LT1305

LT1305 Micropower High Power DC/DC Converter with Low-Battery Detector FEATURES s s s s s s s DESCRIPTIO 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 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. 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. , LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode is a trademark of Linear Technology Corporation APPLICATI s s s S 2-Cell and 3-Cell to 5V Conversion EL Panel Drivers Portable Instruments TYPICAL APPLICATI 2-Cell and 3-Cell to 5V/400mA DC/DC Converter with Low-Battery Detect L1 10µH 316k 1% 2 TO 3 CELLS 90 D1 LOW BATTERY GOES LOW AT VBAT = 2.2V VIN = 4.00V EFFICIENCY (%) VIN LBI LT1305 SHDN GND SW LBO 100k 301k 1% + C1 220µF 412k 1% SHUTDOWN FB PGND C2 100k 220µF 1% + VOUT 5V 400mA C1, C2: AVX TPSE227010R0100 D1: MOTOROLA MBRS130LT3 L1: COILCRAFT D03316-103 LT1305 • TA03 U Efficiency 80 VIN = 3.00V VIN = 2.00V VIN = 2.50V 70 60 1 10 100 LOAD CURRENT (mA) 1000 LT1305 • TA02 UO UO 1 LT1305 ABSOLUTE AXI U RATI GS PACKAGE/ORDER I FOR ATIO TOP VIEW GND 1 LBO 2 SHDN 3 FB 4 8 7 6 5 PGND SW VIN LBI 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 ORDER PART NUMBER LT1305CS8 S8 PART MARKING 1305 S8 PACKAGE 8-LEAD PLASTIC SO TJMAX = 100°C, θJA = 80°C/ W Consult factory for Industrial and Military grade parts. ELECTRICAL CHARACTERISTICS SYMBOL IQ VIN PARAMETER Quiescent Current Input Voltage Range CONDITIONS TA = 25°C, VIN = 2.0V, unless otherwise noted. MIN q q q TYP 120 7 MAX 200 15 UNITS µA µA V V VSHDN = 0.5V, VFB = 2V VSHDN = 1.8V 1.8 2.0 1.22 1.55 1.24 6 7 1.26 12.5 20 185 95 0.15 280 10 2.35 2.50 2.15 1.24 7 0.11 0.1 1.27 20 0.4 5 0.5 Feedback Voltage Comparator Hysteresis Feedback Pin Bias Current Oscillator Frequency Oscillator TC DC tON VCESAT Maximum Duty Cycle Switch On Time Output Line Regulation Switch Saturation Voltage Switch Leakage Current Peak Switch Current Current Limit Not Asserted 1.8V < VIN < 6V ISW = 1A VSW = 5V, Switch Off VIN = 2V VFB = 1V Current Limit Not Asserted q q q 120 q 155 0.2 86 5.6 0.06 140 0.1 %/°C % µs %/V mV µA A A A V nA V µA V V µA µA µA 75 q q q q 1.35 1.20 1.15 1.21 2 VIN = 5V LBI Trip Voltage LBI Input Bias Current LBO Output Low LBO Leakage Current VSHDNH VSHDNL ISHDN Shutdown Pin High Shutdown Pin Low Shutdown Pin Bias Current VSHDN = 5V VSHDN = 2V VSHDN = 0V q q q (Note 2) VLBI = 1V ILOAD = 100µA VLBI = 1.3V, VLBO = 5V q q q q q 1.8 8.0 3.0 0.1 20 1 The q 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. Note 2: Low-battery detector comparator is inoperative when device is in shutdown. 2 U V mV nA kHz W U U WW W LT1305 TYPICAL PERFORMANCE CHARACTERISTICS Switch On Time 8 7 160 150 140 130 120 110 DUTY CYCLE (%) ON TIME (µs) 6 5 4 3 2 –50 FREQUENCY (kHz) – 25 0 25 50 TEMPERATURE (°C) Quiescent Current 200 190 SWITCH OFF VIN = 2V QUIESCENT CURRENT (µA) QUIESCENT CURRENT (µA) 180 170 160 150 140 130 120 110 100 –50 PEAK SWITCH CURRENT (A) –25 25 50 0 TEMPERATURE (°C) LBI Pin Bias Current 20 18 16 14 12 10 8 6 4 2 0 –50 –25 25 50 0 TEMPERATURE (°C) 75 100 14 12 10 8 6 4 2 0 –50 –25 25 50 0 TEMPERATURE (°C) 75 100 FEEDBACK VOLTAGE (V) BIAS CURRENT (nA) BIAS CURRENT (nA) UW 75 LT1305 • G01 Oscillator Frequency 200 190 180 170 100 95 90 85 80 75 70 65 60 55 –25 25 50 0 TEMPERATURE (°C) 75 100 Maximum Duty Cycle 100 100 –50 50 –50 –25 25 50 0 TEMPERATURE (°C) 75 100 LT1305 • G02 LT1305 • G03 Quiescent Current 500 TA = 25°C SWITCH OFF 2.4 2.2 2.0 1.8 1.6 1.4 1.2 Current Limit 400 300 200 100 0 75 100 0 2 6 4 INPUT VOLTAGE (V) 8 10 LT1305 • G05 1.0 – 50 –25 50 25 0 TEMPERATURE (˚C) 75 100 LT1305 • G04 LT1305 • G06 FB Pin Bias Current 20 18 16 1.250 1.245 1.240 1.235 1.230 1.225 1.220 1.215 1.210 1.205 FB Voltage 1.200 –50 –25 25 50 0 TEMPERATURE (°C) 75 100 LT1305 • G07 LT1305 • G08 LT1305 • G09 3 LT1305 TYPICAL PERFORMANCE CHARACTERISTICS Low-Battery Detect Trip Point 1.250 1.245 1.240 SWITCH SATURATION VOLTAGE (mV) 350 300 250 200 150 100 50 0 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 • F12 SWITCH SATURATION VOLTAGE (mV) LBI