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Final Electrical Specifications
LT1308 Single Cell High Current Micropower 600kHz Boost DC/DC Converter
January 1998
FEATURES
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DESCRIPTION
The LT (R)1308 is a micropower, fixed frequency boost DC/DC converter that operates from an input voltage as low as 1V. Capable of delivering 5V at load current of 1A from a single Li-Ion cell, the LT1308 also features power saving Burst Mode operation at light loads. High efficiency is maintained over a broad 1mA to 1A load range. The device contains a low-battery detector with a 200mV reference and shuts down to less than 5A quiescent current. No-load quiescent current is 100A and the internal NPN power switch handles a 2A current with a voltage drop of just 300mV. High frequency 600kHz switching allows the use of small, surface mount components. The LT1308's current mode architecture provides fast response to load and line variations. The device is available in an 8-lead SO package.
, LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode is a trademark of Linear Technology Corporation.
5V at 1A from a Single Li-Ion Cell 3.3V at 300mA from a Single NiCd Cell Low Quiescent Current: 100A Operates with VIN as Low as 1V Fixed Frequency Operation: 600kHz Current Mode PWM Delivers Low Output Ripple Guaranteed Start-Up into Full Load Low Shutdown Current: 3A Low-Battery Comparator Automatic Burst ModeTM Operation at Light Load Low VCESAT Switch: 300mV at 2A
APPLICATIONS
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GSM Terminals Digital Cameras Answer-Back Pagers Cordless Telephones DECT Phones GPS Receivers Battery Backup Supplies
TYPICAL APPLICATION
4.2V TO 3V
Converter Efficiency
95
SHDN LBI LT1308 Li-Ion CELL C1 10F LBO VC RC 47k CC 22nF C1: CERAMIC C2: AVX TPS SERIES D1: INTERNATIONAL RECTIFIER 10BQ015 L1: COILTRONICS CTX5-1 COILCRAFT DO3316-472
VIN SW R1 301k FB GND R2 100k
L1 4.7H
EFFICIENCY (%)
90 85 80
D1 5V 1A
+
C2 100F
75 70
1308F01
65
1
Figure 1. Single Li-Ion Cell to 5V/1A DC/DC Converter
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.
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V IN = 3.6V V IN = 4.2V
V IN = 3V
10 100 LOAD CURRENT (mA)
1000
1308 F01a
1
LT1308 ABSOLUTE AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW VC 1 FB 2 SHDN 3 GND 4 8 7 6 5 LBO LBI VIN SW
VIN, SHDN, LBO Voltage ......................................... 10V SW Voltage ............................................................. 30V FB Voltage ....................................................... VIN + 1V VC Voltage ................................................................ 2V LBI Voltage ............................................ 0V VLBI 1V Current into FB Pin .............................................. 1mA Junction Temperature ...........................................125C Operating Temperature Range Commercial (Note 1) ......................... - 20C to 70C Industrial ........................................... - 40C to 85C Storage Temperature Range ................ - 65C to 150C Lead Temperature (Soldering, 10 sec)................. 300C
ORDER PART NUMBER LT1308CS8 LT1308IS8 S8 PART MARKING 1308 1308I
S8 PACKAGE 8-LEAD PLASTIC SO TJMAX = 125C, JA = 80C/W
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
Commercial Grade 0C to 70C. VIN = 1.1V, VSHDN = VIN, TA = 25C, unless otherwise noted.
