AS1322B-BTTT

AS1322 L o w Vo l ta g e , M i c r o p o w e r, D C - D C St e p - U p C o n v e r t e r s D a ta S he e t 1 General Description The AS1322A and the AS1322B are synchronous, fixed frequency, very high-efficiency DC-DC boost converters capable of supplying 3.3V at 150mA from a single AAsupply. Compact size and minimum external parts requirements make these devices perfect for modern portable devices. High-speed switching frequency (1.2MHz) and internally compensated PWM current mode design provide highlyreliable DC-DC conversion, especially when driving white LEDs. The converters are available as the standard products listed in Table 1. Table 1. Standard Products Model AS1322A AS1322B Light Load Switching Automatic Powersave Operation Continuous Switching 2 Key Features ! ! ! ! ! ! ! ! ! ! ! ! ! ! 95% Efficiency Single-Cell Operation Delivers 160mA @ 3.3V (from Single AA Cell) Delivers 220mA @ 5.0V (from Two AA Cells) Delivers 570mA @ 3.3V (from Two AA Cells) Low Start-Up Voltage: 0.85V High-Speed Fixed-Frequency: 1.2MHz Internal PMOS Synchronous Rectifier Automatic Powersave Operation (AS1322A) Continuous Switching at Light Loads (AS1322B) Anti-Ringing Control Minimizes EMI Logic Controlled Shutdown (< 1µA) Output Range: 2.5 to 5.0V 6-pin TSOT-23 Package The devices contain two internal MOSFET switches: one NMOS switch and one PMOS synchronous rectifier. Anti-ringing control circuitry reduces EMI by damping the inductor in discontinuous mode, and the devices exhibit extremely low quiescent current (< 1µA) in shutdown. In shutdown mode the battery is connected to the output and VOUT is held at approximately VIN - 0.6V. The AS1322 is available in a 6-pin TSOT-23 package. 3 Applications The AS1322 is ideal for low-power applications where ultra-small size is critical as in medical diagnostic equipment, hand-held instruments, pagers, digital cameras, remote wireless transmitters, MP3 players, LCD bias supplies, cordless phones, GPS receivers, and PC cards. Figure 1. Typical Application Diagram – Single Cell to 3.3V Synchronous Boost Converter L1 4.7µH 1 AA Battery C1 10µF 6 SW 5 VOUT VIN AS1322 4 3 R1 1.02MΩ 1% FB C2 10µF VOUT 3.3V 160mA On Off SHDNN 2 GND R2 604kΩ 1% www.austriamicrosystems.com Revision 1.07 1 - 17 AS1322 Data Sheet - Pin Assignments 4 Pin Assignments Figure 2. Pin Assignments (Top View) SW 1 6 VIN GND 2 AS1322 5 VOUT FB 3 4 SHDNN Pin Descriptions Table 2. Pin Descriptions Pin Name Pin Number Description Switch Pin. Connect an inductor between this pin and VIN. Keep the PCB trace lengths as short and wide as is practical to reduce EMI and voltage overshoot. If the inductor current falls to zero, or pin SHDNN is low, an internal 100Ω anti-ringing switch is connected from this pin to VIN to minimize EMI. Note: An optional Schottky diode can be connected between this pin and VOUT. Signal and Power Ground. Provide a short, direct PCB path between this pin and the negative side of the output capacitor(s). Feedback Pin. Feedback input to the gm error amplifier. Connect a resistor divider tap to this pin. The output voltage can be adjusted from 2.5 to 5V by: VOUT = 1.23V[1 + (R1/R2)] Shutdown Pin. Logic controlled shutdown input. 1 = Normal operation, 1.2MHz typical operating frequency. 