L6920DB

L6920DB Synchronous rectifier step up converter General features ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ 0.8V start up input voltage Up to 5.5V operating input voltage Internal synchronous rectifier Adjustable output voltage from 1.8V 3.3V and 5V fixed output voltages Low battery voltage detection Reverse battery protection 750mA input current limit Switching frequency up to 1MHz 1.23V reference voltage available MSOP8 Description The L6920DB is a high efficiency monolithic step up switching converter IC especially designed for battery powered application. Package is MSOP8 in order to minimize PCB space. It requires only three external components to realize the conversion from the battery voltage to the selected output voltage. The minimum output voltage is 1.8V: suitable to supply the most advanced ASIC and µP. High switching frequency allows for a low profile, small sized inductor and output capacitor to be used. Reference voltage, low battery detection and Shutdown are provided together with over current. Applications ■ ■ ■ ■ ■ ■ ■ Conversion from 1 to 3 alkaline, NiMH, NiCd battery cells or 1 lithium ION PDA and handheld instruments Digital cameras Cellular phones GPS Distributed power Application circuit L6920DB 3.3V October 2006 Rev 5 1/16 www.st.com 16 Contents L6920DB Contents 1 Pin settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1 1.2 Pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2 Electrical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.1 2.2 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3 4 5 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Typical performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Detailed description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 5.1 5.2 5.3 5.4 5.5 5.6 5.7 Principle of operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Start-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Shutdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Low battery detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Low battery input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Reverse polarity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Output voltage selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 6 7 8 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Order code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 2/16 L6920DB Pin settings 1 1.1 Pin settings Pin connection Figure 1. Pin connection (top view) 1.2 Pin description Table 1. Pin description N° 1 Type FB Description Output voltage selector. Connect FB to GND for Vout=5V or to OUT for Vout=3.3V. Connect FB to an external resistor divider for adjustable output voltage Battery low voltage detector input. The internal threshold is set to 1.23V. A resistor divider is needed to adjust the desired low battery threshold. Battery low voltage detector output. If the voltage at the LBI pin drops below the internal threshold typ. 1.23V, LBO goes low. The LBO is an open drain output and so a pull-up resistor (about 200KΩ) has to be added for correct output setting . 1.23V reference voltage. Bypass this output to GND with a 100nF capacitor for filtering high frequency noise. No capacitor is required for stability Shutdown pin. When pin 5 is below 0.2V the device is in shutdown, when pin 5 is above 0.6V the device is operating. Ground pin Step-up inductor connection Power OUTPUT pin 2 3 LBI LBO 4 REF 5 6 7 8 SHDN GND LX OUT 3/16 Electrical data L6920DB 2 2.1 Electrical data Maximum ratings Table 2. Absolute maximum ratings Symbol Vccmax Vcc to GND LBI, SHDN, FB to GND Vout max Vout to GND Parameter Value 6 6 6 Unit V V V 2.2 Thermal data Table 3. Thermal data Symbol RthJA TJ Parameter Maximum thermal resistance junction-ambient Maximum junction temperature Value 180 150 Unit ° C/W °C 4/16 L6920DB Electrical characteristics 3 Electrical characteristics Table 