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1、1Linear Technology Chronicle February 1997A Showcase of Linear Technologys Focus ProductsLinear Technology ChronicleFebruary 1997Vol. 6 No. 2Product of the MonthLinear Phase Filter Ideal for Data Communications ApplicationsThe LTC1069-7 is the industrys first monolithic, 8th order, linear phase filt
2、er packaged in an SO-8. It requires no external components except for the power supply bypass capacitors. A maximum cutoff frequency of 200kHz can be obtained with 5V supplies and 140kHz with a single 5V supply. The cutoff frequency is pro- grammed by an external clock and is equal to the clock freq
3、uency divided by 25. The LTC1069-7 is the latest version in the LTC1069 family of 8th order filters and is typically used in digital communication systems for pulse shaping and channel bandwidth limiting.The LTC1069-7, like all members of the LTC1069-X family, requires only a power supply and a cloc
4、k signal to operate, making it ideal for space limited applica- tions. With a single 5V supply it draws just 13mA (typ) and has a dynamic range of over 60dB. As a linear phase filter, theLTC1069-7 maintains the phase integrity of digital signals as theyre processed.Figure 2 shows the frequency respo
5、nse of the LTC1069-7 with single 5V supply operation. The amplitude response of the device approximates a raised cosine filter with an alpha of one. The gain at the cutoff frequency is 3dB and the attenuation at twice the cutoff frequency is 43dB. The LTC1069-7 is immediately available in volume fro
6、m stock in an SO-8 surface mount package. Contact your local Linear Technology sales office for a data sheet and evaluation samples. For more information, visit our web site at www.linear-.Current Controller Optimizes Synchronous Switcher for Battery ChargingThe LT1620 is a rail-to-rail current sens
7、e amplifier with a programmable current controller that extends the output voltage range of Linear Technologys ultrahigh effi- ciency switching regulators. An LT1620/ LTC1435 combination can implement a step-down battery charger with more than 4A charging current at battery voltages up to 36V. Over
8、96% efficiency is possible in these charger applications with very low dropout, as shown in Figure 1. Members of the LTC1435 and LTC1148 controller fami- lies are normally limited to 9V and 10V maximum outputs, respectively. But with the LT1620, output voltage can be extended as high as 36V.In the 8
9、-pin MSOP package, the LT1620 (with the LTC1435) is ideal in space limited applications for charging NiCd, NiMH, lead-acid and Li-Ion batteries. These features greatly ease the PCB layout task for a portable designer, allowing the chip set to be placed at the edge of a board or in a corner without n
10、eed of a heat sink.GNDV+NCVINVINVOUTVOUTVNCCLKLTC1069-7fCLK = 2.5MHz5V0.47F 0.1F1069-7 TA01Figure 1. The LTC1069-7 Operates Up to 140kHz with a Single Supply (5V, GND) and to 200kHz with 5V SuppliesFREQUENCY (kHz)1070GAIN (dB)605040301010010001069-7 TA0220100Figure 2. Frequency Response of LTC1069-7
11、 with Single 5V Supply Provides 100kHz Cutoff Frequency and Over 60dB Dynamic Rangewww.linear-, LTC and LT are registered trademarks of Linear Technology Corporation.Precision Micropower Dual Op Amps Offer Low Offset, Noise and Drift . 2 A Low Power Direct Access Arrangement for Modems . 3Single 5V
12、RS232/RS485 Serial Transceiver . 4Telecommunications Solutions Brochure Now Available. 4Inside This Issue:Continued on page 2BATTERY CHARGE CURRENT (A)0EFFICIENCY (%)909510041620/21 TA02858075 1235VIN = 24VVBATT = 16VVBATT = 12VVBATT = 6VFigure 1. Efficiency of the LT1620 as a High Current/Li-Ion Ba
13、ttery Charger Reaches Up to 96% at 16V2Linear Technology Chronicle February 1997LT1620 from page 1To further support its use in battery charging applications, the LT1620 (in a 16-pin SSOP package) includes a current comparator with programmable current threshold. The comparator turns off the con- st
14、ant-current source some time after the charging current reaches a preset level to ensure a full charge of Li-Ion batteries.The LT1620 is offered in three different package options. For space constrained applications, its available in an 8-leadThe LT1620 also adds programmable output current control
15、to a PWM switcher. It regulates average output current independent of input and output voltage variations. Out- put currents can be easily adjusted via a programming voltage applied to the LT1620s PROG pin (see Figure 2). The LT1621 is a dual version of the LT1620 and incorporates two fully independent current control circuits for dual loop applications.MSOP package as well as in the SO-8 pack- age. The LT1620 is also offered in a 16-lead SSOP to accommodate a current comparator with end-of-cycle output to indicate when a Li-I
