LT1949 600kHz, 1A Switch PWM DC/DC Converter U FEATURES ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO The LT ®1949 is a fixed frequency step-up DC/DC converter with a 1A, 0.5Ω internal switch. Capable of generating 10V at 175mA from a 3.3V input, the LT1949 is ideal for generating bias voltages for large screen LCD panels. Constant frequency 600kHz operation results in a low noise output that is easy to filter and the 30V switch rating allows output voltage up to 28V using a single inductor. An external compensation pin gives the user flexibility in optimizing loop compensation, allowing small low ESR ceramic capacitors to be used at the output. The 8-lead MSOP and SO packages ensure a low profile overall solution. 1A, 0.5Ω, 30V Internal Switch Operates with VIN as Low as 1.5V 600kHz Fixed Frequency Operation Low-Battery Detector Stays Active in Shutdown Low VCESAT Switch: 410mV at 800mA Pin-for-Pin Compatible with the LT1317B Small 8-Lead MSOP and SO Packages U APPLICATIO S ■ ■ ■ ■ ■ LCD Bias Supplies GPS Receivers Battery Backup Portable Electronic Equipment Diagnostic Medical Instrumentation The LT1949 includes a low-battery detector that stays alive when the device goes into shutdown. Quiescent current in shutdown is 25µA, while operating current is 4.5mA. , LTC and LT are registered trademarks of Linear Technology Corporation. U TYPICAL APPLICATIO VIN 3.3V 90 L1 10µH C1 22µF SW VIN 3.6VIN 4.2VIN 3VIN 70 R1 1M LT1949 SHUTDOWN VOUT = 10V 80 FB SHDN GND VC 68k R2 140k VOUT 10V 175mA C2 10µF CERAMIC 330pF C1: AVX TAJA226M006R C2: TAIYO YUDEN LMK325BJ106MN D1: MBRM120LT3 L1: SUMIDA CDRH62B-100 Figure 1. 3.3V to 10V/175mA DC/DC Converter EFFICIENCY (%) + D1 60 50 40 30 1949 F01 20 5 10 50 100 LOAD CURRENT (mA) 300 1949 F02 Figure 2. 3.3V to 10V Converter Efficiency 1 LT1949 W W W AXI U U ABSOLUTE RATI GS (Note 1) VIN, LBO Voltage ..................................................... 12V SW Voltage ............................................... – 0.4V to 30V FB Voltage .................................................... VIN + 0.3V VC Voltage ................................................................ 2V LBI Voltage ............................................ 0V ≤ VLBI ≤ 1V SHDN Voltage ........................................................... 6V Junction Temperature .......................................... 125°C Operating Temperature Range (Note 2) LT1949EMS8 .......................................–40°C to 85°C LT1949ES8/LT1949IS8 .......................–40°C to 85°C Storage Temperature ........................... – 65°C to 150°C Lead Temperature (Soldering, 10sec).................. 300°C U U W PACKAGE/ORDER I FOR ATIO ORDER PART NUMBER TOP VIEW VC FB SHDN GND 1 2 3 4 8 7 6 5 LBO LBI VIN SW LT1949EMS8 MS8 PACKAGE 8-LEAD PLASTIC MSOP MS8 PART MARKING TJMAX = 125°C, θJA = 120°C/W LTJC TOP VIEW VC 1 8 LBO FB 2 7 LBI SHDN 3 6 VIN 5 SW GND 4 ORDER PART NUMBER LT1949ES8 LT1949IS8 S8 PART MARKING S8 PACKAGE 8-LEAD PLASTIC SO TJMAX = 125°C, θJA = 120°C/W 1949E 1949I 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. VIN = 2V, VSHDN = 2V unless otherwise noted. SYMBOL PARAMETER IQ Quiescent Current CONDITIONS VSHDN = 0V VFB MIN ● ● Feedback Voltage ● IB UNITS 4.5 25 7.5 40 mA µA 1.24 1.24 1.26 1.26 V V ● Input Voltage Range ● 1.7 ● 70 700 V/V ● 80 85 % 1 0.95 1.13 ● 1.5 1.5 A A ● 500 600 750 kHz 0.015 – 2.3 0.1 –7 µA µA 200 200 210 220 mV mV V Error Amp Transconductance AV Error Amp Voltage Gain ∆I = 5µA Maximum Duty Cycle Switch Current Limit (Note 4) VIN = 2.5V, Duty Cycle = 30% VIN = 2.5V, Duty Cycle = 30% Switching Frequency Shutdown Pin Current VSHDN = VIN VSHDN = 0V 12 ● ● LBI Threshold Voltage ● 2 MAX FB Pin Bias Current (Note 3) gm fOSC 1.22 1.20 TYP 190 180 140 80 nA 12 V 240 µmhos LBO Output Low ISINK = 10µA ● 0.15 0.25 LBO Leakage Current VLBI = 250mV, VLBO = 5V ● 0.02 0.1 µA LBI Input Bias Current (Note 5) VLBI = 150mV ● 5 60 nA Low-Battery Detector Gain 1MΩ Pull-Up Switch Leakage Current VSW = 5V 2000 ● 0.01 V/V 3 µA LT1949 ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C. VIN = 2V, VSHDN = 2V unless otherwise noted. SYMBOL PARAMETER CONDITIONS Switch VCESAT ISW = 800mA ISW = 500mA ● 1.8V ≤ VIN ≤ 12V ● Reference Line Regulation MIN MAX UNITS 400 mV mV 0.15 %/V 410 SHDN Input Voltage High ● SHDN Input Voltage Low ● Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The LT1949E is guaranteed to meet performance specifications from 0°C to 70°C. Specifications over the – 40°C to 85°C operating temperature range are assured by design, characterization and correlation with statistical process controls. TYP 0.08 1.4 6 V 0.4 V Note 3: Bias current flows into FB pin. Note 4: Switch current limit guaranteed by design and/or correlation to static tests. Duty cycle affects current limit due to ramp generator. Note 5: Bias current flows out of LBI pin. U W TYPICAL PERFOR A CE CHARACTERISTICS –40°C 25°C 85°C 550 500 1.3 1.3 1.2 1.2 SWITCH CURRENT (A) 650 SWITCH CURRENT (A) OSCILLATOR FREQUENCY (kHz) 700 600 Switch Current Limit, Duty Cycle = 30% Switch Current Limit Oscillator Frequency 1.1 1.0 0.8 –50 0.8 2 10 4 6 8 INPUT VOLTAGE 0 12 1.0 0.9 0.9 0 1.1 20 60 40 DUTY CYCLE (%) 80 100 –25 0 25 50 TEMPERATURE (°C) 75 1949 G03 1949 G02 1949 G01 Switch Voltage Drop (VCESAT) Quiescent Current, SHDN = 2V Feedback Voltage 1.0 1.25 0.8 1.24 100 4.6 85°C 0.6 25°C 0.4 –40°C 0.2 QUIESCENT CURRENT (mA) FEEDBACK VOLTAGE (V) SWITCH VOLTAGE (V) 4.5 1.23 1.22 1.21 4.4 4.3 4.2 4.1 4.0 3.9 0 0 0.2 0.4 0.6 0.8 SWITCH CURRENT (A) 1.0 1.2 1949 G04 1.20 –50 –25 0 25 50 TEMPERATURE (°C) 75 100 1949 G05 3.8 –50 –25 0 25 50 TEMPERATURE (°C) 75 100 1949 G06 3 LT1949 U W TYPICAL PERFOR A CE CHARACTERISTICS Quiescent Current, SHDN = 0V SHDN Pin Current FB Pin Bias Current 26 40 2 36 24 23 22 21 32 SHDN PIN CURRENT (µA) FB PIN BIAS CURRENT (nA) QUIESCENT CURRENT (µA) 25 28 24 20 16 12 1 0 –1 –2 8 4 20 –50 –25 0 25 50 TEMPERATURE (°C) 75 100 0 –50 –3 –25 0 25 50 TEMPERATURE (°C) 1317 TPC10 75 100 0 2 4 3 SHDN PIN VOLTAGE (V) 5 6 1317 TPC12 1317 TPC11 Load Regulation Load Regulation Transient Response VOUT 100mV/DIV AC COUPLED VOUT 50mV/DIV DC COUPLED OFFSET ADDED VOUT 50mV/DIV DC COUPLED OFFSET ADDED 1 IL 500mA/DIV ILOAD 200mA 100mA ILOAD 25mA/DIV VIN = 3V VOUT = 10V L1 = 10µH, SUMIDA CD54 COUT = 10µF CERAMIC 1949 G10 ILOAD 50mA/DIV VIN = 4V VOUT = 10V L1 = 10µH, SUMIDA CD54 COUT = 10µF CERAMIC 50µs/DIV VIN = 3.3V VOUT = 10V CIRCUIT OF FIGURE 1 1949 G12 1949 G11 U U U PI FU CTIO S VC (Pin 1): Compensation Pin for Error Amplifier. Connect a series RC network from this pin to