Linear LT1308ACS8, LT1308AIS8, LT1308BCS8, LT1308BIS8, LT1308ACF Schematics
...
LT1308A/LT1308B
High Current, Micropower
Single Cell, 600kHz
DC/DC Converters
FEATURES
n
5V at 1A from a Single Li-Ion Cell
n
5V at 800mA in SEPIC Mode from Four NiCd Cells
n
Fixed Frequency Operation: 600kHz
n
Boost Converter Outputs up to 34V
n
Starts into Heavy Loads
n
Automatic Burst Mode™ Operation at
Light Load (LT1308A)
n
Continuous Switching at Light Loads (LT1308B)
n
Low V
n
Pin-for-Pin Upgrade Compatible with LT1308
n
Lower Quiescent Current in Shutdown: 1µA (Max)
n
Improved Accuracy Low-Battery Detector
Switch: 300mV at 2A
CESAT
Reference: 200mV ±2%
n
Available in 8-Lead SO and 14-Lead TSSOP Packages
APPLICATIONS
n
GSM/CDMA Phones
n
Digital Cameras
n
LCD Bias Supplies
n
Answer-Back Pagers
n
GPS Receivers
n
Battery Backup Supplies
n
Handheld Computers
DESCRIPTION
The LT®1308A/LT1308B are micropower, fi xed 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 signifi cantly tighter than
the LT1308. The 200mV reference is specifi ed 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 V
internal V
clamp results in improved transient response
C
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.
L, LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners.
as on the LT1308. An
IN
TYPICAL APPLICATION
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 Effi ciency
VIN = 3.6V
VIN = 1.5V
10 100 1000
LOAD CURRENT (mA)
VIN = 4.2V
VIN = 2.5V
1308A/B F01b
1308abfb
1
LT1308A/LT1308B
ABSOLUTE MAXIMUM RATINGS
VIN, SHDN, LBO Voltage ........................................... 10V
SW Voltage .............................................. –0.4V to 36V
FB Voltage ......................................................... V
Voltage ................................................................. 2V
V
C
+ 1V
IN
LBI Voltage ................................................. –0.1V to 1V
Current into FB Pin ............................................... ±1mA
PIN CONFIGURATION
TOP VIEW
V
1
C
FB
2
SHDN
3
GND
4
8-LEAD PLASTIC SO
T
= 125°C, θJA = 190°C/W
JMAX
S8 PACKAGE
LBO
8
LBI
7
V
6
IN
SW
5
(Note 1)
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
(NOTE 6)
= 125°C, θJA = 80°C/W
T
JMAX
LBO
14
LBI
13
V
12
IN
V
11
IN
SW
10
SW
9
SW
8
OBSOLETE, FOR INFORMATION PURPOSES ONLY
Contact Linear Technology for Potential Replacement
ORDER INFORMATION
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 specifi ed with wider operating temperature ranges.
For more information on lead free part marking, go to:
This product is only offered in trays. For more information go to:
http://www.linear.com/leadfree/
http://www.linear.com/packaging/
1308abfb
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LT1308A/LT1308B
ELECTRICAL CHARACTERISTICS
The l denotes the specifi cations which apply over the full operating temperature
range, otherwise specifi cations are at T
= 25°C. Commercial Grade 0°C to 70°C. VIN = 1.1V, V
A
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
I
Q
Quiescent Current Not Switching, LT1308A
Switching, LT1308B
V
= 0V (LT1308A/LT1308B)
SHDN
V
FB
I
B
Feedback Voltage
FB Pin Bias Current (Note 3)
Reference Line Regulation 1.1V ≤ V
2V ≤ V
IN
≤ 10V
IN
≤ 2V
Minimum Input Voltage 0.92 1 V
g
A
f
m
V
OSC
Error Amp Transconductance ∆I = 5µA 60 µmhos
Error Amp Voltage Gain 100 V/V
Switching Frequency VIN = 1.2V
Maximum Duty Cycle
Switch Current Limit Duty Cycle = 30% (Note 4) 2 3 4.5 A
Switch V
CESAT
Burst Mode Operation Switch Current Limit
ISW = 2A (25°C, 0°C), VIN = 1.5V
I
= 2A (70°C), VIN = 1.5V
SW
= 2.5V, Circuit of Figure 1 400 mA
V
IN
(LT1308A)
Shutdown Pin Current V
SHDN
V
SHDN
V
SHDN
= 1.1V
= 6V
= 0V
LBI Threshold Voltage
LBO Output Low I
LBO Leakage Current V
LBI Input Bias Current (Note 5) V
= 50µA
SINK
= 250mV, V
LBI
= 150mV 33 100 nA
LBI
LBO
= 5V
Low-Battery Detector Gain 3000 V/V
Switch Leakage Current V
SW
= 5V
= VIN, unless otherwise noted.
