LT1308ACS8 [Linear]
High Current, Micropower Single Cell, 600kHz DC/DC Converters; 大电流，微功率单电池， 600kHz的DC / DC转换器
| 型号： | LT1308ACS8 |
| 厂家： | 
Linear |
| 描述： | High Current, Micropower Single Cell, 600kHz DC/DC Converters |
| 文件： | 总12页 (文件大小：188K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
Fina l Ele c tric a l Sp e c ific a tio ns
LT1308A/ LT1308B
Hig h Curre nt, Mic ro p o we r
Sing le Ce ll, 600kHz
DC/ DC Co nve rte rs
Aug ust 1999
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FEATURES
DESCRIPTION
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
LT1308andarerecommendedforuseinnewdesigns.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
switchingatlightloads andoperates ataquiescentcurrent
of 2.5mA. Both devices consume less than 1µA in
shutdown.
■
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 VCESAT Switch: 300mV at 2A
Pin-for-Pin Upgrade Compatible with LT1308
Lower Quiescent Current in Shutdown: 1µA (Max)
Improved Accuracy Low-Battery Detector
Reference: 200mV ±2%
■
■
■
■
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
■
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APPLICATIONS
■
and does not need to be tied to V as on the LT1308. An
IN
internal V clamp results in improved transient response
C
GSM/CDMA Phones
Digital Cameras
LCD Bias Supplies
Answer-Back Pagers
GPS Receivers
Battery Backup Supplies
Handheld Computers
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
14-lead TSSOP packages.
■
■
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
■
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TYPICAL APPLICATION
L1
4.7µH
Converter Efficiency
D1
5V
1A
95
V
= 3.6V
V = 4.2V
IN
IN
90
85
80
75
70
65
60
55
50
V
SW
IN
+
C1
47µF
R1*
309k
LBO
LBI
LT1308B
+
Li-Ion
CELL
C2
220µF
V
IN
= 2.5V
SHUTDOWN
SHDN
V
C
FB
GND
V
IN
= 1.5V
R2
100k
47k
100pF
C1: AVX TAJC476M010
C2: AVX TPSD227M006
D1: IR 10BQ015
L1: MURATA LQH6N4R7
*R1: 169k FOR V
= 3.3V
= 12V
OUT
1308A/B F01
887k FOR V
OUT
1
10
100
1000
Figure 1. LT1308B Single Li-Ion Cell to 5V/1A DC/DC Converter
LOAD CURRENT (mA)
1308A/B F01a
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 represen-
tationthattheinterconnectionofits circuits as describedhereinwillnotinfringeonexistingpatentrights.
1
LT1308A/ LT1308B
W W W
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(Note 1)
ABSOLUTE AXI U RATI GS
V , SHDN, LBO Voltage ......................................... 10V Operating Temperature Range
IN
SW Voltage ............................................... –0.4V to 36V
FB Voltage ....................................................... V + 1V
V Voltage ................................................................ 2V
C
Commercial ............................................ 0°C to 70°C
Extended Commerial (Note 2) ........... –40°C to 85°C
Industrial ........................................... –40°C to 85°C
IN
LBI Voltage ................................................. –0.1V to 1V Storage Temperature Range ................ –65°C to 150°C
Current into FB Pin .............................................. ±1mA Lead Temperature (Soldering, 10 sec)................. 300°C
W
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/O
PACKAGE RDER I FOR ATIO
TOP VIEW
ORDER PART
NUMBER
ORDER PART
NUMBER
LBO
LBI
V
1
2
3
4
5
6
7
14
13
12
11
10
9
C
TOP VIEW
FB
SHDN
GND
GND
GND
GND
V
1
2
3
4
8
7
6
5
LBO
LBI
LT1308ACF
LT1308BCF
C
LT1308ACS8
LT1308AIS8
LT1308BCS8
LT1308BIS8
V
IN
FB
SHDN
GND
V
IN
V
IN
SW
SW
SW
SW
8
S8 PACKAGE
8-LEAD PLASTIC SO
S8 PART MARKING
F PACKAGE
14-LEAD PLASTIC TSSOP
1308B
1308BI
1308A
1308AI
TJMAX = 125°C, θJA = 80°C/W
(Note 6)
T
JMAX = 125°C, θJA = 80°C/W
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C.
