DS2117MB

DS2117M Ultra3 LVD/SE SCSI Terminator www.maxim-ic.com FEATURES PIN CONFIGURATION 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 TOP VIEW VREF NC NC R1P R1N R2P R2N HS GND HS GND HS GND R3P R3N R4P R4N R5P R5N ISO GND 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 20 19 TPWR HVD LVD SE R9N R9P R8N R8P HS GND HS GND HS GND R7N R7P R6N R6P DIFF_CAP DIFFSENSE MSTR/SLV SSOP DESCRIPTION The DS2117M 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 DS2117M uses LVD termination. If any SE devices 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 110Ω resistors are used. Three DS2117M terminators are needed for a wide SCSI bus. 1 of 9 REV: 112905 DS2117M REFERENCE DOCUMENTS 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 parallel resistors to change the total termination resistance accordingly. Finally, in SE mode the RP pins are 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 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 determine 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 precision laser-trimmed resistor string with two current sources. This configuration yields a 105Ω 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 there is an HVD (high voltage differential) 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, VREF is grounded, and the bus mode indicators (SE/LVD/HVD) remain active. During thermal shutdown, the termination pins are isolated from the SCSI bus, VREF is grounded, and the bus mode indicators (SE/LVD/HVD) remain active. The DIFFSENSE driver is shut down during either of these two events. 2 of 9 DS2117M 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 2.2µF 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 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. To maintain the specified regulation, a 4.7µF capacitor is required between the VREF 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 drivers. 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 internal circuitry capable of driving the DIFFSENS line. DIFF_CAP—Refers to the DS2117M pin name and internal circuitry relating to monitoring the DIFFSENS line. 3 of 9 DS2117M Figure 1. DS2117M Block Diagram 4 of 9 DS2117M Figure 2. SCSI Bus Configuration 5 of 9 DS2117M PIN DESCRIPTION PIN NAME 1 VREF 2, 3 4–7, 11–16, 22–25, 29–32 8, 9, 10, 26, 27, 28 NC 17 18 19 20 21 33 34 35 36 RxP, RxN FUNCTION Reference Voltage. 2.85V reference in SE mode and 1.25V reference in LVD mode; must be decoupled with a 4.7µF capacitor. No Connection. Do not connect these pins. Signal Termination. Connect to SCSI bus signal lines. Heat Sink Ground. Internally connected to the mounting pad. Should be grounded. Isolation. When pulled high, the DS2117M isolates its bus pins (RxP, ISO RxN) from the SCSI bus. GND Ground. Signal ground, 0V. Master/Slave. Mode select for the non-controlling terminator. When MSTR/SLV pulled high (MSTR), the DIFFSENSE driver is enabled. DIFFSENSE DIFFSENSE. Output to drive the SCSI bus DIFFSENS line. DIFFSENSE Capacitor. Connect 0.1µF capacitor for DIFFSENSE DIFF_CAP filter. Input to detect the type of device (differential or single-ended) on the SCSI bus. Single-Ended. SE output of DIFFSENSE receiver; output high SE indicates SE bus operation. Low-Voltage Differential. LVD output of DIFFSENSE receiver; LVD output high indicates LVD bus operation. High-Voltage Differential. HVD output of DIFFSENSE receiver; HVD output high indicates HVD bus operation or thermal shutdown. Termination Power. Connect to the SCSI TERMPWR line and TPWR decouple with 2.2µF capacitor. HS GND 6 of 9 DS2117M RECOMMENDED OPERATING CONDITIONS PARAMETER SE Mode Termpower Voltage LVD Mode Logic 0 Logic 1 Operating Temperature SYMBOL VTPWR(SE) VTPWR(LVD) VIL MIN 4.0 2.7 -0.3 VIH 2.0 VAMB 0 TYP MAX 5.5 5.5 +0.8 VTPWR + 0.3 70 UNITS V V V NOTES MAX 115.5 3.0 25.4 3 UNITS Ω V mA pF NOTES 1 MAX UNITS NOTES V °C 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 3 LOW-VOLTAGE DIFFERENTIAL CHARACTERISTICS PARAMETER Differential-Mode Termination Resistance Common-Mode Termination Resistance Differential-Mode Bias Common-Mode Bias SYMBOL MIN TYP RDM 100 110 Ω RCM 110 190 Ω VDM VCM 100 1.125 125 1.375 mV V 4 PARAMETER Termpower Current Input Leakage High Input Leakage Low Output Current High Output Current Low DIFFSENS SE Operating Range DIFFSENS LVD Operating Range SYMBOL ITPMR IIH IIL IOH IOL VSEOR VLVDOR MIN MAX UNITS mA µA µA mA mA V V NOTES 4 DIFFSENS HVD Operating Range VHVDOR 2.4 DIFFSENSE Driver Output Voltage DIFFSENSE Driver Source Current DIFFSENSE Driver Sink Current Thermal Shutdown VDSO IDSH IDSL 1.2 5 20 DC CHARACTERISTICS TYP 12 -1.0 1.0 -1.0 4.0 -0.3 0.7 +0.5 1.9 VTPWR + 0.3 1.4 15 200 150 7 of 9 5, 7 6, 7 V V mA µA ºC 8, 9 8, 10, 12 8, 11 3 DS2117M REGULATOR CHARACTERISTICS PARAMETER Line Regulation Load Regulation Current Limit Sink Current SYMBOL LIREG LOREG ILIM ISINK NOTES: 1) VLINE = 0 to 3.0V. 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 = 0 to 5mA. 10) VDSO = 0V. 11) VDSO = 2.75V. 12) TPWR = 5.5V 8 of 9 MIN 200 TYP 1.0 1.3 550 MAX 2.5 3.5 UNITS % % mA mA NOTES DS2117M DS2117M 36-PIN SSOP PACKAGE 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. DIM A A1 b c D E E1 e h L MIN MAX 2.44 2.64 0.12 0.29 0.43 0.23 0.32 15.20 15.54 10.11 10.52 7.40 7.60 0.80 BSC 0.25 0.71 0.51 1.02 DIMENSIONS ARE IN MILLIMETERS 9 of 9