0 = Shutdown; quiescent current 2.3V, the start-up circuitry is disabled and normal fixed-frequency PWM operation is initiated. In this mode, the AS1322 operates independent of VIN, allowing extended operating time as the battery can drop to several tenths of a volt without affecting output regulation. The limiting factor for the application is the ability of the battery to supply sufficient energy to the output. www.austriamicrosystems.com Revision 1.07 7 - 17 AS1322 Data Sheet - Detailed Description Low-Noise Fixed-Frequency Operation Oscillator The AS1322 switching frequency is internally fixed at 1.2MHz allowing the use of very small external components. Error Amplifier The integrated error amplifier is an internally compensated trans-conductance (gm) type (current output). The internal 1.23V reference voltage is compared to the voltage at pin FB to generate an error signal at the output of the error amplifier. A voltage divider from VOUT to GND programs the output voltage from 2.5 to 5V via pin FB as: VOUT = 1.23V(1 + (R1/R2)) (EQ 1) Current Sensing A signal representing the internal NMOS-switch current is summed with the slope compensator. The summed signal is compared to the error amplifier output to provide a peak current control command for the PWM. Peak switch current is limited to approximately 850mA independent of VIN or VOUT. Zero Current Comparator The zero current comparator monitors the inductor current to the output and shuts off the PMOS synchronous rectifier once this current drops to 20mA (approx.). This prevents the inductor current from reversing polarity and results in improved converter efficiency at light loads. Anti-Ringing Control Anti-ringing control circuitry prevents high-frequency ringing on pin SW as the inductor current approaches zero. This is accomplished by damping the resonant circuit formed by the inductor and the capacitance on pin SW (CSW). Powersave Operation (AS1322A) In light load conditions, the integrated powersave feature removes power from all circuitry not required to monitor VOUT. When VOUT has dropped approximately 1% from nominal, the AS1322A powers up and begins normal PWM operation. COUT (see Figure 15 on page 7) recharges, causing the AS1322A to re-enter powersave mode as long as the output load remains below the powersave threshold. The frequency of this intermittent PWM is proportional to load current; i.e., as the load current drops further below the powersave threshold, the AS1322A turns on less frequently. When the load current increases above the powersave threshold, the AS1322A will resume continuous, seamless PWM operation. Notes: 1. An optional capacitor (CFF) between pins VOUT and FB in some applications can reduce VOUTp-p ripple and input quiescent current during powersave mode. Typical values for CFF range from 15 to 220pF. 2. In powersave mode the AS1322A draws only 30µA from the output capacitor(s), greatly improving converter efficiency. Shutdown When pin SHDNN is low the AS1322 is switched off and 3.6V Larger inductor values allow greater output current capability by reducing the inductor ripple current. Increasing the inductance above 10µH will increase size while providing negligible improvement in output current capability. The approximate output current capability of the AS1322 versus inductor value is given in: V IN ⋅ D I OUT ( MAX ) = η ⋅ ⎛ I P – ----------------- ⎞ ⋅ ( 1 – D ) ⎝ f ⋅ L ⋅ 2⎠ Where: η is the estimated efficiency; IP is the peak current limit value (0.6A); VIN is the input voltage; D is the steady-state duty ratio = (VOUT - VIN)/VOUT; f is the switching frequency (1.2MHz typ); L is the inductor value. The inductor current ripple is typically set for 20 to 40% of the maximum inductor current (IP). High-frequency ferrite core inductor materials reduce frequency dependent power losses compared to less expensive powdered iron types, which