Commercial Grade 0°C to 70°C. V = 1.1V, VSHDN = V , unless otherwise noted.
IN
IN
SYMBOL PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
I
Q
Quiescent Current
Not Switching, LT1308A
Switching, LT1308B
140
2.5
0.01
240
4
1
µA
mA
µA
V
= 0V (LT1308A/LT1308B)
SHDN
V
Feedback Voltage
●
●
●
1.20
1.22
27
1.24
80
V
FB
I
B
FB Pin Bias Current
Reference Line Regulation
(Note 3)
1.1V ≤ V ≤ 2V
nA
0.03
0.01
0.4
0.2
%/V
%/V
IN
2V ≤ V ≤ 10V
IN
Minimum Input Voltage
0.92
60
1
V
µmhos
V/V
kHz
g
m
Error Amp Transconductance
Error Amp Voltage Gain
Switching Frequency
∆I = 5µA
A
V
100
600
90
f
V
IN
= 1.2V
●
●
500
82
2
700
4.5
OSC
Maximum Duty Cycle
Switch Current Limit
%
Duty Cyle = 30% (Note 4)
= 2A (25°C, 0°C), V = 1.5V
3
A
Switch V
I
SW
290
330
350
400
mV
mV
CESAT
IN
I
SW
= 2A (70°C), V = 1.5V
IN
Burst Mode Operation Switch Current Limit
(LT1308A)
V
IN
= 2.5V, Circuit of Figure 1
400
mA
2
LT1308A/ LT1308B
ELECTRICAL CHARACTERISTICS
The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C.
Commercial Grade 0°C to 70°C. V = 1.1V, VSHDN = V , unless otherwise noted.
IN
IN
SYMBOL PARAMETER
Shutdown Pin Current
CONDITIONS
MIN
TYP
MAX
UNITS
V
V
SHDN
= 1.1V
= 6V
●
●
●
2
20
0.01
5
35
0.1
µA
µA
µA
SHDN
V
SHDN
= 0V
LBI Threshold Voltage
196
194
200
200
204
206
mV
mV
●
●
●
LBO Output Low
I
= 50µA
0.1
0.01
33
0.25
0.1
V
µA
SINK
LBO Leakage Current
V
= 250mV, V = 5V
LBI
LBO
LBI Input Bias Current (Note 5)
Low-Battery Detector Gain
Switch Leakage Current
V
= 150mV
100
nA
LBI
3000
0.01
V/V
µA
V
= 5V
●
10
SW
The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C.
Industrial Grade –40°C to 85°C. V = 1.2V, VSHDN = V , unless otherwise noted.
IN
IN
SYMBOL PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
I
Q
Quiescent Current
Not Switching, LT1308A
Switching, LT1308B
●
●
●
140
2.5
0.01
240
4
1
µA
mA
µA
V
= 0V (LT1308A/LT1308B)
SHDN
V
Feedback Voltage
●
●
1.19
1.22
27
1.25
80
V
FB
I
B
FB Pin Bias Current
Reference Line Regulation
(Note 3)
1.1V ≤ V ≤ 2V
nA
●
●
0.05
0.01
0.4
0.2
%/V
%/V
IN
2V ≤ V ≤ 10V
IN
Minimum Input Voltage
0.92
60
1
V
µmhos
V/V
kHz
g
m
Error Amp Transconductance
Error Amp Voltage Gain
Switching Frequency
∆I = 5µA
A
V
100
600
90
f
●
●
500
82
2
750
4.5
OSC
Maximum Duty Cycle
Switch Current Limit
%
Duty Cyle = 30% (Note 4)
3
A
Switch V
I
= 2A (25°C, –40°C), V = 1.5V
290
330
350
400
mV
mV
CESAT
SW
IN
I
SW
= 2A (85°C), V = 1.5V
IN
Burst Mode Operation Switch Current Limit
(LT1308A)
V
IN
= 2.5V, Circuit of Figure 1
400
mA
Shutdown Pin Current
V
= 1.1V
= 6V
= 0V
●
●
2
20
0.01
5
35
0.1
µA
µA
µA
SHDN
V
SHDN
V
SHDN
LBI Threshold Voltage
196
193
200
200
204
207
mV
mV
●
●
●
LBO Output Low
I
= 50µA
0.1
0.01
33
0.25
0.1
V
µA
SINK
LBO Leakage Current
V
= 250mV, V = 5V
LBI
LBO
LBI Input Bias Current (Note 5)
Low-Battery Detector Gain
Switch Leakage Current
V
= 150mV
= 5V
100
nA
LBI
3000
0.01
V/V
µA
V
●
10
SW
3
LT1308A/ LT1308B
ELECTRICAL CHARACTERISTICS
Note 1: Absolute Maximum Ratings are those values beyond which the life
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).