SYMBOL IQ VFB IB PARAMETER Quiescent Current Feedback Voltage FB Pin Bias Current (Note 2) Reference Line Regulation VFB = VREF 1.1V VIN 2V (25C, 0C) 1.1V VIN 2V (70C) 2V VIN 6V CONDITIONS Not Switching VSHDN = 0V
q q q q
MIN
TYP 80 1
MAX 160 3 1.24 80 1.1 1.5 0.8 1 6
UNITS A A V nA %/V %/V %/V V V mhos V/V V/V
1.20
1.22 27 0.6
q
0.3 0.92 1 40 100 80
Minimum Input Voltage Input Voltage Range gm AV fOSC Error Amp Transconductance Error Amp Voltage Gain Switching Frequency Maximum Duty Cycle Switch Current Limit (Note 3) Switch VCESAT Burst Mode Operation Switch Current Limit Shutdown Pin Current DC = 40% DC = 80% ISW = 2A (25C, 0C) ISW = 2A (70C) L = 3.3H, VOUT = 3.3V, VIN = 1.2V VSHDN = 1.1V VSHDN = 6V VSHDN = 0V ISINK = 10A VLBI = 250mV, VLBO = 5V VLBI = 150mV
q q q q q q q
I = 5A 25C, 0C 70C
q q q
500 80 2.0 1.6
600 88 2.5 2 300 330 200 2.5 13 - 1.5
700 95
350 400 4.0 26 - 2.5 220 0.25 0.1 30
LBI Threshold Voltage LBO Output Low LBO Leakage Current LBI Input Bias Current (Note 4)
180
200 0.1 0.01 5
2
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kHz % A A mV mV mA A A A mV V A nA
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LT1308
ELECTRICAL CHARACTERISTICS
Commercial Grade 0C to 70C. VIN = 1.1V, VSHDN = VIN, TA = 25C unless otherwise noted.
SYMBOL PARAMETER Low-Battery Detector Gain Switch Leakage Current Reverse Battery Current CONDITIONS 1M Load (25C, 0C) 1M Load (70C) VSW = 5V (Note 5)
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MIN 1000 500
TYP 3000 0.01 750
MAX
UNITS V/V V/V
10
A mA
Commercial Grade TA = - 20C, VIN = 1.1V, VSHDN = VIN, unless otherwise noted (Note 1).
SYMBOL IQ VFB gm AV fOSC PARAMETER Quiescent Current Feedback Voltage Error Amp Transconductance Error Amp Voltage Gain Switching Frequency Maximum Duty Cycle Switch VCESAT Shutdown Pin Current LBI Threshold Voltage ISW = 2A, VIN = 1.2V VSHDN = VIN VSHDN = 0V 180 500 I = 5A CONDITIONS VFB = 1.3V, Not Switching VSHDN = 0V 1.195 MIN TYP 80 1 1.22 35 100 600 88 300 2.5 - 1.5 200 350 4.0 - 2.5 220 750 MAX 160 3 1.245 UNITS A A V mhos V/V kHz % mV A A mV
Industrial Grade - 40C to 85C. VIN = 1.2V, VSHDN = VIN, TA = 25C, unless otherwise noted.
SYMBOL IQ VFB IB PARAMETER Quiescent Current Feedback Voltage FB Pin Bias Current (Note 2) Reference Line Regulation VFB = VREF 1.1V VIN 2V (- 40C) 1.1V VIN 2V (85C) 2V VIN 6V CONDITIONS Not Switching VSHDN = 0V
q q q q
MIN
TYP 80 1
MAX 160 3 1.245 80 1.1 1.5 0.8 1.2 6
UNITS A A V nA %/V %/V %/V V V mhos V/V V/V
1.195
1.22 27 0.6
q
0.3 1.2 40 100 80 500 500 80 75 600 600 88 2.5 2 300 330 200
Minimum Input Voltage (- 40C) Input Voltage Range gm AV fOSC Error Amp Transconductance Error Amp Voltage Gain Switching Frequency Maximum Duty Cycle Switch Current Limit (Note 3) Switch VCESAT Burst Mode Operation Switch Current Limit I = 5A - 40C 85C VIN = 1.3V (- 40C) VIN = 1.3V (85C) - 40C 85C DC = 40% DC = 80% ISW = 2A (- 40C) ISW = 2A (85C) L = 3.3H, VOUT = 3.3V
q q
750 750 95
kHz kHz % % A A
2.0 1.6
350 400
mV mV mA
3
LT1308
ELECTRICAL CHARACTERISTICS
Industrial Grade - 40C to 85C. VIN = 1.2V, VSHDN = VIN, TA = 25C, unless otherwise noted.
SYMBOL PARAMETER Shutdown Pin Current CONDITIONS VSHDN = 1.2V VSHDN = 6V VSHDN = 0V ISINK = 10A VLBI = 250mV, VLBO = 5V VLBI = 150mV 1M Load (-40C) 1M Load (85C) VSW = 5V
q q q q q q q q
MIN
TYP 2.5 13 - 1.5
MAX 4.0 26 - 2.5 220 0.25 0.1 30
UNITS A A A mV V A nA V/V V/V
LBI Threshold Voltage LBO Output Low LBO Leakage Current LBI Input Bias Current (Note 4) Low-Battery Detector Gain Switch Leakage Current
180
200 0.1 0.01 5
1000 300
3000 0.01 10
A
The q denotes specifications which apply over the full operating temperature range. Note 1: C grade device specifications are guaranteed over the 0C to 70C temperature range. In addition, C grade device specifications are assured over the -40C to 85C temperature range by design or correlation, but are not production tested. Note 2: Bias current flows into FB pin.
