ltc9709x

A Showcase of Linear Technology’s Focus ProductsVol. 6 No. 9

Product of the MonthDual Current Feedback Amplifier Delivers 125mAOutput Current and 900V/µs Slew Rate The LT®1497 is a dual Current Feed-back Amplifier (CFA) that features a 900V/µs slew rate, 50MHz gain-bandwidth and aguaranteed 125mA minimum output currentover temperature using ±15V supplies.Maximum supply current per amplifier isonly 9mA for ±15V operation and just 7mAfor ±5V operation. High output drive andslew rate combine to provide low distortiontransmission of either analog or digital infor-mation down long distances of twisted pair,shielded coax or other transmission media. The LT1497 is shown below as anHDSL line driver in just one of the manyline driving applications it performs. Anyapplication that requires delivery of a fastsignal into a low impedance load, such as560Ω560ΩSynchronous BuckSwitching Regulator inSO-8 Offers High OutputAccuracy The LTC®1504 is a high efficiencysynchronous buck switching regulator foruse as a board-level 5V to 3.3V converter inmixed voltage systems. A pair of on-chip1.3Ω power switches enable it to supply anoutput current of up to 500mA. Its 200kHzoperating frequency and fast transientresponse reduce the number of outputcapacitors required for most applications.Peak efficiency of 92% is possible. TheLTC1504 is ideal in space limited designsrequiring localized voltage regulation, suchas in SCSI-II termination supplies, I/O sup-ply for split-plane CPUs and as a supply forlow power digital signal processors.NCIMAX5VSHUTDOWNSHDNSWLEXTISDN or video distribution, can benefit fromthe LT1497. The LT1497 can drive a twistedpair with a 1MHz, ±40mA peak signal at–70dBc. Settling time for a 5V step input forthe LT1497 is just 55ns. The LT1497 is offered in a low thermalresistance SO-8 package (θJA = 80°C/W) foroperation with ±5V supplies and anenhanced 16-pin SO (θJA = 40°C/W) pack-age for operation with ±15V supplies.Thermal shutdown protects against excessiveinternal (junction) temperatures by cyclingbetween normal operation and an off-state.For a data sheet and evaluation samples, con-tact your local Linear Technology salesoffice or for more information, visit our website at www.linear-tech.com.+CINVCC3.3V󰀀AT 500mALTC1504-3.3GNDSENSECOMP1000pF1504 • TA01–68.1ΩSSNC1:1*+COUTVIN+1/2 LT1497560Ω560Ω135ΩCIN: AVX TPSC226M016R0375󰀀COUT: AVX TAJC476M010󰀀LEXT: COILTRONICS CTX50-1P–68.1Ω*MIDCOM 671-7807+1/2 LT1497Figure 1. LTC1504 in Synchronous BuckArchitecture Operates over a 4V to 10VInput Voltage Range and Requires OnlyFour External Components1497 TA01Figure 1. HDSL Line Driver Has Thermal and Current Limit Circuitsthat Protect Against Fault ConditionsInside This Issue:

DC/DC Step-Up Controller Meets High Power Demands........................................................2SIM Power Supply and Level Translator Compatible with 3V and 5V Cards...........................23.3V Powered Barometric Pressure Signal Conditioner..........................................................32.5V Micropower Shunt Reference in SO-8 Guarantees 25ppm/°C and 0.05% Initial Accuracy.........................................................................................................3Fixed Voltage Output Step-Down Converters Draw Only 10µA in Standby.............................4 The LTC1504 has an internal 1% refer-ence combined with a sophisticated voltagefeedback loop that provides optimum outputvoltage accuracy and fast load transientresponse and requires no current senseresistor. Synchronous operation allows it tosink or source current for use in an activeContinued on page 4

, LTC and LT are registered trademarks of Linear TechnologyCorporation.Linear Technology Chronicle • September 19971