4. Electrical characteristcs (VIN = 2V, FB = GND, TJ = 25°C unless otherwise specified) Symbol VCC Section VIN Minimum Start Up Input Voltage Vout = 3.3V Il = 0 mA, FB = 1.4V, Vout = 3.3V LBI = SHDN = 2V Quiescent Current Il = 0 mA, FB = 1.4V, Vout = 5V LBI = SHDN = 2V Shut Down Current Reverse battery current Vin = 5V, Il = 0 mA Vin = -4V 11 0.1 0.1 15 1 1 µA µA µA 0.8 9 12 V µA Parameter Test condition Min Typ Max Unit Iq Isd Irev Power section Ron-N Ron-P Active switch ON resistance Synchronous switch ON resistance 300 300 mΩ mΩ Control section Vout Output voltage FB = OUT, Il = 0 mA FB = GND, Il = 0 mA Output voltage range VLBI VLBO Ilim Tonmax Toffmin SHDN LBI threshold LBO logic LOW 3.2 4.9 1.8 3.3 5 3.4 5.1 5.2 V V V V External divider 1.23 Isink = 1mA 0.7 Vout = 3.3V Vout = 3.3V 3.75 0.75 0.2 0.8 5 1 0.4 0.9 6.25 1.25 0.2 0.6 1.18 1.23 1.27 V A µs µs V V V LX switch current limit Maximum on time Minimum off time SHDN logic LOW SHDN logic HIGH Vref Reference Voltage 5/16 Typical performance L6920DB 4 Typical performance Figure 2. Efficiency vs output current @ VOUT = 3.3V 9 5 9 0 8 5 8 0 7 5 7 0 6 5 6 0 5 5 5 0 4 5 4 0 0 .1 1 1 0 10 0 10 00 L90 B 62D Vu 3 V o t= .3 L1 H = 0µ Cu 4 F o t= 7µ C =0F in 1 µ V = .2 in 1 V V = .4 in 2 V Figure 3. Efficiency vs output current @ VOUT = 5V 10 0 9 0 8 0 7 0 6 0 5 0 4 0 3 0 2 0 1 0 0 0 .1 V = .6 in 3 V V = .4 in 2 V V = .2 in 1 V L90 B 62D Vu 5 o t= V L1 H = 0µ Cu 4µ o t= 7 F C =0F in 1 µ 1 1 0 10 0 10 00 Figure 4. Start up voltage vs output current @ Vout = 5V & Vout = 3.3V VStart up vs . out put cur rent VStart up v s. output current 1600 1600 Vout =5V 1500 1400 1300 1500 1400 1300 Vout =3.3V VStart up (mV) 1200 1100 1000 900 800 700 600 0.1 1 10 100 1000 VStart up (mV) 1200 1100 1000 900 800 700 600 0.1 1 10 100 1000 Output cu rrent (mA) Output current (mA) 6/16 L6920DB Detailed description 5 Detailed description The L6920DB is a high efficiency, low voltage step-up DC/DC converter particularly suitable for 1 to 3 cells (Li-Ion/ polymer, NiMH respectively) battery up conversion. These performances are achieved via a strong reduction of quiescent current (10µA only) and adopting a synchronous rectification that implies also a reduced cost in the application (no external diode required). Operation is based on maximum ON time - minimum OFF time control, tailored by a current limit set to 800mA. A simplified block diagram is shown here below. Figure 5. Simplified block diagram OUT ZERO CROSSING VREF SHDN FB VOUT GND R1,R2 Y + VBG Q S R + CURRENT LIMIT LBO + VBG Ton max 5µsec FB GND Y A B C OPAMP (CR) VOUT LX VIN + VBG + -+ VOUT A B C Toff min 1µsec LBI D99IN1041 5.1 Principle of operation In L6920DB the control is based on a comparator that continuously checks the status of output voltage. If the output voltage is lower than the expected value, the control function of the L6920DB directs the energy stored in the inductor to be transferred to the load. This is accomplished by alternating between two basic steps: ● TON phase: the energy is transferred from the battery to the inductor by shorting LX node to ground via the N-channel power switch. The switch is turned off if the current flowing in the inductor reaches 750mA or after a maximum on time set to 5µs. TOFF phase: the energy stored in the inductor is transferred to the load through the synchronous switch for at least a minimum off time equal to 1µs. After this, the synchronous switch is turned off as soon as the output voltage goes lower than the regulated voltage or the current flowing in the inductor goes down to zero. ● 7/16 Detailed description So, in case of light load, the device works in PFM mode, as shown in Figure 8: Figure 6. L6920DB PFM mode condition: Vout = 5V; Vbatt =1.5V ; C2 = Vout ; C3 = Inductor Current Figure 7 shows how the device works in case of heavy load. Figure 7. Heavy load conditions C2 = Vout; C3 = Inductor