SHDN
140
2.5
0.01
l
1.20 1.22 1.24 V
l
l
27 80 nA
0.03
0.01
l
500 600 700 kHz
l
82 90 %
290
330
l
l
l
196
l
194
l
l
l
2
20
0.01
200
200
0.1 0.25 V
0.01 0.1 µA
0.01 10 µA
240
4
1
0.4
0.2
350
400
5
35
0.1
204
206
µA
mA
µA
%/V
%/V
mV
mV
µA
µA
µA
mV
mV
The l denotes the specifi cations which apply over the full operating temperature range, otherwise specifi cations are at 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
Feedback Voltage
FB Pin Bias Current (Note 3)
Reference Line Regulation 1.1V ≤ V
Minimum Input Voltage 0.92 1 V
Error Amp Transconductance ∆I = 5µA 60 µmhos
Error Amp Voltage Gain 100 V/V
= VIN, unless otherwise noted.
SHDN
Switching, LT1308B
V
= 0V (LT1308A/LT1308B)
SHDN
≤ 2V
IN
2V ≤ V
≤ 10V
IN
l
l
l
l
1.19 1.22 1.25 V
l
l
l
140
240
2.5
0.01
27 80 nA
0.05
0.01
0.4
0.2
4
1
mA
µA
%/V
%/V
1308abfb
µA
3
LT1308A/LT1308B
The l denotes the specifi cations which apply over the full operating temperature
ELECTRICAL CHARACTERISTICS
range, otherwise specifi cations are at TA = 25°C. Industrial Grade –40°C to 85°C. VIN = 1.2V, V
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
f
OSC
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 3: Bias current fl ows into FB pin.
Switching Frequency
Maximum Duty Cycle
Switch Current Limit Duty Cycle = 30% (Note 4) 2 3 4.5 A
Switch V
CESAT
Burst Mode Operation Switch Current Limit
ISW = 2A (25°C, –40°C), VIN = 1.5V
I
= 2A (85°C), VIN = 1.5V
SW
= 2.5V, Circuit of Figure 1 400 mA
V
IN
(LT1308A)
Shutdown Pin Current V
SHDN
V
SHDN
V
SHDN
= 1.1V
= 6V
= 0V
LBI Threshold Voltage
LBO Output Low I
LBO Leakage Current V
LBI Input Bias Current (Note 5) V
= 50µA
SINK
= 250mV, V
LBI
= 150mV 33 100 nA
LBI
LBO
= 5V
Low-Battery Detector Gain 3000 V/V
Switch Leakage Current V
SW
= 5V
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 fl ows 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
pins (Pins 11, 12) together at the device.
= VIN, unless otherwise noted.
