LinearTechnologyChronicle A Showcase of Linear Technology's Focus Products November 2000 Product of the Month Tiny, Current Mode Boost DC/DC Converters for Loads Up to 10A--LTC3401/LTC3402/LTC1872/ LT1619 Four new switching regulator ICs provide boost voltage conversion in very small spaces for portable and distributed power systems (Table 1). The LTC(R)3401 and LTC3402 regulate up to 500mA and 1A outputs, respectively, from single cell Li-Ion or alkaline sources. The LTC1872, in a SOT-23 package, regulates up to 2A of load current from various battery inputs and wall adapters. The LT(R)1619 regulates up to 10A from a wide 1.9V to 18V input range. The LTC1872 and LT1619 also function as SEPIC buck-boost converters. The LTC3401 and LTC3402 include power switch transistors while the LTC1872 and LT1619 use external power MOSFETs. Each of the new regulators operates in current mode for superior load regulation and transient response. They include important features such as cycle-by-cycle current limiting, undervoltage lockout, adaptive slope compensation and antiringing circuitry. Each regulator automatically shifts into Burst ModeTM operation in which the MOSFETs switch intermittently, based on load demand, to maintain high efficiency when the output is lightly loaded. (Burst Mode operation is user-selectable for the LTC3401 and LTC3402.) LTC3401 & LTC3402: to 3MHz Switching, 97% Efficient, < 1V Input The LTC3401 and LTC3402 offer the highest power density available for singlecell synchronous boost converters, providing a regulated output of up to 5W in only 0.05in3. Their very small size and high efficiency (Figures 1 and 2) over a wide output current range makes them valuable for compact pagers, cordless phones, GPS receivers and handheld instruments where small size and extended battery operation are critical. The switching regulators each incorporate a 0.16 N-channel MOSFET switch and a 0.18 synchronous rectifier to achieve high efficiency. The LTC3402 delivers up to 1A of load current (2A switch current) with 95% efficiency while drawing only 38A of supply current (in Burst Mode Vol. 9 No. 11 operation) for extended battery life. The LTC3401 is a similar device with a 500mA output capability. Switching frequencies from 300kHz to 3MHz may be programmed with a timing resistor, allowing designers to optimize their circuits for RFI suppression, for the highest efficiency or for a board footprint as small as 0.16in2 (100mm2). The LTC3401 Continued on page 2 16-Bit, 500ksps ADC Offers No Missing Codes Over Complete Temperature Range-- LTC1608 The LTC1608 is a 16-bit, 500ksps ADC that offers true 16-bit, no missing codes performance over the entire industrial (- 40C to 85C) temperature range with no pipeline delay. Its speed, accuracy and no latency architecture make the LTC1608 ideal for a wide array of precision applications, including high speed multiplexed data acquisition, industrial process control and instrumentation. Its AC specs include 90dB S/(N + D) and -100dB total harmonic distortion at a sample rate of 500ksps (see Figure 1). Table 1. New Boost Converters Are Tiny But Powerful 0 Max Output Current** Switch Frequency (Hz) Operating and Shutdown Currents Micro Package LTC3401 0.5V* to 5V 500mA 300k to 3M 39A, 1A MS10 LTC3402 0.5V* to 5V 1A 300k to 3M 38A, 1A MS10 LTC1872 2.5V to 9.8V 2A 550k 270A, 8A SOT-23 LT1619 1.8V to 18V 10A 300k to 500k 140A, 15A MS8 *See text **Dependent upon input and output voltages External switch fSAMPLE = 500kHz fIN = 98.754kHz SINAD = 86.7dB THD = -92.6dB -20 AMPLITUDE (dB) Boost Converter Input Voltage Range -40 -60 -80 -100 -120 -140 0 50 100 150 FREQUENCY (kHz) 200 250 1608 TA02 Inside This Issue: Low Voltage PowerPathTM Driver Switches from a 3.3V or 5V Supply to Battery Backup--LTC1473L ................................................................................... 3 Dual 7ns Rail-to-Rail Input/Output Comparator with Latch Operates On Supplies from 2.4V to 12V--LT1714 ................................................................................. 4 Lowest Noise 2.5V Shunt Reference Now in MS8--LT1009 .................................................. 