MCCS142235DW ON Semiconductor, MCCS142235DW Datasheet - Page 7

• Manufacturer Part Number: MCCS142235DW
• Manufacturer: ON Semiconductor
• Type: SCSI Terminationr

Specifications of MCCS142235DW

• Termination Resistance (rt Or Rterm) (typ): 110Ohm
• Number Of Bits: 18
• Operating Supply Voltage (min): 2.75V
• Package Type: SOIC
• Mounting: Surface Mount
• Pin Count: 24
• Operating Temperature Classification: Commercial
• Lead Free Status / RoHS Status: Not Compliant

AC CHARACTERISTICS (VREG = 2.85, C
TIMING REQUIREMENTS (VREG = 2.85, C
Proper Use of the LV
incorporates features not available in competitor designs. A
primary feature, known as “Local V
future migration to reliable software control of the
termination state (either terminated or high impedance).
When the Enable pin is driven by internal logic within the
SCSI peripheral, it is essential that the peripheral be
powered up. Otherwise the enable signal to the termination
chip may be invalid causing system bus failure due to
improper termination. Imagine a SCSI system with a disk
drive at one end of the bus which is providing termination to
the bus via the MCCS142235 device. A “smart” drive will
be providing an enable signal to the termination chip
through internal logic circuitry to ensure termination is
present. In the event this same disk drive is powered down
by a user while the bus is active, what becomes of the
termination located within that drive? Does it remain
LV
Enable
t
t
t
t
The ON Semiconductor Active SCSI Terminator chip
(Enable)
(Disable)
setup
hold
CC
Symbol
Symbol
t
É É É É É É
É É É É É É
É É É É É É
setup
Max Propagation Delay,
High Impedance to Termination,
Enable to Outputs
Max Propagation Delay,
Termination to High Impedance,
Enable to Outputs
Min Setup Time, LV
Min Hold Time, LV
CC
3.7V
Feature
Parameters
Parameters
50%
* If LV
CC
CC
CC
to Enable
to Enable
CC
MCCS142235 Applications Information
sensing”, facilitates
Enable is grounded then the LV
L
L
= 50 pF, t
Figure 7. Timing Requirements
= 50 pF, t
http://onsemi.com
disabled
enabled
r
0°C to + 70°C
= t
r
25°C
200
50
= t
f
= 6 ns)
f
100
1.0
= 6 ns)
7
0°C to + 70°C
terminated? Does it change state causing the system to
crash? Or does it go into an undetermined state?
operating SCSI bus through the dedicated TERMPWR line.
But the “Local V
may be powered down at any time while the SCSI bus is in
operation. It is this local supply which powers the
peripheral’s logic chips and provides the enable signal to the
SCSI terminator chip. Therefore, it is essential to maintain
the proper enable signal to the switchable terminator even
during peripheral power down.
down a terminating peripheral, ON Semiconductor has an
exclusive “Local V
which latches the enable state of the termination
permanently during peripheral power loss. A comparator
within the MCCS142235 can be connected to the local
The termination power supply is always present on an
To avoid rendering the system inoperable while powering
500
100
Unit
μs
μs
CC
feature is disabled.
Per Truth Table
Per Truth Table
Unit
50%
ns
ns
CC
CC
” power supply within each peripheral
3.7V
sensing” circuit on the MCCS142235
É É É É
É É É É
É É É É
(See Figure 7)
(See Figure 7)
Condition
t
Condition
hold
V
0.0 V
V
0.0 V
CC
CC
V
V