STMICROELECTRONICS L6928 handbook
Contents
1. Once the device starts to switch the output capacitor is recharged The feedback pin increases and when it reaches a value slightly higher than the reference voltage the output of the error amplifier goes down until a clamp is activated At this point the device stops to switch In this phase most of the internal circuitries are off so reducing the device consumption down to a typical value of 25uA 410 S74 L6928 4 1 2 Low Noise Mode If for noise reasons the very low frequencies of the low consumption mode are undesirable the low noise mode can be selected In low noise mode the efficiency is a little bit lower compared with the low consumption mode in very light load conditions but for medium high load currents the efficiency values are very similar Basically the device switches with its internal free running frequency of 1 4MHz Obviously in very light load conditions the device could skip some cycles in order to keep the output voltage in regulation 4 1 3 Synchronization The device can also be synchronized with an external signal from 1MHz up to 2MHz In this case the low noise mode is automatically selected The device will eventually skip some cycles in very light load conditions The internal synchronization circuit is inhibited in shortcircuit and overvoltage conditions in order to keep the protections effective see relative sections 4 2 Short Circuit Protection During the device operation the inductor curr2. SZA L6928 HIGH EFFICIENCY MONOLITHIC SYNCHRONOUS 1 FEATURES m 2V TO 5 5V BATTERY INPUT RANGE m HIGH EFFICIENCY UP TO 95 m INTERNAL SYNCHRONOUS SWITCH m NO EXTERNAL SCHOTTKY REQUIRED m EXTREMELY LOW QUIESCENT CURRENT m uA MAX SHUTDOWN SUPPLY CURRENT m 800mA MAX OUTPUT CURRENT m ADJUSTABLE OUTPUT VOLTAGE FROM 0 6V a LOW DROP OUT OPERATION UP TO100 DUTY CYCLE m SELECTABLE LOW NOISE LOW CONSUMPTION MODE AT LIGHT LOAD m POWER GOOD SIGNAL m 1 OUTPUT VOLTAGE ACCURACY m CURRENT MODE CONTROL m 1 4MHz SWITCHING FREQUENCY a EXTERNALLY SYNCHRONIZABLE FROM 1MHz TO 2MHz m OVP m SHORT CIRCUIT PROTECTION 2 APPLICATIONS m BATTERY POWERED EQUIPMENTS m PORTABLE INSTRUMENTS m CELLULAR PHONES m PDAs AND HAND HELD TERMINALS m DSC m GPS Figure 2 Application Test Circuit COMP c L aF DO1IN1528 November 2005 STEP DOWN REGULATOR Figure 1 Packages R MSOP8 VFQFPN8 Table 1 Order Codes Part Number Package L6928D MSOP8 in Tube L6928D013TR MSOP8 in Tape amp Reel L6928Q1 VFQFPN8 in Tube L6928Q1TR VFQFPN8 in Tape amp Reel 3 DESCRIPTION The device is dc dc monolithic regulator specifically designed to provide extremely high efficiency L6928 supply voltage can be as low as 2V allowing its use in single Li ion cell supplied applications Out put voltage can be selected by an external divider down to 0 6V Duty Cycle can saturate to 100 a
3. When high higher than 1 3V the device is enabled 2 COMP Error amplifier output A compensation network has to be connected to this pin Usually a 220pF capacitor is enough to guarantee the loop stability 3 VFB Error amplifier inverting input The output voltage can be adjusted from 0 6V up to the input voltage by connecting this pin to an external resistor divider 4 GND Ground 5 LX Switch output node This pin is internally connected to the drain of the internal switches 6 vcc Input voltage The start up input voltage is 2 2V typ while the operating input voltage range is from 2V to 5 5V An internal UVLO circuit realizes a 100mV typ hysteresis 7 SYNC Operating mode selector input When high higher than 1 3V the Low Consumption Mode is selected When low lower than 0 5V the Low Noise Mode is selected If connected with an appropriate external synchronization signal from 1MHz up to 2MHz the internal synchronization circuit is activated and the device works at the same switching frequency 8 PGOOD Power good comparator output It is an open drain output A pull up resistor should be connected between PGOOD and VOUT or VCC depending on the requirements The pin is forced low when the output voltage is lower than 90 of the regulated output voltage and goes high when the output voltage is greater than 90 of the regulated output voltage If not used the pin can be left floating 20 S74 L6928 Table 5 Electrical C
