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
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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%
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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.
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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)
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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.
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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.
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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
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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.
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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
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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.
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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.
Disclaimer
Devices sold by austriamicrosystems AG are covered by the warranty and patent indemnification provisions appearing in its Term of Sale. austriamicrosystems AG makes no warranty, express, statutory, implied, or by description regarding the information set forth herein or regarding the freedom of the described devices from patent infringement. austriamicrosystems AG reserves the right to change specifications and prices at any time and without notice. Therefore, prior to designing this product into a system, it is necessary to check with austriamicrosystems AG for current information. This product is intended for use in normal commercial applications. Applications requiring extended temperature range, unusual environmental requirements, or high reliability applications, such as military, medical life-support or lifesustaining equipment are specifically not recommended without additional processing by austriamicrosystems AG for each application. For shipments of less than 100 parts the manufacturing flow might show deviations from the standard production flow, such as test flow or test location. The information furnished here by austriamicrosystems AG is believed to be correct and accurate. However, austriamicrosystems AG shall not be liable to recipient or any third party for any damages, including but not limited to personal injury, property damage, loss of profits, loss of use, interruption of business or indirect, special, incidental or consequential damages, of any kind, in connection with or arising out of the furnishing, performance or use of the technical data herein. No obligation or liability to recipient or any third party shall arise or flow out of austriamicrosystems AG rendering of technical or other services.
Contact Information
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