LT1305 Micropower High Power DC/DC Converter with Low-Battery Detector U DESCRIPTIO FEATURES ■ ■ ■ ■ ■ ■ ■ The LT ®1305 is a micropower step-up DC/DC converter that uses Burst ModeTM operation. Similar to the LT1303, the LT1305 features a 2A internal low-loss switch and can deliver up to four times the output power of the LT1303. 5V at 400mA from 2V Input Supply Voltage As Low As 1.8V 120µA Quiescent Current Low-Battery Detector Low VCESAT Switch: 310mV at 2A Typ Uses Inexpensive Surface Mount Inductors 8-Lead SO Package Quiescent current is only 120µA and the Shutdown pin further reduces current to 10µA. A low-battery detector provides an open-collector output that goes low when the input voltage drops below a preset level. The LT1305 is available in an 8-pin SO, easing board space requirements. UO APPLICATI ■ ■ , LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode is a trademark of Linear Technology Corporation 2-Cell and 3-Cell to 5V Conversion EL Panel Drivers Portable Instruments UO ■ S TYPICAL APPLICATI 2-Cell and 3-Cell to 5V/400mA DC/DC Converter with Low-Battery Detect 2 TO 3 CELLS + C1 220µF VIN LBI 412k 1% SHUTDOWN SW LBO SHDN LOW BATTERY GOES LOW AT VBAT = 2.2V 100k 301k 1% LT1305 GND C1, C2: AVX TPSE227010R0100 D1: MOTOROLA MBRS130LT3 L1: COILCRAFT D03316-103 D1 FB PGND C2 100k 220µF 1% + VOUT 5V 400mA VIN = 4.00V EFFICIENCY (%) 316k 1% Efficiency 90 L1 10µH VIN = 3.00V 80 VIN = 2.00V VIN = 2.50V 70 LT1305 • TA03 60 1 10 100 LOAD CURRENT (mA) 1000 LT1305 • TA02 1 LT1305 U W W W VIN Voltage .............................................................. 10V SW1 Voltage ............................................................ 25V FB Voltage ............................................................... 10V Shutdown Voltage ................................................... 10V LBO Voltage ............................................................. 10V LBI Voltage .............................................................. 10V Maximum Power Dissipation ............................. 500mW Operating Temperature Range ..................... 0°C to 70°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 GND 1 8 PGND LBO 2 7 SW SHDN 3 6 VIN FB 4 5 LBI LT1305CS8 S8 PART MARKING S8 PACKAGE 8-LEAD PLASTIC SO 1305 TJMAX = 100°C, θJA = 80°C/ W Consult factory for Industrial and Military grade parts. ELECTRICAL CHARACTERISTICS TA = 25°C, VIN = 2.0V, unless otherwise noted. SYMBOL PARAMETER CONDITIONS IQ Quiescent Current VSHDN = 0.5V, VFB = 2V VSHDN = 1.8V VIN Input Voltage Range Feedback Voltage Comparator Hysteresis Feedback Pin Bias Current VFB = 1V Oscillator Frequency Current Limit Not Asserted MIN ● ● Maximum Duty Cycle tON Switch On Time VCESAT UNITS 200 15 µA µA 1.8 2.0 1.55 ● 1.22 1.24 1.26 V ● 6 12.5 mV ● 7 20 nA 155 185 kHz 120 V V 0.2 ● 75 Current Limit Not Asserted 86 %/°C 95 % µs 5.6 Output Line Regulation 1.8V < VIN < 6V ● 0.06 0.15 %/V Switch Saturation Voltage ISW = 1A ● 140 280 mV Switch Leakage Current VSW = 5V, Switch Off ● 0.1 10 µA Peak Switch Current VIN = 2V 2 2.35 2.50 A A 2.15 A ● VIN = 5V 1.35 1.20 1.15 LBI Trip Voltage (Note 2) ● 1.24 1.27 V LBI Input Bias Current VLBI = 1V ● 7 20 nA LBO Output Low ILOAD = 100µA ● 0.11 0.4 V LBO Leakage Current VLBI = 1.3V, VLBO = 5V ● 0.1 5 µA VSHDNH Shutdown Pin High VSHDNL Shutdown Pin Low ISHDN Shutdown Pin Bias Current ● VSHDN = 5V VSHDN = 2V VSHDN = 0V The ● denotes specifications which apply over the 0°C to 70°C operating temperature range. Note 1: Hysteresis specified is DC. Output ripple may be higher if output capacitance is insufficient or capacitor ESR is excessive. 