT1308B) 0.01 1 μA
V
SHDN
V
FB
I
B
Feedback Voltage ● 1.20 1.22 1.24 V
FB Pin Bias Current (Note 3) ● 27 80 nA
Reference Line Regulation 1.1V ≤ VIN ≤ 2V ● 0.03 0.4 %/V
2V ≤ V
≤ 10V 0.01 0.2 %/V
IN
Minimum Input Voltage 0.92 1 V
g
A
f
m
V
OSC
Error Amp Transconductance ΔI = 5μA60μmhos
Error Amp Voltage Gain 100 V/V
Switching Frequency VIN = 1.2V ● 500 600 700 kHz
Maximum Duty Cycle ● 82 90 %
Switch Current Limit Duty Cyle = 30% (Note 4) 2 3 4.5 A
Switch V
CESAT
ISW = 2A (25°C, 0°C), VIN = 1.5V 290 350 mV
I
= 2A (70°C), VIN = 1.5V 330 400 mV
SW
Burst Mode Operation Switch Current Limit VIN = 2.5V, Circuit of Figure 1 400 mA
(LT1308A)
Shutdown Pin Current V
= 1.1V ● 25μA
SHDN
= 6V ● 20 35 μA
V
SHDN
= 0V ● 0.01 0.1 μA
V
SHDN
LBI Threshold Voltage 196 200 204 mV
● 194 200 206 mV
LBO Output Low I
LBO Leakage Current V
LBI Input Bias Current (Note 5) V
= 50μA ● 0.1 0.25 V
SINK
= 250mV, V
LBI
= 150mV 33 100 nA
LBI
= 5V ● 0.01 0.1 μA
LBO
Low-Battery Detector Gain 3000 V/V
Switch Leakage Current VSW = 5V ● 0.01 10 μA
The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C.
Industrial Grade –40°C to 85°C. VIN = 1.2V, V
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
I
Q
V
FB
I
B
g
m
A
V
Quiescent Current Not Switching, LT1308A ● 140 240 μA
Feedback Voltage ● 1.19 1.22 1.25 V
FB Pin Bias Current (Note 3) ● 27 80 nA
Reference Line Regulation 1.1V ≤ VIN ≤ 2V ● 0.05 0.4 %/V
Minimum Input Voltage 0.92 1 V
Error Amp Transconductance ΔI = 5μA60μmhos
Error Amp Voltage Gain 100 V/V
= VIN, unless otherwise noted.
SHDN
Switching, LT1308B
V
= 0V (LT1308A/LT1308B) ● 0.01 1 μA
SHDN
2V ≤ V
≤ 10V ● 0.01 0.2 %/V
IN
● 2.5 4 mA
1308abfa
3
LT1308A/LT1308B
ELECTRICAL CHARACTERISTICS
range, otherwise specifications are TA = 25°C. Industrial Grade –40°C to 85°C. VIN = 1.2V, V
The ● denotes specifications which apply over the full operating temperature
= VIN, unless otherwise noted.
SHDN
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
f
OSC
Switching Frequency ● 500 600 750 kHz
Maximum Duty Cycle ● 82 90 %
Switch Current Limit Duty Cyle = 30% (Note 4) 2 3 4.5 A
Switch V
CESAT
ISW = 2A (25°C, –40°C), VIN = 1.5V 290 350 mV
= 2A (85°C), VIN = 1.5V 330 400 mV
I
SW
Burst Mode Operation Switch Current Limit VIN = 2.5V, Circuit of Figure 1 400 mA
(LT1308A)
Shutdown Pin Current V
= 1.1V ● 2 5μA
SHDN
= 6V ● 20 35 μA
V
SHDN
= 0V 0.01 0.1 μA
V
SHDN
LBI Threshold Voltage 196 200 204 mV
● 193 200 207 mV
LBO Output Low I
LBO Leakage Current V
LBI Input Bias Current (Note 5) V
= 50μA ● 0.1 0.25 V
SINK
= 250mV, V
LBI
= 150mV 33 100 nA
LBI
= 5V ● 0.01 0.1 μA
LBO
Low-Battery Detector Gain 3000 V/V
Switch Leakage Current VSW = 5V ● 0.01 10 μA
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: The LT1308ACS8, LT1308ACF, LT1308BCS8 and LT1308BCF are
designed, characterized and expected to meet the industrial temperature
limits, but are not tested at – 40°C and 85°C. I grade devices are
guaranteed over the –40°C to 85°C operating temperature range.
Note 4: Switch current limit guaranteed by design and/or correlation to
static tests. Duty cycle affects current limit due to ramp generator (see
Block Diagram).
Note 5: Bias current flows out of LBI pin.
Note 6: Connect the four GND pins (Pins 4–7) together at the device.
Similarly, connect the three SW pins (Pins 8–10) together and the two V
IN
pins (Pins 11, 12) together at the device.
Note 3: Bias current flows into FB pin.
