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LINEAR TECHNOLOGY LTC3440 Manual

1. 5V 100 snail Vin 4 5V Burst Mode Vin 27V TO 45V 1703440 DE Vour _ 70 Vin 3 6V l Vin 2 7V s FB T 60 22uF 50 3 o CELLS 40 GND 7 30 R 60 fosc 1MHz 20 10 1 Burst Mode OPERATION C1 TAIYO YUDEN JMK212BJ106MG asso those Lfose 1MHz 0 FIXED FREQUENCY C2 TAIYO YUDEN JMK325BJ226MM m 10 um i000 LOCATE COMPONENTS AS 01 ON SEMICONDUCTOR MBRM120T3 CLOSE TO IC AS POSSIBLE L1 SUMIDA CDRH4D28 100 OUTPUT CURRENT mA 3440 TA06b Low Profile 1 1mm Li lon to 3 3V at 200mA Converter L1 4 7uH Vin 2 5V TO 4 2V LTC3440 Vour FB 1 Burst Mode OPERATION C1 TAIYO YUDEN JMK212BJ475MG 3440 ros 0 FIXED FREQUENCY C2 TAIYO YUDEN JMK212BJ475MG fosc 2MHz L1 COILCRAFT LPO1704 472M Efficiency 100 90 Burst Mode 80 OPERATION _ 70 3 e 60 h gt s Vin 2 5V Dn 42V z Vin 3 3V Q 40 30 20 10 0 0 1 1 10 100 1000 OUTPUT CURRENT mA 3440 TAQ4b 16 LIC3440 TYPICAL APPLICATIONS Efficiency of the WCDMA WCDMA Power Amp Power Supply with Dynamic Voltage Control Power Amp Power Supply Vout 3 3V 1 7V Vpac 1 22V 100 OUT Vpac Voyr AV Vout 0 4V TO 5V z Vin 2 5V TO 4 2V LTC3440 g
2. LTC3440 Micropower Synchronous Buck Boost DC DC Converter DESCRIPTION The LTC 3440 is a high efficiency fixed frequency Buck Boost DC DC converter that operates from input voltages above below or equal to the output voltage The topology incorporated in the IC provides a continuous transfer function through all operating modes making the product ideal for single lithium ion multicell alkaline or NiMH applications where the output voltage is within the battery voltage range The device includes two 0 19 N channel MOSFET switches and two 0 220 P channel switches Switching frequencies up to 2MHz are programmed with an external resistor and the oscillator can be synchronized to an external clock Quiescent current is only 25uA in Burst Mode operation maximizing battery life in portable appli cations Burst Mode operation is user controlled and can be enabled by driving the MODE SYNC pin high If the MODE SYNC pin has either a clock or is driven low then fixed frequency switching is enabled Other features include a 1uA shutdown soft start con trol thermal shutdown and current limit The LTC3440 is available in the 10 pin thermally enhanced MSOP and 3mm x 3mm DFN packages 7 LTC and LT are registered trademarks of Linear Technology Corporation Burst Mode is a registered trademark of Linear Technology Corporation Protected by U S Patents including 6404251 6166527 ECHNOLOGY FEATURES Single Ind
3. 2 05V BOOST A ON B OFF PWM CD SWITCHES BOOST REGION 50018 y V3 1 65V FOUR SWITCH PWM BUCK BOOST REGION Dmax i V2 1 55V D ON C OFF PWM SWITCHES BUCK REGION 0 Y V1 0 9V DUTY INTERNAL CYCLE CONTROL VOLTAGE Ve Figure 2 Switch Control vs Internal Control Voltage Vc Buck Region Vin gt Vout Switch D is always on and switch C is always off during this mode When the internal control voltage Vc is above voltage V1 output A begins to switch During the off time of switch A synchronous switch B turns on for the remainder of the time Switches A and B will alternate similar to a typical synchronous buck regulator As the control voltage increases the duty cycle of switch A increases until the maximum duty cycle of the converter in Buck mode reaches Dyax guck given by Dmax Buck 100 D4sw where D4sw duty cycle of the four switch range D4ow 150ns f 100 where f operating frequency Hz Beyond this point the four switch or Buck Boost region is reached Buck Boost or Four Switch Vin Vout When the internal control voltage Vc is above voltage V2 switch pair AD remain on for duty cycle Dmax guck and the switch pair AC begins to phase in As switch pair AC phases in switch pair BD phases out accordingly When the Vc voltage reaches the edge of the Buck Boost range at voltage V3 the AC switch pair completely phase out the BD pair and the boost phase begins
4. 2 5V to 5 5V Voutmin 0 6V lg 20uA DC DC Converter Isp 1uA ThinSOT Package LTC3411 1 25A Ipyr 4MHz Synchronous Step Down 95 Efficiency Viy 2 5V to 5 5V Vourmin 0 8V lq 60pA DC DC Converter Isp 1uA MS10 Package LTC3412 2 5A Igyr 4MHz Synchronous Step Down 95 Efficiency Vin 2 5V to 5 5V Voutmin 0 8V Iq 60pA DC DC Converter Isp lt 1uA TSSOP16E Package LTC3441 LTC3443 1 2A loyr 1MHz 0 6MHz Micropower Synchronous 95 Efficiency Vin 2 4V to 5 5V 2 4V to 5 25V Buck Boost DC DC Converter lg 25uA Isp 1uA DFN Package ThinSOT is a trademark of Linear Technology Corporation Linear Technology Corporation 1630 McCarthy Blvd Milpitas CA 95035 7417 408 432 1900 FAX 408 434 0507 www linear com 3440fa LT TP 1004 1K REV A PRINTED IN USA TECHNOLOGY LINEAR TECHNOLOGY CORPORATION 2001