of a device may be impaired.
Note 2: The LT1308ACS8 and LT1308BCS8 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.
Note 5: Bias current flows out of LBI pin.
Note 6: Connect the four GND pins (Pins 4–7) together at the device.
Note 3: Bias current flows into FB pin.
Similarly, connect the three SW pins (Pins 8–10) together and the two V
IN
pins (Pins 11, 12) together at the device.
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TYPICAL PERFORMANCE CHARACTERISTICS
LT1308B
3.3V Output Efficiency
LT1308A
5V Output Efficiency
LT1308A
3.3V Output Efficiency
95
90
85
80
75
70
65
60
55
50
95
90
85
80
75
70
65
60
55
50
95
90
85
80
75
70
65
60
55
50
V
= 4.2V
IN
V
= 2.5V
IN
V
= 1.8V
V
IN
= 3.6V
V
= 2.5V
IN
IN
V
IN
= 1.8V
V
IN
= 1.2V
V = 1.5V
IN
V
= 1.2V
IN
V
= 2.5V
IN
1
10
100
1000
1
10
100
1000
1
10
100
1000
LOAD CURRENT (mA)
LOAD CURRENT (mA)
LOAD CURRENT (mA)
1308A/B G01
1308A/B G02
1308A/B G03
LT1308B
12V Output Efficiency
Switch Saturation Voltage
vs Current
LT1308A Transient Response
Circuit of Figure 1
90
85
80
75
70
65
60
55
50
500
400
300
200
100
0
V
IN
= 5V
VOUT
100mV/DIV
AC COUPLED
V
= 3.3V
IN
85°C
1A
ILOAD
25°C
0A
–40°C
V
V
IN = 3.6V
OUT = 5V
COUT = 220µF
100µs/DIV
1308 G05
1
10
100
1000
0
0.5
1.0
1.5
2.0
LOAD CURRENT (mA)
SWITCH CURRENT (A)
1308A/B G04
1308 G06
4
LT1308A/ LT1308B
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PIN FUNCTIONS
V (Pin 1): Compensation Pin for Error Amplifier. Con-
C
SW (Pin 5): Switch Pin. Connect inductor/diode here.
nect a series RC from this pin to ground. Typical values
Minimize trace area at this pin to keep EMI down.
are 47kΩ and 100pF. Minimize trace area at V .
C
V (Pin6):SupplyPin. Musthavelocalbypass capacitor
IN
FB (Pin 2): Feedback Pin. Reference voltage is 1.22V.
Connect resistive divider tap here. Minimize trace area at
FB. Set VOUT according to: VOUT = 1.22V(1 + R1/R2).
right at the pin, connected directly to ground.
LBI (Pin 7): Low-Battery Detector Input. 200mV refer-
ence. VoltageonLBImuststaybetween–100mVand1V.
SHDN (Pin 3): Shutdown. Ground this pin to turn off Low-battery detector does not function with SHDN pin
switcher. To enable, tie to 1V or more. SHDN does not
grounded. If not used, float LBI pin.
need to be at V to enable the device.