4. 0 0 950 0 03 0 033 0 037 b 0 250 0 400 0 010 0 016 c 0 130 0 230 0 005 0 009 D 1 2 900 3 000 3 100 0 114 0 118 0 122 E 4 650 4 900 5 150 0 183 0 193 0 20 E1 1 2 900 3 000 3 100 0 114 0 118 0 122 e 0 650 0 026 L 0 400 0 550 0 700 0 016 0 022 0 028 Li 0 950 0 037 k 0 min 6 max aaa 0 100 0 004 MSOP8 Note 1 D and F does not include mold flash or protrusions Mold flash or potrusions shall not exceed 0 15mm Body 3mm 006inch per side mm sh Y d b Al s Qy eee C 0 25 mm SEATING 010 inch 8 5 PLANE GAGE PLANE C PIN 1 IDENTIFICATION a eR hs lt 7 10 L6928 Figure 6 VFQFPN8 Mechanical Data amp Package Dimensions mm inch DIM OUTLINE AND MIN TYP MAX MIN TYP MAX MECHANICAL DATA A 0 80 0 90 1 00 0 0315 0 0354 0 0394 A1 0 02 0 05 0 0008 0 0020 A2 0 70 0 0276 A3 0 20 0 0079 b 0 18 0 23 0 30 0 0071 0 0091 0 0118 D 3 00 0
5. 1181 D2 2 23 2 38 2 48 0 0878 0 0937 0 0976 E 3 00 0 1181 E2 1 49 1 64 1 74 0 0587 0 0646 0 0685 e 0 50 0 0197 L 0 30 0 40 0 50 0 0118 0 0157 0 0197 VFQFPNS8 3x3x1 0 8mm Very thin Fine pitch Quad Packages No lead ddd 0 08 0 0031 SEATING PLANE ge ED b _Ic A3 T ime a lo an S gt E gt ga o pea ee A L A2 I E ho A SEO BOTTOM VIEW PS ddd 7426334 B 8 10 L6928 Table 6 Revision History lt Date Revision Description of Changes October 2004 1 First Issue February 2005 2 Changed from Product Preview to Final datasheet November 2005 3 Updated Table 5 Electrical characteristics Added VFQFPN8 package and new part numbers 9 10 L6928 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 publication are subject to change without notice This publication supersedes and replaces all information previously supplied STMicroelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of
6. Hysteresis Vout Vib 4 Vout VPgood low Power Good Low Voltage Run to GND 0 4 V ILK PGoop Power Good Leakage VpGoop 3 6V 50 nA Current 1 PROTECTIONS HOVP Hard overvoltage threshold Vout Vib 10 Nout Note 1 Guaranteed by design 2 Specification over the 40 to 125 C Tj temperature range are assured by design characterization and statistical correlation ky 3 10 L6928 4 OPERATION DESCRIPTION The main loop uses slope compensated PWM current mode architecture Each cycle the high side MOSFET is turned on triggered by the oscillator so that the current flowing through it the same as the inductor current increases When this current reaches the threshold set by the output of the error amplifier E A the peak current limit comparator PEAK_CL turns off the high side MOSFET and turns on the low side one until the next clock cycle begins or the current flowing through it goes down to zero ZERO CROSSING comparator The peak in ductor current required to trigger PEAK_CL depends on the slope compensation signal and on the output of the error amplifier In particular the error amplifier output depends on the VFB pin voltage When the output current increases the output capacitor is discharged and so the VFB pin decreases This produces increase of the error amplifier out put so allowing a higher value for the peak inductor current For the same reason when due to a load transient the output current decreases the erro
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8. ccur To allow loop stability also in these conditions a slope compensation is present This is realized by reducing the current flowing through the inductor necessary to trigger the COMP comparator with a fixed value for the COMP pin voltage With a given duty cycle higher than 50 the stability problem is particularly present with an higher input voltage due to the increased current ripple across the inductor so the slope compensation effect increases as the input voltage increases From an application point of view the final effect is that the peak current limit depends both on the duty cycle if higher than approximately 40 and on the input voltage ky 5 10 L6928 4 4 Loop Stability Since the device is realized with a current mode architecture the loop stability is usually not a big issue For most of the application a 220pF connected between the COMP pin and ground is enough to guarantee the sta bility In case very low ESR capacitors are used for the output filter such as multilayer ceramic capacitors the zero introduced by the capacitor itself can shift at very high frequency and the transient loop response could be affected Adding a series resistor to the 220pF capacitor can solve this problem The right value for the resistor in the range of 50K can be determined by checking the load transient response of the device Basically the output voltage has to be checked at the scope after the load steps required by the appl