Current; Vout = 5V; Vbatt=1.5V 8/16 L6920DB Detailed description Considering that current in the inductor is limited to 800mA, the maximum load current is defined by the following relationship: Equation 1 V in V out – V in I LOAD_LIM = ---------- ⋅ ⎛ I LIM – T OFF_MIN ⋅ ------------------------ ⎞ ⋅ η ⎝ 2⋅ L ⎠ V out Where ηis the efficiency and ILIM = 750mA Of course, if ILOAD is greater than ILOAD_LIM the regulation is lost (Figure 8). Figure 8. No regulation C2 = Vout ; C3 = Inductor Current 5.2 Start-up One of the key features of L6920DB is the startup at supply voltage down to 0.8V (please see the diagram in Figure 4). The device leaves the startup mode of operation as soon as Vout goes over 1.4V. During startup, the synchronous switch is off and the energy is transferred to the load through its intrinsic body diode. The N-channel switches with a very low RDS(on) thanks to an internal charge pump used to bias the power MOS gate. Because of this modified behavior, TON/TOFF times are lengthened. Current limit and zero crossing detection are still available. 9/16 Detailed description L6920DB 5.3 Shutdown In shutdown mode (SHDN pulled low) all internal circuitries are turned off, minimizing the current provided by the battery (ISHDN < 100 nA, in typical case). Both switches are turned off, and the low battery comparator output is forced in high impedance state. The synchronous switch body diode causes a parasitic path between power supply and output that can't be avoided also in shutdown. 5.4 Low battery detection The L6920DB includes a low battery detector comparator. Threshold is VREF voltage and a hysteresis is added to avoid oscillations when input crosses the threshold slowly. The LBO is an open drain output so a pull up resistor is required for a proper use. 5.5 Low battery input It is possible to fix, using an external resistor divider, the LBO threshold, in order to adapt the LBO detection at the correct input source, by the following equation: Equation 2 V batt-th = 1.23V ⋅ ⎛ 1 + R1⎞ -------⎠ ⎝ R2 Where Vbatt-th is the battery voltage at which the internal comparetor is triggered. 5.6 Reverse polarity A protection circuit has been implemented to avoid that L6920DB and the battery are destroyed in case of wrong battery insertion. In addition, this circuit has been designed so that the current required by the battery is zero also in reverse polarity. If a battery can be inserted in reverse direction, a non polarized capacitor should be installed in location of C2. 5.7 Output voltage selection Output voltage must be selected acting on FB pin. Three choices are available: fixed 3.3V, 5V or adjustable output set via an external resistor divider. 10/16 L6920DB Detailed description Table 5. Output voltage connection Vout = 3.3V Vout = 5V 1.8V < Vout < 5.5V FB pin connected to OUT (see application circuit) FB pin connected to GND FB pin connected to a resistive divider V out = 1.23V ⋅ ⎛ 1 + R4⎞ ------⎝ R5⎠ Figure 9. Test circuit R 1 R 2 LB I V ATT=1.5V B L1 10µH C 2 47µF _____ 2 SD HN 5 V UT O 8 C 1 R 3 47µF V ATT B 7 V UT=2.5V O L6920D B V EF R 4 C 4 100nF L6920DB ___ LB O 3 FB R 4 200K Ω 1 6 GD N R 5 200K Ω 11/16 Package mechanical data L6920DB 6 Package mechanical data In order to meet environmental requirements, ST offers these devices in ECOPACK® packages. These packages have a Lead-free second level interconnect . The category of second level interconnect is marked on the package and on the inner box label, in compliance with JEDEC Standard JESD97. The maximum ratings related to soldering conditions are also marked on the inner box label. ECOPACK is an ST trademark. ECOPACK specifications are available at: www.st.com 12/16 L6920DB Package mechanical data Table 6. MSOP8 Mechanical data mm. Dim. Min A A1 A2 b c D (1) E E1 (1) e L L1 k aaa 0.400 0.050 0.750 0.250 0.130 2.900 4.650 2.900 3.000 4.900 3.000 0.650 0.550 0.950 0° (min.) 6° (max.) 