5. 25MHz High Efficiency Step Up 90 Efficiency Vin 1 6V to 18V Voyr uiy 35V Iq 1 8mA DC DC Converter Isp 1uA MS10 Package LTC1877 600mA lgyr 550kHz Synchronous Step Down 95 Efficiency Vin 2 7V to 10V Voutmin 0 8V Iq 100A DC DC Converter Isp 1uA MS8 Package LTC1878 600 0 550kHz Synchronous Step Down 95 Efficiency Vin 2 7V to 6V Voyrminy 0 8V Ig 109A DC DC Converter Isp lt 1 uA MS8 Package LTC1879 1 2A loyr 550kHz Synchronous Step Down 95 Efficiency Vin 2 7V to 10V Vout min 0 8V Iq 15uA DC DC Converter Isp lt 1uA TSSOP16 Package LT1961 1 5A Isw 1 25MHz High Efficiency Step Up 90 Efficiency Vj to 25V Vour min 35V Iq 0 9mA DC DC Converter Isp 6uA MS8E Package LTC3400 LTC3400B 600mA lsw 1 2MHz Synchronous Step Up 92 Efficiency Vin 0 85V to SV Vout miny 5 lg 1944 30094 DC DC Converter Isp lt 1uA ThinSOT Package LTC3401 1A Isw 3MHz Synchronous Step Up 97 Efficiency Vin 0 5V to SV Voutcminy 6V 38pA DC DC Converter Isp 1uA MS10 Package LTC3402 2A Isw 3MHz Synchronous Step Up 97 Efficiency Vin 0 5V to SV 6V 38pA DC DC Converter Isp 1uA MS10 Package LTC3405 LTC3405A 300mA loyr 1 5MHz Synchronous Step Down 95 Efficiency Vin 2 7V to 6V Voyrminy 0 8V Ig 209A DC DC Converter Isp 1uA ThinSOT Package LTC3406 LTC3406B 600mA loyr 1 5MHz Synchronous Step Down 95 Efficiency Vin
6. EXCEED 0 152mm 006 PER SIDE 4 DIMENSION DOES NOT INGLUDE INTERLEAD FLASH OR PROTRUSIONS INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0 152mm 006 PER SIDE 5 LEAD COPLANARITY BOTTOM OF LEADS AFTER FORMING SHALL BE 0 102mm 004 MAX 3440fa Information furnished by Linear Technology Corporation is believed to be accurate and reliable FAR However no responsibility is assumed for its use Linear Technology Corporation makes no represen ECHNOLOGY tation thatthe interconnection of its circuits as described herein will not infringe on existing patent rights LIC3440 Li lon to 3 3V at 600mA Buck Boost Converter L1 Efficiency 10uH Vout 100 3 3V 600mA 90 Burst Mode OPERATION Vin 2 8V TO 4 2V Vin 4 2 60 TT c2 5 Vin 3 3V C5 300pF 2 50 10 22uF o Li lon 40 30 20 10 1 Burst Mode OPERATION C1 TAIYO YUDEN JMK212BJ106MG Lm 0 0 FIXED FREQUENCY C2 TAIYO YUDEN JMK325BJ226MM 0 1 1 0 10 100 1000 L1 SUMIDA CDRH4D28 100 OUTPUT CURRENT mA PART NUMBER DESCRIPTION COMMENTS LT1613 550mA lsw 1 4MHz High Efficiency Step Up 90 Efficiency Vin 0 9V to 10V Vout miny 34V lg 3 DC DC Converter Isp 1uA ThinSOT Package LT1618 1 5A lew 1
7. at duty cycle D4ow The input voltage Vin where the four switch region begins is given by Vour 1 150ns The point at which the four switch region ends is given by Vin Voyr 1 D 1 150541 V MN Boost Region Vin lt Vout Switch A is always on and switch B is always off during this mode When the internal control voltage Vc is above voltage V3 switch pair CD will alternately switch to providea boosted output voltage This operation is typical to a synchronous boost regulator The maximum duty cycle of the converter is limited to 7596 typical and is reached when Vc is above V4 Burst Mode Operation Burst Mode operation is when the IC delivers energy to the output until itis regulated and then goes into a sleep mode where the outputs are off and the IC is consuming only 25uA In this mode the output ripple has a variable frequency component that depends upon load current During the period where the device is delivering energy to the output the peak current will be equal to 400mA typical and the inductor current will terminate at zero current for each cycle In this mode the maximum average output current is given by 0 1 VN A loUT MAX BURST 77 ns Vour VN Burst Mode operation is user controlled by driving the MODE SYNC pin high to enable and low to disable The peak efficiency during Burst Mode operation is less than the peak efficiency during fixed frequency because the part e
