DS2117M MAXIM | Alldatasheet
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FEATURES
Fully Compliant with Ultra2, Ultra3, and Ultra 160/M SCSI 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 On-Board Thermal Shutdown Circuitry SCSI Bus Hot Plug Compatible Fully Supports Actively Negated SE SCSI Signals PIN CONFIGURATION
DESCRIPTION
The DS2117M Ultra3 LVD/SE SCSI terminator is both a low-voltage differential (LVD) and single- ended (SE) terminator. The multimode operation enab les the designer to implement LVD in current products while allowing the end user SE-backward compatibility with le gacy devices. If the device is connected in an LVD-only bus, the DS2117M uses LVD termination. If any SE de vices are connected to the bus, the DS2117M uses SE termination. This is accomplished automatically inside the part by sensing the voltage on the SCSI bus DIFFSENS line. For the LVD termination, the DS2117M integrates two current sources with nine precision resistor strings. For the SE termination, one regulator and nine precision 110 Ω resistors are used. Three DS2117M terminators are needed for a wide SCSI bus. DS2117M Ultra3 LVD/SE SCSI Terminator www.maxim-ic.com LVD SE R9N R8N R8P HS GND HS GND HS GND R7N R7P R6N R9P NC R1P R1N R2N HS GND HS GND R3P R3N R4P R4N R2P SSOP VREF NC TPWR HVD HS GND R5P R5N ISO GND DIFF_CAP DIFFSENSE MSTR/SLV R6P TOP VIEW
Small Computer Systems Interface (SCSI-3) SCSI Parallel Interface (SPI) Project: 0855-M, 1995 Small Computer Systems Interface (SCSI-3) SCSI Parallel Interface 2 (SPI-2) Project: 1142-M, 1998 Small Computer Systems Interface (SCSI-3) SCSI Parallel Interface 3 (SPI-3) Project: 1302-D, 1999 Small Computer Systems Interface (SCSI-3) SCSI Parallel Interface 4 (SPI-4) Project: 1365-D, xxxx 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 FUNCTIONAL DESCRIPTION The DS2117 combines LVD and SE termination with DIFFSENSE 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 are applied to the termination resistors. If the SCSI bus is in LVD mode, the 1.25V reference is used. If the SCSI bus is in SE mode, the 2.85V reference is used. That same control logic switches in/out para llel resistors to change the total termination resistance accordingly. Finally, in SE mode the R P pins are switched to ground. The DIFFSENSE circuitry decodes trinary logic. Ther e 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 HVD, SE, or LVD, respectively. The DS2117M’s DIFF_CAP pin monitors the DIFFSENS line to determine the proper operating mode of the device; this mode is indicated by the SE/LVD /HVD outputs. The DIFFSENSE pin can also drive the SCSI DIFFSENS line (when MSTR/SLV = 1) to de termine the SCSI bus operating mode. The DS2117M switches to the termination mode that is appropriate for the bus based on the value of the DIFFSENS voltage. These modes are LVD mode, SE mode, and HVD isolation mode. LVD Mode LVD termination is provided by a pr ecision laser-trimmed resistor string with two current sources. 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 pulls that signal line to 2.85V (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 110Ω value. HVD Isolation Mode The DS2117M identifies that ther e is an HVD (high voltage differen tial) device on the SCSI bus and isolates the termination pins from the bus. When ISO is pulled high, the termination pins are isolated from the SCSI bus, V REF is grounded, and the bus mode indicators (SE/LVD/HVD) remain active. During thermal shutdown, the termination pins are isolated from the SCSI bus, V REF is grounded, and the bus mode indicators (SE/LVD/HVD) remain active. 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 V DD lines should be bypassed locally. A 2.2 µF capacitor and a 0.01µF high frequency capacitor are recommended between TPWR and ground and placed as close as possible to the DS2117M. The DS2117M should be pl aced as close as possible to the SCSI connector to minimize signal and power trace length, thereby re sulting in less input cap acitance and reflections which can degrade the bus signals. To maintain the specified regulation, a 4.7 µF capacitor is required between the V REF pin (VREF) and ground of each DS2117M. A high frequency cap (0.1µF ceramic recommended) can also be placed on the VREF pin in applications that use fast rise/fall time dr ivers. A typical SCSI bus configuration is shown in Figure 2. DIFFSENS NOISE FILTERING The DS2117M 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. The external filter can be used in addition to the digital filter if the DS2117M and DS2118M are to be used interchangeably. NOTE: DIFFSENS—Refers to the SCSI bus signal. DIFFSENSE—Refers to the DS2117M pin name and intern al circuitry capable of driving the DIFFSENS line. DIFF_CAP—Refers to the DS2117M pin name and in ternal circuitry relating to monitoring the DIFFSENS line.
