AS1322_13 AMSCO
Document overview
- Manufacturer or author: Provided By digicamel.com
- PDF pages: 18
Technical content
1 General Description
DC conversion, especially when driving white LEDs. switch and one PMOS synchronous rectifier. quiescent current (< 1µA) in shutdown. is held at approximately VIN - 0.6V. The AS1322 is available in a 6-pin TSOT-23 package. Figure 1. Typical Application Diagram – Single Cell to 3.3V
2 Key Features
3 Applications
4 Pin Assignments
Figure 2. Pin Assignments (Top View)
4.1 Pin Descriptions
Note: An optional Schottky diode can be connected between this pin and VOUT . negative side of the output capacitor(s).
4 SHDNN
Shutdown Pin . Logic controlled shutdown input. 1 = Normal operation, 1.2MHz typical operating frequency. 0 = Shutdown; quiescent current <1µA. If SHDNN is undefined, pin SW may ring.
5 VOUT
Output Voltage Sense Input and Drain of the Internal PMOS Synchronous Rectifier . approximately VIN - 0.6V during shutdown.
6 VIN
series resistance of the supply.
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5 Absolute Maximum Ratings
Stresses beyond those listed in Table 3 may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in Section 6 Electrical Characteristics on page 4 is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. T able 3. Absolute Maximum Ratings Parameter Min Max Units Notes VIN to GND -0.3 7 V SHDNN, SW to GND -0.3 7 V FB to GND -0.3 5 V VOUT -0.3 7 V Operating Temperature Range -40 +85 ºC Storage Temperature Range -65 +125 ºC Package Body Temperature +260 ºC The reflow peak soldering temperature (body temperature) specified is in accordance with IPC/ JEDEC J-STD-020 “Moisture/Reflow Sensitivity Classification for Non-Hermetic Solid State Surface Mount Devices”. The lead finish for Pb-free leaded packages is matte tin (100% Sn). Moisture Sensitive Level 1 Represents an unlimited floor life time
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6 Electrical Characteristics
Note: All limits are guaranteed. The parameters with min and max values are guaranteed with production tests or SQC (Statistical Quality Control) methods. T able 4. Electrical Characteristics Symbol Parameter Conditions Min Typ Max Units Minimum Start-Up Voltage I LOAD = 1mA 0.85 1 V Minimum Operating Voltage SHDNN = VIN 1. Minimum VIN operation after start-up is only limited by the battery’s ability to provide the necessary power as it enters a deeply dis- charged state. 0.65 0.85 V Output Voltage Adjust Range T AMB = 25ºC 2.5 5 V VFB Feedback Voltage T AMB = TMIN to TMAX 1.192 1.23 1.268 V IFB Feedback Input Current VFB = 1.25V 2. Specification is guaranteed by design and not 100% production tested. 1 nA IQPWS Quiescent Current (Powersave Operation) VFB = 1.4V , AS1322A only 3. IQPWS is measured at VOUT . Multiply this value by VOUT /VIN to get the equivalent input (battery) current. 30 50 µA IQSHDNN Quiescent Current (Shutdown) V SHDNN = 0V 0.01 1 µA IQ Quiescent Current (Active) VFB = 1.4V , AS1322B only 150 300 µA INMOSSWL NMOS Switch Leakage V SW = 5V 0.1 5 µA IPMOSSWL PMOS Switch Leakage V SW = 0V 0.1 5 µA RONNMOS NMOS Switch On Resistance VOUT = 3.3V 0.35 0.8 Ω VOUT = 5V 0.20 0.7 RONPMOS PMOS Switch On Resistance VOUT = 3.3V 0.45 0.8 Ω VOUT = 5V 0.30 0.7 INMOS NMOS Current Limit V IN = 2.5V 850 mA IPS Powersave Operation Current Threshold AS1322A only 2 3 mA Max Duty Cycle V FB = 1V, TAMB = TMIN to TMAX 80 87 % fSW Switching Frequency TAMB = 25ºC 0.95 1.2 1.5 MHz TAMB = TMIN to TMAX 0.85 1.2 1.5 VSHDNNH SHDNN Input High 1 V VSHDNNL SHDNN Input Low 0.35 V ISHDNN SHDNN Input Current V SHDNN = 5.0V 0.01 1 µA
7 Typical Operating Characteristics
Figure 3. Powersave mode threshold vs. VIN , Figure 4. Efficiency vs. Output Current, Figure 5. Output Voltage vs. T emperature; Figure 6. Output Voltage vs. Battery Voltage; Figure 7. Startup Voltage vs. Output Current; Figur e 8. Output Current vs. Battery Voltage;
8 Detailed Description
maintain high-efficiency from light to heavy loads. a wide output power range, thus increasing battery life in these types of devices. ripple at the expense of light load efficiency. Figure 15. AS1322 - Block Diagram
8.1 Low-Voltage Start-Up
maximum peak inductor current of 850mA (typ), with 1.5ms (approx.) off-time during start-up, allowing the devices to start up into an output load. limiting factor for the application is the ability of the battery to supply sufficient energy to the output.
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8.2 Low-Noise Fixed-Frequency Operation
8.2.1 Oscillator
The AS1322 switching frequency is internally fixed at 1.2MHz allowing the use of very small external components.
8.2.2 Error Amplifier
The integrated error amplifier is an internally compensated trans-conductance (g m ) 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 + (R 1/R 2)) (EQ 1)
8.2.3 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 .
8.2.4 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.
8.2.5 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 (C SW ).
