LinearTechnologyChronicle A Showcase of Linear Technology's Focus Products September 2000 Product of the Month Vol. 9 No. 9 LTC1878 switch at 550kHz and may be synchronized to frequencies from 400kHz to 700kHz. Burst ModeTM operation may be enabled for highest efficiency or disabled for lower output ripple. The LTC1877 and LTC1878 are capable of turning on continuously Monolithic Synchronous Step-Down Regulators Pack 500mA Output Current in MSOP Packages-- LTC1877, LTC1878 and LT1612 Continued on page 2 The LTC(R)1877, LTC1878 and LT 1612 are the new generation of synchronous switching regulators capable of supplying more than 500mA of output current. They are available in the tiny MSOP package. Their internal switches increase efficiency and eliminate Schottky diodes, saving components and board space (Figure 1). The operating ranges of the three devices allow the use of a single or dual Li-Ion battery and 2- to 6-cell NiCd and NiMH battery packs. For long battery life, shutdown reduces the current drain for these products to 1A. LTC1877 and LTC1878 Extend Battery Life with 10A Quiescent Current The BiCMOS technology in the LTC1877 and LTC1878 allows them to achieve ultrahigh efficiency at low load (R) currents. Their supply currents are only 10A while regulating the output voltage. These devices maintain better than 90% efficiency over three decades of output load current (Figure 2). The LTC1877 is designed for higher input voltages, 2.65V to 10V, whereas the LTC1878 is optimized for lower input voltages, 2.65V to 6V. Both incorporate a constant frequency, current mode step-down architecture with on-chip power MOSFETs. They include protection against output overvoltage, short circuit and excessive power dissipation. The LTC1877 and 100 95 VIN = 3.6V 90 VIN = 10V VIN 2.65V TO 10V 7 10F** CER 6 1 2 SW SYNC VIN 5 20pF GND VFB + 47F*** LTC1877 RUN ITH VOUT 3.3V 3 887k 75 VIN = 7.2V VIN = 5V 70 65 55 4 *TOKO D62CB A920CY-100M **TAIYO-YUDEN CERAMIC LMK325BJ106MN ***SANYO POSCAP 6TPA47M VOUT CONNECTED TO VIN FOR 2.65V < VIN < 3.3V 80 60 280k 220pF EFFICIENCY (%) 85 10H* 50 0.1 VOUT = 3.3V L = 10H Burst Mode OPERATION 1000 1.0 100 10 OUTPUT CURRENT (mA) 1877 * TA02 1877 TA01 Figure 1. High Efficiency Step-Down Converter Figure 2. High Efficiency Over Three Decades of Output Current Single Resistor Gain Programmable, Micropower Precision Instrumentation Amplifier--LT1168 The LT1168 is a micropower, precision instrumentation amplifier that requires only one external resistor to set gains of 1 to 10,000. The low voltage noise of 10nV/ Hz (at 1kHz) is not compromised by the part's low power dissipation (350A typical for 15V supplies). The wide supply range of 2.3V to 18V allows the LT1168 to fit into a wide variety of industrial and batterypowered applications. The high accuracy of the LT1168 is due to a 20ppm maximum nonlinearity and 0.4% max gain error (G = 10). While most monolithic instrumentation amps cannot handle low load resistor values, the nonlinearity of the LT1168 is specified for loads as low as 2k. The LT1168 is laser trimmed for very low input offset voltage (40V max), drift (0.3V/C), high CMRR (90dB, G = 1) and PSRR (103dB, G = 1) and low input bias Continued on page 2 Inside This Issue: Smallest Dual 14-Bit Voltage Output DAC--LTC1654 ........................................................... Measure Resistances Easily, Without Reference Resistor or Current Source--LT1168 ....... SOT-23 Fan Controller Includes SMBus Interface--LTC1695 ............................................... 