IN
LBO (Pin 8): Low-Battery Detector Output. Open collec-
tor, can sink 50µA. A 1MΩpull-up is recommended. LBO
is high impedance when SHDN is grounded.
GND (Pin 4): Ground. Connect directly to local ground
plane. Ground plane should enclose all components
associated with the LT1308. PCB copper connected to
Pin 4 also functions as a heat sink. Maximize this area to
keep chip heating to a minimum.
W
BLOCK DIAGRAM
V
IN
V
IN
Q4
2V
BE
6
V
IN
R5
40k
R6
40k
SHDN
3
SHUTDOWN
+
V
C
g
1
m
V
OUT
LBI
7
–
+
–
+
–
R1
LBO
8
ERROR
AMPLIFIER
(EXTERNAL)
*
FB
2
ENABLE
200mV
Q1
Q2
×10
FB
BIAS
A4
A1
COMPARATOR
R2
R3
30k
(EXTERNAL)
SW
5
–
DRIVER
R4
140k
FF
RAMP
GENERATOR
Q3
R
Q
+
+
Σ
S
A2
+
+
A = 3
–
0.03Ω
600kHz
OSCILLATOR
4
*HYSTERESIS IN LT1308A ONLY
1308 BD
GND
Figure 2. LT1308A/LT1308B Block Diagram
5
LT1308A/ LT1308B
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APPLICATIONS INFORMATION
OPERATION
Low-battery detector A4’s open-collector output (LBO)
pulls low when the LBI pin voltage drops below 200mV.
There is no hysteresis in A4, allowing it to be used as an
amplifier in some applications. The entire device is dis-
abled when the SHDN pin is brought low. To enable the
converter, SHDN must be at 1V or greater. It need not be
The LT1308A combines a current mode, fixed frequency
PWM architecture with Burst Mode micropower operation
to maintain high efficiency at light loads. Operation can be
bestunderstoodbyreferringtotheblockdiagraminFigure
2. Q1 and Q2 form a bandgap reference core whose loop
tied to V as on the LT1308.
IN
is closed around the output of the converter. When V is
IN
1V, the feedback voltage of 1.22V, along with an 80mV
drop across R5 and R6, forward biases Q1 and Q2’s base
collector junctions to 300mV. Because this is not enough
to saturate either transistor, FB can be at a higher voltage
The LT1308B differs from the LT1308A in that there is no
hysteresis in comparator A1. Also, the bias point on A1 is
set lower than on the LT1308B so that switching can occur
at inductor current less than 100mA. Because A1 has no
hysteresis, there is no Burst Mode operation at light loads
and the device continues switching at constant frequency.
This results intheabsenceoflowfrequencyoutputvoltage
ripple at the expense of efficiency.
than V . When there is no load, FB rises slightly above
IN
1.22V, causing VC (the error amplifier’s output) to
decrease. When V reaches the bias voltage on hysteretic
C
comparator A1, A1’s output goes low, turning off all
circuitry except the input stage, error amplifier and low-
battery detector. Total current consumption in this state is
120µA. As output loading causes the FB voltage to
decrease, A1’s output goes high, enabling the rest of the
IC. Switch current is limited to approximately 400mA
initially after A1’s output goes high. If the load is light, the
output voltage (and FB voltage) will increase until A1’s
output goes low, turning off the rest of the LT1308A. Low
frequency ripple voltage appears at the output. The ripple
frequency is dependent on load current and output capaci-
tance. This Burst Mode operation keeps the output regu-
lated and reduces average current into the IC, resulting in
high efficiency even at load currents of 1mA or less.
The difference between the two devices is clearly illus-
trated in Figure 3. The top two traces in Figure 3 shows an
LT1308A/LT1308B circuit, using the components indi-
cated in Figure 1, set to a 5V output. Input voltage is 3V.
Load current is stepped from 50mA to 800mA for both
circuits. Low frequency Burst Mode operation voltage
ripple is observed on Trace A, while none is observed on
Trace B.