8.3 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 (C FF ) between pins VOUT and FB in some applications can reduce VOUTp-p ripple and input quiescent current during powersave mode. Typical values for C FF range from 15 to 220pF. 2. In powersave mode the AS1322A draws only 30µA from the output capacitor(s), greatly improving converter efficiency.
8.4 Shutdown
When pin SHDNN is low the AS1322 is switched off and <1µA current is drawn from battery; when pin SHDNN is high the device is switched on. If SHDNN is driven from a logic-level output, the logic high-level (on) should be referenced to VOUT to avoid intermittently switching the device on. Note: If pin SHDNN is not used, it should be connected directly to pin OUT. V OUT is held at approximately VIN - 0.6V during shutdown. In shutdown the battery input is connected to the output through the inductor and the internal synchronous rectifier P-FET. Due to the body diode of the internal synchronous rectifier PFET, VOUT is held at approximately VIN - 0.6V during shutdown. This allows the input battery to provide backup power for devices such as an idle microcontroller, memory, or real-time-clock, without the usual diode forward drop. In this way a separate backup battery is not needed.
9 Application Information
goods, professional audio equipment, medical equipment, industrial controllers to name a few applications. Along with Figure 1 on page 1 , Figures 16-19 depict a few of the many applications for which the AS1322 converters are perfectly suited. Figure 16. Single AA Cell to 3.3V Synchronous Boost Converter with Load Disconnect in Shutdown Figure 17. Single Lithium Cell to 5V, 250mA
9.1 Output Voltage Ripple
Use a higher output capacitor, up to 44µF and a higher input capacitor (22µF). divider to GND, R1 should not be less than 100k Ω . Due to noise and to their non linear behavior, the use of potentiometers is not recommended. Figure 20. AS1322 - Typical Application for lower Output Voltage Ripple deliver a more accurate measurement result. voltage ripple. If VIN is higher than VOUT the AS1322 stops switching and VIN is connected to VOUT via the inductor and the internal P-FET. Figure 21. Output Voltage Ripple vs. Input Voltage; VOUT = 2.8V, IOUT = 0.8mA
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9.2 External Component Selection
9.2.1 Inductor Selection
The fast switching frequency (1.2MHz) of the AS1322 allows for the use of small surface mount or chip inductor for the external inductor (see Figure 15 on page 7) . The required minimum values for the external inductor are: 3.3µH for applications ≤ 3.6V 4.7µH for applications > 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: Where: η is the estimated efficiency; I P 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 (I P). 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. T able 5. Recommended Inductors Part Number L DCR Current Rating Dimensions (L/W/T) Manufacturer MOS6020-103ML 10µH 93m Ω 1A 6.8x6.0x2.4mm Coilcraft CDRH4D18-100 10µH 200m Ω 0.61A 6.9x5.0x2.0mm Sumida (EQ 2) IOUT MAX ( ) η IP V IN D⋅
Figure 22. Efficiency Comparison of Different Inductors, VIN = 1.5V, VOUT = 3.3V
9.2.2 Output Capacitor Selection
used to obtain extremely low output voltage ripple and improve transient response. dielectric materials are recommended due to their ability to maintain capacitance over wide voltage and temperature ranges. Input Capacitor Selection. Low ESR input capacitors reduce input switching noise and reduce the peak current drawn from the battery. is sufficient for most applications. Larger values may be used without limitations. 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. Table 6. Recommended Output Capacitor
9.3 PCB Layout Guidelines
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 23. Recommended Single-Layer Component Placement
The device is available in a 6-pin TSOT-23 package. Figure 24. 6-pin TSOT-23 Package
Figure 25. 6-pin TSOT-23 Marking
www.ams.com/DC-DC_Step-Up/AS1322 Revision 1.10 17 - 18 AS1322 Datasheet The device is available as the standard products listed in Table 8 . Note: All products are RoHS compliant. Buy our products or get free samples online at ICdirect: http://www.ams.com/ICdirect Technical Support is found at http://www.ams.com/Technical-Support For further information and requests, please contact us mailto:sales@ams.com or find your local distributor at http://www.ams.com/distributor T able 8. Ordering Information Ordering Code Marking Description Delivery Form Package AS1322A-BTTT ASKQ Low Voltage, Micropower, DC-DC Step-Up Converter with Automatic Powersave Operation Tape and Reel 6-pin TSOT-23 AS1322B-BTTT ASKZ Low Voltage, Micropower, DC-DC Step-Up Converter with Continuous Switching Tape and Reel 6-pin TSOT-23
www.ams.com/DC-DC_Step-Up/AS1322 Revision 1.10 18 - 18 AS1322 Datasheet - O r d e r i n g I n f o r m a t i o n Copyrights Copyright © 1997-2010, ams AG, Tobelbaderstrasse 30, 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 ams AG are covered by the warranty and patent indemnification provisions appearing in its Term of Sale. ams 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. ams 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 ams 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 life-sustaining equipment are specifically not recommended without additional processing by ams 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 ams AG is believed to be correct and accurate. However, ams 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 indi- rect, special, incidental or consequential damages, of any kind, in connection with or arising out of the furnishing, performance or use of the tech- nical data herein. No obligation or liability to recipient or any third party shall arise or flow out of ams AG rendering of technical or other services. Contact Information Headquarters ams AG Tobelbaderstrasse 30 A-8141 Unterpremstaetten, Austria Tel: +43 (0) 3136 500 0 Fax: +43 (0) 3136 525 01 For Sales Offices, Distributors and Representatives, please visit: http://www.ams.com/contact