8. 0 10 A epe 2 SIDES NOTE 1 DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0 229 VARIATION OF WEED 2 CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT 2 DRAWING NOT TO SCALE 3 ALL DIMENSIONS ARE IN MILLIMETERS 4 DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH MOLD FLASH IF PRESENT SHALL NOT EXCEED 0 15mm ON ANY SIDE 5 EXPOSED PAD SHALL BE SOLDER PLATED 6 SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE 18 LIC3440 PACKAGE DESCAIPTION MS Package 10 Lead Plastic MSOP Reference LTC DWG 05 08 1661 0 889 0 127 025 gt 005 3 n 3 45 MH iu 136 ponti TC NN 0 305 gt 0 038 0 50 0004 004 0 497 0 076 0120 0015 0197 NOTE 3 ED 376 0196 003 TYP BSC REF RECOMMENDED SOLDER PAD LAYOUT MTM 3 00 0 102 ETT 118 004 0254 JP 133 006 NOTE 4 010 0 GAUGE PLANE 1 12345 TI 0 53 0 152 021 006 140 0 86 DETAIL 1 pen 0 18 i SEATING Vy Y PLANE 017 027 he 0 127 0 076 007 011 0 50 005 gt 003 TYP TE 3 MSOP MS 0603 NOTE 0197 1 DIMENSIONS IN MILLIMETER INCH BSC 2 DRAWING NOT TO SCALE 3 DIMENSION DOES NOT INGLUDE MOLD FLASH PROTRUSIONS OR GATE BURRS MOLD FLASH PROTRUSIONS OR GATE BURRS SHALL NOT
9. Current Active Vc OV MODE SYNC OV Note 3 600 1000 uA NMOS Switch Leakage Switches B and C 0 1 5 uA PMOS Switch Leakage Switches A and D 0 1 10 uA NMOS Switch On Resistance Switches B and C 0 19 Q PMOS Switch On Resistance Switches A and D 0 22 Q Input Current Limit 1 Maximum Duty Cycle Boost Switch C On 55 75 Buck 9o Switch A On e 100 Minimum Duty Cycle e 0 Frequency Accuracy 0 8 1 1 2 MHz MODE SYNC Threshold 0 4 2 V MODE SYNC Input Current VMODE SYNC 5 5V 0 01 1 uA Error Amp AVOL 90 dB Error Amp Source Current 15 uA Error Amp Sink Current 380 uA 2 LIC3440 ELECTRICAL CHARACTERISTICS The e denotes specifications that apply over the full operating temperature range otherwise specifications are at TA 25 C Vin Vout 3 6V 60k unless otherwise noted PARAMETER CONDITIONS MIN TYP MAX UNITS SHDN SS Threshold When IC is Enabled 04 1 1 5 V When EA is at Maximum Boost Duty Cycle 2 2 V SHDN SS Input Current VSHDN 5 5V 0 01 1 uA Note 1 Absolute Maximum Ratings are those values beyond which the life temperature range are assured by design characterization and correlation of the device may be impaired with statistical process controls Note 2 The LTC3440E is guaranteed to meet performance specifications Note 3 Current measurements are performed when the outputs are not from 0 C to 70 C Specifications over the 40 C to 85 C operating sw
10. IV 3440 605 Vin 4 15V 50ns DIV 3440606 Vout 3 3V Vout 3 3V Vout 3 3V lout 250mA loyr 250mA lour 250mA 3440fa LI MYR B LIC3440 TYPICAL PERFORMANCE CHARACTERISTICS Switch Pins in Buck Mode Switch Pins in Boost Mode swt swt 2V DIV 4 ovpiv Vour 10mV DIV ane hou di AC Coupled 2V DIV SW2 d 2V DIV Vin 5V 250ns DIV 3440 607 Vin 2 5V 250ns DIV 3440 608 Vout 3 3V Vout 3 3V lour 250mA lour 250mA Active Quiescent Current Burst Mode Quiescent Current 550 40 r Vin Vout 3 6V Vin Vout 3 6V 500 30 EE 3 3 E 5 2 450 gt 20 z od gt gt 10 55 235 5 35 65 95 125 55 25 5 35 65 95 125 TEMPERATURE C TEMPERATURE C 3440 G10 3440 G11 Output Frequency NMOS Rps on 110 Vin Vout 3 6V 230 Vin Vout 3 6V SWITCHES B AND C 1 05 amp 2 1 00 O E 0 95 0 90 55 235 5 35 65 95 125 55 25 5 35 65 95 125 TEMPERATURE C TEMPERATURE C 3440 G13 3440 G14 Vout Ripple During Buck Buck Boost and Boost Modes h voten oreet N 124 L 10uH Cour 22uF 250mA fosc 1MHz tus DIV 3440 609 Error Amp Source Current 20 Vin Vou
11. NS INFORMATION Ripple allowable inductor current ripple e g 0 2 20 minimum input voltage V Vin max maximum input voltage V Vout output voltage V lour MAx Maximum output load current For high efficiency choose an inductor with a high fre quency core material such as ferrite to reduce core loses The inductor should have low ESR equivalent series resistance to reduce the IR losses and must be able to handle the peak inductor current without saturating Molded chokes or chip inductors usually do not have enough core to support the peak inductor currents in the 1A to 2A region To minimize radiated noise use a toroid pot core or shielded bobbin inductor See Table 1 for suggested components and Table 2 for alist of component suppliers Table 1 Inductor Vendor Information The output capacitance is usually many times larger in order to handle the transient response of the converter For a rule of thumb the ratio of the operating frequency to the unity gain bandwidth of the converter is the amount the output capacitance will have to increase from the above calculations in order to maintain the desired tran sient response The other component of ripple is due to the ESR equiva lent series resistance of the output capacitor Low ESR capacitors should be used to minimize output voltage ripple For surface mount applications Taiyo Yuden ce ramic capacitors AVX TPS series tantalum capacitors