At light loads, the LT1308B will begin to skip alternate
cycles. The load point at which this occurs can be de-
creased by increasing the inductor value. However, output
ripplewillcontinuetobesignificantlyless thantheLT1308A
output ripple. Further, the LT1308B can be forced into
micropower mode, where IQ falls from 3mA to 200µA by
If the output load increases sufficiently, A1’s output
remains high, resulting in continuous operation. When the
LT1308A is running continuously, peak switch current is
sinking 40µA or more out of the V pin. This stops
C
switching by causing A1’s output to go low.
controlled by V to regulate the output voltage. The switch
C
is turned on at the beginning of each switch cycle. When
the summation of a signal representing switch current and
a ramp generator (introduced to avoid subharmonic oscil-
TRACE A: LT1308A
VOUT, 100mV/DIV
AC COUPLED
lations at duty factors greater than 50%) exceeds the V
C
signal,comparatorA2changes state,resettingtheflip-flop
and turning off the switch. Output voltage increases as
switch current is increased. The output, attenuated by a
resistor divider, appears at the FB pin, closing the overall
loop. Frequency compensation is provided by an external
TRACE B: LT1308B
VOUT, 100mV/DIV
AC COUPLED
800mA
ILOAD
50mA
V
IN = 3V
200µs/DIV
1308 F03
(CIRCUIT OF FIGURE 1)
series RC network connected between the V pin and
ground.
C
Figure 3. LT1308A Exhibits Burst Mode Operation Output
Voltage Ripple at 50mA Load, LT1308B Does Not
6
LT1308A/ LT1308B
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APPLICATIONS INFORMATION
Table 1
VENDOR
Murata
LAYOUT HINTS
PART NO.
LQH6C4R7
CDRH734R7
CTX5-1
VALUE
4.7µH
4.7µH
5µH
PHONE NO.
770-436-1300
847-956-0666
561-241-7876
TheLT1308A/LT1308Bswitchcurrentathighspeed, man-
dating careful attention to layout for proper performance.
You will not get advertised performance with careless
layouts. Figure 4 shows recommended component place-
ment for a boost (step-up) converter. Follow this closely in
your PC layout. Note the direct path of the switching loops.
Input capacitor C1 must be placed close (<5mm) to the IC
Sumida
Coiltronics
Capacitors
package. As little as 10mm of wire or PC trace from C to
IN
Equivalent Series Resistance (ESR) is the main issue
regarding selection of capacitors, especially the output
capacitors.
V will cause problems such as inability to regulate or
IN
oscillation.
The negative terminal of output capacitor C2 should tie
close to Pin 4 of the LT1308A/LT1308B. Doing this
reduces dI/dt in the ground copper which keeps high
frequency spikes to a minimum. The DC/DC converter
ground should tie to the PC board ground plane at one
place only, to avoid introducing dI/dt in the ground plane.
The output capacitors specified for use with the LT1308A/
LT1308B circuits have low ESR and are specifically
designed for power supply applications. Output voltage
ripple of a boost converter is equal to ESR multiplied by
switchcurrent.TheperformanceoftheAVXTPSD227M006
220µF tantalum can be evaluated by referring to Figure 4.
When the load is 800mA, the peak switch current is
A SEPIC (Single-Ended Primary Inductance Converter)
schematic is shown in Figure 5. This converter topology
produces a regulated output over an input voltage range
that spans (i.e., can be higher or lower than) the output.
Recommended component placement for a SEPIC is
shown in Figure 6.
approximately 2A. Output voltage ripple is about 60mV
P-
P,sotheESRoftheoutputcapacitoris 60mV/2Aor0.03Ω.
Ripplecanbefurtherreducedbyparallelingceramicunits.
Table 2 lists some capacitors we have found to perform
well in the LT1308A/LT1308B application circuits. This is
not an exclusive list.
COMPONENT SELECTION
Inductors
Table 2
VENDOR
AVX
SERIES
TPS
PART NO.
VALUE
PHONE NO.
