DS2125+ Maxim Integrated, DS2125+ Datasheet - Page 5

• Manufacturer Part Number: DS2125+
• Description: SCSI Interface IC
• Manufacturer: Maxim Integrated
• Series: DS2125r
• Type: SCSI Terminationr

Specifications of DS2125+

• Rohs: yes
• Operating Supply Voltage: 2.7 V to 5.5 V
• Supply Current: 32 mA
• Maximum Operating Temperature: + 70 C
• Minimum Operating Temperature: 0 C
• Mounting Style: SMD/SMT
• Package / Case: TQFP-48
• Resistance: 110 Ohms
• Part # Aliases: 90-21250+000

Figure 2. SCSI Bus Configuration
Note: The following terms are used throughout this data sheet:
DIFFSENS: Refers to the SCSI bus signal.
DIFFSENSE: Refers to the DS2125 pin name and internal circuitry capable of driving the DIFFSENS line.
DIFF_CAP: Refers to the DS2125 pin name and internal circuitry relating to monitoring the DIFFSENS line.
DETAILED DESCRIPTION
The DS2125 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.
The DIFFSENSE circuitry decodes trinary logic. There is 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, which indicates the mode of the bus as SE, HVD, or LVD, respectively.
TERMPWR
TPWR
TPWR
ISO
V
ISO
V
REF
REF
4.7µF
4.7µF
DIFFSENS
DIFF_CAP
DIFFSENS
DIFF_CAP
0.1µF
20kΩ
CONTROL LINES (15)
CONTROL LINES (15)
DIFFSENSE
5 of 7
20kΩ
DIFF_CAP
DIFF_CAP
DIFFSENS
DIFFSENS
0.1µF
TPWR
TPWR
V
V
REF
REF
ISO
ISO
4.7µF
4.7µF
TERMPWR
p