ground. Typical values for compensation are a 68k/330pF combination when using ceramic output capacitors. Minimize trace area at VC. FB (Pin 2): Feedback Pin. Reference voltage is 1.24V. Connect resistor divider tap here. Minimize trace area at FB. Set VOUT according to: VOUT = 1.24V(1 + R1/R2). SHDN (Pin 3): Shutdown. Pull this pin low for shutdown mode (only the low-battery detector remains active). Leave this pin floating or tie to a voltage between 1.4V and 6V to enable the device. SHDN pin is logic level and need only meet the logic specification (1.4V for high, 0.4V for low). 4 GND (Pin 4): Ground. Connect directly to local ground plane. 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 be bypassed close to the pin. LBI (Pin 7): Low-Battery Detector Input. 200mV reference. Voltage on LBI must stay between ground and 700mV. Low-battery detector remains active in shutdown mode. LBO (Pin 8): Low-Battery Detector Output. Open collector, can sink 10µA. A 1MΩ pull-up is recommended. LT1949 W BLOCK DIAGRA LBI 1.24V REFERENCE + FB 2 1 ERROR AMPLIFIER + – + 7 VC gm LBO 8 – 200mV A4 ENABLE SHDN VOUT BIAS R1 (EXTERNAL) – SHUTDOWN SW FB R2 (EXTERNAL) 3 A1 COMPARATOR 5 – RAMP GENERATOR + Σ + + FF Q3 Q R A2 COMPARATOR DRIVER S + A=2 600kHz OSCILLATOR 0.06Ω – 4 GND 1949 BD Figure 3. LT1949 Block Diagram U OPERATIO The LT1949 is a current mode, fixed frequency step-up DC/DC converter with an internal 1A NPN power transistor. Operation can best be understood by referring to the Block Diagram. At the beginning of each oscillator cycle, the flip-flop is set and the switch is turned on. Current in the switch ramps up until the voltage at A2’s positive input reaches the VC pin voltage, causing A2’s output to change state and the switch to be turned off. The signal at A2’s positive input is a summation of a signal representing switch current and a ramp generator (introduced to avoid subharmonic oscillations at duty factors greater than 50%). If the load increases, VOUT (and FB) will drop slightly and the error amplifier will drive VC to a higher voltage, causing current in the switch to increase. In this way, the error amplifier drives the VC pin to the voltage necessary to satisfy the load. Frequency compensation is provided by an external series RC network connected between the VC pin and ground. Layout Hints The LT1949 switches current at high speed, mandating careful attention to layout for proper performance. You will not get advertised performance with careless layouts. Figure 4 shows recommended component placement 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 package. As little as 10mm of wire or PC trace from CIN to VIN will cause problems such as inability to regulate or oscillation. The ground terminal of output capacitor C2 should tie close to Pin 4 of the LT1949. 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. 5 LT1949 U OPERATIO LBI LBO GROUND PLANE C1 1 + VIN 8 R1 2 R2 SHUTDOWN LT1949 7 3 6 4 5 L1 MULTIPLE VIAs C2 GND VOUT 1949 F04 Figure 4. Recommended Component Placement for Boost Converter. Note Direct High Current Paths Using Wide PC Traces. Minimize Trace Area at Pin 1 (VC) and Pin 2 (FB). 