12. SS Lead Temperature Soldering 10 sec 300 C MODE SYNC Voltage 0 3V to 6V PACKAGE ORDER INFORMATION TOP VIEW ORDER PART TOP VIEW ORDER PART NUMBER Rr 1 10 Ve NUMBER T MODE SYNC 2 9 PB MODE SYNC FB SWI 3 8 SHDN SS sw SAD SS LTC3440EDD SW2 4 7 Vw LTC3440EMS SW Vin GND 5 6 Vout MS PACKAGE ME Vour DD 10 LEAD PLASTIC MSOP MS 10 LEAD lt dmm PLASTIC DFN PART MARKING Tow 12570 PART MARKING EXPOSED PAD PIN 11 IS GND ya 130 C W 1 LAYER BOARD MUST BE SOLUERED PCB LBKT 100 C W 4 LAYER BOARD LTNP Tymax 125 C 43 C W 3 C W 8jc 45 C W Consult LTC Marketing for parts specified with wider operating temperature ranges ELECTRICAL CHARACTERISTICS The e denotes specifications that apply over the full operating temperature range otherwise specifications are at TA 25 C Vin Vgyr 3 6V 60k unless otherwise noted PARAMETER CONDITIONS MIN TYP MAX UNITS Input Start Up Voltage e 24 2 5 V Input Operating Range B 2 5 5 5 V Output Voltage Adjust Range e 25 5 5 V Feedback Voltage e 1 196 1 22 1 244 V Feedback Input Current Veg 1 22V 1 50 nA Quiescent Current Burst Mode Operation Vc OV MODE SYNC 3V Note 3 25 40 uA Quiescent Current Shutdown SHDN OV Not Including Switch Leakage 0 1 1 uA Quiescent
13. ain is typically rolled off before the RHP zero frequency A simple Type compensation network can be incorpo rated to stabilize the loop but at a cost of reduced band width and slower transient response To ensure proper phase margin the loop requires to be crossed over a decade before the LC double pole The unity gain frequency of the error amplifier with the Type compensation is given by 1 1 Mostapplications demand an improvedtransient response to allow a smaller output filter capacitor To achieve a higher bandwidth Type Ill compensation is required Two zeros are required to compensate for the double pole response fuc 3440fa 13 LTC3440 APPLICATIONS INFORMATION 1 traces and external components Following the recom POLE 20103263 R Cpi Hz mendations for output voltage gt 4 3V and input voltage gt 4 5V will improve this condition Additional short circuit protection can be accomplished with some external cir Which is extremely close to DC fZERO1 2 In an overload or short circuit condition the 1703440 1 voltage loop opens and the error amp control voltage on X mt the Vc pin slams to the upper clamp level This condition e forces boost mode operation in orderto attemptto provide 1 Hz more output voltage and the IC hits a peak switch current 2 x limit of 2 7A When switch current limit is reached switche
14. ation components are configured around the amplifier to provide loop compensation for the converter The SHDN SS pin will clamp the error amp output Vc to provide a soft start function Supply Current Limit The current limit amplifier will shut PMOS switch A off once the current exceeds 2 7A typical The current ampli fier delay to output is typically 50ns Reverse Current Limit The reverse current limit amplifier monitors the inductor currentfrom the outputthrough switch D Once a negative inductor current exceeds 400mA typical the IC will shut off switch D Output Switch Control Figure 1 shows a simplified diagram of how the four internal switches are connected to the inductor Vin Vout and GND Figure 2 shows the regions of operation for the LTC3440 as a function of the internal control voltage The Vc voltage is a level shifted voltage from the output of the error amp Vc pin see Figure 5 The output switches are properly phased so the transfer between operation modes is continuous filtered and transparent to the user When Vin approaches Voyr the Buck Boost region is reached where the conduction time of the four switch region is typically 150ns Referring to Figures 1 and 2 the various regions of operation will now be described VIN Vour PMOS D NMOS B Figure 1 Simplified Diagram of Output Switches NMOS C TZ LIC3440 75 DMax n V4
