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DS2119M Ultra3 LVD/SE SCSI Terminator
www.maxim-ic.com
FEATURES
Fully compliant with SCSI SPI-2, SPI-3, SPI-4, Ultra160, and Ultra320 Provides multimode low-voltage differential/single-ended (LVD/SE) termination for nine signal-line pairs Auto-selection of LVD or SE termination 5% tolerance on SE and LVD termination resistance Low power-down capacitance of 3pF Onboard thermal-shutdown circuitry SCSI-bus hot-plug compatible Fully supports actively negated SE SCSI signals
PIN ASSIGNMENT
VREF RIP RIN R2P R2N HS GND R3P R3N R4P R4N R5P R5N ISO GND 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 TPWR TPWR R9N R9P R8N R8P HS GND R7N R7P R6N R6P DIFF_CAP DIFFSENSE MSTR/SLV
DS2119ME 28-Pin TSSOP
DESCRIPTION
The DS2119M Ultra3 LVD/SE SCSI Terminator is both a low-voltage differential (LVD) and singleended (SE) terminator. The multimode operation enables the designer to implement LVD in current products while allowing the end-user SE-backward compatibility with legacy devices. If the device is connected in an LVD-only bus, the DS2119M will use LVD termination. If any SE devices are connected to the bus, the DS2119M will use SE termination. This is accomplished automatically inside the part by sensing the voltage on the SCSI bus DIFFSENS line. For the LVD termination, the DS2119M integrates two current sources with nine precision resistor strings. For the SE termination, one regulator and nine precision 110 resistors are used. Three DS2119M terminators are needed for a wide SCSI bus.
REFERENCE DOCUMENTS
Small Computer Systems Interface (SCSI-3) Small Computer Systems Interface (SCSI-3) Small Computer Systems Interface (SCSI-3) Small Computer Systems Interface (SCSI-3) SCSI Parallel Interface (SPI) SCSI Parallel Interface 2 (SPI-2) SCSI Parallel Interface 3 (SPI-3) SCSI Parallel Interface 4 (SPI-4) Project: 0855-M, 1995 Project: 1142-M, 1998 Project: 1302-D, 1999 Project: 1365-D, 200x
Available From: American National Standards Institute (ANSI) Phone: (212) 642-4900 Global Engineering Documents 15 Inverness Way East; Englewood, CO 80112 Phone: (800) 854-7179
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DS2119M
FUNCTIONAL DESCRIPTION
The DS2119 combines LVD and SE termination with DIFFSENS sourcing and detection. A bandgap reference is fed into two amplifiers, which creates a 1.25V reference voltage and a 2.85V reference voltage. The control logic determines which of these references will be applied to the termination resistors. If the SCSI bus is in LVD mode, then the 1.25V reference will be used. If the SCSI bus is in SE mode, then the 2.85V reference will be used. That same control logic will switch in/out parallel resistors to change the total termination resistance accordingly. Finally, in SE mode, the Rp pins will be switched to ground. The DIFFSENSE circuitry decodes trinary logic. There will be one of three voltages on the SCSI control line called DIFFSENS. Two comparators and a NAND gate determine if the voltage is below 0.6V, above 2.15V, or in between. That indicates the mode of the bus to be SE, HVD, or LVD, respectively. The DS2119M's DIFF_CAP pin monitors the DIFFSENS line to determine the proper operating mode of the device. The DIFFSENSE pin can also drive the SCSI DIFFSENS line (when MSTR/SLV = 1) to determine the SCSI bus-operating mode. The DS2119M switches to the termination 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 laser-trimmed resistor string with two current sources. This configuration yields a 105 differential and 150 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 2.85V (quiescent state). When used with an active negation driver, the power amp can sink 22mA per line and the reference voltage will move less than 100mV. The terminating resistors maintain their 110=value. HVD Isolation Mode: The DS2119M identifies that there is an HVD (high-voltage differential) device on the SCSI bus and isolates the termination pins from the bus. When ISO = 1, the termination pins are isolated from the SCSI bus, VREF remains active. During thermal shutdown, the termination pins are isolated from the SCSI bus and VREF becomes high impedance. 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 and VDD lines should be bypassed locally. A 2.2F capacitor and a 0.01F high-frequency capacitor are recommended between TPWR and ground and placed as close as possible to the DS2119M. The DS2119M should be placed as close as possible to the SCSI connector to minimize signal and power-trace length, thereby resulting in less input capacitance and reflections, which can degrade the bus signals.
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To maintain the specified regulation, a 4.7F capacitor is required between the VREF pin (VREF) and ground of each DS2119M. A high frequency cap (0.1F 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. DIFFSENS Noise Filtering: The DS2119M incorporates a digital filter to remove high-frequency transients on the DIFFSENS control line, thereby eliminating erroneous switching between modes. This filter eliminates the need for the external capacitor and resistor, which heretofore performed this function.
NOTES:
1) DIFFSENS. Refers to the SCSI bus signal. 2) DIFFSENSE. Refers to the Dallas Semiconductor pin name and internal circuitry relating the DIFFSENS driver.