Note 3: 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 4: Bias current flows out of LBI pin. Note 5: The LT1308 will withstand continuous application of 1.6V applied to GND pin while VIN and SW are grounded.
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency
90 85 80
EFFICIENCY (%)
VIN = 1.2V VOUT = 3.3V R1 = 169k
SWITCH VCESAT (mV)
75 70 65 60 55 50 1 10 100 LOAD CURRENT (mA) 1000
1308 G01
PIN FUNCTIONS
VC (Pin 1): Compensation Pin for Error Amplifier. Connect a series RC from this pin to ground. Typical values are 47k and 22nF. Minimize trace area at VC. 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). SHDN (Pin 3): Shutdown. Ground this pin to turn off switcher. Must be tied to VIN (or higher voltage) to enable switcher. Do not float the SHDN pin. GND (Pin 4): Ground. Connect directly to local ground plane. Ground plane should enclose all components associated with the LT1308.
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Transient Response
500 VOUT 200mV/DIV AC COUPLED 100mA 5mA 500s/DIV VIN = 1.2V VOUT = 5V C2 = 22F RC, CC = 47k, 6.8nF L = 4.7H
1308 G02
Switch Saturation Voltage vs Current
400 85C 300 25C -40C
ILOAD
200
100
0
0
1.0 0.5 1.5 SWITCH CURRENT (A)
2.0
1308 G03
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LT1308
PIN FUNCTIONS
SW (Pin 5): Switch Pin. Connect inductor/diode here. Minimize trace area at this pin to keep EMI down. VIN (Pin 6): Supply Pin. Must have local bypass capacitor right at the pin, connected directly to ground. LBI (Pin 7): Low-Battery Detector Input. 200mV reference. Voltage on LBI must stay between ground and 700mV. Low-battery detector does not function with SHDN pin grounded. If not used, float LBI pin. LBO (Pin 8): Low-Battery Detector Output. Open collector, can sink 10A. A 1M pullup is recommended. LBO is high impedance when SHDN is grounded.
BLOCK DIAGRAM
VIN 6 R5 40k
VOUT R1 (EXTERNAL) FB R2 (EXTERNAL)
FB 2
R4 140k
RAMP GENERATOR
600kHz OSCILLATOR
APPLICATIONS INFORMATION
LAYOUT HINTS The LT1308 switches current at high speed, mandating careful attention to layout for proper performance. You will not get advertised performance with careless layouts. Figure 2 shows recommended component placement. Follow this closely in your PC layout. Note the direct path of the switching loops. Input capacitor CIN must be placed close (< 5mm) to the IC package. As little as 10mm of wire or PC trace from CIN to VIN will cause problems such as inability to regulate or oscillation. A 10F ceramic bypass capacitor is the only input capacitance required provided the battery has a low inductance path to the circuit. The battery itself provides the bulk capacitance the device requires for proper operation. If the battery is located some
Figure 2. Recommended Component Placement. Traces Carrying High Current Are Direct. Trace Area at FB Pin and VC Pin is Kept Low. Lead Length to Battery Should Be Kept Short. Ground Plane Should Be Placed Under All Components
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+ +
-
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VIN R6 40k SHDN
+
gm
VC 1 LBI ERROR AMPLIFIER BIAS
SHUTDOWN
3
-
Q1 Q2 x10 R3 30k
+
ENABLE
7
+ -
A4
LBO 8
-
A1 COMPARATOR
200mV
SW FF R Q S DRIVER 5 Q3
A2
+
A=3 0.03
-
4 GND
1308 BD
GROUND PLANE 1 2 3 4 LT1308 8 7 6 5 L VIN
MULTIPLE VIAs
CIN COUT GND
D
VOUT
1308 F02
5
LT1308
APPLICATIONS INFORMATION
distance from the circuit, an additional input capacitor may be required. A 220F aluminum electrolytic unit works well in these cases. This capacitor need not have low ESR. OPERATION FROM A LABORATORY POWER SUPPLY If a lab supply is used, the leads used to connect the circuit to the supply can have significant inductance at the LT1308's switching frequency. As in the previous situation, an electrolytic capacitor may be required at the circuit in order to reduce the AC impedance of the input sufficiently. An alternative solution is to attach the circuit directly to the power supply at the supply terminals, without the use of leads. The power supply's output capacitance will then provide the bulk capacitance the LT1308 circuit requires. SHUTDOWN PIN The LT1308 has a shutdown pin (SHDN) that must be grounded to shut the device down or tied to a voltage equal or greater than VIN to operate. The shutdown circuit is shown in Figure 3. Note that allowing SHDN to float turns on both the startup current (Q2) and the shutdown current (Q3) for VIN > 2VBE. The LT1308 doesn't know what to do in this situation and behaves erratically. SHDN voltage above VIN is allowed. This merely reverse-biases Q3's base emitter junction, a benign condition.