0.100 0.004 0.700 0.016 0.850 Typ Max 1.10 0.150 0.950 0.400 0.230 3.100 5.150 3.100 0.002 0.03 0.010 0.005 0.114 0.183 0.114 0.118 0.193 0.118 0.026 0.022 0.037 0.028 0.033 Min Typ Max 0.043 0.006 0.037 0.016 0.009 0.122 0.20 0.122 inch 1. D and F does not include mold flash or protrusions. Mold flash or potrusions shall not exceed 0.15mm (.006inch) per side. Figure 10. Package dimensions 13/16 Order code L6920DB 7 Order code Table 7. Order code Part number L6920DB L6920DBTR Package MSOP8 MSOP8 Packaging Tube Tape and reel 14/16 L6920DB Revision history 8 Revision history Table 8. Revision history Date 18-Mar-2005 03-Aug-2005 01-Jun-2006 13-Oct-2006 30-Oct-2006 Revision 1 2 3 4 5 First issue Changed from “Preliminary Data” to “Datasheet”. Modified Section 1 and Table 5. Added Figg. 3, 6 and new Section 3. New template, modified application circuit and Figure 9. Cover page description updated. Typo in Figure 7 on page 8 Changes 15/16 L6920DB Please Read Carefully: Information in this document is provided solely in connection with ST products. STMicroelectronics NV and its subsidiaries (“ST”) reserve the right to make changes, corrections, modifications or improvements, to this document, and the products and services described herein at any time, without notice. All ST products are sold pursuant to ST’s terms and conditions of sale. Purchasers are solely responsible for the choice, selection and use of the ST products and services described herein, and ST assumes no liability whatsoever relating to the choice, selection or use of the ST products and services described herein. No license, express or implied, by estoppel or otherwise, to any intellectual property rights is granted under this document. If any part of this document refers to any third party products or services it shall not be deemed a license grant by ST for the use of such third party products or services, or any intellectual property contained therein or considered as a warranty covering the use in any manner whatsoever of such third party products or services or any intellectual property contained therein. UNLESS OTHERWISE SET FORTH IN ST’S TERMS AND CONDITIONS OF SALE ST DISCLAIMS ANY EXPRESS OR IMPLIED WARRANTY WITH RESPECT TO THE USE AND/OR SALE OF ST PRODUCTS INCLUDING WITHOUT LIMITATION IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE (AND THEIR EQUIVALENTS UNDER THE LAWS OF ANY JURISDICTION), OR INFRINGEMENT OF ANY PATENT, COPYRIGHT OR OTHER INTELLECTUAL PROPERTY RIGHT. UNLESS EXPRESSLY APPROVED IN WRITING BY AN AUTHORIZED ST REPRESENTATIVE, ST PRODUCTS ARE NOT RECOMMENDED, AUTHORIZED OR WARRANTED FOR USE IN MILITARY, AIR CRAFT, SPACE, LIFE SAVING, OR LIFE SUSTAINING APPLICATIONS, NOR IN PRODUCTS OR SYSTEMS WHERE FAILURE OR MALFUNCTION MAY RESULT IN PERSONAL INJURY, DEATH, OR SEVERE PROPERTY OR ENVIRONMENTAL DAMAGE. ST PRODUCTS WHICH ARE NOT SPECIFIED AS "AUTOMOTIVE GRADE" MAY ONLY BE USED IN AUTOMOTIVE APPLICATIONS AT USER’S OWN RISK. Resale of ST products with provisions different from the statements and/or technical features set forth in this document shall immediately void any warranty granted by ST for the ST product or service described herein and shall not create or extend in any manner whatsoever, any liability of ST. ST and the ST logo are trademarks or registered trademarks of ST in various countries. Information in this document supersedes and replaces all information previously supplied. The ST logo is a registered trademark of STMicroelectronics. All other names are the property of their respective owners. © 2006 STMicroelectronics - All rights reserved STMicroelectronics group of companies Australia - Belgium - Brazil - Canada - China - Czech Republic - Finland - France - Germany - Hong Kong - India - Israel - Italy - Japan Malaysia - Malta - Morocco - Singapore - Spain - Sweden - Switzerland - United Kingdom - United States of America www.st.com 16/16