2 MAX 120 7 ● Oscillator TC DC TYP ● ● ● 1.21 1.8 V 8.0 3.0 0.1 0.5 V 20 µA µA µA 1 Note 2: Low-battery detector comparator is inoperative when device is in shutdown. LT1305 U W TYPICAL PERFORMANCE CHARACTERISTICS Switch On Time Maximum Duty Cycle Oscillator Frequency 8 200 100 190 95 6 5 4 3 2 –50 – 25 0 25 50 TEMPERATURE (°C) 75 100 180 90 170 85 DUTY CYCLE (%) FREQUENCY (kHz) ON TIME (µs) 7 160 150 140 65 120 60 110 55 100 –50 50 –50 –25 25 50 0 TEMPERATURE (°C) 75 150 140 130 120 100 2.2 400 PEAK SWITCH CURRENT (A) 160 75 2.4 TA = 25°C SWITCH OFF SWITCH OFF VIN = 2V 170 25 50 0 TEMPERATURE (°C) Current Limit Quiescent Current 180 –25 LT1305 • G03 500 QUIESCENT CURRENT (µA) QUIESCENT CURRENT (µA) 100 LT1305 • G02 Quiescent Current 190 75 70 130 LT1305 • G01 200 80 300 200 100 2.0 1.8 1.6 1.4 1.2 110 100 –50 0 –25 25 50 0 TEMPERATURE (°C) 75 100 0 2 6 4 INPUT VOLTAGE (V) 1.0 – 50 10 LBI Pin Bias Current FB Pin Bias Current 1.250 18 18 1.245 16 10 8 6 14 12 10 8 6 4 4 1.235 1.230 1.225 1.220 1.215 1.210 2 2 1.205 0 –50 0 –50 1.200 –50 –25 25 50 0 TEMPERATURE (°C) 75 100 LT1305 • G07 100 1.240 FEEDBACK VOLTAGE (V) BIAS CURRENT (nA) 16 75 FB Voltage 20 12 50 25 0 TEMPERATURE (˚C) LT1305 • G06 20 14 –25 LT1305 • G05 LT1305 • G04 BIAS CURRENT (nA) 8 –25 25 50 0 TEMPERATURE (°C) 75 100 LT1305 • G08 –25 25 50 0 TEMPERATURE (°C) 75 100 LT1305 • G09 3 LT1305 U W TYPICAL PERFORMANCE CHARACTERISTICS Low-Battery Detect Trip Point Switch Saturation Voltage 1.235 1.230 1.225 1.220 1.215 1.210 1.205 350 300 250 200 150 100 50 0 –25 25 50 0 TEMPERATURE (°C) 75 100 SWITCH SATURATION VOLTAGE (mV) SWITCH SATURATION VOLTAGE (mV) 1.240 LBI VOLTAGE (V) 300 TA = 25°C 1.245 1.200 –50 Switch Saturation Voltage 400 1.250 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 SWITCH CURRENT (A) LT1305 • G10 LT1305 • F12 ISW = 1A 250 200 150 100 50 0 – 50 – 25 0 25 50 TEMPERATURE (°C) 75 100 LT1305 • G13 U U U PI FU CTIO S GND (Pin 1): Signal Ground. Tie to PGND under the package. LBI (Pin 5): Low-Battery Comparator Input. When voltage on this pin is below 1.24V, LBO is low. LBO (Pin 2): Open-Collector Output of Comparator C3. Can sink 100µA. High impedance when device is in shutdown. VIN (Pin 6): Supply Pin. Must be bypassed with a large value capacitor to gound. Keep bypass within 0.2" of the device. SHDN (Pin 3): Shutdown. Pull high to shut down the LT1305. Ground for normal operation. SW (Pin 7): Switch Pin. Connect inductor and diode here. Keep layout short and direct to minimize radio frequency interference. FB (Pin 4): Feedback Input. Connects to main comparator C1 input. 4 PGND (Pin 8): Power Ground. Tie to signal ground (pin 1) under the package. Bypass capacitor from VIN should be tied directly to PGND within 0.2" of the device. LT1305 W BLOCK DIAGRAM D1 L1 VIN + C5 6 VIN 7 + HYSTERETIC COMPARATOR OFF – OSCILLATOR C1 R2 REFERENCE 1.24V – FB C4 R1 3Ω C2 4 + 36mV CURRENT COMPARATOR R1 SW A3 DRIVER Q2 1× Q1 160× + – C3 + GND 1 LBI 5 LBO 2 SHUTDOWN 3 8 PGND LT1305 • F01 Figure 1. LT1305 Block Diagram U OPERATION Operation of the LT1305 is best understood by referring to the Block Diagram in Figure 1. When C1’s negative input, related to the output voltage by the appropriate resistordivider ratio, is higher than the 1.24V reference voltage, C1’s output is low. C2, A3 and the oscillator are turned