AS1337_1 AMSCO
Document overview
- Manufacturer or author: Provided By digicamel.com
- PDF pages: 14
Technical content
1 General Description
Buck Boost function is realized. the supply of real-time-clocks or memories. is disconnected and the output is discharged. which detects output power fail of 10%.
2 Key Features
3 Applications
Table 1. Standard Products Figure 1. AS1337 - Typical Application Diagram – Dual Cell to 3.3V Synchronous Boost Converter
4 Pin Assignments
Figure 2. Pin Assignments (Top View) Table 2. Pin Descriptions switch is connected from this pin to VIN to minimize EMI. Note: An optional Schottky diode can be connected between this pin and VOUT. Enable Pin. Logic controlled enable input. POK 6 POK. High when VOUT is within regulation. power level and the internal series resistance of the supply.
5 Absolute Maximum Ratings
Table 3. Absolute Maximum Ratings State Surface Mount Devices”. packages is matte tin (100% Sn).
6 Electrical Characteristics
Table 4. Electrical Characteristics
- Minimum VIN operation after start-up is only limited by the battery’s ability to provide the necessary power as it
enters a deeply discharged state.
- IQPWS is measured at VOUT. Multiply this value by VOUT/VIN to get the equivalent input (battery) current.
SQC (Statistical Quality Control) methods.
7 Typical Operating Characteristics
VOUT = 3.3V, CIN = 10µF, COUT = 22µF, L1 = 4.7µH, TAMB = +25°C (unless otherwise specified). Figure 3. Efficiency vs. IOUT - Down Conversion Mode Figure 4. Efficiency vs. I OUT - Step-up Mode Figure 5. Efficiency vs. Input Voltage Figure 6. Output Current vs. Input Voltage
8 Detailed Description
and PMOS switches, the device maintains high-efficiency from light to heavy loads. power conversion efficiency over a wide output power range, thus increasing battery life in these types of devices. falls below a factory programmed threshold. Figure 13. AS1337 - Block Diagram
www.austriamicrosystems.com/DC-DC_Step-Up/AS1337 Revision 1.04 8 - 14 AS1337 Datasheet - Detailed Description Low-Voltage Start-Up and Soft Start The AS1337 requires a VIN of only 0.85V (typ) or higher to start up. The low-voltage start-up circuitry controls the inter- nal switches and provides a soft start function, where the inductor current during start up is limited for a certain time. This soft start and in rush current limitation feature provides also a smooth curve of VOUT after start up and makes the overshoot of VOUT minimal. To achieve this, a 100pF capacitor as CFF is needed (see Figure 13 on page 7) to speed up the feedback loop. After a certain time a bigger inductor current is allowed and the soft start is disabled. Low-Noise Fixed-Frequency Operation Oscillator The AS1337 switching frequency is internally fixed at 1.2MHz allowing the use of very small external components. 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 LX as the inductor current approaches zero. This is accomplished by damping the resonant circuit formed by the inductor and the capacitance on pin LX. Setting Output Voltage A voltage divider from VOUT to GND programs the output voltage from 2.5V to 5V via pin FB as: VOUT = 1.23V(1 + (R1/R2)) (EQ 1) Powersave Operation 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 AS1337 powers up and begins normal PWM operation. COUT (see Figure 13 on page 7) recharges, causing the AS1337 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 AS1337 turns on less frequently. When the load current increases above the powersave threshold, the AS1337 will resume continuous, seamless PWM operation. Note: 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 15pF to 220pF. Buck Mode The AS1337A offers a low power buck mode for VIN > VOUT operation. The switching during buck mode is similar to boost mode, but with forced reduction of some energy internal to be able to provide a buck conversion.
www.austriamicrosystems.com/DC-DC_Step-Up/AS1337 Revision 1.04 9 - 14 AS1337 Datasheet - Detailed Description Shutdown When pin EN is low the AS1337 is switched off and <1µA current is drawn from battery; when pin EN is high the device is switched on. If EN 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 EN is not used, it should be connected directly to pin VOUT. Caution: Because of the feedthrough the output voltage is the same as the input voltage during shutdown. If VIN > VOUT the output voltage will jump to the value of the input voltage when the device switches into shut- down. During normal operation the device is in down conversion mode. Shutdown Battery Feedthrough (AS1337A) In shutdown the battery input of the AS1337A is connected to the output through the inductor and the small internal synchronous rectifier P-FET. This allows the input battery to provide backup power for devices such as an idle micro- controller, memory, or real-time-clock, without the usual diode forward drop. In this way a separate backup battery is not needed. Shutdown Battery Disconnect (AS1337B) The AS1337B is designed to allow true output disconnect by opening both P-channel MOSFET rectifiers. During Shut- down VOUT is discharged via the internal NMOS transistor and connected to GND. POK Function The POK output indicates if the output voltage is within 88% (typ.) of the nominal voltage level. As long as the output voltage is within regulation the open-drain POK output is high impedance. The POK output can be tied to VIN or to VOUT or to any external voltage up to VIN or VOUT via a pull-up resistance (see Figure 1 on page 1). If the output volt- age drops below 88% (typ.) of the nominal voltage the POK pin is pulled to GND. Note: It is important to consider that in shutdown mode the POK output is pulled to VIN in order to save current.
9 Application Information
converters are perfectly suited. Figure 14. Single AA Cell to 3.3V Synchronous Boost Converter Figure 15. Single Lithium Cell to 5V
allow the use of low value, low profile inductors and tiny external ceramic capacitors. compared to less expensive powdered iron types, which result in improved converter efficiency. radiated noise is a concern, a toroidal or shielded inductor can be used. A 10µF capacitor is recommend for CIN as well as a 22µF for COUT. Small-sized ceramic capacitors are recommended. wide voltage and temperature ranges. input capacitor is sufficient for most applications. Larger values may be used without limitations. The high-speed operation of the AS1337 requires proper layout for optimum performance. ! 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. Table 5. Recommended External Components
The devices are available in a TDFN (3x3mm) 8-pin package. Figure 16. TDFN (3x3mm) 8-pin Package
- Figure 16 is shown for illustration only.
- All dimensions are in millimeters; angles in degrees.
- Dimensioning and tolerancing conform to ASME Y14.5 M-1994.
- N is the total number of terminals.
- The terminal #1 identifier and terminal numbering convention shall conform to JEDEC 95-1, SPP-012. Details of ter-
- Dimension b applies to metallized terminal and is measured between 0.15mm and 0.30mm from the terminal tip.
- ND refers to the maximum number of terminals on side D.
- Unilateral coplanarity zone applies to the exposed heat sink slug as well as the terminals
The device is available as the standard products listed in Table 6. Note: All products are RoHS compliant and Pb-free. Table 6. Ordering Information
www.austriamicrosystems.com/DC-DC_Step-Up/AS1337 Revision 1.04 14 - 14 AS1337 Datasheet Copyrights Copyright © 1997-2009, austriamicrosystems 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 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 life-sustaining 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 Headquarters austriamicrosystems 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.austriamicrosystems.com/contact