VOLTAGE (V) 1.235 1.230 1.225 1.220 1.215 1.210 1.205 1.200 –50 –25 25 50 0 TEMPERATURE (°C) 75 100 PI FU CTIO S GND (Pin 1): Signal Ground. Tie to PGND under the package. LBO (Pin 2): Open-Collector Output of Comparator C3. Can sink 100µA. High impedance when device is in shutdown. SHDN (Pin 3): Shutdown. Pull high to shut down the LT1305. Ground for normal operation. FB (Pin 4): Feedback Input. Connects to main comparator C1 input. LBI (Pin 5): Low-Battery Comparator Input. When voltage on this pin is below 1.24V, LBO is low. VIN (Pin 6): Supply Pin. Must be bypassed with a large value capacitor to gound. Keep bypass within 0.2" of the device. SW (Pin 7): Switch Pin. Connect inductor and diode here. Keep layout short and direct to minimize radio frequency interference. 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. 4 UW LT1305 • G10 Switch Saturation Voltage 400 TA = 25°C 300 Switch Saturation Voltage ISW = 1A 250 200 150 100 50 0 – 50 – 25 0 25 50 TEMPERATURE (°C) 75 100 LT1305 • G13 U U U LT1305 BLOCK DIAGRAM VIN + C5 6 C2 4 FB – C1 OFF OSCILLATOR A3 DRIVER Q2 1× Q1 160× R2 REFERENCE 1.24V + – C3 + GND 1 5 LBI 2 LBO SHUTDOWN 3 8 PGND Figure 1. LT1305 Block Diagram 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 Figure 2. Burst Mode Operation – R1 HYSTERETIC COMPARATOR + W L1 VIN SW D1 + C4 7 CURRENT COMPARATOR 36mV R1 3Ω LT1305 • F01 U 50µs/DIV LT1305 • F02 5 LT1305 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. VBAT LT1305 5V R4 47k LBO R1 1.24V LBI R2 49.9k 1% R1 = (VTRIP –1.24V) (43.5k) HYSTERESIS ≈ 30mV Figure 3. R3 Adds Hysteresis to Low-Battery Detector VIN 100k 2N3906 R2 VIN LBO LT1305 VREF OUTPUT + VREF = 1.24V 1 + R2 R1 VIN ≥ VREF + 200mV R1 + R2 ≈ 33k Figure 4. Accessing Internal Reference 6 U 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 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. Diode Selection 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. – + R3 2M LT1305 • F03 LBI 2.2µF R1 GND () LT1305 • F04 LT1305 TYPICAL APPLICATIONS N Setting Output Voltage L1 VIN VIN SW VOUT LT1305 GND FB PGND R2 1N5817 3.5V to 6.5V + 4 CELLS VIN 100µF LT1305 SW 5V 400mA 309k FB PGND 22µH* 100k + 100µF + 220µF SHDN GND SHUTDOWN R1 VOUT = 1.24V 1 + R2 R1 () LT1305 • TA03 * COILCRAFT DO3316-223 OR SUMIDA CD105-220 ** SANYO OS-CON 5V Step-Up Converter with Reference Output 1.8V TO 4.5V INPUT 100k 2N3906 VREF OUTPUT 1.24V VIN 10µH* MBRS130LT3 SW LT1305 309k FB PGND 100k + LBO 100µF LBI GND 5V 400mA + + 220µF 2.2µF 33k *COILCRAFT DO3316-103 LT1305 • TA06 EL Panel Driver VIN 1.5V TO 8V 10Ω T1** 1:15 •6 4, 5 • 1, 2 10 1N5818 4.7µF 160V MUR160 C1* 50pF + VIN 47µF †† 0.1µF CERAMIC LT1305 SHDN GND SHUTDOWN SW 3.3M 3.3M 1N4148 1k 1/2W 10k ZETEX FZT658 FB PGND R1† 25k 51k 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. + 3.3M LT1305 • TA04 + U 4-Cell-to-5V Converter L1* 22µH 100µF** MBRS130LT3 + 150µF** LT1305 • TA05 EL PANEL CPANEL ≤ 100nF 7 LT1305 PACKAGE DESCRIPTION U 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 0.228 – 0.244 (5.791 – 6.197) 0.150 – 0.157* (3.810 – 3.988) 1 0.010 – 0.020 × 45° (0.254 – 0.508) 0.008 – 0.010 (0.203 – 0.254) 0°– 8° TYP 2 3 4 0.053 – 0.069 (1.346 – 1.752) 0.004 – 0.010 (0.101 – 0.254) 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 LT1129 LT1182/83/84 LT1301 LT1302 LT1303 LT1372 LTC ®1472 DESCRIPTION Micropower Low Dropout Regulator LCD and CCFL Backlight Controller 5V to 12V/200mA Step-Up DC/DC Converter 2-Cell to 5V/600mA Step-Up DC/DC Converter Micropower DC/DC Converter with Low-Battery Detect 500kHz Step-Up PWM, 1.5A Switch PCMCIA Host Switch with Protection COMMENTS 700mA Output Current in SO-8 Package High Efficiency and Excellent Backlight Control Range 120µA Quiescent Current 200µA Quiescent Current 2V to 5V at 200mA Low Noise, Fixed Frequency Operation Includes Current Limit and Thermal Shutdown 8 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7487 (408) 432-1900 q FAX: (408) 434-0507 q TELEX: 499-3977 LT/GP 0595 10K • PRINTED IN USA © LINEAR TECHNOLOGY CORPORATION 1995