4

UCC5672

TRMPWR = 2.7V to 5.25V.

PARAMETER

TEST CONDITIONS

MIN

TYP

MAX

UNITS

Time Delay/Filter Section

Mode Change Delay

A new mode change can start any time after a

previous mode change has been detected.

(Note4 )

100

180

300

ms

Note 1: Guaranteed by design. Not 100% tested in production.

Note 2:

() ()

Z

V

II

CM

VV

VV

CM

CM

=

−

+−

12

06

06

.

..

; Where VCM = Voltage measured with L+ tied to L– and zero current applied;

Note 4: Noise on DIFFB will not cause a false mode change. The time delay is that same for a change from any mode to any

other mode. Within 300ms after power is applied the mode is defined by the voltage of DIFFB.

PIN DESCRIPTIONS

DIFFB:

Input pin for the comparators that select SE,

LVD SCSI, or HIPD modes of operation. This pin should

be decoupled with a 0.1

µF capacitor to ground and then

coupled to the DIFSENS pin through a 20k

Ω resistor.

DIFSENS: Connects to the Diff Sense line of the SCSI

bus. The bus mode is controlled by the voltage level on

this pin.

DISCNCT: Input pin used to shut down the terminator if

the terminator is not connected at the end of the bus.

Connect this pin to ground to activate the terminator or

open pin to disable the terminator.

HS/GND: Heat sink ground pins. These should be con-

nected to large ground area PC board traces to increase

the power dissipation capability.

GND: Power Supply return.

L1– thru L9–: Termination lines. These are the active

lines in SE mode and are the negative lines for LVD

SCSI mode. In HIPD mode, these lines are high imped-

ance.

L1+ thru L9+: Termination lines. These lines switch to

ground in SE mode and are the positive lines for LVD

SCSI mode. In HIPD mode, these lines are high imped-

ance.

REG: Regulator bypass pin, must be connected to a

4.7 F capacitor to ground.

TRMPWR: 2.7V to 5.25V power input pin. Bypass near

the terminators with a 4.7 F capacitor to ground.

All SCSI buses require a termination network at each

end to function properly. Specific termination require-

ments differ, depending on which types of SCSI devices

are present on the bus.

The UCC5672 is used in multi-mode active termination

applications, where single ended (SE) and low voltage

differential (LVD) SCSI devices might coexist. The

UCC5672 has both SE and LVD SCSI termination net-

works integrated into a single monolithic component. The

correct termination network is automatically determined

by the SCSI bus "DIFSENS" signal.

The SCSI bus DIFSENS signal line is used to identify

which types of SCSI devices are present on the bus. On

power-up, the UCC5672 DIFSENS drivers will try to de-

liver 1.3V to the DIFSENS line. If only LVD SCSI devices

are present, the DIFSENS line will be successfully driven

to 1.3V and the terminators will configure for LVD SCSI

operation. If any single ended devices are present, they

will present a short to ground on the DIFSENS line, sig-

naling the UCC5672(s) to configure into the SE mode,

accommodating the SE devices. Or, if any high voltage

differential

(HVD)

SCSI

devices

are

present,

the

DIFSENS line is pulled high and the terminator will enter

a high impedance state, effectively disconnecting from

the bus.

The DIFSENS line is monitored by each terminator

through a 50Hz noise filter at the DIFFB input pin. A set

of comparators detect and select the appropriate termi-

APPLICATION INFORMATION