4 Linear Technology Chronicle * November 2000 Figure 1. LTC1608 4096 Point FFT Continued on page 3 , LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode and PowerPath are trademarks of Linear Technology Corporation. 1 L1 4.7H 2 CELLS L1: COILCRAFT DO3316P-472 fOSC = 1MHz 10F 470pF 20pF 30k 40.2k VIN SW PGOOD VOUT LTC3402 VC FB Rt SHDN MODE/SYNC GND 909k 3.3V 1A + 47F 549k 3402 TA01 Figure 1. 2-Cell to 3.3V at 1A Step-Up Converter 100 Burst Mode OPERATION 90 EFFICIENCY (%) 80 1MHz CONSTANT FREQUENCY 70 60 50 40 30 20 10 0 VIN = 2.4V WITH SCHOTTKY 0.1 1 10 IOUT (mA) 100 1000 3402 TA02 Figure 2. Efficiency for the Circuit in Figure 1 or LTC3402 oscillator can be synchronized to an external clock for improved suppression of switching harmonics in sensitive audio and IF bands. Burst Mode operation is inhibited during synchronization or when the MODE /SYNC pin is pulled low, preventing interference from low frequency ripple. The LTC3401 and LTC3402 are designed to start up at input voltages of 0.85V (typical). Once started, the IC operates from VOUT instead of VIN. At this point, the internal circuitry has no dependency on the input voltage, eliminating the requirement for a large input capacitor. The input voltage can drop below 0.5V without affecting the operation, provided that the power source can supply sufficient energy at that low voltage. Other features include a power good output and antiringing control. The devices are available in the 10-lead thermally enhanced MSOP package. LTC1872: Output to 4A, SOT-23, Constant 550kHz The LTC1872 is a SOT-23 current mode, step-up DC/DC controller with a 550kHz operating frequency. It provides the smallest solution for converting an input in the range of 2.5V to 9.8V to a higher output voltage at load currents of up to 2A. Applications include 1- and 2-cell Li-Ion-powered portable devices such as PDAs, GPS systems and board-level boost conversion for networking systems. The device's high operating frequency (550kHz) reduces the value and size of the inductor and capacitors (Figure 3). The design may be packed in an area less than 110mm2. Low operating current of 270A, shutdown current of 8A and operating efficiency as high as 90% all help to extend battery life. The LTC1872 guarantees 2.5% output voltage accuracy. The output voltage is limited only by the capability of the external components. To prevent operation of the N-channel MOSFET below safe input voltage levels, an undervoltage lockout feature is incorporated into the LTC1872. When the input supply voltage drops below 2V, the N-channel MOSFET and the controller are turned off, except for the undervoltage circuitry, which draws only a few microamperes. 1 10k ITH/RUN 5 VIN L1 4.7H LTC1872 220pF 2 3 4 GND SENSE - 6 NGATE VFB VIN 3.3V C1 10F 10V R1 0.03 LT1619: Output to 10A, 90% Efficient, 1.9V to 18V Input Range, MSOP The LT1619 is a fixed frequency, current mode controller that implements boost, SEPIC and flyback converters with a minimum of external parts. Low parts count, small size and high efficiency make the LT1619 a perfect solution when a moderate amount of 5V power is required in a predominately 3.3V system (Figure 4). Conversion efficiency at heavy loads surpasses competing devices by means of a 50mV current sense voltage. This low value reduces energy loss in the sense resistor. Burst Mode operation (Figure 5) keeps efficiency high at light loads. The operating frequency, typically 300kHz, may be synchronized to an external clock of up to 500kHz. The device's no-load quiescent current of 140A drops to 15A in shutdown. The internal rail-to-rail gate drive circuit is capable of switching a low side N-channel power MOSFET with up to 60nC of total gate charge. The upper supply of the gate driver is brought out as a device pin (DRV) for design flexibility. In boost converters, the DRV pin can be tied to the converter output (see Figure 4) if the minimum input voltage is insufficient to fully enhance the power MOSFET. The DRV pin can also be powered from the input or from a separate supply. The LT1619 is not limited to low output voltage supplies. It is also suitable for SLIC voltage generation, for 5V to - 48V conversion in other telecommunications systems and for SEPIC conversion in automotive systems with an input range of 4V to 28V. A few external components enable trickle start from high voltage input sources, such as 36V to 72V telecom supplies. M1 D1 + C1: TAIYO YUDEN CERAMIC EMK325BJ106MNT C2: AVX TPSE476M016R0150 D1: MOTOROLA MBRS340T3 L1: COILTRONICS UP1B-4R7 M1: Si9804DV R1: DALE 0.25W C2 2x 47F 16V 100pF VOUT 5V 1A 412k 78.7k 1872 TA01 Figure 3. 