LT1308CS8#PBF

Final Electrical Specifications LT1308 Single Cell High Current Micropower 600kHz Boost DC/DC Converter January 1998 U DESCRIPTION FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ 5V at 1A from a Single Li-Ion Cell 3.3V at 300mA from a Single NiCd Cell Low Quiescent Current: 100µA 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: 3µA Low-Battery Comparator Automatic Burst ModeTM Operation at Light Load Low VCESAT Switch: 300mV at 2A U APPLICATIONS ■ ■ ■ ■ ■ ■ The device contains a low-battery detector with a 200mV reference and shuts down to less than 5µA quiescent current. No-load quiescent current is 100µA 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. GSM Terminals Digital Cameras Answer-Back Pagers Cordless Telephones DECT Phones GPS Receivers Battery Backup Supplies , LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode is a trademark of Linear Technology Corporation. U ■ The LT ®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. TYPICAL APPLICATION Converter Efficiency 4.2V TO 3V 95 VIN LBI SW C1 10µF LBO 90 D1 85 5V 1A FB VC RC 47k CC 22nF C1: CERAMIC C2: AVX TPS SERIES D1: INTERNATIONAL RECTIFIER 10BQ015 L1: COILTRONICS CTX5-1 COILCRAFT DO3316-472 V IN = 3.6V V IN = 4.2V R1 301k LT1308 Li-Ion CELL L1 4.7µH GND R2 100k + C2 100µF EFFICIENCY (%) SHDN 80 V IN = 3V 75 70 1308F01 65 1 10 100 LOAD CURRENT (mA) 1000 1308 F01a 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. 1 LT1308 U W W W 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 ...........................................125°C Operating Temperature Range Commercial (Note 1) ......................... – 20°C to 70°C Industrial ........................................... – 40°C to 85°C Storage Temperature Range ................ – 65°C to 150°C Lead Temperature (Soldering, 10 sec)................. 300°C U RATI GS W AXI U U ABSOLUTE PACKAGE/ORDER I FOR ATIO ORDER PART NUMBER TOP VIEW VC 1 8 LBO FB 2 7 LBI SHDN 3 6 VIN GND 4 5 SW LT1308CS8 LT1308IS8 S8 PART MARKING S8 PACKAGE 8-LEAD PLASTIC SO 1308 1308I TJMAX = 125°C, θJA = 80°C/W Consult factory for Military grade parts. ELECTRICAL CHARACTERISTICS Commercial Grade 0°C to 70°C. VIN = 1.1V, VSHDN = VIN, TA = 25°C, unless otherwise noted. SYMBOL PARAMETER CONDITIONS IQ Quiescent Current Not Switching VSHDN = 0V VFB Feedback Voltage IB FB Pin Bias Current (Note 2) VFB = VREF Reference Line Regulation 1.1V ≤ VIN ≤ 2V (25°C, 0°C) 1.1V ≤ VIN ≤ 2V (70°C) 2V ≤ VIN ≤ 6V MIN ● ● ● 1.20 ● TYP MAX UNITS 80 1 160 3 µA µA 1.22 1.24 V 27 80 nA 0.6 1.1 1.5 0.8 %/V %/V %/V 0.3 ● Minimum Input Voltage 0.92 Input Voltage Range ● 1 1 V 6 V gm Error Amp Transconductance ∆I = 5µA 40 µmhos AV Error Amp Voltage Gain 25°C, 0°C 70°C 100 80 V/V V/V fOSC Switching Frequency ● Maximum Duty Cycle 600 700 kHz 95 % ● 80 88 ● 2.0 1.6 2.5 2 Switch Current Limit (Note 3) DC = 40% DC = 80% Switch VCESAT ISW = 2A (25°C, 0°C) ISW = 2A (70°C) 300 330 Burst Mode Operation Switch Current Limit L = 3.3µH, VOUT = 3.3V, VIN = 1.2V 200 Shutdown Pin Current VSHDN = 1.1V VSHDN = 6V VSHDN = 0V LBI Threshold Voltage 2 500 ● ● ● 180 A A 350 400 mV mV mA 2.5 13 – 1.5 4.0 26 – 2.5 µA µA µA 200 220 mV LBO Output Low ISINK = 10µA ● 0.1 0.25 V LBO Leakage Current VLBI = 