DC/DC Step-Up Controller Meets High Power Demands The LT1680 is a high power currentmode step-up switching regulator controllerthat drives N-channel MOSFETs with asource voltage up to 60V and gate capaci-tance up to 10,000pF. Its high powercapability makes it ideal for high voltage,high current step-up applications (Figure 1)that require hundreds of watts of outputpower at very high efficiency (Figure 2).PWM operating frequency is programmableand can be synchronized up to 200kHz to anexternal system clock for lower EMI. TheLT1680 is ideal as a switcher in the highpower industrial/automotive and telecomareas. The LT1680 incorporates program-mable average current limiting allowingaccurate limiting of DC current in the mag-netics, independent of ripple current. Useradjustable slope compensation providesstable operation at duty cycles up to 90%. Itscurrent sense common mode range up to60V allows current sensing to be referencedto the input supply, eliminating the need for12VIN10V TO 15V󰀀24A (DC)RSENSE0.005Ωsense blanking circuits. Its 5V referencewith 10mA sourcing capability provides alocal 5V supply for micropower ancillarycircuits. The LT1680 is available in 16-leadPDIP or wide SO packages over the com-mercial and industrial temperature ranges.For a data sheet and evaluation samples,contact your local Linear Technology salesoffice or for more information, visit our website at www.linear-tech.com .Kool Mµ is a registered trademark of Magnetics, Inc.C2󰀀1µFR1󰀀15kLT16801󰀀2󰀀C3, 2.2nFC4, 0.22µFC5, 4.7nFC6󰀀0.1µFR7󰀀2k3󰀀4󰀀5󰀀R2, 4.7k6󰀀7󰀀8SL/ADJ󰀀CTIAVGSS󰀀VCVFBVREF5VREFSYNC󰀀12VINGATE󰀀PGND󰀀SENSE–SENSE+16󰀀15󰀀14󰀀13󰀀12󰀀11󰀀10󰀀9R6󰀀75k++C1󰀀1nFCIN680µF󰀀25V󰀀×4C12󰀀1µFL1󰀀25µH100VOUT = 48V95EFFICIENCY (%)M1󰀀IRFZ44󰀀×390SGND󰀀RUN/SHDN󰀀R9󰀀100kC11, 1nF85D1󰀀MBR20100CT󰀀×280+L1: Kool Mµ®, 18T #14 ON 77314-A7COUT680µF󰀀63V󰀀1680 TA01×3VOUT48V󰀀5.2A75050150200100OUTPUT POWER (W)2501680 TA02Figure 1. The LT1680 as a Step-Up Converter GeneratesHigh Current 48V Bus VoltagesFigure 2. Efficiencies Approach 95% in12V to 48V Boost ApplicationsSIM Power Supply and Level Translator Compatible with 3V and 5V Cards The LTC1555/ LTC1556 are integratedsolutions providing the power conversion,digital signal level-shifting and 10kV ESDprotection needed for 3V or 5V GSM cellu-lar telephone SIMs (Subscriber IdentityModules). This permits new phones to main-tain compatibility with older 5V SIM cardsas well as the newer 3V versions. TheLTC1555/LTC1556 have a step-up/step-down charge pump that delivers a regulated3V GSM󰀀CONTROLLER3V1󰀀2󰀀3󰀀4󰀀VCC5󰀀6󰀀7󰀀8LTC1555CIN󰀀RIN󰀀DATA󰀀DDRV󰀀DVCCSS󰀀M1󰀀M0CLK󰀀RST󰀀I/O󰀀VCCVIN16󰀀15󰀀14󰀀13󰀀12󰀀0.1µF5V to the SIM card. Output voltage can alsobe programmed to 3V, 5V or be directlyconnected to the VIN pin—useful whenVIN = 3V to pass through the SIM card sup-ply voltage. The input voltage to thesedevices may range from 2.7V to 10V, per-mitting a direct connection to the battery. The LTC1555’s output current is 10mAwhen VIN ≥ 2.7V and 20mA whenVIN ≥ 3V. It is short-circuit protected and inVIN2.7V TO 10VCLK󰀀RST󰀀I/O󰀀SIM++10µF10µF11󰀀C1+C1–GND10󰀀9VCC5V ±5%󰀀IVCC ≤ 10mA󰀀GND1555/56 TA01addition has a soft start feature to controlinrush current at turn-on and tolerates indefi-nite short-circuit conditions. The switched-capacitor charge pump operates at a switch-ing frequency of 650kHz. All SIM contactpins on the LTC1555/LTC1556 are ESDprotected to 10kV—essential during inser-tion and removal of the SIM card in normaluse. The LTC1556 includes all of the fea-tures of the LTC1555 plus an internal 4.3Vlow dropout linear regulator with 5mA to10mA output current capability. TheLTC1555 is available in a 16-lead narrowSSOP package and the LTC1556 in a 20-lead narrow SSOP package. Contact yourlocal Linear Technology sales office for adata sheet and evaluation samples or visitour web site at www.linear-tech.com formore information.Figure 1. LTC1555 in the GSM Cellular Phone SIM Interface

