DATASHEET SEARCH SITE
Document overview
- Manufacturer or author: Provided By digicamel.com
- PDF pages: 16
Technical content
The technical content of this austriamicrosystems datasheet is still valid. Contact information: Headquarters: ams AG Tobelbaderstrasse 30
8141 Unterpremstaetten, Austria
Tel: +43 (0) 3136 500 0 e-Mail: ams_sales@ams.com Please visit our website at www.ams.com
1 General Description
that a Buck Boost function is realized. nected and the output is discharged.
2 Key Features
3 Applications
Figure 1. AS1337 - Typical Application Diagram – Dual Cell to 3.3V Synchronous Boost Converter
4 Pin Assignments
Figure 2. Pin Assignments (T op View) VOUT to the output filter capacitor(s) should be as short and wide as is practical. Note: An optional Schottky diode can be connected between this pin and VOUT. PGND 3 Power Ground. Provide a short, direct PCB path between this pin and the output capacitor(s). Enable Pin. Logic controlled enable input. POK 6 POK. High when VOUT is within regulation. FB 8 Feedback Pin. Feedback input to the gm error amplifier. Connect a resistor divider tap to this pin.
5 Absolute Maximum Ratings
absolute maximum rating conditions for extended periods may affect device reliability. Table 3. Absolute Maximum Ratings
6 Electrical Characteristics
Table 4. Electrical Characteristics
- Minimum V IN operation after start-up is only limited by the battery’s ability to provide the necessary power as it enters a deeply dis-
- I QPWS is measured at VOUT. Multiply this value by VOUT/VIN to get the equivalent input (battery) current.
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. IOUT - Step-up Mode Figure 5. Efficiency vs. Input Voltage Figure 6. Output Current vs. Input Voltage
8 Detailed Description
ciency from light to heavy loads. thus increasing battery life in these types of applications. power converter at light loads. The powersave mode is initiated if the output load current falls below a factory programmed threshold. The Overtemperature protection circuitry turn-off both switches for a short time when the temperature reaches 145ºC in the device . Figure 13. AS1337 - Block Diagram
www.austriamicrosystems.com/DC-DC_Step-Up/AS1337 Revision 1.05 8 - 15 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 internal 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 pro- vides 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 damp- ing 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 pow- ersave threshold. The frequency of this intermittent PWM is proportional to load current; i.e., as the load current drops further below the power- save 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 Both devices, the AS1337A and the AS1337B, offer a low power buck mode for VIN > VOUT operation. The switching during buck mode is simi- lar to boost mode, but with forced reduction of some energy internal to be able to provide a buck conversion. 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 shutdown. During normal operation the device is in down conversion mode. ams AG Technical content still valid
www.austriamicrosystems.com/DC-DC_Step-Up/AS1337 Revision 1.05 9 - 15 AS1337 Datasheet - Detailed Description 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 microcontroller, 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 Shutdown 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 voltage 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. ams AG Technical content still valid
9 Application Information
goods, professional audio equipment, medical equipment, industrial controllers to name a few applications. Figure 14. Single AA Cell to 3.3V Synchronous Boost Converter Figure 15. Single Lithium Cell to 5V
external ceramic capacitors. The inductor should have low ESR to reduce the I²R power losses, and must be able to handle the peak inductor current without saturating. which result in improved converter efficiency. cern, a toroidal or shielded inductor can be used. capacitors are recommend as they retain capacitance over wide ranges of voltages and temperatures. 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. tions. 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
Figure 16. TDFN (3x3mm) 8-pin Marking Table 6. Packaging Code YYWWIZZ
Figure 17. TDFN (3x3mm) 8-pin Package
The device is available as the standard products listed in Table 7. Note: All products are RoHS compliant and Pb-free. Table 7. Ordering Information
www.austriamicrosystems.com/DC-DC_Step-Up/AS1337 Revision 1.05 15 - 15 AS1337 Datasheet Copyrights Copyright © 1997-2010, 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 ams AG Technical content still valid