Datenblatt-Suchmaschine für elektronische Bauteile |
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SS8219GDTR Datenblatt(PDF) 2 Page - Silicon Standard Corp. |
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SS8219GDTR Datenblatt(HTML) 2 Page - Silicon Standard Corp. |
2 / 10 page www.SiliconStandard.com 2 of 10 12/06/2005 Rev.3.01 SS8219G ORDERING INFORMATION SS8219GX XX TR = tape and reel; TB = tubes For example: SS8219GD TR GD = RoHS-compliant TSSOP-28 => SS8219 in RoHS-compliant TSSOP-28 GS = RoHS-compliant SSOP-36 supplied on tape and reel APPLICATION INFORMATION The SS8219G is used in multi-mode active-termination applications where single ended (SE) and low voltage differential (LVD) devices might coexist. The LVD termin- ation section consists of 18 source/sink amplifiers (VTOP, VBOT), biasing circuitry and nine precision resistor strings (RTOP, RMID, RBOT). The SE termination section consists of a 2.85V source/sink regulator with nine precision 110 Ω resistors. The DIFFSENSE section consists of a 1.3V, 5mA driver and a sensing circuit (Fig.1). DIFFSENS is used to identify which types of SCSI devices are present on the bus. If the voltage on DIFFSENS is between 0V and 0.5V the bus is single- ended; if it is between 0.7V and 1.9V, the bus is LVD; and if it is greater than 2.4V, the bus is HVD. The SS8219G DIFFB pin monitors the DIFFSENS line to determine the proper operating mode of the device. HVD Isolation Mode: The SS8219G 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, or 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 are recommended between TPWR and ground and placed as close as possible to the SS8219G. The IC should be placed as close as possible to the SCSI connector to minimize both signal and power trace length, thereby reducing the input capacitance 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 SS8219G switches to the appropriate termination mode 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 regulation. 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 SS8219G. A high frequency capacitor (0.1µF ceramic recommended) can also be placed on the VREF pin in applications that use fast rise/fall time drivers. A typical SCSI bus configuration is shown in Figure 2. An internal pull-down resistor assures that the SS8219G will still terminate the bus if the DISCNCT pin is left floating. DIFFSENS noise filtering The SS8219G incorporates an internal digital filter to remove the noise signal on the DIFFSENS control line, thereby eliminating erroneous switching between modes. An external filter may also be used in addition to this internal digital filter. DIFFSENS - refers to the SCSI bus signal. DIFFSENSE - refers to the SS8219G pin name and internal circuitry related to differential sensing. DIFFB - refers to the SS8219G pin name and internal circuitry related to monitoring the DIFFSENS line. Please note for the following sections : |
Ähnliche Teilenummer - SS8219GDTR |
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Ähnliche Beschreibung - SS8219GDTR |
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