UW
TYPICAL PERFORMANCE CHARACTERISTICS
LT1308B
3.3V Output Efficiency
95
90
85
80
75
70
EFFICIENCY (%)
65
60
55
50
1 100 1000
VIN = 1.8V
10
LOAD CURRENT (mA)
VIN = 2.5V
VIN = 1.2V
1308A/B G01
LT1308A
3.3V Output Efficiency
95
90
85
80
75
70
EFFICIENCY (%)
65
60
55
50
VIN = 1.8V
1 100 1000
10
LOAD CURRENT (mA)
VIN = 2.5V
VIN = 1.2V
1308A/B G02
4
LT1308A
5V Output Efficiency
95
90
VIN = 3.6V
85
80
75
70
EFFICIENCY (%)
65
60
55
50
1
LOAD CURRENT (mA)
VIN = 4.2V
VIN = 1.5V
10 100 1000
VIN = 2.5V
1308A/B G03
1308abfa
UW
TEMPERATURE (°C)
–50 –25
V
REF
(mV)
05025
75
100
1308 • G09
203
202
201
200
199
198
197
196
195
TYPICAL PERFORMANCE CHARACTERISTICS
LT1308A/LT1308B
LT1308B
12V Output Efficiency
90
85
80
75
70
65
EFFICIENCY (%)
60
55
50
1 100 1000
VIN = 5V
VIN = 3.3V
10
LOAD CURRENT (mA)
SHDN Pin Bias Current vs Voltage
50
40
30
20
SHDN PIN CURRENT (μA)
10
0
2
0
SHDN PIN VOLTAGE (V)
6
4
8
1308A/B G04
–40°C
25°C
85°C
1308 G07
Switch Current Limit vs
Duty Cycle
4.0
3.5
3.0
CURRENT LIMIT (A)
2.5
2.0
20
0
DUTY CYCLE (%)
60
80
40
100
1308 • G05
FB, LBI Bias Current vs
Temperature
80
70
60
50
40
30
BIAS CURRENT (nA)
20
10
0
10
–50 –25
LBI
05025
TEMPERATURE (°C)
FB
75
100
1308 • G08
Switch Saturation Voltage
vs Current
500
400
(mV)
300
CESAT
200
SWITCH V
100
0
0
0.5
SWITCH CURRENT (A)
25°C
1.0
Low Battery Detector Reference
vs Temperature
1.5
85°C
–40°C
2.0
1308 G06
Oscillator Frequency vs
Temperature
800
750
700
650
600
550
FREQUENCY (kHz)
500
450
400
–50 –2.5
05025
TEMPERATURE (°C)
75
1308 • G10
100
LT1308A Quiescent Current vs
Temperature
180
170
160
150
140
130
120
QUIESCENT CURRENT (μA)
110
100
–50 –25
05025
TEMPERATURE (°C)
75
1308 • G11
100
Feedback Pin Voltage vs
Temperature
1.25
1.24
1.23
1.22
(V)
FB
V
1.21
1.20
1.19
1.18
–50 –25
05025
TEMPERATURE (°C)
75
1308 • G12
1308abfa
100
5
LT1308A/LT1308B
UUU
PIN FUNCTIONS
(SO/TSSOP)
VC (Pin 1/Pin 1): Compensation Pin for Error Amplifier.
Connect a series RC from this pin to ground. Typical
values are 47kΩ and 100pF. Minimize trace area at V
FB (Pin 2/Pin 2): Feedback Pin. Reference voltage is
1.22V. Connect resistive divider tap here. Minimize trace
area at FB. Set V
V
= 1.22V(1 + R1/R2).
OUT
SHDN (Pin 3/Pin 3): Shutdown. Ground this pin to turn
off switcher. To enable, tie to 1V or more. SHDN does not
need to be at VIN to enable the device.
GND (Pin 4/Pins 4, 5, 6, 7): Ground. Connect directly to
local ground plane. Ground plane should enclose all
components associated with the LT1308. PCB copper
connected to these pins also functions as a heat sink. For
the TSSOP package, connect all pins to ground copper to
get the best heat transfer. This keeps chip heating to a
minimum.
according to:
OUT
.
C
SW (Pin 5/Pins 8, 9, 10): Switch Pins. Connect inductor/
diode here. Minimize trace area at these pins to keep EMI
down. For the TSSOP package, connect all SW pins
together at the package.
(Pin 6/Pins 11, 12): Supply Pins. Must have local
V
IN
bypass capacitor right at the pins, connected directly to
ground. For the TSSOP package, connect both V
together at the package.
LBI (Pin 7/Pin 13): Low-Battery Detector Input. 200mV
reference. Voltage on LBI must stay between –100mV
and 1V. Low-battery detector does not function with
SHDN pin grounded. Float LBI pin if not used.
LBO (Pin 8/Pin 14): Low-Battery Detector Output. Open
collector, can sink 50μA. A 220kΩ pull-up is recom-
mended. LBO is high impedance when SHDN is grounded.
IN
pins
6
1308abfa
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