DS2117MB Maxim Integrated Products, DS2117MB Datasheet - Page 2

• Manufacturer Part Number: DS2117MB
• Description: IC TERM SCSI LVD/SE ULT-3 36SSOP
• Manufacturer: Maxim Integrated Products
• Type: SCSI, LVD, SEr

Specifications of DS2117MB

• Number Of Terminations: 9
• Voltage - Supply: 4 V ~ 5.5 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 36-SSOP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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: [phone]
Global Engineering Documents 15 Inverness Way East; Englewood, CO 80112 Phone: [phone]
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 R
pins are switched to ground.
P
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, V
is grounded, and the
REF
bus mode indicators (SE/LVD/HVD) remain active. During thermal shutdown, the termination pins are
isolated from the SCSI bus, V
is grounded, and the bus mode indicators (SE/LVD/HVD) remain
REF
active. The
driver is shut down during either of these two events.
DIFFSENSE
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