9. ent increases during the high side turn on phase and decrease during the high side turn off phase based on the following equations Vin V Min Your Alon L ON Vout Alore ToFF In strong overcurrent or shortcircuit conditions the Vout can be very close to zero In this case Alon increases and Alorr decreases When the inductor peak current reaches the current limit the high side mosfet turns off and so the Ton is reduced down to the minimum value 250ns typ in order to reduce as much as possible Alon Anyway if Vout is low enough it can be that the inductor peak current further increases because during the Torr the current decays very slowly Due to this reason a second protection that fixes the maximum inductor valley current has been introduced This protection doesn t allow the high side MOSFET to turn on if the current flowing through the inductor is higher that a specified threshold valley current limit Basically the Torr is increased as much as required to bring the inductor current down to this threshold So the maximum peak current in worst case conditions will be Vin Ipeak lvaLLey Ton_mIN Where IPEAK is the valley current limit 1 4A typ and Ton_min is the minimum Ton of the high side MOSFET 4 3 Slope Compensation In current mode architectures when the duty cycle of the application is higher than approximately 50 a pulse by pulse instability the so called sub harmonic oscillation can o
10. evice has an internal overvoltage protection circuit to protect the load If the voltage at the feedback pin goes higher than an internal threshold set 10 typ higher than the reference voltage the low side power mosfet is turned on until the feedback voltage goes lower than the reference one During the overvoltage circuit intervention the zero crossing comparator is disabled so that the device is also able to sink current 5 5 THERMAL SHUTDOWN The device has also a thermal shutdown protection activated when the junction temperature reaches 150 C In this case both the high side MOSFET and the low side one are turned off Once the junction temperature goes back lower than 95 C the device restarts the normal operation 6 10 ky L6928 6 Package Information 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 Figure 5 MSOP8 Mechanical Data amp Package Dimensions mm inch nar MIN TYP MAX MIN TYP MAX OUTLINE AND i i i i i i MECHANICAL DATA A 1 10 0 043 A1 0 050 0 150 0 002 0 006 A2 0 750 0 85
11. haracteristics Tj 25 C Vcc 3 6V unless otherwise specified Specification Referred to Tj from 40 to 125 C Symbol Parameter Test Condition Min Typ Max Unit Vcc Operating input voltage After Turn on ij 2 5 5 V Vec ON Turn On threshold 2 2 V Voc OFF Turn Off threshold 2 V High side Ron Vece 3 6V lix 100MA 240 300 mQ 400 Low side Ron Vec 3 6V lix 100MA 215 300 mQ 2 400 Peak current limit 1 1 2 1 5 A yi 0 85 1 65 Valley current limit 1 1 4 1 7 A 0 9 1 85 Output voltage range Vib Vcc V Oscillator frequency 1 4 MHz fsync Sync mode clock 1 2 MHz DC CHARACTERISTICS lq Quiescent current low Vsync OV no load 230 uA noise mode Vreg gt 0 6V Quiescent current low Vsync Vcc no load H 25 50 uA cunsumption mode VpB gt 0 6V Ish Shutdown current RUN to GND Vcc 5 5V 0 2 uA lix LX leakage current 1 RUN to GND VLx 5 5V 1 uA Vcc 5 5V RUN to GND VLx OV 1 uA Vec 5 5V ERROR AMPLIFIER CHARACTERISTICS Vib Voltage feedback 0 593 0 600 0 607 V lto Feedback input current VFB 0 6V 25 nA RUN Vrun_H RUN threshold high 1 3 V Vrun _L RUN threshold low 0 4 V lrun RUN input current 25 nA SYNC MODE FUNCTION Vsync_H Sync mode threshold high 1 3 V Vsync_L Sync mode threshold low 0 5 V PGOOD SECTION VPGooD Power Good Threshold Vout Vib 90 Nout AVpgoop Power Good