Figure 1. DS2117M Block Diagram
Figure 2. SCSI Bus Configuration
1 VREF Reference Voltage. 2.85V reference in SE mode and 1.25V reference in LVD mode; must be decoupled with a 4.7µF capacitor. 2, 3 NC No Connection. Do not connect these pins. 4–7, 11–16, 22–25, 29–32 RxP, RxN Signal Termination. Connect to SCSI bus signal lines. 8, 9, 10, 26, 27, 28 HS GND Heat Sink Ground. Internally connected to the mounting pad. Should be grounded. 17 ISO Isolation. When pulled high, the DS2117M isolates its bus pins (RxP, RxN) from the SCSI bus. 18 GND Ground. Signal ground, 0V. 19 MSTR/SLV Master/Slave. Mode select for the non-controlling terminator. When pulled high (MSTR), the DIFFSENSE driver is enabled. 20 DIFFSENSE DIFFSENSE. Output to drive the SCSI bus DIFFSENS line.
21 DIFF_CAP
DIFFSENSE Capacitor. Connect 0.1µF capacitor for DIFFSENSE filter. Input to detect the type of device (differential or single-ended) on the SCSI bus. 33 SE Single-Ended. SE output of DIFFSENSE receiver; output high indicates SE bus operation. 34 LVD Low-Voltage Differential. LVD output of DIFFSENSE receiver; output high indicates LVD bus operation. 35 HVD High-Voltage Differential. HVD output of DIFFSENSE receiver; output high indicates HVD bus operation or thermal shutdown. 36 TPWR Termination Power. Connect to the SCSI TERMPWR line and decouple with 2.2µF capacitor.
RECOMMENDED OPERATING CONDITIONS PARAMETER SYMBOL MIN TYP MAX UNITS NOTES SE Mode V TPWR(SE) 4.0 5.5 V Termpower Voltage LVD Mode V TPWR(LVD) 2.7 5.5 V Logic 0 V IL -0.3 +0.8 V Logic 1 V IH 2.0 VTPWR + 0.3 V Operating Temperature V AMB 0 70 °C SINGLE-ENDED CHARACTERISTICS PARAMETER SYMBOL MIN TYP MAX UNITS NOTES SE Termination Resistance R SE 104.5 110 115.5 Ω 1 SE Voltage Reference V REF 2.7 3.0 V SE Output Current L OSE 25.4 mA 2 Output Capacitance C OUT 3 pF 3 LOW-VOLTAGE DIFFERENTIAL CHARACTERISTICS PARAMETER SYMBOL MIN TYP MAX UNITS NOTES Differential-Mode Termination Resistance RDM 100 110 Ω Common-Mode Termination Resistance RCM 110 190 Ω Differential-Mode Bias V DM 100 125 mV 4 Common-Mode Bias V CM 1.125 1.375 V DC CHARACTERISTICS PARAMETER SYMBOL MIN TYP MAX UNITS NOTES Termpower Current I TPMR 12 mA 4 Input Leakage High I IH -1.0 µA Input Leakage Low I IL 1.0 µA Output Current High I OH -1.0 mA 5, 7 Output Current Low I OL 4.0 mA 6, 7 DIFFSENS SE Operating Range V SEOR -0.3 +0.5 V DIFFSENS LVD Operating Range V LVDOR 0.7 1.9 V DIFFSENS HVD Operating Range V HVDOR 2.4 VTPWR + 0.3 V DIFFSENSE Driver Output Voltage V DSO 1.2 1.4 V 8, 9 DIFFSENSE Driver Source Current I DSH 5 15 mA 8, 10, 12 DIFFSENSE Driver Sink Current I DSL 20 200 µA 8, 11 Thermal Shutdown 150 ºC 3
PARAMETER SYMBOL MIN TYP MAX UNITS NOTES Line Regulation LI REG 1.0 2.5 % Load Regulation LO REG 1.3 3.5 % Current Limit I LIM 550 mA Sink Current I SINK 200 mA NOTES: 1) V LINE = 0 to 3.0V. 2) V LINE = 0.2V. 3) Guaranteed by design. 4) All lines open. 5) V OUT = 2.4V. 6) V OUT = 0.4V. 7) SE/LVD/HVD pins only. 8) MSTR/SLV = 1. 9) I DS = 0 to 5mA. 10) VDSO = 0V. 11) VDSO = 2.75V. 12) TPWR = 5.5V
DS2117M 36-PIN SSOP PACKAGE DIM MIN MAX A 2.44 2.64 A1 0.12 - b 0.29 0.43 c 0.23 0.32 D 15.20 15.54 E 10.11 10.52 E1 7.40 7.60 e 0.80 BSC h 0.25 0.71 L 0.51 1.02 DIMENSIONS D AND E1 INCLUDE MOLD MISMATCH, BUT DO NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.254mm PER SIDE. SECTION A-A DIMENSIONS APPLY TO THE FLAT SECTION OF THE LEAD BETWEEN 0.13mm TO 0.25mm FROM THE LEAD TIP. THE CHAMFER ON THE BODY IS OPTIONAL. IF IT IS NOT PRESENT, A VISUAL INDEX FEATURE MUST BE LOCATED WITHIN THE CROSS-HATCHED AREA. DIMENSIONS ARE IN MILLIMETERS