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Linear Technology Chronicle • September 1997

Application of the Month3.3V Powered Barometric Pressure Signal Conditioner The move to 3.3V digital supply volt-age creates problems for analog signalconditioning. In particular, transducer-based circuits often require higher voltagefor proper transducer excitation. DC/DCconverters in standard configurations canaddress this issue but increase power con-sumption. Figure 1 shows a way to provideproper transducer excitation for a baromet-ric pressure sensor while minimizing powerrequirements. The 6kΩ transducer T1 requires pre-cisely 1.5mA of excitation, necessitating arelatively high voltage drive. A1 sensesT1’s current by monitoring the voltage dropacross the resistor string in T1’s return path. A1’s output biases the LT1172 switch-ing regulator’s operating point, producing astepped-up DC voltage which appears asT1’s drive and A2’s supply voltage. T1’sreturn current out of Pin 6 closes a loopback at A1 which is slaved to the 1.2V ref-erence. This arrangement provides therequired high voltage drive (≈10V) whileminimizing power consumption. This is sobecause the switching regulator producesonly enough voltage to satisfy T1’s currentrequirements. Instrumentation amplifiersA2 and A3 provide gain and the LTC1287A/D converter gives a 12-bit digital output.A2 is bootstrapped off the transducer sup-ply, enabling it to accept T1’s commonmode voltage. Circuit current consumptionis about 14mA. If the shutdown pin isdriven high, the switching regulator turnsoff, reducing total power consumption toabout 1mA. In shutdown the 3.3V poweredA/D’s output data remains valid. In prac-tice, the circuit provides a 12-bitrepresentation of ambient barometric pres-sure after calibration. To calibrate, adjustT1󰀀PRESSURE󰀀TRANSDUCER5the “bridge current trim” for exactly 0.1500Vat the indicated point. This sets T1’s currentto the manufacturers specified point. Next,adjust A3’s trim so that the digital output cor-responds to the known ambient barometricpressure. If a pressure standard is not avail-able, the transducer is supplied withindividual calibration data, permitting circuitcalibration.≈ 10V DURING OPERATIONTO PROCESSOR3.3V1046A2󰀀1µFLT1101󰀀+–A = 103.3V1/2󰀀LT1078󰀀–0.05µF+A3󰀀CSCLKDOUT+INLTC1287VCC10k*1N752󰀀5.6V–INGNDVREF+22µF1M󰀀CALIB3.3VMUR110L1󰀀150µH1N4148700Ω*BRIDGE󰀀CURRENT󰀀TRIMBRIDGE󰀀CURRENT󰀀MONITOR󰀀(0.1500V)50Ω1µF100Ω**100k3.3V–A1󰀀1N41482.2µF1/2󰀀LT1078󰀀++VINVCLT1172VSWFBGNDNC * = 1% FILM RESISTOR󰀀** = 0.1% FILM RESISTOR󰀀L1 = TOKO 262-LYF-0095K󰀀T1 = NOVASENSOR󰀀 (FREMONT, CA)󰀀 NPH-8-100AHLT1034󰀀1.2V100k10k3.3V2N3904SHUTDOWNE1E2Figure 1. 3.3V Powered, Digital Output, Barometric Pressure Signal Conditioner2.5V Micropower Shunt Reference in SO-8Guarantees 25ppm/°C and 0.05% Initial Accuracy The LT1634-2.5 is a precision 2.5V out-put shunt reference with an initial accuracyof 0.05% and a maximum guaranteed drift of25ppm/°C. The initial release in this family, a1.2V output device, was introduced in theAugust issue of Chronicle. The LT1634 isstable with any value of output capacitor,including none, saving components andboard space. These features make it an excel-lent reference for use in portable meters,precision regulators and in data conversionapplications. Advances in design, processingand packaging techniques guarantee an oper-4REVERSE VOLTAGE CHANGE (mV)3210–1–2–3–4

–40–20

2040600

TEMPERATURE (°C)

80

100

IR = 10µAating current of only 10µA and low tem-perature cycling hysteresis. The compact-ness of the product makes it ideal for spacelimited applications. The LT1634-2.5 is immediately avail-able in volume from stock in 8-lead SO orMSOP surface mount packages. Contactyour local Linear Technology sales officefor a data sheet and evaluation samples.Visit our web site at www.linear-tech.comfor more information.1634-2.5 TA02