15. ill provide a lower voltage drop during the break before make time typically 15ns of the NMOS to PMOS transition General purpose diodes such as a 1N914 are not recommended due to the slow recovery times and will compromise efficiency If desired a large Schottky diode such as an MBRM120T3 can be used from SW2 to Voy A low capacitance Schottky diode is recommended from GND to SW1 such as a Phillips PMEG2010EA or equivalent 12 LIC3440 APPLICATIONS INFORMATION Output Voltage gt 4 3V A Schottky diode from SW to Voyt is required for output voltages over 4 3V The diode must be located as close to the pins as possible in order to reduce the peak voltage on SW2 due to the parasitic lead and trace inductance Input Voltage 4 5V For applications with input voltages above 4 5V which could exhibit an overload or short circuit condition a 2Q 1nF series snubber is required between the SW1 pin and GND A Schottky diode such as the Phillips PMEG2010EA or equivalent from SW1 to Vin should also be added as close to the pins as possible For the higher input voltages Vin bypassing becomes more critical therefore a ceramic bypass capacitor as close to the Vj and GND pins as possible is also required Operating Frequency Selection There are several considerations in selecting the operating frequency of the converter The first is what are the sensitive frequency bands that cannot tolerate any spec tral noise For example i
16. ing the Feedback Loop 400mA IINDUCTOR lINDUCTOR t 3440 400 3440 F04 T2 Figure 4 Inductor Discharge Cycle During Burst Mode Operation 10 LIC3440 OPERATION SOFT START The soft start function is combined with shutdown When the SHDN SS pin is brought above typically 1V the IC is enabled but the EA duty cycle is clamped from the Vc pin SOFT START CLAMP TO PWM COMPARATORS A detailed diagram of this function is shown in Figure 5 The components Rss and Css provide a slow ramping voltage on the SHDN SS pin to provide a soft start function ERROR AMP ENABLE SIGNAL 3440 FOS Figure 5 Soft Start Circuitry APPLICATIONS INFORMATION COMPONENT SELECTION VIAS 3440 F06 Figure 6 Recommended Component Placement Traces Carrying High Current are Direct Trace Area at FB and Vc Pins are Low Lead Length to Battery Should be Kept Short Inductor Selection The high frequency operation of the 1763440 allows the use of small surface mount inductors The inductor cur rent ripple is typically set to 20 to 40 of the maximum inductor current For a given ripple the inductance terms are given as follows V A Ls IN MIN uH f loutimax Ripple Vout Vour V Ls OUT our uH f e loutmax Ripple Vimax where f operating frequency MHz 3440fa LI MYR 11 LIC3440 APPLICATIO
17. itching TYPICAL PERFORMANCE CHARACTERISTICS Li lon to 3 3V Efficiency Li lon to 3 3V Efficiency Li lon to 3 3V Efficiency fosc 300kHz Power Loss 105 1MHz fosc 2MHz 100 100 1000 100 90 Burst Mode 90 F Burst Mode 90 OPES Mad OPERATION OPERATION 80 80 m 80 100 Vin 4 2V Vin 4 2V S 7 3 70 70 Vcc TTT WN Vin 25V 3 22 Vin 4 2V Vin 2 5V f f Vin 3 3V B 60 0 2 60 Vin 2 5V 8 2 2 Vin 3 3V E 50 x 50 amp 9 T Vin 3 3V 40 40 1 40 B f 1MH fosc 2MHz 3j fosc 300kHz 20 1050511 le 04 20 0 1 1 10 100 1000 0 1 1 10 100 1000 04 1 10 100 1000 OUTPUT CURRENT mA OUTPUT CURRENT mA OUTPUT CURRENT mA 3440 G01 3440 G02 9440 608 Switch Pins on the Edge of Switch Pins on the Edge of Switch Pins During Buck Boost Buck Boost and Approaching Boost Buck Boost and Approaching Buck swi swi swi 2V DIV 2V DIV 2V DIV SW2 4 SW2 4 SW 4 2V DIV 2V DIV 2V DIV Vin 3 78V 50ns DIV 3440 G04 Vin 3 42V 50ns D
18. n products incorporating RF communications the 455kHz IF frequency is sensitive to any noise therefore switching above 600kHz is desired Some communications have sensitivity to 1 1 MHz and in that case a 2MHz converter frequency may be employed Other considerations are the physical size of the converter and efficiency As the operating frequency goes up the inductor and filter capacitors go down in value and size Thetrade off is in efficiency sincethe switching losses due to gate charge are going up proportional with frequency Additional quiescent current due to the output switches GATE charge is given by Buck 5006 12 Vin oF Boost 250612 Vin F Buck Boost F 750612 Vy 2506712 Vy where F switching frequency Closing the Feedback Loop The LTC3440 incorporates voltage mode PWM control The control to output gain varies with operation region Buck Boost Buck Boost but is usually no greater than 15 The output filter exhibits a double pole response is given by 1 f FILTER POLE 747 Com Hz in Buck mode Vin f __ Hz in Boost mode FILTER POLE Ine JL our where Cour is the output filter capacitor The output filter zero is given by 1 FILTER ZERO 77 ery Hz where Resp is the capacitor equivalent series resistance A troublesome feature in Boost mode is the right half plane zero RHP and is given by 2 Vin 2em loyr L Vour fRupz The loop g
