UCC5638
DESCRIPTION
The UCC5638 Multimode SCSI Terminator provides a smooth transition
into the next generation of the SCSI Parallel Interface (SPI-2). It automati-
cally senses the bus, via DIFFB, and switches the termination to either sin-
gle ended (SE) or low voltage differential (LVD) SCSI, dependent on which
type of devices are connected to the bus. The UCC5638 can not be used
on a HVD, EIA485, differential SCSI bus. If the UCC5638 detects a HVD
SCSI device, it switches to a high impedance state.
The Multimode terminator contains all functions required to terminate and
auto detect and switch modes for SPI-2 bus architectures. Single Ended
and Differential impedances and currents are trimmed for maximum effec-
tiveness. Fail Safe biasing is provided to insure signal integrity. Device/Bus
type detection circuitry is integrated into the terminator to provide automatic
switching of termination between single ended and LVD SCSI and a high
impedance for HVD SCSI. The multimode function provides all the perform-
ance analog functions necessary to implement SPI-2 termination in a sin-
gle monolithic device.
The UCC5638 is offered in a 48 pin LQFP package for a temperature range
of 0C to 70C.
Multimode SCSI 15 Line Terminator
FEATURES
Auto Selection Single Ended (SE) or
Low Voltage Differential (LVD)
Termination
Meets SCSI-1, SCSI-2, SCSI-3, SPI,
Ultra (Fast-20), Ultra2 (SPI-2 LVD
SCSI) and Ultra3/Ultra160 Standards
2.7V to 5.25V Operation
Differential Failsafe Bias
Thermal packaging for low junction
temperature and better MTBF.
SLUS271A - FEBRUARY 2000
REF
1.25V
36
DISCNCT
REG
L1+
L15
L15+
SOURCE/SINK REGULATOR
REF
1.3V
4.7
F
.
35
DIFFSEN
15mA
I
SOURCE
5mA
50
A
I
SINK
200
A
HIGH POWER
DIFFERENTIAL
LOW VOLTAGE
DIFFERENTIAL
SINGLE ENDED
34
DIFFB
0.6V
2.15V
52.5
2
52.5
1
110
10
REF
2.7V
SE GND SWITCH
3
TRMPWR
27
GND
4-9
HS/GND
28-33
HS/GND
L1
124
52.5
12
52.5
11
110
124
10
A
1.3V
(NOISE LOAD)
MODE
SE
LVD
DISCNCT
ALL SWITCHES
UP
DOWN
OPEN
SE GND SWITCH
56mV
+
+
+
56mV
56mV
56mV
+
BLOCK DIAGRAM
UDG-98063
2
UCC5638
(TOP VIEW)
FQP Package
ABSOLUTE MAXIMUM RATINGS
TRMPWR Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +6V
Signal Line Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . 0V to 5V
Package Dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2W
Storage Temperature . . . . . . . . . . . . . . . . . . . 65C to +150C
Junction Temperature . . . . . . . . . . . . . . . . . . . 55C to +150C
Lead Temperature (Soldering, 10 sec.) . . . . . . . . . . . . . +300C
Recommended Operating Conditions . . . . . . . . . 2.7V to 5.25V
Currents are positive into negative out of the specified terminal.
Note: Consult Packaging Section of Databook for thermal limi-
tations and considerations of package.
RECOMMENDED OPERATING CONDITIONS
TRMPWR Voltage . . . . . . . . . . . . . . . . . . . . . . . . 2.7V to 5.25V
Temperature Ranges . . . . . . . . . . . . . . . . . . . . . . 0C to +70C
12
11
10
9
13
8
7
6
5
4
3
2
1
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
48
47
46
45
44
43
42
41
40
39
38
37
L15+
L15
TRMPWR
HS/GND
HS/GND
HS/GND
L1
L1+
REG
HS/GND
HS/GND
HS/GND
L9
L10+
L9+
DIFFSENS
DISCNCT
HS/GND
DIFFB
HS/GND
HS/GND
L8+
L8
GND
HS/GND
HS/GND
HS/GND
L4+
L3
L3+
L2
L2+
L4
L5+
L6+
L5
L7+
L6
L7
L11+
L11
L10
L12
L13+
L12+
L14+
L14
L13
CONNECTION DIAGRAMS
ELECTRICAL CHARACTERISTICS
Unless otherwise stated, these specifications apply for T
A
= T
J
= 0C to 70C,
TRMPWR = 3.3V.