12. ication In case of stability problems the output voltage could oscillates before to reach the regulated value after a load step 5 ADDITIONAL FEATURES AND PROTECTIONS 5 1 DROPOUT Operation The Li lon battery voltage ranges from approximately 3V and 4 1V 4 2V depending on the anode material In case the regulated output voltage is from 2 5V and 3 3V it can be that close to the end of the battery life the battery voltage goes down to the regulated one In this case the device stops to switch working at 100 of duty cycle so minimizing the dropout voltage and the device losses 5 2 PGOOD Power Good Output A power good output signal is available The VFB pin is internally connected to a comparator with a threshold set at 90 of the of reference voltage 0 6V Since the output voltage is connected to the VFB pin by a resistor divider when the output voltage goes lower than the regulated value the VFB pin voltage goes lower than 90 of the internal reference value The internal comparator is triggered and the PGOOD pin is pulled down The pin is an open drain output and so a pull up resistor should be connected to him If the feature is not required the pin can be left floating 5 3 ADJUSTABLE OUTPUT VOLTAGE The output voltage can be adjusted by an external resistor divider from a minimum value of 0 6V up to the input voltage The output voltage value is given by Vout 0 6 1 R2 R1 5 4 OVP Overvoltage Protection The d
13. l lowing low drop out operation The device is based on a 1 4MHz fixed frequency current mode architec ture Low Consumption Mode operation can be se lected at light load conditions allowing switching losses to be reduced L6928 is externally synchroni zable with a clock which makes it useful in noise sen sitive applications Other features like Powergood Overvoltage protection Shortcircuit protection and Thermal Shutdown 150 C are also present Vout 1 BV O C4 10uF 6 3V Rev 3 1 10 L6928 Table 2 Absolute Maximum Ratings Symbol Parameter Value Unit Input voltage 0 3 to 6 Output switching voltage 1 to Vcc Shutdown 0 3 to Vcc Feedback voltage 0 3 to Vcc Error amplifier output voltage 0 3 to Vcc PGOOD 0 3 to Vcc Synchronization mode selector 0 3 to Vcc Power dissipation at Tamb 70 C 0 45 Junction operating temperature range for MSOP8 package 40 to 150 Storage temperature range 65 to 150 Maximum Withstanding Voltage Range Test Condition CDF Other pins AEC Q100 002 Human Body Model Acceptance Criteria Normal Performance Figure 3 Pin Connection DO1IN1239AMOD Table 3 Thermal Data Symbol Tai Rthj amb Thermal Resistance Junction to Ambient for MSOP8 Max 180 C W Table 4 Pin Functions N Name Description 1 RUN Shutdown input When connected to a low level lower than 0 4V the device stops working
14. r amplifier output goes low so reducing the peak inductor current to meet the new load requirements The slope compensation signal allows the loop stability also in high duty cycle conditions see related section Figure 4 Device Block Diagram SYNC RUN VCC O O OSCILLATOR SENSE g MOS LOW COMPO NOISE CONSUMPTION SLOPE GND LOOP PEAK FBO CONTROL cL DRIVER LX Y ZERO CROSSING GND VALLEY CL GND 4 1 Modes of Operation Depending on the SYNC pin value the device can operate in low consumption or low noise mode If the SYNC pin is high higher than 1 3V the low consumption mode is selected while the low noise mode is selected if the SYNC pin is low lower than 0 5V 4 1 1 Low Consumption Mode In this mode of operation at light load the device operates discontinuously based on the COMP pin voltage in order to keep the efficiency very high also in these conditions While the device is not switching the load dis charges the output capacitor and the output voltage goes down When the feedback voltage goes lower than the internal reference the COMP pin voltage increases and when an internal threshold is reached the device starts to switch In these conditions the peak current limit is set approximately in the range of 200mA 400mA depending on the slope compensation see related section
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STMICROELECTRONICS L6928 handbook