L6920 STMICROELECTRONICS | Alldatasheet
Document overview
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Technical content
1 Features
1.1 Applications
2 Description
Figure 1. Application Circuit Figure 1. Package Table 1. Order Codes
Table 1. Pin Description Figure 2. Pin Connection (Top view) Table 2. Absolute Maximum Ratings Table 3. Thermal Data external resistor divider for adjustable output voltage (from 2V to 5.2V) [see R4 and R5, fig. 7]. 2 LBI Battery low voltage detector input. The internal threshold is set to 1.23V. threshold typ. 1.23V, LBO goes low. correct output setting [see R3, fig. 7].
6 GND Ground pin
7 LX Step-up inductor connection
8 OUT Power OUTPUT pin
Table 4. Electrical Characteristcs
3 Detailed Description
polymer, NiMH respectively) battery up conversion. chronous rectification, that implies also a reduced cost in the application (no external diode required). simplified block diagram is shown here below. Figure 6. Simplified Block Diagram
4 Principle of Operation
In L6920 the control is based on a comparator that cont inuously checks the status of output voltage. voltage goes lower than the regulated voltage or the current flowing in the inductor goes down to zero. So, in case of light load, the device works in PFM mode, as shown in figures 7 to 10.
Figure 11. No regulation. Iload > Iload_lim Trace1: Vout (100mV~/div) Trace 4: IL (200mA/div).
4.1 Start-up
Figure 5. in case of heavy load). ferred to the load through its intrinsic body diode. zero crossing detection are still available.
4.2 Shutdown
SHDN < 100 nA, in typical case). comparator output is forced in high impedance state. be avoided also in shutdown.
4.3 Low battery detection
put so a pull up resistor is required for a proper use.
4.4 Reverse polarity
5 Application Information
5.1 Output voltage selection
Output voltage must be selected acting on FB pin. able output set via an external resistor divider. Table 5. Output Voltage Selection
Figure 12. Demoboard Circuit
5.2 Output capacitor selection
The capacitance value should be in the range of about 10 µF-100µF. Ceramic capacitors are the lowest ESR but they are very expensive. capacitors from SANYO and polymeric capacitors from PANASONIC are also good.
Table 7. Capacitors distributors main list
5.3 Inductor selection
Usually, inductors ranging between 5µH to 40µH satisfy most of the applications. way, the saturation current of the choke should be highe r than the peak current limit of the device (1A). es. In the following table are listed some suggested components. Table 8. Inductors distributors main list
5.4 Layout Guidelines
resonance problems. So, the output and input cap should be very close to the device. as far as possible from the high current circulating paths, to avoid pick up noise. For an example of recommended layout see the following evaluation board.
6 Package Information
Figure 16. TSSOP8 Mechanical Data & Package Dimensions Note: 1. D and F does not include mold flash or protrusions.
7 Revision History
Table 9. Revision History February 2005 2 Modified the max. value of the I sd parameter in the Table 4 pag. 3.
Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of STMicroelectronics. Specifications mentioned in this publicati on are subject to change without notice. This publication supersedes and replac es all information previously supplied. STMicroelectronics prod ucts are not authorized for use as critical components in life support devices or systems without express written approval of STMicroelectro nics. The ST logo is a registered trademark of STMicroelectronics. All other names are the property of their respective owners © 2005 STMicroelectronics - All rights reserved STMicroelectronics group of companies Australia - Belgium - Brazil - Canada - China - Czech Republic - Finland - France - Germany - Hong Kong - India - Israel - Ital y - Japan - Malaysia - Malta - Morocco - Singapore - Spain - Sweden - Switzerland - United Kingdom - United States of America L6920