3.3V to 5V Boost Converter in SOT-23 Provides 1A Output 95 R1 37.4k R2 12.4k 1 S/S VIN VIN 3.3V 8 + 0.1F 2 3 RC 75k CG 15nF 4 FB DRV LT1619 VC GND GATE SENSE 220pF 7 6 5 0.1F C1 22F L1 5.6H 5A 90 D1 VOUT 5V 2.2A M1 Si9804 + RSENSE 0.01 COUT 470F EFFICIENCY (%) LTC3401/LTC3402/LTC1872/LT1619 from page 1 85 80 75 1619 F01 70 C1: PANASONIC EEFCDOK220R D1: MBRD835L L1: COILCRAFT DO5022P-562 1 10 100 LOAD CURRENT (mA) 1000 1619 F01a Figure 4. High Efficiency 3.3V to 5V DC/DC Converter Figure 5. Efficiency of the Circuit in Figure 4 Contact your local Linear Technology sales office for a data sheet and evaluation samples. For more information, visit our web site at www.linear-tech.com. 2 Linear Technology Chronicle * November 2000 Application of the Month Low Voltage PowerPath Driver Switches from a 3.3V or 5V Supply to Battery Backup--LTC1473L The LTC1473L solves the problem of seamless power switching between 3.3V or 5V supplies and backup battery packs (3- or 4-cell NiMH) at high current levels. By driving two sets of back-to-back N-channel MOSFET switches, the LTC1473L routes power to the input of a low voltage (3.3V to 10V) system efficiently and inexpensively. Figure 1 is a schematic showing the LTC1473L switch controller in conjunction with an LT1512 battery charger. In this application, the 4-cell NiMH battery is fully charged by the 3.3V DC supply through the LT1512 buck-boost converter to ensure that it is always "topped off" and ready to provide backup power. R3 is set at 1 to C3 22F 25V L1A* C2** 22F VIN SYNC AND/OR SHDN S/S charge the NiMH battery pack at a constant 100mA rate. In both applications, the value of CTIMER determines the amount of time the external NMOS switches are allowed to be in current limit, and the value of RSENSE determines the inrush current limit, which is set at 2x to 3x of the maximum required output current. When V+ falls below 2.5V, the LTC1473L's undervoltage lockout circuit turns off both switches. With a built-in hysteresis of 100mV, the LTC1473L becomes active again when V+ rises above 2.6V. Therefore, for 3.3V systems, small Schottky LT1512 GND GND 100mA VSW BAT54C L1B* LTC1473L FB R1 47.5k VC IFB R4 24 C5 0.1F R5 1k Si4936DY DCIN 3.3V D1 MBRS130LT3 C4 0.22F R3 1 diodes are used to power V+ from both DCIN and BAT1 so that the undervoltage lockout circuit will not be falsely tripped. Since the LTC1473L has an IQ of less than 100A at 3.3V, the drop across the Schottky diode is less than 0.4V, leaving enough room for a typical 5% supply tolerance. Glitch-free and seamless transition of power is crucial for maintaining normal operation in low voltage electronic equipment. The LTC1473L makes the transition transparent and trouble free. (For systems using supply voltages between 6V and 28V, refer to the LTC1473 data sheet.) C1 22F 25V R2 12.4k CTIMER 4700pF GA1 IN2 SAB1 DIODE GB1 TIMER SENSE + V+ + *L1A, L1B ARE TWO 33H WINDINGS ON A SINGLE CORE: COILTRONICS CTX33-3 (561) 241-7876 **TOKIN CERAMIC 1E22ZY5U-C203-F (408) 432-8020 IN1 1mH 1F + 1F SENSE RSENSE 0.04 + - VGG GA2 SW SAB2 GND GB2 BAT1 4 NiMH 3.3V OR VBAT1 COUT Si4936DY Figure 1. Battery Backup Circuit with LT1512 Battery Charger LTC1608 from page 1 The LTC1608 operates from 5V supplies and has an input range of 2.5V. It dissipates only 270mW of power and offers NAP (7mW) and SLEEP (10W) modes for further power reduction. This easy-to-use ADC includes an internal clock and a 15ppm/C precision reference that can be overdriven externally. The LTC1608's parallel digitial interface can communicate with both 3V and 5V logic, enabling communication with a variety of DSPs and microcontrollers. The LTC1608 is available in the 36-pin SSOP package in both the commercial and industrial temperature ranges. The LTC1608 is pin compatible with the LTC1604, a 16-bit, 333ksps ADC, offering an easy