SHDN
l
500 600 750 kHz
l
82 90 %
290
330
l
l
2
20
0.01
196
l
193
l
l
l
200
200
0.1 0.25 V
0.01 0.1 µA
0.01 10 µA
350
400
5
35
0.1
204
207
mV
mV
µA
µA
µA
mV
mV
IN
TYPICAL PERFORMANCE CHARACTERISTICS
LT1308B
3.3V Output Effi ciency
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 Effi ciency
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
4
1308A/B G02
LT1308A
5V Output Effi ciency
95
90
VIN = 3.6V
85
80
75
70
EFFICIENCY (%)
65
60
55
50
1
VIN = 4.2V
VIN = 1.5V
10 100 1000
LOAD CURRENT (mA)
VIN = 2.5V
1308A/B G03
1308abfb
TYPICAL PERFORMANCE CHARACTERISTICS
LT1308A/LT1308B
LT1308B
12V Output Effi ciency
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
10
Switch Current Limit vs
Duty Cycle
4.0
3.5
3.0
CURRENT LIMIT (A)
2.5
2.0
20
0
40
DUTY CYCLE (%)
FB, LBI Bias Current vs
Temperature
80
70
60
50
40
30
BIAS CURRENT (nA)
20
10
0
–50 –25
LBI
05025
TEMPERATURE (°C)
Switch Saturation Voltage
vs Current
500
400
1.5
85°C
–40°C
2.0
1308 G06
(mV)
300
CESAT
200
SWITCH V
100
0
60
80
100
1308 • G05
0
0.5
SWITCH CURRENT (A)
25°C
1.0
Low Battery Detector Reference
vs Temperature
203
202
201
200
(mV)
199
REF
V
FB
75
100
1308 • G08
198
197
196
195
–50 –25
05025
TEMPERATURE (°C)
75
100
1308 • G09
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
1308abfb
100
1308 • G12
5
LT1308A/LT1308B
PIN FUNCTIONS
VC (Pin 1/Pin 1): Compensation Pin for Error Amplifi er.
Connect a series RC from this pin to ground. Typical values
are 47k 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
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 V
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.
= 1.22V(1 + R1/R2).
OUT
according to:
OUT
IN
(SO/TSSOP)
to enable the device.
.
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 220k pull-up is recommended. LBO is high impedance when SHDN is grounded.
pins
IN
6
1308abfb
BLOCK DIAGRAMS
V
IN
6
R5
40k
V
OUT
R1
(EXTERNAL)
FB
R2
(EXTERNAL)
FB
Q1
2
R6
40k
Q2
×10
R3
30k
R4
140k
V
IN
+
g
m
–
AMPLIFIER
RAMP
GENERATOR
600kHz
OSCILLATOR
ERROR
V
IN
Q4
V
C
1
2V
BE
+
*
BIAS
–
A1
COMPARATOR
–
+
Σ
+
*HYSTERESIS IN LT1308A ONLY
+
A2
LT1308A/LT1308B
SHUTDOWN
LBI
7
+
ENABLE
–
200mV
R
FF
Q
S
A4
DRIVER
+
A = 3
–
SHDN
3
LBO
8
SW
5
4
GND
Q3
0.03
1308 BD2a
V
OUT
R1
(EXTERNAL)
R2
(EXTERNAL)
Figure 2a. LT1308A/LT1308B Block Diagram (SO-8 Package)
V
IN
+
*
–
A1
COMPARATOR
–
+
A2
2V
BE
SHDN
3
LBO
14
SW
8SW9
SW
10
Q3
ENABLE
200mV
R
SHUTDOWN
LBI
13
+
–
A4
FF
Q
S
DRIVER
+
A = 3
0.03Ω
–
4
GND5GND6GND
GND
7
1308 BD2b
V
11
IN
V
IN
12
R5
40k
R6
40k
V
IN
+
g
m
Q4
V
C
1
–
ERROR
FB
FB
Q1
2
Q2
×10
R3
30k
R4
140k
AMPLIFIER
RAMP
GENERATOR
BIAS
+
Σ
+
600kHz
OSCILLATOR
*HYSTERESIS IN LT1308A ONLY
Figure 2b. LT1308A/LT1308B Block Diagram (TSSOP Package)
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