250mV, VLBO = 5V ● 0.01 0.1 µA LBI Input Bias Current (Note 4) VLBI = 150mV ● 5 30 nA LT1308 ELECTRICAL CHARACTERISTICS Commercial Grade 0°C to 70°C. VIN = 1.1V, VSHDN = VIN, TA = 25°C unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP Low-Battery Detector Gain 1MΩ Load (25°C, 0°C) 1MΩ Load (70°C) 1000 500 3000 Switch Leakage Current VSW = 5V Reverse Battery Current (Note 5) 0.01 ● MAX UNITS V/V V/V 10 750 µA mA Commercial Grade TA = – 20°C, VIN = 1.1V, VSHDN = VIN, unless otherwise noted (Note 1). SYMBOL PARAMETER CONDITIONS IQ Quiescent Current VFB = 1.3V, Not Switching VSHDN = 0V VFB Feedback Voltage gm Error Amp Transconductance AV Error Amp Voltage Gain fOSC Switching Frequency MIN 1.195 ∆I = 5µA 500 Maximum Duty Cycle TYP MAX UNITS 80 1 160 3 µA µA 1.22 1.245 V 35 µmhos 100 V/V 600 750 kHz 88 % Switch VCESAT ISW = 2A, VIN = 1.2V 300 350 mV Shutdown Pin Current VSHDN = VIN VSHDN = 0V 2.5 – 1.5 4.0 – 2.5 µA µA 180 200 220 mV MIN TYP MAX UNITS 80 1 160 3 µA µA 1.22 1.245 V LBI Threshold Voltage Industrial Grade – 40°C to 85°C. VIN = 1.2V, VSHDN = VIN, TA = 25°C, unless otherwise noted. SYMBOL PARAMETER CONDITIONS IQ Quiescent Current Not Switching VSHDN = 0V VFB Feedback Voltage IB FB Pin Bias Current (Note 2) VFB = VREF Reference Line Regulation 1.1V ≤ VIN ≤ 2V (– 40°C) 1.1V ≤ VIN ≤ 2V (85°C) 2V ≤ VIN ≤ 6V ● ● ● 1.195 ● 27 80 nA 0.6 1.1 1.5 0.8 %/V %/V %/V 0.3 ● Minimum Input Voltage (– 40°C) Input Voltage Range ● 1.2 1.2 V 6 V gm Error Amp Transconductance ∆I = 5µA 40 µmhos AV Error Amp Voltage Gain – 40°C 85°C 100 80 V/V V/V fOSC Switching Frequency VIN = 1.3V (– 40°C) VIN = 1.3V (85°C) 500 500 600 600 750 750 kHz kHz Maximum Duty Cycle – 40°C 85°C 80 75 88 95 % % Switch Current Limit (Note 3) DC = 40% DC = 80% 2.0 1.6 2.5 2 Switch VCESAT ISW = 2A (– 40°C) ISW = 2A (85°C) 300 330 Burst Mode Operation Switch Current Limit L = 3.3µH, VOUT = 3.3V 200 ● A A 350 400 mV mV mA 3 LT1308 ELECTRICAL CHARACTERISTICS Industrial Grade – 40°C to 85°C. VIN = 1.2V, VSHDN = VIN, TA = 25°C, unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN Shutdown Pin Current VSHDN = 1.2V VSHDN = 6V VSHDN = 0V ● ● ● LBI Threshold Voltage 180 ● TYP MAX UNITS 2.5 13 – 1.5 4.0 26 – 2.5 µA µA µA 200 220 mV LBO Output Low ISINK = 10µA ● 0.1 0.25 V LBO Leakage Current VLBI = 250mV, VLBO = 5V ● 0.01 0.1 µA LBI Input Bias Current (Note 4) VLBI = 150mV ● 5 30 nA Low-Battery Detector Gain 1MΩ Load (–40°C) 1MΩ Load (85°C) Switch Leakage Current VSW = 5V The ● denotes specifications which apply over the full operating temperature range. Note 1: C grade device specifications are guaranteed over the 0°C to 70°C temperature range. In addition, C grade device specifications are assured over the –40°C to 85°C temperature range by design or correlation, but are not production tested. Note 2: Bias current flows into FB pin. 1000 300 3000 0.01 ● V/V V/V µA 10 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. U W TYPICAL PERFORMANCE CHARACTERISTICS Switch Saturation Voltage vs Current Transient Response Efficiency 90 500 85 VOUT 200mV/DIV AC COUPLED EFFICIENCY (%) 80 400 75 70 ILOAD 65 100mA 5mA 500µs/DIV VIN = 1.2V VOUT = 5V C2 = 22µF RC, CC = 47k, 6.8nF L = 4.7µH 60 55 50 10 100 LOAD CURRENT (mA) 1 1000 1308 G02 SWITCH VCESAT (mV) VIN = 1.2V VOUT = 3.3V R1 = 169k 85°C 300 25°C 200 –40°C 100 0 0 1.0 0.5 1.5 SWITCH CURRENT (A) 2.0 1308 G01 1308 G03 U U U PIN FUNCTIONS VC (Pin 1): Compensation Pin for Error Amplifier. Connect a series RC from this pin to ground. Typical values are 47kΩ and 22nF. Minimize trace area at VC. 