AS1341 AMSCO
Document overview
- Manufacturer or author: Provided By digicamel.com
- PDF pages: 16
Technical content
1 General Description
supply voltages of up to 20V. and draws only 0.8µA in shutdown mode. of small surface-mount inductors and output capacitors. Figure 1. Typical Application
2 Key Features
3 Applications
tery-operated, portable device.
7 SHDNN
6 ILIMIT
4 Pinout
Figure 2. Pin Assignments (Top View) Table 1. Pin Descriptions Power OK. Active-low open-drain reset output. Note: Connect pin POK to GND when the Power-Ok feature is not used. 4L X Inductor Connection. Connect this pin to an external inductor. (see Setting Current Limit on page 10). current is reduced to 0.8µA and LX goes high-impedance. the internal resistor-divider network. Connect this pin to GND when not used.
5 Absolute Maximum Ratings
Table 2. Absolute Maximum Ratings Solid State Surface Mount Devices”.
6 Electrical Characteristics
VIN = +12V, SHDNN = VIN, TAMB = -40 to +85ºC. Typical values are at TAMB = +25ºC (unless otherwise specified). Specifications based on circuit shown in Figure 1 on page 1. Table 3. Electrical Characteristics
7 Typical Operating Characteristics
Figure 3. Efficiency vs. IOUT; VOUT = 5V, Circuit 1 Figure 4. Efficiency vs. IOUT; VOUT = 5V, Circuit 3 Figure 7. Efficiency vs. IOUT; VOUT = 5V, VIN = 12V Figure 8. Efficiency vs. I OUT; VOUT = 5V, VIN = 12V
8 Detailed Description
mode it draws only 0.8µA to further reduce power consumption and extend battery life. for minimal PCB space and external component requirements. Figure 21. Block Diagram verter pulses as needed to maintain regulation, resulting in a variable switching frequency that increases with the load. (PWM) controllers that unnecessarily switch the MOSFET. charging the output capacitor and servicing the load (see Figure 19 on page 7). remains on, allowing a duty cycle up to 100%. This feature ensures the lowest possible dropout voltage. FET remains off until the 0.4µs minimum off-time expires, and the output voltage goes out of regulation.
www.austriamicrosystems.com Revision 1.00 9 - 16 AS1341 Data Sheet - Detailed Description Dropout Voltage A buck converter’s minimum input-to-output voltage differential (dropout voltage) determines the lowest usable supply voltage. In battery-powered systems, this limits the useful end-of-life battery voltage. To maximize battery life, the AS1341 operates with duty cycles up to 100%, which minimizes the dropout voltage and eliminates switching losses while in dropout. When the supply voltage approaches the output voltage, the P-channel MOSFET remains on contin- uously to supply the load. Note: Dropout voltage is defined as the difference between the input and output voltages when the input is low enough for the output to drop out of regulation. For a step-down converter with 100% duty cycle, dropout is related to the MOSFET drain-to-source on-resistance (RDSON) and inductor series resistance (RINDUCTOR), and thus it is proportional to the load current: VDROPOUT = IOUT x (RDSON + RINDUCTOR)( E Q 1 ) Shutdown A logic low on pin SHDNN shuts down the AS1341; a logic high on SHDNN powers on the device. In shutdown mode the supply current drops to 0.8µA to maximize battery life, and the internal P-channel MOSFET turns off to isolate the output from the input. The output capacitance and load current determine the output voltage decay rate. Note: Pin SHDNN should not be left floating. If the shutdown feature is not used, connect SHDNN to IN. Power-OK Output The AS1341 provides a Power OK output (POK) that goes high-impedance when the output reaches 92.5% of its reg- ulation point. POK goes low when the output is below 92.5% of the regulation point and the AS1341 is turned on (IN ≥ 4.5V and SHDNN ≥ 2.4V). A 12kΩ to 1MΩ pullup resistor between pin POK and pin IN or pin OUT or another volt- age (≤ IN) can provide a microprocessor logic control signal. Note: Connect pin POK to GND when the Power-Ok feature is not used. Thermal-Overload Protection Integrated thermal-overload protection limits total power dissipation in the AS1341. During continuous thermal-over- load conditions, when the AS1341 junction temperature exceeds TJ = +145ºC, the internal thermal sensor turns off the pass transistor, allowing the AS1341 to cool down. When the AS1341 junction temperature cools by 10ºC, the thermal sensor turns the pass transistor on again resulting in a pulsed output.
9 Application Information
The AS1341 feedback input features dual-mode operation. Connect FB to GND for the 5.0V preset output voltage. Adjust the output voltage by connecting a voltage-divider from the output to GND (Figure 4). Figure 22. Adjustable Output Voltage Circuit Select a value for R2 between 10k and 1MΩ. VOUTPUT may range from 1.25V to VIN. The AS1341 adjustable peak current limit is set by connecting ILIMIT as shown in Table 4. higher inductance (see Inductor Selection on page 10) and does not allow for reduced inductor package size. thereby improve efficiency and EMI. Note: The four key factors in inductor selection are inductance value, saturation rating, series resistance, and size. Table 4. Setting Peak Current Limit
mum performance, select an inductor with the lowest possible DC resistance that fits in the allotted dimensions. Table 5. Recommended Inductors
IPEAK is the peak inductor current (see Inductor Selection on page 10). The worst-case ripple occurs at no-load. or evaluation circuit. As a general rule, a smaller amount of charge delivered in each pulse results in less output ripple. voltage ripple increases with larger inductance, and as the input voltage decreases. temperature rise at the RMS input current for optimal circuit life. Table 6. Recommended Output Capacitor Table 7. Recommended Input Capacitor
turns off. To avoid excessive losses, the diode must have a fast turn-on time and a low forward voltage. Current Limit on page 10), and that its breakdown voltage exceeds VIN. Schottky diodes are recommended. bility, or degraded performance.
- High-power traces (see Figure 22 on page 10) should be as short and wide as possible.
mon node in a star-ground configuration.
- Separate noisy traces, such as the LX node, from the feedback network with grounded copper.
- Keep the extra copper on the PCB and integrate it into a pseudo-ground plane.
- When using external feedback, place the resistors as close to pin FB as possible to minimize noise coupling.
Table 8. Recommended Components
Figure 23. TDFN-8 3x3mm Package
- Dimensioning and tolerancing conform to ASME Y14.5 M-1994.
- All dimensions are in millimeters; angles in degrees.
- 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.
- Figure 23 is shown for illustration only.
- Unilateral coplanarity zone applies to the exposed heat sink slug as well as the terminals
The device is available as the standard products shown in Table 9. Table 9. Ordering Information
www.austriamicrosystems.com Revision 1.00 16 - 16 AS1341 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, trans- lated, 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. austriami- crosystems 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 tech- nical 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 A-8141 Schloss Premstaetten, 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