off, drawing no current. Only the reference and C1 consume current, typically 120µA. When C1’s negative input drops below 1.24V and overcomes C1’s 6mV hysteresis, C1’s output goes high, enabling the oscillator, current comparator C2 and driver A3. Quiescent current increases to 2mA as the device goes into active switching mode. Q1 then turns on in controlled saturation for nominally 6µs or until current comparator C2 trips, whichever comes first. The switch then turns off for approximately 1.5µs, then turns on again. The LT1305’s switching causes current to alternately build up in L1 and dump into output capacitor C4 via D1, increasing the output voltage. When the output is high enough to cause C1’s output to go high, switching action ceases. Capacitor C4 is left to supply current to the load until VOUT decreases enough to force C1’s output high, and the entire cycle repeats. Figure 2 details relevant waveforms. C1’s cycling causes low-to-mid-frequency ripple voltage on the output. Ripple can be reduced by making the output capacitor large. The 220µF unit specified results in ripple of 50mV to 100mV on the 5V output. Paralleling two capacitors will decrease ripple by approximately 50%. VOUT 100mV/DIV AC COUPLED VSW 5V/DIV IL 1A/DIV 50µs/DIV LT1305 • F02 Figure 2. Burst Mode Operation 5 LT1305 U OPERATION If switch current reaches 2A, causing C2 to trip, switch on time is reduced and off time increases slightly. This allows continuous operation during bursts. C2 monitors the voltage across 3Ω resistor R1 which is directly related to the switch current. Q2’s collector current is set by the emitter-area ratio to 0.6% of Q1’s collector current. When R1’s voltage drop exceeds 36mV, corresponding to 2A switch current, C2’s output goes high, truncating the on time portion of the oscillator cycle and increasing off time to about 2µs. Response time of C2, which determines minimum on time, is approximately 300ns. Low-Battery Detector The low-battery detector is enabled when SHDN is low and disabled when SHDN is high. The comparator has no hysteresis built in, but hysteresis can be added by connecting a high-value resistor from LBI to LBO as shown in Figure 3. The internal reference can be accessed via the comparator as shown in Figure 4. Inductor Selection Inductors used with the LT1305 must fulfill two requirements. First, the inductor must be able to handle current of 2A to 2.5A without runaway saturation. Rod or drum core units usually saturate gradually and it is acceptable to exceed manufacturer’s published saturation current by 20% or so. Second, the unit must have low DCR, under 0.05Ω so that copper loss is kept low and excess heating is avoided. Inductance value is not critical. Generally, for low voltage inputs below 3V a 10µH inductor is recommended (such as Coilcraft DO3316-103). For inputs above 4V to 5V use a 22µH unit (such as Coilcraft DO3316-223). Switching frequency can reach up to 300kHz so the core material should be able to operate at high frequency without excessive core loss. Ferrite or molypermalloy cores are a better choice than powdered iron. If EMI is a concern, a toroidal inductor is suggested, such as Coiltronics CTX20-4. Capacitor Selection VBAT 5V LT1305 R1 R4 47k – 1.24V LBI LBO + R2 49.9k 1% R3 2M R1 = (VTRIP –1.24V) (43.5k) HYSTERESIS ≈ 30mV LT1305 • F03 Figure 3. R3 Adds Hysteresis to Low-Battery Detector VIN 100k Diode Selection VIN A 2A Schottky diode such as Motorola MBRS130LT3 is a good