VIN Q3 R2 400k SHDN 400k START-UP CURRENT Q2 Q1
1308 F03
SHUTDOWN CURRENT
Figure 3. Shutdown Circuit
LOW-BATTERY DETECTOR The LT1308's low-battery detector is a simple PNP input gain stage with an open collector NPN output. The nega-
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tive input of the gain stage is tied internally to a 200mV reference. The positive input is the LBI pin. Arrangement as a low-battery detector is straightforward. Figure 4 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 reference can also be accessed as shown in Figure 5.
3.3V R1 LBI R2 100k VIN LT1308 1M LBO TO PROCESSOR
+ -
200mV INTERNAL REFERENCE GND
1308 F04
VBAT
R1 =
VLB - 200mV 2A
Figure 4. Setting Low-Battery Detector Trip Point
200k 2N3906 VBAT VREF 200mV 10k LBO
VIN LT1308
+
10F
LBI GND
1308 F05
Figure 5. Accessing 200mV Reference
GSM PHONES The LT1308 is suitable for converting a single Li-Ion cell to 5V for powering GSM RF power stages. Figure 6 details a Li-Ion to 5V converter circuit using frequency compensation optimized for a typical GSM pulsed load. Figure 7 details transient response of Figure 6's circuit with a 100mA to 1A pulsed load. A slower time sweep is used to show several transmit pulses in Figure 8. At a VIN of 2.7V, additional output capacitance is recommended to help minimize VOUT droop. Figure 9 shows VOUT with an input voltage of 2.7V. Figure 10 expands the horizontal sweep speed to 500s/division to show detail of one transmit pulse.
LT1308
APPLICATIONS INFORMATION
DECT PHONES The DECT standard specifies a transmit pulse 416s in duration. The LT1308 is capable of delivering a 400mA pulse load from a 1.2V input with output capacitance of 100F. Figure 11 depicts VOUT transient response of Figure 6's circuit, configured for a 3.3V output by changing resistor R1 to 169k. Figure 12 shows detail of one transmit pulse at a higher sweep speed.