TPSD227M006 220µF, 6V 803-448-9411
TPSD107M010 100µF, 10V 803-448-9411
LMK432BJ226 22µF, 10V 408-573-4150
TMK432BJ106 10µF, 25V 408-573-4150
Suitable inductors for use with the LT1308A/LT1308B
must fulfill two requirements. First, the inductor must be
able to handle current of 2A steady-state, as well as
support transient and start-up current over 3A without
inductancedecreasingbymorethan50%to60%.Second,
theDCRoftheinductorshouldhavelowDCR,under0.05Ω
so that copper loss is minimized. Acceptable inductance
values range between 2µH and 20µH, with 4.7µH best for
most applications. Lower value inductors are physically
smaller than higher value inductors for the same current
capability.
AVX
TPS
Taiyo Yuden
Taiyo Yuden
X5R
X5R
Diodes
We have found Motorola MBRS130 and International
Rectifier10BQ015toperformwell. Forapplications where
VOUT exceeds 30V, use 40V diodes such as MBRS140 or
10BQ040.
Table1lists someinductors wehavefoundtoperformwell
in LT1308A/LT1308B application circuits. This is not an
exclusive list.
7
LT1308A/ LT1308B
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APPLICATIONS INFORMATION
LBI
LBO
GROUND PLANE
C2
4.7µF
CERAMIC
L1A
CTX10-2
C1
D1
V
3V TO
10V
IN
+
V
IN
V
IN
SW
+
L1B
C1
R1
47µF
1
2
3
4
8
7
6
5
R1
309k
LT1308B
V
OUT
5V
500mA
SHUTDOWN
SHDN
FB
GND
LT1308A
LT1308B
L1
R2
V
C
SHUTDOWN
R2
100k
+
C3
220µF
47k
680pF
6.3V
MULTIPLE
VIAs
+
D1
C2
GND
C1: AVX TAJC476M016
C2: TAIYO YUDEN EMK325BJ475(X5R)
C3: AVX TPSD227M006
D1: IR 10BQ015
L1: COILTRONICS CTX10-2
1308A/B F05
V
OUT
Figure 5. SEPIC (Single-Ended Primary
Inductance Converter) Converts 3V to 10V
Input to a 5V/500mA Regulated Output
1308 F04
Figure 4. Recommended Component Placement for Boost
Converter. Note Direct High Current Paths Using Wide PC
Traces. Minimize Trace Area at Pin 1 (V ) and Pin 2 (FB).
C
Use Multiple Vias to Tie Pin 4 Copper to Ground Plane. Use
Vias at One Location Only to Avoid Introducing Switching
Currents into the Ground Plane
LBI
LBO
GROUND PLANE
C1
+
V
IN
R1
1
2
8
7
6
5
LT1308A
LT1308B
R2
SHUTDOWN
3
4
L1A
C2
L1B
MULTIPLE
VIAs
C3
+
GND
D1
V
OUT
1308 F06
Figure 6. Recommended Component Placement for SEPIC
8
LT1308A/ LT1308B
U
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APPLICATIONS INFORMATION
SHDN PIN
START-UP
The LT1308A/LT1308B SHDN pin is improved over the
The LT1308A/LT1308B can start up into heavy loads,
unlike many CMOS DC/DC converters that derive operat-
ing voltage from the output (a technique known as
“bootstrapping”). Figure10 details start-upwaveforms of
LT1308. The pin does not require tying to V to enable the
IN
device, but needs only a logic level signal. The voltage on
the SHDN pin can vary from 1V to 10V independent of V .
IN
Further, floatingthis pinhas thesameeffectas grounding,
which is to shut the device down, reducing current drain
to 1µA or less.
Figure1’s circuitwitha20ΩloadandV of1.5V. Inductor
IN
current rises to 3.5A as the output capacitor is charged.
After the output reaches 5V, inductor current is about 1A.
In Figure 11, the load is 5Ω and input voltage is 3V. Output
voltage reaches 5V 500µs after the device is enabled.
Figure 12 shows start-up behavior of Figure 5’s SEPIC
circuit, driven from a 9V input with a 10Ω load. The output
reaches 5V in about 1ms after the device is enabled.
