DS2119M

DS2119M DALLAS | Alldatasheet

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Technical content

FEATURES

/elevenoclock/floppy5Fully compliant with SCSI SPI-2, SPI-3, SPI-4, Ultra160, and Ultra320 /elevenoclock/floppy5Provides multimode low-voltage differential/single-ended (LVD/SE) termination for nine signal-line pairs /elevenoclock/floppy5Auto-selection of LVD or SE termination /elevenoclock/floppy55% tolerance on SE and LVD termination resistance /elevenoclock/floppy5Low power-down capacitance of 3pF /elevenoclock/floppy5Onboard thermal-shutdown circuitry /elevenoclock/floppy5SCSI-bus hot-plug compatible /elevenoclock/floppy5Fully supports actively negated SE SCSI signals PIN ASSIGNMENT

DESCRIPTION

The DS2119M Ultra3 LVD/SE SCSI Terminator is both a low-voltage differential (LVD) and single- ended (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 Ω resistors are used. Three DS2119M terminators are needed for a wide SCSI bus. 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, 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 DS2119M Ultra3 LVD/SE SCSI Terminator www.maxim-ic.com R9N R9P R8N HS GND R7N R7P R6N R6P DIFF_CAP DIFFSENSE MSTR/SLV R8P RIN R2P R2N R3P R4P R4N R5P R5N ISO GND HS GND DS2119ME 28-Pin TSSOP VREF RIP TPWR TPWR R3N

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: /elevenoclock/floppy5LVD Mode: LVD termination is provided by a precision laser-trimmed resistor string with two current sources. This configuration yields a 105 Ω differential and 150 Ω common-mode impedance. A fail-safe bias of 112mV is maintained when no drivers are connected to the SCSI bus. /elevenoclock/floppy5SE 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 110Ω =value. /elevenoclock/floppy5HVD 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, V REF remains active. During thermal shutdown, the termination pins are isolated from the SCSI bus and V REF 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 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 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.

To maintain the specified regulation, a 4.7 µF capacitor is required between the V REF pin (VREF) and ground of each DS2119M. 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. /elevenoclock/floppy5DIFFSENS 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.

Figure 1. DS2119M BLOCK DIAGRAM

Figure 2. SCSI BUS CONFIGURATION

Table 1. PIN DESCRIPTION LVD mode; must be decoupled with a 4.7µF cap. Signal Termination. Connect to SCSI bus signal lines. 14 GND Ground. Signal ground; 0V. pulled high, MSTR enables the DIFFSENSE driver. 16 DIFFSENSE DIFFSENSE. Output to drive the SCSI bus DIFFSENS line. single-ended) on the SCSI bus. decouple with a 2.2µF capacitor.

SINGLE-ENDED CHARACTERISTICS PARAMETER SYMBOL MIN TYP MAX UNITS NOTES SE Termination Resistance RSE 104.5 110 115.5 Ω 1 SE Voltage Reference V REF 2.7 2.85 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 VSEOR -0.3 0.5 V DIFFSENS LVD Operating Range VLVDOR 0.7 1.9 V DIFFSENS HVD Operating Range VHVDOR 2.4 V TPWR + 0.3 V DIFFSENSE Driver Output Voltage VDSO 1.2 1.4 V 8, 9 DIFFSENSE Driver Source Current IDSH 5 15 mA 8, 10, 12 DIFFSENSE Driver Sink Current IDSL 20 200 µA 8, 11 Thermal Shutdown 150 ºC 3

REGULATOR CHARACTERISTICS (0°C to +70°C) 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 = 0V to 3V. 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 = 0mA to 5mA. 10) VDSO = 0V. 11) VDSO = 2.75V. 12) TPWR = 5.5V.

DS2119M 28-PIN SSOP PACKAGE NOTES: 1) DIMENSION “D” DOES NOT INCLUDE MOLD MISMATCH, FLASH, OR PROTRUSIONS. MOLD MISMATCH, FLASH, AND PROTRUSIONS SHALL NOT EXCEED 0.15 PER SIDE. 2) DIMENSION “B” DOES NOT INCLUDE DAMBAR PROTRUSION. DAMBAR PROTRUSION SHALL NOT BE LOCATED ON THE LOWE R RADIUS OF THE FOOT. PKG 28-PIN DIM MIN MAX A MM - 1.10 MM 0.05 - MM 0.75 1.05 c MM 0.09 0.20 L MM 0.50 0.75 MM 0.65 BSC b MM 0.18 0.30 D MM 9.60 9.80 MM 4.40 BSC E MM 6.20 6.60