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. 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). GND (Pin 4): Ground. Connect directly to local ground plane. Ground plane should enclose all components associated with the LT1308. 4 LT1308 U U U PIN FUNCTIONS SW (Pin 5): Switch Pin. Connect inductor/diode here. Minimize trace area at this pin to keep EMI down. 700mV. Low-battery detector does not function with SHDN pin grounded. If not used, float LBI pin. VIN (Pin 6): Supply Pin. Must have local bypass capacitor right at the pin, connected directly to ground. LBO (Pin 8): Low-Battery Detector Output. Open collector, can sink 10µA. A 1MΩ pullup is recommended. LBO is high impedance when SHDN is grounded. LBI (Pin 7): Low-Battery Detector Input. 200mV reference. Voltage on LBI must stay between ground and W BLOCK DIAGRAM VIN VIN 6 R5 40k R6 40k SHDN + gm VOUT R1 (EXTERNAL) FB 1 LBI – FB 2 Q1 R2 (EXTERNAL) Q2 ×10 + ERROR AMPLIFIER + 7 LBO 8 ENABLE BIAS – R3 30k R4 140k 3 SHUTDOWN VC A1 – 200mV A4 SW COMPARATOR – RAMP GENERATOR + Σ + Q3 Q R + 5 DRIVER FF S A2 + A=3 600kHz OSCILLATOR 0.03Ω – 4 GND 1308 BD U W U U APPLICATIONS INFORMATION GROUND PLANE LAYOUT HINTS 1 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 10µF 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 2 8 LT1308 7 3 6 4 5 L D CIN MULTIPLE VIAs VIN COUT GND VOUT 1308 F02 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 5 LT1308 U U W U APPLICATIONS INFORMATION distance from the circuit, an additional input capacitor may be required. A 220µF 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. 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 VIN LBI LT1308 1M + LBO R2 100k TO PROCESSOR – 200mV INTERNAL REFERENCE GND VBAT R1 = SHUTDOWN PIN VLB – 200mV 2µA 1308 F04 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. Figure 4. Setting Low-Battery Detector Trip Point 200k 2N3906 VIN LBO VBAT LT1308 VREF 200mV 10k LBI + 10µF GND 1308 F05 Figure 5. Accessing 200mV Reference VIN Q3 R2 400k SHDN SHUTDOWN CURRENT 400k START-UP CURRENT Q2 Q1 1308 F03 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- 6 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 500µs/division to show detail of one transmit pulse. LT1308 U U W U APPLICATIONS INFORMATION DECT PHONES VIN = 2.7V The DECT standard specifies a transmit pulse 416µs in duration. The LT1308 is capable of delivering a 400mA pulse load from a 1.2V input with output capacitance of 100µF. 