choice for the rectifier diode. A 1N5821 or MBRS130T3 are suitable as well. Do not use “general purpose” diodes such as 1N4001. They are much too slow for use in switching regulator applications. LBO 2N3906 LT1305 VREF OUTPUT R2 LBI + 2.2µF R1 GND ( ) VREF = 1.24V 1 + R2 R1 VIN ≥ VREF + 200mV R1 + R2 ≈ 33k LT1305 • F04 Figure 4. Accessing Internal Reference 6 Output and input capacitors should have low ESR for best performance. Inexpensive aluminum electrolytics sometimes have ESR above 1Ω, even for relatively large values such as 100µF, 16V units. Since the LT1305 has a 2A current limit, 2V of ripple voltage would result with such a capacitor at the output. Keep ESR below 0.05Ω to 0.1Ω for reasonable ripple voltage. Tantalum capacitors such as AVX TPS series or Sprague 593D have low ESR and are surface mount components. For lowest ESR, use Sanyo OS-CON units (OS-CON is also available from Vishay). These capacitors have superior ESR, small size and perform well at cold temperatures. LT1305 U TYPICAL APPLICATIONS N Setting Output Voltage 4-Cell-to-5V Converter 1N5817 L1 VIN VIN + SW R2 GND MBRS130LT3 SW 5V 400mA 100µF LT1305 + 309k 4 CELLS SHDN 220µF FB PGND +100µF** VIN + VOUT LT1305 100µF L1* 22µH 3.5V to 6.5V FB PGND GND R1 22µH* + 150µF** 100k SHUTDOWN ( ) VOUT = 1.24V 1 + R2 R1 * COILCRAFT DO3316-223 OR SUMIDA CD105-220 ** SANYO OS-CON LT1305 • TA03 LT1305 • TA05 5V Step-Up Converter with Reference Output 100k VIN 2N3906 VREF OUTPUT 1.24V SW 5V 400mA LBO + LT1305 100µF LBI GND + 2.2µF MBRS130LT3 10µH* 1.8V TO 4.5V INPUT 309k + FB PGND 220µF 100k 33k *COILCRAFT DO3316-103 LT1305 • TA06 EL Panel Driver T1** 1:15 •6 4, 5 VIN 1.5V TO 8V 10Ω • 1, 2 MUR160 C1* 50pF 10 1N5818 4.7µF +160V 3.3M + VIN SW 3.3M 47µF †† 0.1µF CERAMIC LT1305 SHDN GND SHUTDOWN 3.3M 1N4148 FB PGND 1k 1/2W 10k ZETEX FZT658 EL PANEL CPANEL ≤ 100nF 51k R1† 25k LT1305 • TA04 100Hz TO 1000Hz SQUARE WAVE DRIVE *ADD C1 FOR OPEN-PANEL PROTECTION **DALE LPE5047-A132 1:15 TURNS RATIO 10µH PRIMARY INDUCTANCE (605) 666-9301 † R1 ADJUSTS VOUT 83VRMS TO 115VRMS †† AVX TPS OR SANYO OS-CON MUST HAVE ESR ≤ 0.15Ω 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. 7 LT1305 U PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted. S8 Package 8-Lead Plastic SOIC 0.189 – 0.197* (4.801 – 5.004) 8 7 6 5 0.150 – 0.157* (3.810 – 3.988) 0.228 – 0.244 (5.791 – 6.197) 1 0.010 – 0.020 × 45° (0.254 – 0.508) 0.008 – 0.010 (0.203 – 0.254) 2 3 4 0.053 – 0.069 (1.346 – 1.752) 0.004 – 0.010 (0.101 – 0.254) 0°– 8° TYP 0.016 – 0.050 0.406 – 1.270 0.014 – 0.019 (0.355 – 0.483) 0.050 (1.270) BSC SO8 0294 *THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006 INCH (0.15mm). RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1129 Micropower Low Dropout Regulator 700mA Output Current in SO-8 Package LT1182/83/84 LCD and CCFL Backlight Controller High Efficiency and Excellent Backlight Control Range LT1301 5V to 12V/200mA Step-Up DC/DC Converter 120µA Quiescent Current LT1302 2-Cell to 5V/600mA Step-Up DC/DC Converter 200µA Quiescent Current LT1303 Micropower DC/DC Converter with Low-Battery Detect 2V to 5V at 200mA LT1372 500kHz Step-Up PWM, 1.5A Switch Low Noise, Fixed Frequency Operation LTC ®1472 PCMCIA Host Switch with Protection Includes Current Limit and Thermal Shutdown 8 Linear Technology Corporation LT/GP 0595 10K • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7487 (408) 432-1900 ● FAX: (408) 434-0507 ● TELEX: 499-3977 LINEAR TECHNOLOGY CORPORATION 1995