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| DS21T26 PRODUCT PREVIEW DS21T26 SCSI Terminator, 27-Line, SE FEATURES PIN ASSIGNMENT R8 R9 R23 R24 R25 R26 R27 GND GND GND PD R10 R11 R12 R13 R14 R1 R2 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 DS21T26 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 20 19 R7 R6 R5 R22 R21 R20 R19 VREF GND GND GND TPWR R18 R17 R16 R15 R4 R3 * Fully compliant with SCSI, Fast SCSI and Ultra SCSI * Provides active termination for 27 signal lines * 5% tolerance on termination resistance and termination current * Low power down capacitance of 3 pF * Onboard thermal shutdown circuitry * SCSI bus hot-plug compatible * Fully supports actively negated SCSI signals * Active high power-down 36-PIN SSOP (TOP VIEW) B PACKAGE DESCRIPTION Fast SCSI and Ultra SCSI require the use of active termination at both ends of every cable segment in a SCSI system with single ended drivers and receivers. Ultra SCSI requires the support of active negation and hot plugging. The DS21T26 is fully compliant with these standards. The DS21T26 integrates a low drop out regulator and 27 precise switched 100 Ohm termination resistors into a 36 pin SSOP 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. A single DS21T26 can be used to terminate a wide SCSI bus (27 lines). For the SE termination, one low drop-out regulator and 27 precise 110 Ohm resistors are used. 022798 1/6 DS21T26 DS2126 BLOCK DIAGRAM Figure 1 TERMPWR POWER DOWN CIRCUITRY BANDGAP REFERENCE 110 OHMS R1 110 OHMS R2 110 OHMS R3 110 OHMS R4 110 OHMS R5 110 OHMS R6 110 OHMS R7 110 OHMS GND 75K PD R8 110 OHMS R9 110 OHMS R10 110 OHMS R11 110 OHMS R12 110 OHMS R13 110 OHMS R14 110 OHMS R15 110 OHMS R16 110 OHMS R17 110 OHMS R18 110 OHMS R19 110 OHMS R20 110 OHMS R21 110 OHMS R22 110 OHMS R23 110 OHMS R24 110 OHMS R25 110 OHMS R26 110 OHMS R27 VREF 022798 2/6 DS21T26 TYPICAL SCSI BUS CONFIGURATION Figure 2 Termination Power Line DS21T26 TERMPWR + C2 DS21T26 TERMPWR C1 + VREF SCSI CABLE GND R1 R27 C1 + VREF GND R1 R27 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. 2. If the DS21T26 is to be embedded into a peripheral that will act as a target on a SCSI bus, it is that recommended 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. 022798 3/6 DS21T26 PIN DESCRIPTION Table 1 PIN 1-7, 12-24, 30-36 8-10, 26-28 11 25 29 SYMBOL Rx GND PD TPWR VREF DESCRIPTION Signal Termination. Connect to SCSI bus signal lines. Ground. Signal ground; 0.0 volts. Internally connected to the mounting pad for heat sinking. Power Down. When pulled high, the DS21T26 enters power-down mode. Power down when the device is not at the end of the SCSI bus. Termination Power. Connect to SCSI bus TERMPWR line and decouple with 2.2 F capacitor. Reference Voltage. 2.85 volt reference; must be decoupled with a 4.7 F capacitor. 022798 4/6 DS21T26 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. 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 1.0 105 150 3 4 MIN TYP 10 100 110 MAX 700 14 150 115 UNITS mA A Ohms C pF A A (0C to 70C) NOTES 1, 3 1, 4 1, 2, 5 1, 2 1, 6 1, 2, 5, 6 1, 8 1, 7 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 600 21.6 MIN 2.79 TYP 2.85 0.50 22.8 1.0 1.3 900 MAX 2.93 0.75 25.2 2.0 3.0 UNITS V V mA % % mA mA (0C to 70C) NOTES 1, 2 3, 6 9 1, 4 1, 3 1 1 NOTES: 1. 4.00V < TERMPWR < 5.25V. 2. 0.0V < signal lines < 3.0V. 3. All signal lines = 0.0V. 4. All signal lines open. 5. Power-down enabled; PD = 5.0V. 6. Guaranteed by design; not production tested. 7. R1 through R27 only. 8. R1 through R27 and PD/. 9. VSIGNAL = 0.2V. 022798 5/6 DS21T26 DS21T26 36-PIN SSOP PACKAGE Figure 3 022798 6/6 |
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