19. nters full time 4 switch mode when servicing the output with discontinuous inductor current as illus trated in Figures 3 and 4 During Burst Mode operation the control loop is nonlinear and cannot utilize the control 3440fa 9 LIC3440 OPERATION voltage from the error amp to determine the control mode therefore full time 4 switch mode is required to maintain the Buck Boost function The efficiency below 1mA becomes dominated primarily by the quiescent current and not the peak efficiency The equation is given by nbm li Efficiency Burst 25uA I where is typically 79 during Burst Mode opera tion for an ESR of the inductor of 50mQ For 200mQ of inductor ESR the peak efficiency drops to 75 dl Vour aa es gt dT GND Burst Mode Operation to Fixed Frequency Transient Response When transitioning from Burst Mode operation to fixed frequency the system exhibits a transient since the modes of operation have changed For most systems this tran sient is acceptable but the application may have stringent input current and or output voltage requirements that dictate a broad band voltage loop to minimize the tran sient Lowering the DC gain of the loop will facilitate the task 10M FB to Vc at the expense of DC load regulation Type 3 compensation is also recommended to broad band the loop and roll off past the two pole response of the LC of the converter see Clos
20. or Sanyo POSCAP are recommended Input Capacitor Selection Since the Vin pin is the supply voltage for the IC it is recommended to place at least a 4 7uF low ESR bypass capacitor Table 2 Capacitor Vendor Information SUPPLIER PHONE FAX WEB SITE AVX 803 448 9411 803 448 1943 WWW avxcorp com Sanyo 619 661 6322 www sanyovideo com SUPPLIER PHONE FAX WEB SITE Coilcraft 847 639 6400 847 639 1469 www coilcraft com Coiltronics 561 241 7876 561 241 9339 www coiltronics com Murata USA USA www murata com 814 237 1431 814 238 0490 800 831 9172 Sumida USA www japanlink com 847 956 0666 847 956 0702 sumida Japan 81 3 3607 5111 81 3 3607 5144 Output Capacitor Selection The bulk value of the capacitor is set to reduce the ripple due to charge into the capacitor each cycle The steady State ripple due to charge is given by Vour M 100 x Ripple Boost Vour 100 Cour our f lour max Vout 100 i Ripple Buck Cour Vout where Cour output filter capacitor F 619 661 1055 Taiyo Yuden 408 573 4150 408 573 4159 www t yuden com Optional Schottky Diodes Toachievea 1 2 efficiency improvementabove 50mW Schottky diodes can be added across synchronous switches SW1 to GND and D SW2 to Voyr The Schottky diodes w
21. r to Program the Oscillator Frequency The programming frequency range is 300kHz to 2MHz 601010 RT MODE SYNC Pin 2 MODE SYNC External CLK Syn chronization of the internal oscillator A clock frequency of twice the desired switching frequency and with a pulse width between 100ns and 2us is applied The oscillator free running frequency is set slower than the desired synchronized switching frequency to guarantee sync The oscillator component value required is given by Hz fosc 1010 R 8210 cw where few desired synchronized switching frequency SW1 Pin 3 Switch Pin Where the Internal Switches and Bare Connected Connect inductorfrom SW1 to SW2 An optional Schottky diode can be connected from SW1 to ground Minimize trace length to keep EMI down SW2 Pin 4 Switch Pin Where the Internal Switches C and D are Connected For applications with output volt ages over 4 3V a Schottky diode is required from SW to Vout to ensure the SW pin does not exhibit excess voltage GND Pin 5 Signal and Power Ground for the IC Voyr Pin 6 Output of the Synchronous Rectifier A filter capacitor is placed from Voyr to GND Vin Pin 7 Input Supply Pin Internal Veg for the IC A ceramic bypass capacitor as close to the Viy pin and GND Pin 5 is required SHDN SS Pin 8 Combined Soft Start and Shutdown Grounding this pin shuts down the IC Tie to 1 5V to enable the IC and gt 2 5V to ens