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNITS
TRMPWR Supply Current Section
TRMPWR Supply Current
LVD SCSI Mode
20
25
mA
SE SCSI Mode
1.6
10
mA
Disabled Terminator
250
400
A
Regulator Section
1.25V Regulator
LVD SCSI Mode
1.15
1.25
1.35
V
1.25V Regulator Source Current
V
REG
= 0V
375
700
1000
mA
1.25V Regulator Sink Current
V
REG
= 3.3V
170
300
700
mA
1.3V Regulator
Diff Sense
1.2
1.3
1.4
V
1.3V Regulator Source Current
V
REG
= 0V
15
5
mA
1.3V Regulator Sink Current
V
REG
= 3.3V
50
200
A
2.7V Regulator
SE SCSI Mode
2.5
2.7
3.0
V
2.7V Regulator Source Current
V
REG
= 0V
375
700
1000
mA
2.7V Regulator Sink Curren
V
REG
= 3.3V
170
300
700
mA
Differential Termination Section
Differential Impedance
100
105
110
Common Mode Impedence
(Note 2)
110
150
165
Differential Bias Voltage
100
125
mV
Common Mode Bias
1.15
1.25
1.35
V
Output Capacitance
Single Ended Measurement to Ground (Note 1)
3
pF
3
UCC5638
PIN DESCRIPTIONS
DIFFB: Diff sense filter pin should be connected at a
0.1 F capacitor.
DIFFSENS: The SCSI bus Diff Sense line to detect what
types of devices are connected to the SCSI bus.
DISCNCT: Disconnect pin shuts down the terminator
when it is not at the end of the bus. The disconnect pin
low enables the terminator.
Note: In Disconnect Mode, the comparitor set powers down for
low idle current.
LINE
n
: Signal line active line for single ended or nega-
tive line in differential applications for the SCSI bus.
LINE
n
+: Ground line for single ended or positive line for
differential applications for the SCSI bus.
REG: Regulator bypass pin, must be connected to a
F capacitor.
TRMPWR: V
IN
2.7V to 5.25V supply, bypass near the
terminator with a 4.7
F capacitor to ground.
ELECTRICAL CHARACTERISTICS
Unless otherwise stated, these specifications apply for T
A
= T
J
= 0C to 70C,
TRMPWR = 3.3V.
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNITS
Single Ended Termination Section
Impedance
Z
VL
V
IL
X
X
=
-
(
.
)
0 2
, (Note 3)
102.3
110
117.7
Termination Current
Signal Level 0.2V, All Lines Low
21
24
25.4
mA
Signal Level 0.5V
18
22.4
mA
Output Leakage
400
nA
Output Capacitance
Single Ended Measurement to Ground (Note 1)
3
pF
Single Ended GND SE Impedance
I= 10mA
20
60
Disconnect and Diff Buffer Input Section
DISCNCT Threshold
0.8
2.0
V
DISCNCT Input Current
10
30
A
Diff Buffer Single Ended to LVD Threshold
0.5
0.7
V
Diff Buffer LVD to HPD Threshold
1.9
2.4
V
DIFFB Input Current
10
10
A
Note 1: Guaranteed by design. Not 100% tested in production.
Note 2: Line+ (positive) tied to Line (negative);
[
]
1 2
.
(
max)
(
min)
V
I
I
VCM
VCM
Note 3: VL
X
= Output voltage for each terminator minus output pin (L1 through L15) with each pin unloaded.
IL
X
= Output current for each terminator minus output pin (L1 through L15) with the minus output pin forced to 0.2V.
4
UCC5638
The UCC5638 is a Multi-mode active terminator with se-
lectable single ended (SE) and low voltage differential
(LVD) SCSI termination integrated into a monolithic com-
ponent.
Mode selection is accomplished with the "diff
sense" signal.
The diff sense signal is a three level signal, which is
driven at each end of the bus by one active terminator.
