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G219 데이터시트(PDF) 2 Page - List of Unclassifed Manufacturers |
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G219 데이터시트(HTML) 2 Page - List of Unclassifed Manufacturers |
2 / 9 page Ver 1.2 Feb 08, 2002 TEL: 886-3-5788833 http://www.gmt.com.tw 2 G219 Global Mixed-mode Technology Inc. Ordering Information PART NUMBER TEMP. RANGE PIN-PACKAGE G219T-D3 0ºC-70ºC TSSOP-28 pin / Tube G219R-D3 0ºC-70ºC TSSOP-28 pin / Tape & Reel Note: DIFFSENS Refers to the SCSI bus signal. DIFFSENSE Refers to the G219 pin name and internal circuitry relating to differential sensing. DIFFB Refers to the G219 pin name and internal circuitry relating to monitoring the DIFFSENS line. Functional Description The G219 is used in multi-mode active termination applications, where single ended (SE) and low voltage differential (LVD) devices might coexist. The LVD ter- mination section consists of 18 source/sink amplifiers (VTOP, VBOT), biasing circuitry and nine precision resistor strings (RTOP, RMID, RBOT). The SE termi- nation section consists of a 2.85V source/sink regula- tor with 9 precision 110ohm resistor. The DIFFSENSE section consists of a 1.3V, 5mA driver and a sensing circuit (Figure 1) DIFFSENS is used to identify which types of SCSI devices are present on the bus. If the voltage on DIFFSENS is between 0-0.5V the bus is single-ended; if it is between 0.7-1.9V the bus is LVD; and if it is greater than 2.4V, the bus is HVD. The G219 DIFFB pin monitors the DIFFSENS line to determine the proper operating mode of the device. HVD Isolation Mode The G219 identifies that there is an HVD (high voltage differential) device on the SCSI bus and isolates the termination pins from the bus. When DISCNCT is pulled high, the termination pins are isolated from the SCSI bus, and VREF is grounded. During thermal shutdown, the termination pins are isolated from the SCSI bus and VREF is grounded. The DIFFSENSE driver is shut down during either of these two events. To ensure proper operation, the TPWR pin should be connected to the SCSI bus TERMPWR line. As with all analog circuitry, the TERMPWR lines should be by- passed locally. A 2.2µF capacitor and a 0.01µF high frequency capacitor is recommended between TPWR and ground and placed as close as possible to the G219. The G219 should be placed as close as possi- ble to the SCSI connector to minimize signal and power trace length, thereby resulting in less input ca- pacitance and reflections which can degrade the bus signals. The DIFFSENSE pin can drive the SCSI DIFFSENS line (when M/S is pulled high) to determine the SCSI bus operating mode. The G219 switches to the termi- nation mode that is appropriate for the bus based on the value of the DIFFSENS voltage. These modes are: LVD mode LVD termination is provided by a precision resistor string with two amplifiers. This configuration yields a 105 Ω differential and 150Ω common mode impedance. A fail safe bias of 112mV is maintained when no drivers are connected to the SCSI bus. SE mode When the external driver for a given signal line turns off, the active terminator will pull that signal line to 2.85 volts (quiescent state). When used with an active negation driver, the power amp can sink 22mA per line while keeping the voltage reference in regula- tion. The terminating resistors maintain their 110 Ω value. To maintain the specified regulation, a 4.7µF capacitor is required between the VREF pin and ground of each G219. A high frequency cap (0.1µF ceramic recom- mended) can also be placed on the VREF pin in ap- plications that use fast rise/fall time drivers. A typical SCSI bus configuration is shown in Figure2. An internal pull down resistor assures that the G219 will be terminating the bus if the DISCNCT pin is left floating. DIFFSENS noise filtering The G219 incorporates a internal digital filter to re- move the noise signal on the DIFFSENS control line, thereby eliminating erroneous switching between modes. The external filter may be used in addition to the internal digital filter. |
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유사한 설명 - G219 |
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