result in improved converter efficiency. The inductor should have low ESR to reduce the I R power losses, and must be able to handle the peak inductor current without saturating. Molded chokes and some chip inductors normally do not have enough core to support the peak inductor currents of the AS1322 (850mA typ). To minimize radiated noise, use a toroid, pot core, or shielded bobbin inductor. Table 5. Recommended Inductors Part Number MOS6020-103ML MOS6020-472ML MOS6020-332ML CDRH4D18-100 CDRH4D18-6R8 CR43-6R8 CDRH4D18-4R7 L 10µH 4.7µH 3.3µH 10µH 6.8µH 6.8µH 4.7µH DCR 93mΩ 50mΩ 46mΩ 200mΩ 200mΩ 131.2mΩ 162mΩ Current Rating Dimensions (L/W/T) 1A 1.5A 1.8A 0.61A 0.76A 0.95A 0.84A 6.8x6.0x2.4mm 6.8x6.0x2.4mm 6.8x6.0x2.4mm 6.9x5.0x2.0mm 6.9x5.0x2.0mm 4.8x4.3x3.5mm 6.9x5.0x2.0mm Sumida www.sumida.com Manufacturer Coilcraft www.coilcraft.com 2 (EQ 2) www.austriamicrosystems.com Revision 1.07 11 - 17 AS1322 Data Sheet - Application Information Figure 20. Efficiency Comparison of Different Inductors, VIN = 1.5V, VOUT = 3.3V 90 85 80 75 92 90 88 Efficiency (%) Efficiency (%) 70 65 60 55 50 45 40 0.1 1 10 10uH - Coi l cr af t (M OS6020-103M L) 10uH - Sumi da(CDRH4D18-100) 6. 8uH - Sumi da(CDRH4D18-6R8) 6. 8uH - Sumi da(CR43-6R8) 4. 7uH - Coi l cr af t (M OS6020-472M L) 4. 7 uH - Sumi da(CDRH4D18-4R7) 3. 3 uH - Coi l cr af t (M OS6020-332M L) 86 84 82 10uH - Coi l cr af t (M OS6020-103M L) 80 78 76 10uH - Sumi da(CDRH4D18-100) 6. 8uH - Sumi da(CDRH4D18-6R8) 6. 8uH - Sumi da(CR43-6R8) 4. 7uH - Coi l c r af t (M OS6020-472M L) 4. 7 uH - Sumi da(CDRH4D18-4R7) 3. 3 uH - Coi l c r af t (M OS6020-332M L) S i 8 Output Current (mA) 10 Output Current (mA) 100 Output Capacitor Selection Low ESR capacitors should be used to minimize VOUT ripple. Multi-layer ceramic capacitors are recommended since they have extremely low ESR and are available in small footprints. A 2.2 to 10µF output capacitor is sufficient for most applications. Larger values up to 22µF may be used to obtain extremely low output voltage ripple and improve transient response. An additional phase lead capacitor may be required with output capacitors larger than 10µF to maintain acceptable phase margin. X5R and X7R dielectric materials are recommended due to their ability to maintain capacitance over wide voltage and temperature ranges. Table 6. Recommended Output Capacitor Part Number JMK212BJ226MG-T Input Capacitor Selection Low ESR input capacitors reduce input switching noise and reduce the peak current drawn from the battery. Ceramic capacitors are recommended for input decoupling and should be located as close to the device as is practical. A 4.7µF input capacitor is sufficient for most applications. Larger values may be used without limitations. Table 7. Recommended Input Capacitor Part Number C TC Code Rated Voltage Dimensions (L/W/T) X7R 6.3V 3.2x1.6x1.6mm Manufacturer Murata www.murata.com C 22µF ±20% TC Code Rated Voltage X5R 6.3V Dimensions (L/W/T) 2x1.3x1.3mm Manufacturer Taiyo Yuden www.t-yuden.com GRM31CR70J106KA01L 10µF ±10% Diode Selection A Schottky diode should be used to carry the output current for the time it takes the PMOS synchronous rectifier to switch on. For VOUT < 4.5V a Schottky diode is optional, although using one will increase device efficiency by 2 to 3%. Note: Do not use ordinary rectifier diodes, since the slow recovery times will compromise efficiency. www.austriamicrosystems.com Revision 1.07 12 - 17 AS1322 Data Sheet - Application Information PCB Layout Guidelines The high-speed operation of the AS1322 requires proper layout for