upgrade path for applications requiring higher speed. Contact your local Linear Technology sales office for a data sheet and evaluation samples. For more information, visit our web site at www.linear-tech.com. Linear Technology Chronicle * November 2000 3 The LT1714 is the first dual comparator that features 7ns propagation delay (see Figure 1), a rail-to-rail input voltage range, complimentary rail-to-rail CMOS/TTL compatible outputs, internal data latches and an operating supply range of 2.4V to 12V. This unique combination of features greatly expands the variety of applications in which the LT1714 can be used. The LT1714's fast response and 2.4V operation, combined with its rail-to-rail inputs and CMOS compatible outputs, make it ideal for use in a wide variety of low voltage digital applications such as clock recovery or line receiver in broadband 9.0 8.5 PROPAGATION DELAY (ns) Dual 7ns Rail-to-Rail Input/Output Comparator with Latch Operates On Supplies from 2.4V to 12V--LT1714 8.0 tPD+ 7.5 TJ = 25C VSTEP = 100mV VOD = 20mV V + = 5V V - = 0V tPD- 7.0 6.5 6.0 5.5 5.0 0 10 20 40 50 30 INPUT OVERDRIVE (mV) 60 1714 TA02 Figure 1. Propagation Delay vs Input Overdrive communications systems. Additionally, the LT1714's 12V operational capability, low (5mA/comparator) supply current and high speed in a small SSOP package make it well suited for use in automatic test equipment. The dual internal latches make it suitable for use in data sampling circuits. With rail-to-rail complimentary outputs that can sink and source 10mA and output latches with built-in hysteresis, the LT1714 simplifies the design of discrete PWM circuits, current sensing circuits for switching power supplies, bang-bang controllers and a host of other applications. The LT1714 is available in a 16-pin SSOP package that occupies the same footprint as a conventional SO-8 package in both commercial and industrial temperature ranges. Lowest Noise 2.5V Shunt Reference Now In MS8--LT1009 The LT1009 is the lowest noise 2.5V shunt reference available from Linear Technology. Now available in the MS8 package, it is also the smallest (in both footprint and height) of any of LTC's shunt references. The LT1009 is a precision trimmed 2.5V shunt regulator diode featuring a maximum initial tolerance of only 5mV. This 0.2% reference tolerance is achieved by on-chip trimming, which not only minimizes the initial voltage tolerance but also minimizes the temperature drift to a mere 25ppm/C. The LT1009 excels in noise performance, with only 13VRMS typical output noise. Although no adjustments are needed with the LT1009, a third terminal allows the reference voltage to be adjusted 5% to calibrate out system errors. For a lower drift 2.5V reference, see the LT1019 data sheet or refer to Table 1. The LT1009 is available in the small MS8 package as well as SO-8 and TO-92 packages in commercial and industrial temperature ranges. Table 1. Linear Technology's Family of Precision References Part Number Initial Accuracy Drift Supply Current LT1009 0.2% 25ppm/C * Low Noise Shunt Reference MS8, SO-8, TO-92 LT1019 0.05% 3ppm/C 0.65mA Precision Series Reference SO-8, DIP LT1236 0.05% 5ppm/C 0.8mA Precision Series Reference SO-8, DIP LT1460 0.2% 20ppm/C 115A Micropower Precision Series Reference SOT-23, MS8, SO-8 LT1461 0.04% 3ppm/C 35A Micropower Precision Series Reference SO-8 LT1634 0.05% 10ppm/C 10A Micropower Precision Shunt Reference MS8, SO-8 LT1790 0.05% 10ppm/C 60A Micropower Low Dropout Reference SOT-23 LTC1798 0.15% 40ppm/C 4A Micropower Low Dropout Reference SO-8 Comments Package Linear Technology Products Are Distributed By: Arrow Electronics Arrow/Zeus Components Digi-Key Gerber Electronics Avnet Wyle Electronics *Supply current for shunt reference depends on circuit conditions. (c) 2000 Linear Technology Corporation/Printed in USA Contact your local Linear Technology sales office for a data sheet and evaluation samples. For more information, visit our web site at www.linear-tech.com. * www.linear-tech.com * For Literature 1-800-4-LINEAR 4Linear Technology Corporation * 1630 McCarthy Blvd. * Milpitas, CA 95035-7417 * (408) 432-1900 * FAX: (408) 434-0507 Linear Technology Chronicle * Only: November 2000