LOW-BATTERY DETECTOR
The low-battery detector on the LT1308A/LT1308B fea-
tures improved accuracy and drive capability compared to
theLT1308.The200mVreferencehas anaccuracyof±2%
andtheopen-collectoroutputcansink50µA.TheLT1308A/
LT1308B low-battery detector is a simple PNP input gain
stage with an open-collector NPN output. The negative
GSM AND CDMA PHONES
TheLT1308A/LT1308Baresuitableforconvertingasingle
input of the gain stage is tied internally to a 200mV Li-Ion cell to 5V for powering RF power stages in GSM or
reference. The positive input is the LBI pin. Arrangement
as a low-battery detector is straightforward. Figure 7
details hookup. R1 and R2 need only be low enough in
value so that the bias current of the LBI pin doesn’t cause
large errors. For R2, 100k is adequate. The 200mV refer-
ence can also be accessed as shown in Figure 8.
CDMA phones. Improvements in the LT1308A/LT1308B
error amplifiers allow external compensation values to be
reduced, resulting in faster transient response compared
to the LT1308. The circuit of Figure 13 (same as Figure 1,
printed again for convenience) provides a 5V, 1A output
from a Li-Ion cell. Figure 14 details transient response at
the LT1308A operating at a V of 4.2V, 3.6V and 3V.
IN
A cross plot of the low-battery detector is shown in
Figure 9. The LBI pin is swept with an input which varies
from 195mV to 205mV, and LBO with a 100k pull-up
resistor, is displayed.
Ripple voltage in Burst Mode operation can be seen at
10mA load. Figure 15 shows transient response of the
LT1308B under the same conditions. Note the lack of
Burst Mode ripple at 10mA load.
5V
R1
V
IN
LT1308A
LT1308B
100k
LBI
+
–
200k
V
IN
LBO
TO PROCESSOR
R2
100k
2N3906
LBO
LBI
V
BAT
LT1308A
LT1308B
V
REF
200mV
+
GND
200mV
10k
10µF
V
– 200mV
LB
R1 =
INTERNAL
REFERENCE
V
BAT
2µA
1308 F08
GND
1308 F07
Figure 8. Accessing 200mV Reference
Figure 7. Setting Low-Battery Detector Trip Point
9
LT1308A/ LT1308B
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APPLICATIONS INFORMATION
VOUT
1V/DIV
V
LBO
1V/DIV
IL1
2A/DIV
V
SHDN
5V/DIV
195
200
205
500µs/DIV
VLBI (mV)
1308 F09
1308 F11
Figure 11. 5V Boost Converter of Figure 1.
Start-Up from 3V Input into 5Ω Load
Figure 9. Low-Battery Detector
Input/Output Characteristic
VOUT
2V/DIV
V
OUT
2V/DIV
IL1
1A/DIV
ISW
2A/DIV
V
SHDN
V
SHDN
5V/DIV
5V/DIV
1ms/DIV
500µs/DIV
1308 F10
1308 F12
Figure 10. 5V Boost Converter of Figure 1.
Start-Up from 1.5V Input into 20Ω Load
Figure 12. 5V SEPIC Start-Up from
9V Input into 10Ω Load
L1
4.7µH
D1
5V
1A
V
SW
IN
+
C1
47µF
R1
LBO
LBI
309k
LT1308B
+
Li-Ion
CELL
C2
220µF
SHUTDOWN
SHDN
V
C
FB
GND
R2
100k
47k
100pF
C1: AVX TAJC476M010
C2: AVX TPSD227M006
D1: IR 10BQ015
L1: MURATA LQH6N4R7
1308A/B F13
Figure 13. Li-Ion to 5V Boost Converter Delivers 1A
10
LT1308A/ LT1308B
U
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APPLICATIONS INFORMATION
VOUT
VOUT
VIN = 4.2V
VIN = 4.2V
VOUT
VOUT
VIN = 3.6V
VIN = 3.6V
VOUT
VOUT
VIN = 3V
VIN = 3V
ILOAD
1A
10mA
ILOAD
1A
10mA
VOUT TRACES =
200µs/DIV
V
OUT TRACES =
100µs/DIV
200mV/DIV
1308 F14
200mV/DIV
1308 F15
Figure 14. LT1308A Li-Ion to 5V Boost Converter
Transient Response to 1A Load Step
Figure 15. LT1308B Li-Ion to 5V Boost
Converter Transient Response to 1A Load Step
U
PACKAGE DESCRIPTION
Dimensions in inches (millimeters) unless otherwise noted.