L1 4.7H SHDN NiCd OR Li-Ion CELL C1 10F CERAMIC LBI LT1308 LBO VC 47k 33nF L1: TOKO 636CY4R7M COILTRONICS CTX5-1 FOR VOUT = 5V: R1 = 309k FOR VOUT = 3.3V: R1 = 169k FB GND VIN SW R1 D1 MBRS120 5V/1A OR 3.3V/300mA VOUT 200mV/DIV AC COUPLED VIN = 2.7V VOUT 200mV/DIV AC COUPLED VIN = 2.7V
+
100k
C2 100F ILOAD 1A 100mA 500s/DIV
1308F06 1308 F10
Figure 6. DC/DC Converter for GSM/DECT Application
VOUT 200mV/DIV AC COUPLED VIN = 3.6V VOUT 200mV/DIV AC COUPLED VIN = 1.2V
IL, 1A/DIV 1A ILOAD 100mA 100s/DIV
1308 F07
Figure 7. GSM Load Transient Response. 100mA to 1A Transient Response for Figure 6's Circuit. Pulse Width = 577s
VIN = 3.6V VOUT 200mV/DIV AC COUPLED
1A ILOAD 100mA 1ms/DIV
1308 F08
Figure 8. GSM Load Transient Response. Slower Sweep Speed (1ms/DIV) Shows VOUT over Several Transmit Pulses
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1A ILOAD 100mA 1ms/DIV
1308 F09
Figure 9. GSM Load Transient Response. At Low VIN, Large Output Capacitor (2200F) Serves to Hold up VOUT
IL, 1A/DIV
Figure 10. GSM Load Transient Response. Faster Sweep Speed (500s/DIV) Details VOUT and Inductor Current of One Transmit Pulse
ILOAD
400mA 50mA 2ms/DIV
1308 F11
Figure 11. DECT Load Transient Response. With a Single NiCd Cell the LT1308 Provides 3.3V with 400mA Pulsed Load. Pulse Width = 416s
VOUT 200mV/DIV AC COUPLED IL, 1A/DIV
VIN = 1.2V
ILOAD
400mA 50mA 100s/DIV
1308 F09
Figure 12. DECT Load Transient Response. Faster Sweep Speed (100s/DIV) Details VOUT and Inductor Current of Single DECT Transmit Pulse
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LT1308
TYPICAL APPLICATION
Digital Camera Power Supply 2-4 Cell to 3.3V/175mA, 5V/175mA, 18V/10mA, - 10V/10mA
L1A N=1 10H 1 SW LT1308 GND R1 100k R2 2.08M C2 100F C6 10F 2 3 L1C 3 N = 0.3 R3 340k FB
VIN 1.6V TO 6V C1 + 100F R4 47k C7 22nF
VIN SHDN VC C8 1nF
C1, C2, C3 = AVX TPS C4, C5 = AVX TAJ C6 = CERAMIC
PACKAGE DESCRIPTION
0.010 - 0.020 x 45 (0.254 - 0.508) 0.008 - 0.010 (0.203 - 0.254) 0- 8 TYP
0.016 - 0.050 0.406 - 1.270
*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
RELATED PARTS
PART NUMBER LTC(R)1163 LTC1174 LT1302 LT1304 LT1307 LT1316 LTC1440/1/2 LTC1516 LT1521 DESCRIPTION Triple High Side Driver for 2-Cell Inputs Micropower Step-Down DC/DC Converter High Output Current Micropower DC/DC Converter 2-Cell Micropower DC/DC Converter Single Cell Micropower 600kHz PWM DC/DC Converter Micropower DC/DC Converter with Programmable Peak Current Limit Ultralow Power Single/Dual Comparators with Reference 2-Cell to 5V Regulated Charge Pump Micropower Low Dropout Linear Regulator COMMENTS 1.8V Minimum Input, Drives N-Channel MOSFETs 94% Efficiency, 130A IQ, 9V to 5V at 300mA 5V/600mA from 2V, 2A Internal Switch, 200A IQ Low-Battery Detector Active in Shutdown, 5V at 200mA for 2 Cells 3.3V at 75mA from 1 Cell, MSOP Package Works with High Source Impedance, 1.5V Minimum Input, Low-Battery Detector Active in Shutdown, 33A IQ, MSOP Package 2.8A IQ, Adjustable Hysteresis 12A IQ, No Inductors, 5V at 50mA from 3V Input 500mV Dropout, 300mA Current, 12A IQ
1308i LT/TP 0198 4K * PRINTED IN USA
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Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417q (408)432-1900 FAX: (408) 434-0507q TELEX: 499-3977 q www.linear-tech.com
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L1B N = 0.7
D1
D2 5V 175mA D3 7 L1D N = 3.5 6 6 CCD BIAS 18V 10mA
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+
+
3.3V 175mA C3 100F
+
C4 10F
D1, D2 = IR10BQ015 D3, D4 = BAT-85 L1 = COILTRONICS CTX02-13973 5
+
L1E N=2
C5 10F CCD BIAS -10V 10mA
D4
1308 TA01
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) 0.053 - 0.069 (1.346 - 1.752) 8 0.004 - 0.010 (0.101 - 0.254) 0.228 - 0.244 (5.791 - 6.197) 0.150 - 0.157** (3.810 - 3.988) 7 6 5
0.014 - 0.019 (0.355 - 0.483)
0.050 (1.270) BSC
1
2
3
4
SO8 0695
(c) LINEAR TECHNOLOGY CORPORATION 1998

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