22. s B and D turn on for the remainder of the cycle to reverse the volts seconds on the inductor Although this prevents current run away this condition produces four switch operation producing a current foldback characteristic and the average input current drops The IC is trimmed to guarantee greater than 1A average input current to meet the maximum load demand but in a short circuit or overload condition the foldback characteristic will occur producing higher peak switch currents To minimize this affect during this condition the following circuits can be utilized Restart Circuit For a sustained short circuit the circuit in Figure 9 will force a soft start condition The only design constraint is that R2 C2 time constant must be longer than the soft start components R1 C1 to ensure start up 3440 F08 Figure 8 Error Amplifier with Type Compensation 50 55 Short Circuit Improvements Ci The LTC3440 is current limited to 2 7A peak to protect the IC from damage At input voltages above 4 5V a current limit condition may produce undesirable voltages to the IC due to the series inductance of the package as wellasthe Figure 9 Soft Start Reset Circuitry for Sustained Short Circuit 14 LIC3440 APPLICATIONS INFORMATION Simple Average Input Current Control INPUT VOLTAGE A simple average current limit circuit is shown in Figure 10 Once the input current of the IC is above approximately 1A Q1
23. t 3 6V E 15 tr Em cC c C Q 10 x 5 55 235 5 35 65 95 125 TEMPERATURE C 3440 G12 Feedback Voltage 1 236 Vin Vout 3V 1421 lt 3 S 1 216 ae e lt ca H 1 196 55 2 5 35 65 95 125 TEMPERATURE C 3440 615 LIC3440 TYPICAL PERFORMANCE CHARACTERISTICS Feedback Voltage Line Regulation 90 Vin Vout 2 5V TO 5 5V 80 e 3 2 oO cc 70 60 55 25 5 35 65 95 125 TEMPERATURE C 3440 G16 Boost Max Duty Cycle 90 Vin Vout 3 6V 60k 85 a S 8 c gt 2 ea 75 70 55 25 5 35 65 95 125 TEMPERATURE C 3440 G19 430 Error Amp Sink Current Vin Vout 3 6V 410 390 E A SINK CURRENT uA 370 55 25 5 35 65 95 125 2 40 a po MINIMUM START VOLTAGE V TEMPERATURE C 3440 G17 Minimum Start Voltage 55 25 5 35 65 95 125 TEMPERATURE C 3440 G20 CURRENT LIMIT A PMOS Rps oN Vin Vout 3 6V SWITCHES A AND D 55 25 5 35 65 95 125 TEMPERATURE C 3440 G18 Current Limit 3000 Vin Vout 3 6V 2500 2000 AVERAGE INPUT 1500 TEMPERATURE C 3440 G21 3440fa LIC3440 PIN FUNCTIONS Rr Pin 1 Timing Resisto
24. t lout 250mA Vin Vour 5 SHDN SS FB E nm C4 150pF TM MODE SYNC Vc dU E Rr C5 10pF 30 1k fosc 2MHz 25 3 35 4 45 5 1 Burst Mode OPERATION C1 C2 TAIYO JMK212BJ106MM TREE REA RUE 0 FIXED FREQUENCY D1 ON SEMICONDUCTOR MBRM120T3 940 TAOTO LOCATE COMPONENTS AS 11 SUMIDA CDRH4D28 3R3 CLOSE TO IC AS POSSIBLE GSM Modem Powered from USB or PCMCIA with 500mA Input Current Limit L1 V 10uH Hd 2A PULSED Vi 2 5V TO 55V cp USB PCMCIA POWER 500mA MAX C6 TO 09 SHDN SS FB 470uF x4 MODE SYNG Vc 3440 TAOS C1 TAIYO YUDEN JMK212BJ106MG C2 TAIYO YUDEN JMK325BJ226MM L1 SUMIDA CDRH 4D28 100 1 Burst Mode OPERATION ICURRENTLIMIT 7 cres 0 FIXED FREQUENCY 2N3906 1 2 LT1490A 3440fa LI MYR 17 LIC3440 PACKAGE DESCRIPTIO 3 50 0 05 1 65 0 05 n DD Package 10 Lead Plastic DFN 3mm x 3mm Reference LTC DWG 05 08 1699 0 675 0 05 2 15 0 05 2 SIDES 4 H0000 0 25 0 05 r 0 50 BSC I lt 2 38 0 05 gt 2 SIDES Ler PACKAGE OUTLINE RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS R 0 115 0 38 0 10 3 00 0 10 1 65 x 0 10 4 SIDES 2 SIDES E PIN 1 TOP MARK SEE Y 0010 DFN 1103 0 200 REF 0 75 0 05 Bt ns 0 25 0 05 1 0 50 BSC BOTTOM VIEW EXPOSED PAD lt 2 38
25. uctor Fixed Frequency Operation with Battery Voltages Above Below or Equal to the Output m Synchronous Rectification Up to 96 Efficiency 25uA Quiescent Current in Burst Mode Operation Up to 600mA Continuous Output Current m No Schottky Diodes Required Voyr lt 4 3V m Voyr Disconnected from Vin During Shutdown m 2 5V to 5 5V Input and Output Range Programmable Oscillator Frequency from 300kHz to 2MHz Synchronizable Oscillator Burst Mode Enable Control m lt tuA Shutdown Current m Small Thermally Enhanced 10 Pin MSOP and 3mm x 3mm DFN Packages APPLICATIONS m Palmtop Computers Handheld Instruments MP3 Players Digital Cameras TYPICAL APPLICATION Li lon to 3 3V at 600mA Buck Boost Converter LTC3440 Vin Vout Vin 2 7V TO 4 2V SHDN SS C2 MODE SYNC Vc 1 Burst Mode OPERATION 0 FIXED FREQUENCY C1 TAIYO YUDEN JMK212BJ106MG C2 TAIYO YUDEN JMK325BJ226MM L1 SUMIDA CDRH6D38 100 3440 01 Efficiency vs Vin Vout 3 3 98 Flour 100mA 96 fosc 1MHz EFFICIENCY 26 9 3440 2 3440fa 1 LTC3440 ABSOLUTE MAXIMUM RATINGS Note 1 Vin Voir 0 3V to 6V Operating Temperature Range Note 2 40 C to 85 C SW1 SW2 Voltage 0 3V to 6V Storage Temperature Range 65 C to 125 C Vc FB SHDN