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. VOUT 200mV/DIV AC COUPLED 1A ILOAD 100mA 1ms/DIV Figure 9. GSM Load Transient Response. At Low VIN, Large Output Capacitor (2200µF) Serves to Hold up VOUT L1 4.7µH VIN SHDN LT1308 LBO C1 10µF CERAMIC D1 MBRS120 SW LBI NiCd OR Li-Ion CELL 1308 F09 R1 5V/1A OR 3.3V/300mA FB VOUT 200mV/DIV AC COUPLED GND VC + 100k 47k VIN = 2.7V IL, 1A/DIV C2 100µF ILOAD 33nF 1A 100mA 500µs/DIV L1: TOKO 636CY4R7M COILTRONICS CTX5-1 FOR VOUT = 5V: R1 = 309k FOR VOUT = 3.3V: R1 = 169k 1308 F10 1308F06 Figure 10. GSM Load Transient Response. Faster Sweep Speed (500µs/DIV) Details VOUT and Inductor Current of One Transmit Pulse Figure 6. DC/DC Converter for GSM/DECT Application VOUT 200mV/DIV AC COUPLED VIN = 3.6V VOUT 200mV/DIV AC COUPLED ILOAD IL, 1A/DIV VIN = 1.2V 400mA 50mA 1A ILOAD 100mA 100µs/DIV 2ms/DIV 1308 F11 1308 F07 Figure 11. DECT Load Transient Response. With a Single NiCd Cell the LT1308 Provides 3.3V with 400mA Pulsed Load. Pulse Width = 416µs Figure 7. GSM Load Transient Response. 100mA to 1A Transient Response for Figure 6’s Circuit. Pulse Width = 577µs VOUT 200mV/DIV AC COUPLED VIN = 3.6V VOUT 200mV/DIV AC COUPLED VIN = 1.2V IL, 1A/DIV 1A ILOAD ILOAD 100mA 1ms/DIV 1308 F08 Figure 8. GSM Load Transient Response. Slower Sweep Speed (1ms/DIV) Shows VOUT over Several Transmit Pulses 400mA 50mA 100µs/DIV 1308 F09 Figure 12. DECT Load Transient Response. Faster Sweep Speed (100µs/DIV) Details VOUT and Inductor Current of Single DECT Transmit Pulse 7 LT1308 U TYPICAL APPLICATION Digital Camera Power Supply 2-4 Cell to 3.3V/175mA, 5V/175mA, 18V/10mA, – 10V/10mA VIN 1.6V TO 6V 8 L1A N=1 10µH 1 VIN C1 + 100µF C6 10µF 2 SW R3 340k SHDN VC C8 1nF R4 47k 3 L1C 3 N = 0.3 LT1308 L1B N = 0.7 D1 D2 4 5V 175mA FB GND R1 100k C7 22nF R2 2.08M C2 100µF + + 3.3V 175mA C3 100µF D3 L1D N = 3.5 + C4 10µF 6 6 C1, C2, C3 = AVX TPS C4, C5 = AVX TAJ C6 = CERAMIC CCD BIAS 18V 10mA 7 D1, D2 = IR10BQ015 D3, D4 = BAT-85 L1 = COILTRONICS CTX02-13973 + C5 10µF L1E N=2 CCD BIAS –10V 10mA 5 D4 U PACKAGE DESCRIPTION 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) 0.010 – 0.020 × 45° (0.254 – 0.508) 0.008 – 0.010 (0.203 – 0.254) 0.053 – 0.069 (1.346 – 1.752) 0°– 8° TYP 0.016 – 0.050 0.406 – 1.270 0.014 – 0.019 (0.355 – 0.483) 8 7 6 5 0.004 – 0.010 (0.101 – 0.254) 0.050 (1.270) BSC 0.150 – 0.157** (3.810 – 3.988) 0.228 – 0.244 (5.791 – 6.197) *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 3 2 4 SO8 0695 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC®1163 Triple High Side Driver for 2-Cell Inputs 1.8V Minimum Input, Drives N-Channel MOSFETs LTC1174 Micropower Step-Down DC/DC Converter 94% Efficiency, 130µA IQ, 9V to 5V at 300mA LT1302 High Output Current Micropower DC/DC Converter 5V/600mA from 2V, 2A Internal Switch, 200µA IQ LT1304 2-Cell Micropower DC/DC Converter Low-Battery Detector Active in Shutdown, 5V at 200mA for 2 Cells LT1307 Single Cell Micropower 600kHz PWM DC/DC Converter 3.3V at 75mA from 1 Cell, MSOP Package LT1316 Micropower DC/DC Converter with Programmable Peak Current Limit Works with High Source Impedance, 1.5V Minimum Input, Low-Battery Detector Active in Shutdown, 33µA IQ, MSOP Package LTC1440/1/2 Ultralow Power Single/Dual Comparators with Reference 2.8µA IQ, Adjustable Hysteresis LTC1516 2-Cell to 5V Regulated Charge Pump 12µA IQ, No Inductors, 5V at 50mA from 3V Input LT1521 Micropower Low Dropout Linear Regulator 500mV Dropout, 300mA Current, 12µA IQ 8 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417● (408)432-1900 FAX: (408) 434-0507● TELEX: 499-3977 ● www.linear-tech.com 1308i LT/TP 0198 4K • PRINTED IN USA  LINEAR TECHNOLOGY CORPORATION 1998