1.5A Charger for Multicell Li-Ion Batteries and Other Chemistries--LT1571 ......................... Tiny Quad 10-Bit Rail-to-Rail VOUT DAC Consumes Only 60A per DAC--LTC1664 ........... Linear Technology Chronicle * September 2000 2 3 3 4 4 , LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode is a trademark of Linear Technology Corporation. I2C is a trademark of Philips Electronics N.V. 1 LTC1877, LTC1878 and LT1612 from page 1 (100% duty cycle) when the input voltage falls near the output voltage. All the components shown in Figure 3 are surface mount and minimize the board space and height. Figure 3. The LT1878 Converter (Actual Size) LT1612 Steps Down from 2V Input For low voltage operation in a buck regulator, a bipolar NPN top-side power switch is needed. The LT1612 can supply 500mA with input supply voltages from 2V to 5.5V (Figure 4). The LT1612 is a low cost alternative when a quiescent current of 150A suffices. The internal reference of 0.62V allows outputs below 1V. The LT1612 is capable of Burst Mode operation or of constant frequency 800kHz switching. It exhibits less than one fourth the power loss of a linear regulator at an input of 3V. LT1168 from page 1 currents of 250pA max. The output can handle capacitive loads up to 1000pF in any gain configuration while the inputs are ESD protected up to 13kV (human body). With two external 5k resistors, the LT1168 passes the IEC 1000-4-2 level 4 specification. Offered in 8-pin PDIP and SO packages, this part requires significantly less PC board area than discrete op amp designs. The LT1168 is available in both industrial and commercial temperature ranges. 1 3 8 3.5k L1 10H BOOST VIN SW SHDN LT1612 MODE C1 10F VC VOUT 1.2V 500mA 100pF FB GND 33k R2 232k 1% 330pF R1 215k 1% C2 68F 3.15V C1: TAIYO-YUDEN JMK325BJ106MN C2: PANASONIC EEFCDOF680R L1: SUMIDA CD43-100 1612 F01a Figure 4. Compact 2V to 1.2V Converter BI TECHNOLOGIES 67-8-3 R40KQ, (0.02% RATIO MATCH) 5V 3.5k 0.1F VIN 2V 3.5k 3.5k + 40k 7 REF R1 G = 200 249 6 LT1168 1 2 5 - IN ADC LTC1286 20k 3 4 40k 2 + 1/2 LT1112 1 DIGITAL DATA OUTPUT AGND - 1168 TA01 Figure 1. Single Supply Pressure Monitor Smallest Dual 14-Bit Voltage Output DAC-- LTC1654 The LTC1654 is a dual 14-bit voltage output digital-to-analog converter (DAC) in the narrow 16-pin SSOP package, requiring the same board space as an SO-8. This tiny dual DAC draws only 225A per DAC (typ) from a single 3V to 5V supply. Two rail-to-rail output buffers and a 3-wire cascadable serial interface allow ease of use and conserve system board space. High resolution, small size and low power make this low cost, dual DAC ideal for digital calibration, industrial process control and automatic test equipment applications. The LTC1654 offers two individually programmable speed modes (3.5s settling time and 8s settling time), which allow the user to choose speed vs power based on the application. The reference input can be conveniently tied to the supply and the output can swing from 0V to either VCC or VCC /2, depending on which gain mode is selected. The differential nonlinearity (DNL) of the LTC1654 is only 1LSB (max), which guarantees 14-bit monotonic performance, critical in control loop applications. Linearity is guaranteed over the entire operating CS/LD SCK temperature range. The LTC1654 is available in the narrow 16-pin SSOP package in both the commercial and industrial temperature grades. REFHI B CONTROL LOGIC INPUT LATCH SDI DAC REGISTER + DAC B VOUT B - 32-BIT SHIFT REGISTER X1/X1/2 B REFHI A INPUT LATCH DAC REGISTER + DAC A VOUT A - SDO CLR POWER-ON RESET X1/X1/2 A REFLO B REFLO A 1654 BD Figure 1. LTC1654 Dual Rail-to-Rail Voltage Output 14-Bit DAC 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 * September 2000 Application of the Month Measure Resistances Easily Without Reference Resistor or Current Source--LT1168 15V 3 + 8 1 RT 2 7 6 LT1168 - reference establishes a fixed input voltage so that the variable to be measured is now the resistance. The equation for VOUT vs RT is VOUT = 1.25V * 49.4k/RT. Given the limitation on output swing (with the supply voltages shown), the smallest measurable resistance is about 4.5k. The highest resolvable resistance is limited to about 