 |
|
| If you can't view the Datasheet, Please click here to try to view without PDF Reader . |
|
|
|
| If you can't view the Datasheet, Please click here to try to view without PDF Reader . |
|
|
| Datasheet File OCR Text: |
| DS21T11 PRODUCTION DS21T11 SCSI Terminator FEATURES PIN ASSIGNMENT * Fully compliant with SCSI-1, Fast SCSI and Ultra SCSI PD R1 R2 R3 R4 R5 HS-GND HS-GND HS-GND R6 R7 R8 R9 TPWR 1 2 3 4 5 6 7 8 9 10 11 12 13 14 28 27 26 25 24 23 22 21 20 19 18 17 16 15 GND R18 R17 R16 R15 R14 HS-GND HS-GND HS-GND R13 R12 R11 R10 VREF * Provides active termination for 18 signal lines * 5% tolerance on termination resistors and voltage regulator * 5% tolerance on termination current * Low power down capacitance of 3 pF * Onboard thermal shutdown circuitry * SCSI bus hot plug compatible * Fully supports actively negated SCSI signals DS21T11S 28-PIN SOIC (300 MIL) DESCRIPTION Fast SCSI and Ultra SCSI require the use of active terminations at both ends of every cable segment in a SCSI system with single-ended drivers and receivers. Ultra SCSI requires support of active negation and hot plugging. The DS21T11 is fully compliant with these standards. The DS21T11 integrates a low drop-out regulator and 18 precise switched 110 ohms termination resistors into a 28-pin 300 mil SOIC package. Active termination provides: greater immunity to voltage drops on the TERMPWR (TERMination PoWeR) line, enhanced high-level noise immunity, intrinsic TERMPWR decoupling, and very low quiescent current consumption. One DS21T11 can be used to terminate the Narrow SCSI bus, and a DS21T07 can be used with a DS21T11 for termination of a Wide SCSI bus. 070198 1/6 DS21T11 REFERENCE DOCUMENTS SCSI-2 (X3.131-1994) SCSI-3 Parallel Interface (X3T10/855D) SCSI-3 Fast-20 (X3T10/1071D) Available from: Global Engineering Documents 15 Inverness Way East Englewood, CO 80112-5704 Phone: (800) 854-7179,(303) 792-2181 Fax: (303) 792-2192 an active state, the PD pin should be left open circuited or tied low. 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 bypassed locally. A 2.2 F capacitor and a 0.01 F high frequency capacitor is recommended between TPWR and ground and placed as close as possible to the DS21T11. The DS21T11 should be placed as close as possible to the connector to minimize signal and power trace length, thereby resulting in less input capacitance and reflections which can degrade the bus signals. To maintain the specified regulation, a 4.7 F capacitor is required between the VREF pin and ground of each DS21T11. A high frequency cap (0.1 F ceramic recommended) can also be placed on the VREF pin in applications that use fast rise/fall time drivers. Figure 2 details a typical SCSI bus configuration. In an 8-bit data SCSI bus (Narrow SCSI), one DS21T11 is needed for proper termination of the 18 active signal lines. One DS21T11 and one DS21T07 can be used to terminate the 27 active signal lines in a 16-bit data SCSI bus (Wide SCSI). FUNCTION DESCRIPTION The DS21T11 is designed to be a single chip termination subsystem for use in Narrow SCSI systems. The DS21T11 consists of a bandgap reference, buffer amplifier, and 18 termination resistors (Figure 1). The voltage regulator circuitry (bandgap reference and class AB power amplifier) produces a precise laser trimmed 2.85 volt level and is capable of sourcing 25 mA into each of the terminating resistors when the signal line is low (active). 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 22 mA per line while keeping the voltage reference in regulation; the terminating resistors maintain their 110 ohms value over the entire voltage range. When all lines settle in the quiescent state, the regulator will consume about 10 mA. When the DS21T11 is put into power-down mode by bringing PD, the power-down circuitry will turn off the transistors on each signal line. This will isolate the DS21T11 from the signal lines and effectively remove it from the circuit. The power-down pin (PD) has an internal 50K pull-down resistor. To place the DS21T11 into DS21T11 BLOCK DIAGRAM Figure 1 PD TPWR 50K Ohm POWER DOWN CIRCUITRY BANDGAP REFERENCE 110 Ohms + R18 110 Ohms R17 - 110 Ohms R1 VREF 070198 2/6 DS21T11 TYPICAL SCSI BUS CONFIGURATION Figure 2 Termination Power