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Figure 1. DS2119M BLOCK DIAGRAM
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Figure 2. SCSI BUS CONFIGURATION
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Table 1. PIN DESCRIPTION
PIN 1 2-5, 7-12, 18-21, 23-26 6, 22 13 14 15 16 17 27, 28 SYMBOL VREF RxP, RxN HS GND DESCRIPTION Reference Voltage. 2.85V reference in SE mode and 1.25V reference in LVD mode; must be decoupled with a 4.7F cap. Signal Termination. Connect to SCSI bus signal lines.
Heat Sink Ground. Internally connected to the mounting pad. Should be grounded. ISO Isolation. When pulled high, the DS2119M isolates its bus pins (RxP, RxN) from the SCSI bus. GND Ground. Signal ground; 0V. MSTR/SLV Master/Slave. Mode-select for the noncontrolling terminator. When pulled high, MSTR enables the DIFFSENSE driver. DIFFSENSE DIFFSENSE. Output to drive the SCSI bus DIFFSENS line. DIFF_CAP DIFFSENSE CAPACITOR. Connect a 0.1F capacitor for DIFFSENSE filter. Input to detect the type of device (differential or single-ended) on the SCSI bus. TPWR Termination Power. Connect to the SCSI TERMPWR line and decouple with a 2.2F capacitor.
RECOMMENDED OPERATING CONDITIONS
PARAMETER Termpower Voltage SE Mode LVD Mode Logic 0 Logic 1 Operating Temperature SYMBOL VTPWR(SE) VTPWR(LVD) VIL VIH VAMB MIN 4.0 2.7 -0.3 2.0 0 TYP MAX 5.5 5.5 +0.8 VTPWR + 0.3 70 UNITS V V V V C NOTES
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SINGLE-ENDED CHARACTERISTICS
PARAMETER SE Termination Resistance SE Voltage Reference SE Output Current Output Capacitance SYMBOL RSE VREF lOSE COUT MIN 104.5 2.7 TYP 110 2.85 MAX 115.5 3.0 25.4 3 UNITS V mA pF NOTES 1 2 3
LOW-VOLTAGE DIFFERENTIAL CHARACTERISTICS
PARAMETER Differential Mode Termination Resistance Common Mode Termination Resistance Differential Mode Bias Common Mode Bias SYMBOL RDM RCM VDM VCM MIN 100 110 100 1.125 TYP MAX 110 190 125 1.375 UNITS mV V NOTES
4
DC CHARACTERISTICS
PARAMETER Termpower Current Input Leakage High Input Leakage Low Output Current High Output Current Low DIFFSENS SE Operating Range DIFFSENS LVD Operating Range DIFFSENS HVD Operating Range DIFFSENSE Driver Output Voltage DIFFSENSE Driver Source Current DIFFSENSE Driver Sink Current Thermal Shutdown SYMBOL ITPMR IIH IIL IOH IOL VSEOR VLVDOR VHVDOR VDSO IDSH IDSL MIN -1.0 1.0 -1.0 4.0 -0.3 0.7 2.4 1.2 5 20 150 0.5 1.9 VTPWR + 0.3 1.4 15 200 TYP 12 MAX UNITS mA A A mA mA V V V V mA A C 8, 9 8, 10, 12 8, 11 3 NOTES 4 5, 7 6, 7
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REGULATOR CHARACTERISTICS
PARAMETER Line Regulation Load Regulation Current Limit Sink Current SYMBOL LIREG LOREG ILIM ISINK MIN TYP 1.0 1.3 550 MAX 2.5 3.5
(0C to +70C)
UNITS % % mA mA NOTES
200
NOTES:
1) VLINE = 0V to 3V. 2) VLINE = 0.2V. 3) Guaranteed by design. 4) All lines open. 5) VOUT = 2.4V. 6) VOUT = 0.4V. 7) SE/LVD/HVD pins only. 8) MSTR/SLV = 1. 9) IDS = 0mA to 5mA. 10) VDSO = 0V. 11) VDSO = 2.75V. 12) TPWR = 5.5V.
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DS2119M 28-PIN SSOP PACKAGE NOTES:
1) 2)
DIMENSION "D" DOES NOT INCLUDE MOLD MISMATCH, FLASH, OR PROTRUSIONS. MOLD MISMATCH, FLASH, AND PROTRUSIONS SHALL NOT EXCEED 0.15 PER SIDE. DIMENSION "B" DOES NOT INCLUDE DAMBAR PROTRUSION. DAMBAR PROTRUSION SHALL NOT BE LOCATED ON THE LOWER RADIUS OF THE FOOT.
PKG DIM A MM A1 MM A2 MM c MM L MM e1 MM b MM D MM E1 MM E MM
28-PIN MIN MAX 0.05 0.75 0.09 0.50 1.10 1.05 0.20 0.75
0.65 BSC 0.18 9.60 0.30 9.80
4.40 BSC 6.20 6.60
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