200M by the 300mV output offset voltage of the LT1168. The 0.05% accuracy of the LT1634 is not an issue here because it is subtracted at the REF pin of the LT1168 and only contributes to gain error. Figure 2 shows output voltage vs temperature for 10k and 100k (at 25C) 4 5 REF VOUT = 1.25 * 4.49k RT thermistors from two manufacturers. Thermistors are difficult to linearize; although the output is still not linear with temperature, it can at least be read directly by an ADC and compared against a lookup table. The circuit has good noise immunity but does not tolerate capacitance at Pin 1 or Pin 8 and so it is not ideal for resistive devices placed remotely from the LT1168. 14 THERMOMETRICS DC95F103W 12 OUTPUT VOLTAGE (V) Measuring the resistance of a device, a thermistor for example, usually requires biasing it with a precision current source or combining it with several other precision resistors in a bridge. The circuit of Figure 1 shows how to use the new LT1168 instrumentation amplifier to achieve a precision resistance-to-voltage conversion as simply as possible. Normally the resistor across Pin 1 and Pin 8 is the gain-set resistor and the voltage across Pin 3 and Pin 2 is the variable to be measured. In this case, however, the 1.25V THERMOMETRICS DC95G104Z 10 8 6 YSI #44006 4 2 YSI #44011 0 -40 -20 -15V LT16341.25 22k -15V Figure 1. Simple Resistance-to-Voltage Converter SOT-23 Fan Controller Includes SMBus Interface--LTC1695 The LTC1695 fan speed controller integrates a low dropout linear regulator, 6-bit DAC and a simple 2-wire SMBus/I2CTM digital interface into a tiny SOT-23 package. The LDO offers 180mA of output current for driving 5V brushless DC fans. The DAC and SMBus interface allow easy communication with a power management controller to regulate the speed of the fan. A user selectable "boost start" feature automatically forces full power to the fan for the first 250ms of operation, ensuring clean start-up. Only two small, http://www.linear-tech.com/ezone/zone.html Articles, Design Ideas, Tips from the Lab... inexpensive external capacitors are required to form an operational circuit, greatly reducing board space requirements for laptop computers and portable battery-powered equipment. The LTC1695 employs a linear regulator approach as opposed to a PWM 5V 1 + 10F VOUT 5 + LTC1695 2 3 SYSTEM CONTROLLER VCC 4.7F GND SCL SDA 5V DC FAN 4 1695 * TA01 Figure 1. LTC1695 Controls 5V DC Fan 0 20 40 60 80 TEMPERATURE (C) 100 120 Figure 2. Output Voltage vs Temperature for Thermistors from Two Manufacturers. Curves are Approximations to Aid Design--Contact Manufacturers for Exact Lookup Tables: YSI (800) 765-4974 Thermometrics (723) 287-2870 technique. This fan speed control method greatly reduces rotor vibrations resulting in lower mechanical noise and longer fan life. It also prevents electrical noise from being introduced on the 5V supply line. In a typical system design, the microcontroller uses available temperature data to program the LTC1695 for the required fan speed to maintain a system's temperature profile. The LTC1695 also includes output current limiting and thermal shutdown as well as status monitors that can be read back by the power management controller during fault conditions. The LTC1695 is available in a 5-lead SOT-23 package specified over the commercial temperature range. 