Line DS21T11 TPWR + C2 C3 DS21T11 TPWR C1 + VREF2 SCSI CABLE GND R1 R8 R18 C1 + VREF GND R1 R2 R18 SCSI BUS TRANSCEIVER SCSI BUS TRANSCEIVER SCSI BUS TRANSCEIVER SCSI BUS TRANSCEIVER NOTES: 1. C1 = 4.7 F tantalum C2 = 2.2 F tantalum or 4.7 F aluminum C3 = 0.01 F ceramic 2. If the DS21T11 is to be embedded into a peripheral that will act as a target on a SCSI bus, it is recommended that TERMPWR be derived from the SCSI cable, not generated locally. In this configuration, if a power failure occurs in the peripheral, it will not affect the bus. 3. A high frequency bypass capacitor (0.1 F recommended) can be added in parallel to C1 for applications using fast rise/fall time drivers. 070198 3/6 DS21T11 PIN DESCRIPTION Table 1 PIN 1 SYMBOL PD DESCRIPTION Power Down. When tied high, the DS21T11 enters power-down mode. Contains an internal 50K pull-down resistor. Strap high to deactivate the DS21T11; tie low or leave open circuited to activate the DS21T11. Signal Termination 1. 110 ohms termination. Connect to SCSI bus signal lines. 2 -6, 10 - 13, 16 - 19, 23 - 27 7 - 9, 20 - 22 14 15 28 R1...R13 R14...R18 HS-GND TPWR VREF GND Heat Sink Ground. Internally connected to the mounting pad. Should be either grounded or electrically isolated from other circuitry. Termination Power. Connect to the SCSI TERMPWR line. 2.2 F cap. Bypass with a Reference Voltage. 2.85 volt reference; must be decoupled with a 4.7 F capacitor. Ground. Signal ground; 0.0 volts. 070198 4/6 DS21T11 ABSOLUTE MAXIMUM RATINGS* Voltage on Any Pin Relative to Ground Operating Temperature Storage Temperature Soldering Temperature -1.0V to +7.0V 0C to 70C -55C to +125C 260C for 10 seconds * This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operation sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect reliability. The Dallas Semiconductor DS21T11 is built to the highest quality standards and manufactured for long term reliability. All Dallas Semiconductor devices are made using the same quality materials and manufacturing methods. However, the DS21T11 is not exposed to environmental stresses, such as burn-in, that some industrial applications require. For specific reliability information on this product, please contact the factory in Dallas at (972) 371-4448. RECOMMENDED OPERATING CONDITIONS PARAMETER TERMPWR Voltage PD Inactive PD Active SYMBOL VTP VPDI VPDA MIN 4.00 -0.3 2.0 TYP MAX 5.50 0.8 VTP +0.3 UNITS V V V (0C to 70C) NOTES DC CHARACTERISTICS PARAMETER TERMPWR Current Power Down Current Termination Resistance Die Thermal Shutdown Power Down Termination Capacitance Input Leakage High Input Leakage Low SYMBOL ITP ITP IPD RTERM TSD CPD IIH IIL -1.0 1.0 107.5 150 3 MIN TYP 10 500 119.5 MAX 500 14 UNITS mA A ohms C pF A A (0C to 70C) NOTES 1, 3 1, 4 1, 2, 5 1, 2 1 1, 2, 5, 6 1 1, 8 REGULATOR CHARACTERISTICS PARAMETER Output Voltage Drop Out Voltage Output Current Line Regulation Load Regulation Current Limit Sink Current SYMBOL VREF VDROP IOUT LIREG LOREG IL ISINK 1.0 1.3 700 400 MIN 2.7 TYP 2.85 0.75 MAX 3.0 1.0 25.2 2.0 3.0 UNITS V V mA % % mA mA (0C to 70C) NOTES 1, 2 3, 6 9 1, 4 1, 2 1 1 070198 5/6 DS21T11 NOTES: 1. 4.00V < TERMPWR < 5.50V. 2. 0.0V < signal lines < TERMPWR. 3. All signal lines = 0.0V. 4. All signal lines open. 5. Power down enabled; PD > 2.0V. 6. Guaranteed by design; not production tested. 7. R1 through R18 and PD. 8. VSIGNAL = 0.2V. 28-PIN SOIC (300 MIL) PKG DIM A IN. MM A1 IN. MM A2 IN. MM b IN. MM C IN MM D IN. MM e IN. MM 28-PIN MIN 0.094 2.39 0.004 0.102 0.089 2.26 0.013 0.33 0.009 0.229 0.698 17.73 MAX 0.105 2.67 0.012 0.30 0.095 2.41 0.020 0.51 0.013 0.33 0.712 18.08 0.050 BSC 1.27 BSC 0.290 7.37 0.398 10.11 0.016 0.40 0 0.300 7.62 0.416 10.57 0.040 1.02 8 The chamfer on the body is optional. If it is not present, a terminal 1 identifier must be positioned so that 1/2 or more of its area is contained in the hatched zone. E1 IN. MM H IN MM L IN MM 070198 6/6 |
Price & Availability of DS21T11
 |
|
|
|
|
All Rights Reserved © IC-ON-LINE 2003 - 2022 |
| [Add Bookmark] [Contact Us] [Link exchange] [Privacy policy] |
|
Mirror Sites : [www.datasheet.hk]
[www.maxim4u.com] [www.ic-on-line.cn]
[www.ic-on-line.com] [www.ic-on-line.net]
[www.alldatasheet.com.cn]
[www.gdcy.com]
[www.gdcy.net] |