Final Electrical Specifications LT1949-1 1.1MHz, 1A Switch PWM DC/DC Converter June 2000 U DESCRIPTIO FEATURES ■ ■ ■ ■ ■ ■ ■ ■ 1A, 0.5Ω, 30V Internal Switch 1.1MHz Fixed Frequency Operation Operates with VIN as Low as 1.5V Low-Battery Detector Stays Active in Shutdown Low VCESAT Switch: 410mV at 800mA Pin-for-Pin Compatible with the LT1317B Uses Ceramic Capacitors Small 8-Lead MSOP Package U APPLICATIO S ■ ■ ■ ■ LCD Bias Supplies GPS Receivers Battery Backup Portable Electronic Equipment Diagnostic Medical Instrumentation The LT1949-1 includes a low-battery detector that stays alive when the device goes into shutdown. Quiescent current in shutdown is 50µA, while operating current is 8mA. , LTC and LT are registered trademarks of Linear Technology Corporation. U ■ The LT ®1949-1 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 LT1949-1 is ideal for generating bias voltages for large screen LCD panels. Constant frequency 1.1MHz 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. The high switching frequency allows the use of ceramic output capacitors. 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 package ensures a low profile overall solution. TYPICAL APPLICATIO 90 VIN 3.3V L1 4.7µH C1 3.3µF CERAMIC VIN SHUTDOWN SHDN VOUT = 10V D1 80 SW VOUT 10V 175mA FB GND VC 3pF EFFICIENCY (%) LT1949-1 3.6VIN 4.2VIN 3VIN 70 R1 196k 1% 60 50 40 84.5k R2 28k 1% 50pF C2 3.3µF CERAMIC 30 20 C1, C2: TAIYO YUDEN LMK325BJ335MD D1: MBRM120LT3 L1: SUMIDA CLQ4D10-4R7 1949-1 F01 Figure 1. 3.3V to 10V/175mA DC/DC Converter 5 10 50 100 LOAD CURRENT (mA) 300 1949-1 F02 Figure 2. 3.3V to 10V Converter Efficiency 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 LT1949-1 W W W AXI U U ABSOLUTE RATI GS U U W PACKAGE/ORDER I FOR ATIO (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) ...–40°C to 85°C Storage Temperature ........................... – 65°C to 150°C Lead Temperature (Soldering, 10sec).................. 300°C ORDER PART NUMBER TOP VIEW VC FB SHDN GND 1 2 3 4 8 7 6 5 LBO LBI VIN SW LT1949-1EMS8 MS8 PACKAGE 8-LEAD PLASTIC MSOP MS8 PART MARKING TJMAX = 125°C, θJA = 120°C/W LTQX Consult factory for Industrial and Military grade parts. ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 2V, VSHDN = 2V unless otherwise noted. SYMBOL PARAMETER IQ Quiescent Current CONDITIONS ● ● VSHDN = 0V VFB MIN Feedback Voltage ● IB FB Pin Bias Current (Note 3) ● Input Voltage Range gm Error Amp Transconductance AV Error Amp Voltage Gain ∆I = 5µA Maximum Duty Cycle Switch Current Limit (Note 4) fOSC 8 50 14 80 1.24 1.24 1.26 1.26 V V 24 150 nA 12 V 280 480 µmhos mA µA 1.7 140 700 V/V ● 80 85 % 1 1.1 1.5 A 0.85 ● ● LBI Threshold Voltage ● 190 180 1.1 1.35 MHz 0.015 –5 0.1 – 14 µA µA 200 200 210 220 mV mV LBO Output Low ISINK = 10µA ● 0.15 0.25 V LBO Leakage Current VLBI = 250mV, VLBO = 5V ● 20 100 nA LBI Input Bias Current (Note 5) VLBI = 150mV ● 30 120 Low-Battery Detector Gain 1MΩ Pull-Up Switch Leakage Current VSW = 5V Switch VCESAT ISW = 800mA ISW = 500mA Reference Line Regulation 1.8V ≤ VIN ≤ 12V nA 2000 ● 0.01 ● 410 270 V/V 3 µA 400 mV mV 0.08 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 LT1949-1E 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. 2 UNITS ● ● VSHDN = VIN VSHDN = 0V MAX ● VIN = 2.5V, Duty Cycle = 30% Switching Frequency Shutdown Pin Current 1.22 1.20 TYP 1.4 %/V 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. LT1949-1 U W TYPICAL PERFOR A CE CHARACTERISTICS Oscillator Frequency 85°C 25°C 1.1 –40°C 1.0 0.9 1.3 1.3 1.2 1.2 SWITCH CURRENT (A) SWITCH CURRENT (A) OSCILLATOR FREQUENCY (MHz) 1.3 1.2 Switch Current Limit, Duty Cycle = 30% Switch Current Limit 1.1 1.0 0.8 –50 0.8 2 4 6 8 INPUT VOLTAGE (V) 10 12 1.0 0.9 0.9 0 1.1 0 20 60 40 DUTY CYCLE (%) 1949-1 G01 80 100 –25 0 25 50 TEMPERATURE (°C) 75 1949-1 G03 1949-1 G02 Switch Voltage Drop (VCESAT) Feedback Voltage 1.0 1.25 0.8 1.24 100 Quiescent Current, SHDN = 2V 8.5 85°C 0.6 25°C 0.4 –40°C 0.2 QUIESCENT CURRENT (mA) FEEDBACK VOLTAGE (V) SWITCH VOLTAGE (V) 8.0 1.23 1.22 1.21 7.5 7.0 6.5 6.0 5.5 5.0 0 0 0.2 0.4 0.6 0.8 SWITCH CURRENT (A) 1.0 1.20 –50 1.2 –25 0 25 50 TEMPERATURE (°C) 1949-1 G04 75 4.5 –50 100 –25 0 25 50 TEMPERATURE (°C) 75 1949-1 G06 1949-1 G05 Quiescent Current, SHDN = 0V SHDN Pin Current FB Pin Bias Current 60 100 60 2 55 50 45 40 35 50 SHDN PIN CURRENT (µA) FB PIN BIAS CURRENT (nA) QUIESCENT CURRENT (µA) 55 45 40 35 30 25 1 0 –2 –4 20 15 30 –50 –25 0 25 50 TEMPERATURE (°C) 75 100 1949-1 G07 10 –50 –6 –25 0 25 50 TEMPERATURE (°C) 75 100 1949-1 G08 0 1 2 4 3 SHDN PIN VOLTAGE (V) 5 6 1949-1 G09 3 LT1949-1 U W TYPICAL PERFOR A CE CHARACTERISTICS Transient Response VOUT 100mV/DIV AC COUPLED IL 500mA/DIV 20µs/DIV VIN = 3.3V VOUT = 10V 40mA TO 140mA LOAD STEP CIRCUIT FIGURE 1 1949-1 G10 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 30k/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. LT1949-1 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 R A2 COMPARATOR DRIVER Q3 Q S + A=2 1.1MHz OSCILLATOR 0.06Ω – 4 1949-1 BD GND Figure 3. LT1949-1 Block Diagram U OPERATIO The LT1949-1 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 LT1949-1 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 LT1949-1. 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 LT1949-1 U OPERATIO LBI LBO GROUND PLANE C1 VIN 1 8 R1 2 7 L1 LT1949-1 R2 SHUTDOWN 3 6 4 5 MULTIPLE VIAs C2 GND VOUT 1949-1 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 W U U APPLICATIO S I FOR ATIO Low-Battery Detector The LT1949-1’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, 49.9k 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 200k LT1949-1 + LBO R2 49.9k 2N3906 1M TO PROCESSOR LT1949-1 VREF 200mV LBI + 10k – VIN LBO 10µF GND 1949-1 F06 200mV INTERNAL REFERENCE GND R1 = VLB – 200mV 4µA 1949-1 F05 Figure 5. Setting Low-Battery Detector Trip Point 6 Figure 6. Accessing 200mV Reference LT1949-1 U TYPICAL APPLICATIO 4 Cell to 5V SEPIC Converter C2 4.7µF 16V L1 10µH VIN 4V TO 9V 1M VIN SW D1 L2 10µH VOUT 5V 250mA 100k 1% LT1949-1 C1 4.7µF 16V GND VC 1M C3 10µF 6.3V FB SHDN 33.2k 1% 40.2k 330pF C1, C2: TAIYO YUDEN EMK316BJ475ML C3: TAIYO YUDEN JMK316BJ106ML D1: MOTOROLA MBRM120LT3 L1, L2: SUMIDA CR32-100KC U PACKAGE DESCRIPTIO 1949-1 TA02 Dimensions in inches (millimeters) unless otherwise noted. MS8 Package 8-Lead Plastic MSOP (LTC DWG # 05-08-1660) 0.118 ± 0.004* (3.00 ± 0.102) 8 7 6 5 0.118 ± 0.004** (3.00 ± 0.102) 0.193 ± 0.006 (4.90 ± 0.15) 1 0.040 ± 0.006 (1.02 ± 0.15) 0.007 (0.18) 2 3 4 0.034 ± 0.004 (0.86 ± 0.102) 0° – 6° TYP 0.021 ± 0.006 (0.53 ± 0.015) SEATING PLANE 0.012 (0.30) 0.0256 REF (0.65) BSC 0.006 ± 0.004 (0.15 ± 0.102) MSOP (MS8) 1098 * 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 7 LT1949-1 U TYPICAL APPLICATIO Low Profile Triple Output LCD Bias Generator D1 D3 D2 D4 23V 5mA C7 0.1µF C8 1µF C9 0.1µF C4 1µF L1 4.7µH VIN 3.3V SW VIN SHUTDOWN SHDN R2 40.2k LT1949-1 C1 4.7µF C6 1µF 8V 200mA FB GND VC R1 30.1k C3 330pF C2 4.7µF R3 7.5k C1, C2, C5: TAIYO YUDEN LMK325BJ475MF C4, C6, C8: TAIYO YUDEN EMK316BJ105MF D1 TO D6: BAT-54S, DUAL DIODE D7: MBRM120LT3 L1: SUMIDA CLQ4D10-4R7 D5 C5 4.7µF D6 1949-1 TA02 –8V 10mA RELATED PARTS PART NUMBER DESCRIPTION COMMENTS 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 36V Switch, Fixed Frequency Operation, SO-8 and TSSOP Packages LT1317B Micropower, 600kHz PWM DC/DC Converter 2 Cells to 3.3V at 200mA, MSOP Package LT1377 Monolithic 1MHz, 1.5A Switching Regulator Regulates Positive or Negative Outputs, Ext Synchronization LT1613 Single Cell 1.4MHz PWM DC/DC Converter 3.3V to 5V at 200mA, SOT-23 Package LT1615 Micropower Boost Converter in SOT-23 IQ = 20µA, < 1µA in Shutdown, VOUT Up to 34V LT1930 1.2MHz Boost Converter in SOT-23 1A, 36V Internal Switching, VIN = 2.6V to 16V LT1949 600kHz, 1A Switch PWM DC/DC Converter 1A, 0.5Ω, 30V Internal Switch, 8-Lead MSOP and SO Packages 8 Linear Technology Corporation 19491i LT/TP 0600 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 2000