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 * September 2000 3 1.5A Charger for Multicell Li-Ion Batteries and Other Chemistries--LT1571 The LT1571-1 and LT1571-2 currentmode PWM battery chargers deliver up to 1.5A charge current for products such as handheld computers and portable instruments. The chargers feature 1% constant voltage and 5% constant current accuracy over the full operating temperature range. The LT1571-2 includes preset charge voltages of 8.2V or 8.4V (pin selectable) while the LT1571-1 is adjustable from 2.5V to 24V using external resistors. Both versions includes an internal current sense resistor which allows the charge current to be easily adjusted using a single external resistor, DAC or PWM signal. They also include adjustable soft start, undervoltage lockout and an end-of-charge flag output D3 MBRM120T3 D1 MBRM120T3 SW C1 0.22F L1** 33H with a threshold that is programmable from 7.5% to 20% of the full charge current. A shutdown mode (with VIN present) drops the quiescent current to 150A, and a sleep mode drops the battery drain current to 5A when VIN is removed. The LT1571-2 is designed to charge two Li-Ion cells (Figure 1), while the LT1571-1, with its adjustable output, can be used to charge three or four Li-Ion cells as well as NiCd, NiMH and SLA batteries. The previously introduced 500kHz LT1571-5, in a 16-lead SSOP with a maximum charge current of 1A, charges 4.1V or 4.2V singlecell Li-Ion systems. The wide 8V to 28V input range of the LT1571 series accommodates most wall VCC BOOST PROG D2 MMBD914L 1F 0.3F SENSE VC SELECT GND 4.93k 100k 300 1k CAP 0.1F VIN 11V TO 26V CIN* 10F LT1571-2 FLAG BAT BAT2 + COUT 22F TANT NOTE: COMPLETE LITHIUM-ION CHARGER, NO TERMINATION REQUIRED * TOKIN OR MARCON CERAMIC SURFACE MOUNT ** COILTRONICS CTX33-2 adapter and automotive input voltage ranges. An onboard 2A saturating switch produces up to 87% efficiency. Its built-in undervoltage lockout avoids overloading wall adapter supplies at start-up. Designed to be used with all surface mount components including compact low profile inductors, the 200kHz battery charger circuit occupies a minimum of board space. The LT1571 devices are packaged in a fused lead frame, narrow 28-lead SSOP package for good thermal performance in a small space. Other chargers are optimized for higher or lower charge currents, with or without the end-of-charge function (Table 1). + 8.4V Table 1. Constant Current, Constant Voltage, Single Chip Battery Chargers Charge Current <1A 1A 1.5A >1.5A No End-ofCharge Indicator LTC1731 LT1510-5 LT1769 LT1769 LT1511 With End-ofCharge Indicator LTC1731 LT1571-5 (500kHz) LT1571-1or -2 (200kHz) LT1505 Up to 6A 1571 F04 Figure 1. 200kHz Charging Li-Ion Batteries (Efficiency at 1A Exceeds 87%) Tiny Quad 10-Bit Rail-to-Rail VOUT DAC Consumes Only 60A per DAC--LTC1664 The LTC1664 is a quad, 10-bit, rail-torail voltage output micropower DAC. The part consumes only 60A per DAC during normal operation and in sleep mode the supply current drops to only 1A. This ultralow power consumption makes the LTC1664 ideal for battery-powered applications. The LTC1664 is available in the tiny 16-pin narrow SSOP package, fitting in the footprint of a standard SO-8. The LTC1664's reference input pin has a constant impedance over all codes. This feature eliminates external reference buffers necessary with other DACs to ensure constant linearity over the entire full scale. In addition, its reference input can be tied to the supply pin for ratiometric rail-to-rail output. The LTC1664 has a differential nonlinearity (DNL) of only 0.75LSB (max), guaranteeing the monotomic performance critical in control-loop applications. Its 3-wire cascadable serial interface simplifies transmitting through isolation barriers or to remote locations and allows several LTC1664s to be connected together for daisy chain operation. In addition to the 16-pin SSOP, the LTC1664 is also available in the 16-pin PDIP package. Both are available in commercial and industrial temperature ranges. Linear Technology Products Are Distributed By: Arrow Electronics Arrow/Zeus Components Digi-Key Gerber Electronics Avnet Wyle Electronics (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 Only: 1-800-4-LINEAR 4Linear Technology Corporation * 1630 McCarthy Blvd. * Milpitas, CA 95035-7417 * (408) 432-1900 * FAX: (408) 434-0507 Linear Technology Chronicle * September 2000