optimum performance. Figure 21 shows the recommended component layout. ! ! ! ! ! A large ground pin copper area will help to lower the device temperature. A multi-layer board with a separate ground plane is recommended. Traces carrying large currents should be direct. Trace area at pin FB should be as small as is practical. The lead-length to the battery should be as short as is practical. Figure 21. Recommended Single-Layer Component Placement Optional 1 SW VIN 6 AS1322 VIN CIN R2 2 GND VOUT 5 SHDNN 3 FB SHDNN 4 R1 COUT VOUT www.austriamicrosystems.com Revision 1.07 13 - 17 AS1322 Data Sheet - Package Drawings and Markings 10 Package Drawings and Markings The device is available in a 6-pin TSOT-23 package. Figure 22. 6-pin TSOT-23 Package 3 4 A A 3 4 6 7 Notes: 1. Dimensioning and tolerancing conform to ASME Y14.5M - 1994. 2. Dimensions are in millimeters. 3. Dimension D does not include mold flash, protrusions, or gate burrs. Mold flash, protrusions, and gate burrs shall not exceed 0.15mm per end. Dimension E1 does not include interlead flash or protrusion. Interlead flash or protrusion shall not exceed 0.15mm per side. Dimensions D and E1 are determined at datum H. 4. The package top can be smaller than the package bottom. Dimensions D and E1 are determined at the outermost extremes of the plastic body exclusive of mold flash, tie bar burrs, gate burrs, and interlead flash, but include any mistmatches between the top of the package body and the bottom. D and E1 are determined at datum H. 5. Datums A and B are to be determined at datum H. www.austriamicrosystems.com Revision 1.07 14 - 17 AS1322 Data Sheet - Package Drawings and Markings 6. These dimensions apply to the flat section of the lead between 0.08 and 0.15mm from the lead tip. 7. Dimension b does not include dambar protrusion. Allowable dambar protrusion shall be 0.08mm total in excess of the b dimension at the maximum material condition. The dambar cannot be located on the lower radius of the foot. Minimum space between the protrusion and an adjacent lead shall not be less than 0.77mm. Symbol A A1 A2 b b1 c c1 D E E1 e e1 L L1 L2 N R R1 Min 0.01 0.84 0.30 0.31 0.12 0.08 Typ 0.05 0.87 0.35 0.15 0.13 2.90BSC 2.80BSC 1.60BSC 0.95BSC 1.90BSC 0.40 0.60REF 0.25BSC 6 Max 1.00 0.10 0.90 0.45 0.39 0.20 0.16 Notes 6,7 6,7 6 6 3,4 3,4 3,4 0.30 0.50 0.10 0.10 0º 4º 0.25 8º θ θ1 aaa bbb ccc ddd 4º 10º 12º Tolerances of Form and Position 0.15 0.25 0.10 0.20 1,2 1,2 1,2 1,2 www.austriamicrosystems.com Revision 1.07 15 - 17 AS1322 Data Sheet - Ordering Information 11 Ordering Information The device is available as the standard products listed in Table 8. Table 8. Ordering Information Model AS1322A-BTTT AS1322B-BTTT Marking ASKQ ASKZ Descriptiom Low Voltage, Micropower, DC-DC Step-Up Converter with Automatic Powersave Operation Low Voltage, Micropower, DC-DC Step-Up Converter with Continuous Switching Delivery Form Tape and Reel Tape and Reel Package 6-pin TSOT-23 6-pin TSOT-23 All devices are RoHS compliant and free of halogene substances. www.austriamicrosystems.com Revision 1.07 16 - 17 AS1322 Data Sheet Copyrights Copyright © 1997-2007, austriamicrosystems AG, Schloss Premstaetten, 8141 Unterpremstaetten, Austria-Europe. Trademarks Registered ®. All rights reserved. The material herein may not be reproduced, adapted, merged, translated, stored, or used without the prior written consent of the copyright owner. All products and companies mentioned are trademarks or registered trademarks of their respective companies. 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