26. ure the error amp is not clamped from soft start An RC from the shutdown com mand signal to this pin will provide a soft start function by limiting the rise time of the Vc pin FB Pin 9 Feedback Pin Connect resistor divider tap here The output voltage can be adjusted from 2 5V to 5 5V The feedback reference voltage is typically 1 22V Vc Pin 10 Error Amp Output A frequency compensation network is connected from this pin to the FB pin to compensate the loop See the section Compensating the Feedback Loop for guidelines Exposed Pad Pin 11 DFN Package Only Ground This pin must be soldered to the PCB and electrically connected to ground LIC3440 BLOCK DIAGRAM Vour V 2 5V TO 5 5V IN 2 5V TO 5 5V GATE DRIVERS AND ANTICROSS CONDUCTION REVERSE CURRENT LIMIT SUPPLY CURRENT LIMIT PWM LOGIC PWM AND OMPARATOR ourpur 098 PHASING Burst Mode OPERATION CONTROL SHUTDOWN 5us DELAY MODE SYNC 1 Burst Mode OPERATION 0 FIXED FREQUENCY TT 3440 BD 3440fa LI MYR 7 LIC3440 OPERATION The LTC3440 provides high efficiency low noise power for applications such as portable instrumentation The LTG proprietary topology allows input voltages above below or equal to the output voltage by properly phasing the output switches The error amp output voltage on the Vc pin determines the output duty cycle of the switches Since the Vg pin is a filtered signal it pro
27. vides rejection of frequencies from well below the switching frequency The low Rps on low gate charge synchronous switches pro vide high frequency pulse width modulation control at high efficiency Schottky diodes across the synchronous switch D and synchronous switch B are not required but provide a lower drop during the break before make time typically 15ns The addition of the Schottky diodes will improve peak efficiency by typically 1 to 2 at 600kHz High efficiency is achieved at light loads when Burst Mode operation is entered and when the IC s quiescent current is a low 25uA LOW NOISE FIXED FREQUENCY OPERATION Oscillator The frequency of operation is user programmable and is set through a resistor from the pin to ground where 6e10 An internally trimmed timing capacitor resides inside the IC The oscillator can be synchronized with an external clock applied to the MODE SYNC pin A clock frequency of twice the desired switching frequency and with a pulse width between 100ns and 2us is applied The oscillator Ry component value required is given by e1010 Ry 8 10 fsw where fsw desired synchronized switching frequency For example to achieve a 1 2MHz synchronized switching frequency the applied clock frequency to the MODE SYNC pin is set to 2 4MHz and the timing resistor Rr is set to 66 5k closest 1 value Error Amp The error amplifier is a voltage mode amplifier The loop compens
28. will start sourcing current into the FB pin and lower the output voltage to maintain the average input current Since the voltage loop is utilized to perform average current limit the voltage control loop is maintained and the Vc voltage does not slam The averag Ms 10 Simple Input Current Control ilizing the Voltage Loop ing function of current comes from the fact that voltage loop compensation is also used with this circuit FB PIN TYPICAL APPLICATIONS 3 Cell to 3 3V at 600mA Converter 1 02 3 3V D1 600mA VIN psv TO 4 5V LTC3440 Vout FB Ca tL MODE SYNC xd 3 CELLS em Rr GND RT fosc 1 5MHz C5 10pF 1 Burst Mode OPERATION C1 TAIYO YUDEN JMK212BJ106MG 09 0 FIXED FREQUENCY C2 TAIYO YUDEN JMK325BJ226MM D1 D2 CENTRAL SEMICONDUCTOR CMDSH2 3 L1 SUMIDA CDR43 4R7M 3 Cell to 3 3V Efficiency 100 30 Burst Mode 80 OPERATION aan Vin 2 7V is Vin 4 5V 2 50 E Q 40 12 30 20 10 f 0 fosc 1 5MHz 0 1 1 10 100 1000 OUTPUT CURRENT mA 3440 3440fa LI MYR 15 LIC3440 TYPICAL APPLICATIONS 3 Cell to 5V Boost Converter with Output Disconnect s 10uH Di 3 Cell to 5V Boost Efficiency

LINEAR TECHNOLOGY LTC3440 Manual

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