F Package
14-Lead Plastic TSSOP (4.4mm)
(LTC DWG # 05-08-1650)
4.90 – 5.10*
(0.193 – 0.201)
14 13 12 11 10
9 8
6.25 – 6.50
(0.246 – 0.256)
5
7
6
1
2
3
4
1.10
(0.0433)
MAX
4.30 – 4.48**
(0.169 – 0.176)
0° – 8°
0.65
(0.0256)
BSC
0.50 – 0.70
(0.020 – 0.028)
0.09 – 0.18
(0.0035 – 0.0071)
0.05 – 0.15
(0.002 – 0.006)
0.18 – 0.30
(0.0071 – 0.0118)
F14 TSSOP 1299
NOTE: DIMENSIONS ARE IN MILLIMETERS
*DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.152mm (0.006") PER SIDE
**DIMENSIONS DO NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.254mm (0.010") PER SIDE
11
LT1308A/ LT1308B
U
TYPICAL APPLICATION
SEPIC Converts 3V to 10V Input to a 5V/500mA Regulated Output
3.3V to 12V/300mA Step-Up DC/DC Converter
C2
4.7µF
CERAMIC
L1A
L1
4.7µH
D1
CTX10-2
LT1308B
V
3V TO
10V
D1
IN
12V
300mA
V
SW
IN
V
SW
IN
+
+
L1B
C1
47µF
C1
47µF
R1
LBO
LBI
R1
309k
887k
LT1308B
SHDN
V
OUT
5V
500mA
+
Li-Ion
CELL
C2
100µF
SHUTDOWN
FB
GND
SHUTDOWN
SHDN
FB
GND
V
C
V
C
R2
R2
100k
100k
47k
100pF
L1: MURATA LQH6N4R7
+
C3
220µF
6.3V
47k
680pF
C1: AVX TAJC476M010
C2: AVX TPSD107M016
D1: IR 10BQ015
C1: AVX TAJC476M016
D1: IR 10BQ015
L1: COILTRONICS CTX10-2
1308A/B F05
C2: TAIYO YUDEN EMK325BJ475(X5R)
C3: AVX TPSD227M006
1308A/B TA01
U
PACKAGE DESCRIPTION
Dimensions in inches (millimeters) unless otherwise noted.
S8 Package
8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.189 – 0.197*
(4.801 – 5.004)
0.010 – 0.020
(0.254 – 0.508)
7
5
8
6
× 45°
0.053 – 0.069
(1.346 – 1.752)
0.004 – 0.010
(0.101 – 0.254)
0.008 – 0.010
(0.203 – 0.254)
0°– 8° TYP
0.150 – 0.157**
(3.810 – 3.988)
0.228 – 0.244
(5.791 – 6.197)
0.016 – 0.050
(0.406 – 1.270)
0.050
(1.270)
BSC
0.014 – 0.019
(0.355 – 0.483)
TYP
*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
1
2
3
4
SO8 1298
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600kHz, 1A Switch PWM DC/DC Converter
Regulated 5V ±4% Output, 20mA from 3V Input
3V at 30mA from 1V, 1.7MHz Fixed Frequency
–5V at 150mA from 5V Input, Tiny SOT-23 package
5V at 200mA from 4.4V Input, Tiny SOT-23 package
20µA I , 36V, 350mA Switch
Q
Adjustable or Fixed 3.3V, 5V Outputs, 60µV
Output Noise
RMS
1.1A, 0.5Ω, 30V Internal Switch, V as Low as 1.5V
IN
1308abis, sn1308ab LT/TP 0899 4K • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
12
●
●
(408)432-1900 FAX:(408)434-0507 www.linear-tech.com
LINEAR TECHNOLOGY CORPORATION 1999
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