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1、Linear Technology Chronicle September 20001A Showcase of Linear Technologys Focus ProductsProduct of the Month, 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.Linear Tech
2、nology ChronicleSeptember 2000Vol. 9 No. 9Inside This Issue:Smallest Dual 14-Bit Voltage Output DACLTC1654 . 2 Measure Resistances Easily, Without Reference Resistor or Current SourceLT1168 . 3 SOT-23 Fan Controller Includes SMBus InterfaceLTC1695 . 3 1.5A Charger for Multicell Li-Ion Batteries and
3、Other ChemistriesLT1571 . 4 Tiny Quad 10-Bit Rail-to-Rail VOUT DAC Consumes Only 60A per DACLTC1664 . 4Figure 1. High Efficiency Step-Down ConverterMonolithic Synchronous Step-Down Regulators Pack 500mA Output Current in MSOP Packages LTC1877, LTC1878 and LT1612The LTC1877, LTC1878 and LT1612 are th
4、e new generation of synchro- nous switching regulators capable of supply- ing more than 500mA of output current. They are available in the tiny MSOP pack- age. Their internal switches increase effi- ciency and eliminate Schottky diodes, saving components and board space (Figure 1). The operating ran
5、ges 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
6、LTC1877 and LTC1878 allows them to achieve ultrahigh efficiency at low loadcurrents. 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 inpu
7、t voltages, 2.65V to 10V, whereas the LTC1878 is optimized for lower input volt- ages, 2.65V to 6V. Both incorporate a con- stant frequency, current mode step-down architecture with on-chip power MOSFETs. They include protection against output overvoltage, short circuit and excessive power dissipati
8、on. The LTC1877 andLTC1878 switch at 550kHz and may be syn- chronized 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 continuously47F*7612534SWVFBLTC1877GND10H*10
9、F* CER 220pFVOUT 3.3V887k280k1877 TA01SYNCVINRUNITHVIN 2.65V TO 10V20pF*TOKO D62CB A920CY-100M*TAIYO-YUDEN CERAMIC LMK325BJ106MN *SANYO POSCAP 6TPA47MVOUT CONNECTED TO VIN FOR 2.65V 1.5ANo End-of-LTC1731LT1510-5LT1769LT1769 Charge IndicatorLT1511With End-of-LTC1731LT1571-5LT1571-1or -2LT1505 Charge
10、Indicator(500kHz)(200kHz)Up to 6AThe LT1571-1 and LT1571-2 current- mode PWM battery chargers deliver up to 1.5A charge current for products such as handheld computers and portable instru- ments. The chargers feature 1% constant voltage and 5% constant current accuracy over the full operating temper
11、ature range. The LT1571-2 includes preset charge volt- ages 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 cur- rent sense resistor which allows the charge current to be easily adjusted using a single ex
12、ternal resistor, DAC or PWM signal. They also include adjustable soft start, undervolt- age lockout and an end-of-charge flag outputwith 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 m
13、ode 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 LT
14、1571-5, in a 16-lead SSOP with a maximum charge current of 1A, charges 4.1V or 4.2V single- cell Li-Ion systems. The wide 8V to 28V input range of the LT1571 series accommodates most walladapter and automotive input voltage ranges. An onboard 2A saturating switch produces up to 87% efficiency. Its b
15、uilt-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 fram
16、e, narrow 28-lead SSOP package for good ther- mal 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). The LTC1664 is a quad, 10-bit, rail-to- rail voltage output micropower DAC. The part consumes only 60A per DAC dur