Figure 1. LT1634-2.5 Reference Has LowDrift over a Wide Temperature RangeLinear Technology Chronicle • September 19973

Fixed Voltage Output Step-Down Converters DrawOnly 10µA in Standby Fixed 3.3V and 5V output voltageversions of the LTC1474/LTC1475micropower converters are now available in8-lead MSOP and SO packages. These highefficiency (up to 92%) step-down DC/DCconverters draw only 10µA of standby cur-rent while regulating the output voltage.They have an on-chip power switch withprogrammable peak current control tomaximize the life of alkaline batteries forloads ranging from 1mA to 300mA. Thesefeatures permit a minimum area solutionideally suited for battery-powered, handheldproducts. The LTC1474-3.3/ LTC1474-5/LTC1475-3.3/LTC1475-5 operate over awide input voltage range of 3V to 18V (20VVIN4V TO 18VAbsolute Maximum). They have an adjust-able output voltage and are short-circuitprotected. Their 100% duty cycle capabilityensures low dropout operation and allowsmaximum energy to be extracted from thebatteries. Burst ModeTM operation maintainshigh efficiency over a wide range of loadcurrents. A low-battery comparator isincluded and is functional during shutdown. The LTC1475 is identical to theLTC1474 except that it has a push-buttonON/OFF operation. Momentarily pushingthe ON button pin latches the LTC1475 onand pushing the OFF button pin turns it off(shutdown to 6µA IQ). This user interfacepermits two-button operation without theneed for an external microcontroller or one- 100󰀀90󰀀EFFICIENCY (%)VIN = 5VVIN = 10VVIN = 15V80󰀀70󰀀60󰀀500.03L = 100µH󰀀VOUT = 3.3V󰀀RSENSE = 0Ω0.3303LOAD CURRENT (mA)3001474/75 TA01Figure 2. Efficiencies over 92% ArePossible for Various Load Currentsbutton operation with a microcontroller,greatly simplifying ON/OFF control ofhandheld products. The LTC1474/LTC1475 are immedi-ately available in 8-lead MSOP and SOpackages and are screened over both thecommercial and industrial temperatureranges. Contact your local LinearTechnology sales office for a data sheet andevaluation samples. Visit our web site atwww.linear-tech.com for more information.+10µF󰀀25V0.1µF63100k8SENSELBIRUN7VINVOUT125LOW BATTERY OUTLOW BATTERY INRUN SHDNLTC1474-3.3LBOSWL1󰀀100µH+VOUT󰀀3.3V AT 300mA100µF󰀀6.3VGND4D1󰀀MBR05301474/75 FIX F01L1 = SUMIDA CDRH74Figure 1. The LTC1474-3.3 High Efficiency Step-Down ConverterOperates over a 4V to 18V Input RangeBurst Mode is a trademark of Linear Technology Corporation.LTC1504 from page 1

termination. An adjustable current limit cir-cuit provides protection from overloads. TheLTC1504 fills the need for a low cost 5V to3.3V switching regulator where high effi-ciency at light load currents is not critical. The LTC1504 is available in adjustableand fixed 3.3V output versions—the latter(LTC1504-3.3) uses an internal resistor pairfor improved space efficiency. Both devicesare offered in an 8-lead SO surface mountpackage. Contact your local LinearTechnology sales office for a data sheet andevaluation samples. Visit our web siteat www.linear-tech.com for moreinformation.100󰀀90󰀀80󰀀70󰀀EFFICIENCY (%)60󰀀50󰀀40󰀀30󰀀20󰀀10󰀀010100LOAD CURRENT (mA)5001504 • TA02Linear TechnologyProducts AreDistributed By:Almac/ArrowArrow/SchweberArrow/ZeusDigi-KeyElectrosonicGerber ElectronicsFarnell ElectronicsMarshall IndustriesPhase 1© 1997 Linear Technology Corporation/Printed in USAFigure 2. LTC1504 Self-ContainedSwitching Regulator Offers Up to 92%Peak Efficiency over a Wide Range ofLoad Current4Linear Technology Corporation • 1630 McCarthy Blvd. • Milpitas, CA 95035-7417 • (408) 432-1900 • FAX: (408) 434-0507 • www.linear-tech.com • For Literature Only: 1-800-4-LINEAR Linear Technology Chronicle • September 1997