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 U U W U APPLICATIONS INFORMATION Low-Battery Detector The LT1949’s low-battery detector is a simple PNP input gain stage with an open collector NPN output. The negative input of the gain stage is tied internally to a 200mV ±5% reference. The positive input is the LBI pin. Arrangement as a low-battery detector is straightforward. Figure␣ 5 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␣ 6. The low-battery detector remains active in shutdown. 3.3V R1 VIN LBI LT1949 1M + LBO R2 100k 200k TO PROCESSOR – 2N3906 LT1949 VREF 200mV 200mV INTERNAL REFERENCE GND V – 200mV R1 = LB 2µA VIN LBO LBI + 10k 10µF GND 1949 F06 1949 F05 Figure 6. Accessing 200mV Reference Figure 5. Setting Low-Battery Detector Trip Point 6 LT1949 U TYPICAL APPLICATIO 4 Cell to 5V SEPIC Converter C2 4.7µF 16V L1 10µH VIN 4V TO 9V SW VIN 1M D1 L2 10µH VOUT 5V 250mA 1M 1% LT1949 C1 4.7µF 16V GND VC 1M C3 10µF 6.3V FB SHDN 332k 1% 33k 3.3nF C1, C2: TAIYO YUDEN EMK316BJ475ML C3: TAIYO YUDEN JMK316BJ106ML D1: MOTOROLA MBRM120LT3 L1, L2: SUMIDA CR32-100KC 1949 TA02 U PACKAGE DESCRIPTIO Dimensions in inches (millimeters) unless otherwise noted. MS8 Package 8-Lead Plastic MSOP (LTC DWG # 05-08-1660) 0.040 ± 0.006 (1.02 ± 0.15) 0.007 (0.18) 0.118 ± 0.004* (3.00 ± 0.102) 0.034 ± 0.004 (0.86 ± 0.102) 8 7 6 5 0° – 6° TYP SEATING PLANE 0.012 (0.30) 0.0256 REF (0.65) BSC 0.021 ± 0.006 (0.53 ± 0.015) 0.118 ± 0.004** (3.00 ± 0.102) 0.193 ± 0.006 (4.90 ± 0.15) 0.006 ± 0.004 (0.15 ± 0.102) MSOP (MS8) 1098 1 * DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE ** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE 2 3 4 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) 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 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) SO8 1298 1 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. 2 3 4 7 LT1949 U TYPICAL APPLICATIO Low Profile Triple Output LCD Bias Generator D1 D2 C7 0.1µF L1 10µH VIN 3.3V SHUTDOWN + 23V 5mA C9 0.1µF 8V 200mA R2 40.2k 1% SHDN LBI C1 22µF C8 0.1µF D4 D7 SW VIN D3 LT1949 C2 10µF FB LB0 VC GND R3 7.5k 1% R1 47k C3 680pF C6 4.7µF C1: AVX TAJB226M010 C2: TAIYO YUDEN TMK432BJ106MN X7R 1210 C4, C5, C6: TAIYO YUDEN LMK316BJ475ML X5R1206 C7, C8, C9: 0.1µF CERAMIC, 50V D1 TO D6: FMMD7000, DUAL DIODE D7: MBRM120LT3 L1: SUMIDA CDRH62B-100 C4 4.7µF D5 C5 4.7µF D6 –8V 10mA 1949 TA01 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1054 High Power Regulated Charge Pump Up to 100mA Output with No Inductors 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 LT1307B Single Cell Micropower 600kHz PWM DC/DC Converter 3.3V at 75mA from 1 Cell, MSOP Package LT1308B 2A 600kHz PWM DC/DC Converter TSSOP Package LT1317B Micropower, 600kHz PWM DC/DC Converter 2 Cells to 3.3V at 200mA, MSOP Package LTC®1516 2-Cell to 5V Regulated Charge Pump 12µA IQ, No Inductors, 5V at 50mA from 3V Input LT1613 Single Cell 1.4MHz PWM DC/DC Converter 3.3V to 5V at 200mA, SOT-23 Package LTC1682 Doubler Charge Pump with Low Noise Linear Regulator 3.3V and 5V Outputs with 60µVRMS Noise, Up to 80mA Output LTC1754 Micropower 3.3V/5V Charge Pump with Shutdown Up to 50mA Output, IQ = 13µA, SOT-23 Package 8 Linear Technology Corporation 1949f LT/TP 0300 4K • PRINTED IN THE USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408)432-1900 ● FAX: (408) 434-0507 ● www.linear-tech.com LINEAR TECHNOLOGY CORPORATION 1999