An LVD SCSI or multi-mode terminator drives the diff
sense line to 1.3 V. If diff sense is at 1.3 V, then bus is in
LVD SCSI mode. If a single ended SCSI device is
plugged into the bus, the diff sense line is shorted to
ground. With diff sense shorted to ground, the terminator
changes to single ended mode to accommodate the SE
device. If an HVD SCSI device is plugged in to the bus,
the diff sense line is pulled high and the terminator shuts
down.
The diff sense line is driven and monitored by the termi-
nator through a 50Hz noise filter at the DIFFB input pin.
A set of comparators, that allow for ground shifts, deter-
mine the bus status as follows. Any diff sense signal be-
low 0.5V indicates single ended, between 0.7V and 1.9V
is LVD SCSI and above 2.2V is HVD SCSI.
In the single ended mode, a multi-mode terminator has a
110
terminating resistor connected to a 2.7V termina-
tion voltage regulator. The 2.7V regulator is used on all
Unitrode terminators designed for 3.3V systems. This re-
quires the terminator to operate in specification down to
2.7V TRMPWR voltage to allow for the 3.3V supply toler-
ance, an unidirectional fusing device and cable drop. At
each L+ pin, a ground driver drives the pin to ground,
while in single ended mode.
The ground driver is spe-
cially designed so it will not effect the capacitive balance
of the bus when the device is in LVD SCSI or disconnect
mode. The device requirements call for 0.5pF balance on
the lines of a differential pair. The terminator capacitance
has to be a small part of the capacitance imbalance.
Layout is very critical for Ultra2 and Ultra3/Ultra160 sys-
tems. Multi-layer boards need to adhere to the 120
im-
pedance standard, including connector and feed-through.
This is normally done on the outer layers with 4 mil etch
and 4 mil spacing between the runs within a pair, and a
minimum of 8 mil spacing to the next pair. This spacing
between the pairs reduces potential crosstalk. Beware of
feed-throughs and each through hole connection adds a
lot of capacitance. Standard power and ground plane
spacing yields about 1pF to each plane. Each feed-
through will add about 2.5pF to 3.5pF.
Enlarging the
clearance holes on both power and ground planes can
reduce the capacitance and opening up the power and
ground planes under the connector can reduce the ca-
pacitance for through hole connector applications. Mi-
crostrip technology is normally too low of impedance and
should not be used. It is designed for 50
rather than
120
differential systems.
Capacitance
balance
is
critical
for
Ultra2
and
Ultra3/Ultra160. The balance capacitance standard is
0.5pF per line with the balance between pairs of 2pF.
The components are designed with very tight balance,
typically 0.1pF between pins in a pair and 0.3pF between
pairs. Layout balance is critical, feed-throughs and etch
length must be balanced, preferably no feed-throughs
would be used. Capacitance for devices should be meas-
ured in the typical application, material and components
above and below the circuit board effect the capacitance.
Multi-mode terminators need to consider power dissipa-
tion; the UCC5638 is offered in a power package with
heat sink ground pins. These heat sink/ground pins are
directly connected to the die mount paddle under the die
and conduct heat from the die to reduce the junction
temperature. These pins need to be connected to etch
area or a feed-through per pin connecting to the ground
plane layer on a multi-layer board.
In 3.3V TRMPWR systems, the UCC3912 should be
used to replace the fuse and diode. This reduces the
voltage drop, allowing for cable drop to the far end termi-
nator. 3.3V battery systems normally have a 10% toler-
ance. The UCC3912 is 150mV drop under LVD SCSI
loads, allowing 150mV drop in the cable system. All Uni-
trode LVD SCSI and multi-mode terminators are de-
signed for 3.3V systems, operating down to 2.7V.
APPLICATION INFORMATION
5
UCC5638
UNITRODE CORPORATION
7 CONTINENTAL BLVD. MERRIMACK, NH 03054
TEL. (603) 424-2410 FAX (603) 424-3460
REG
TRMPWR
DISCNCT
TRMPWR
DIFF B
REG
DIFF B
TRMPWR
TERMPWR
4.7
F
.
0.1
F
.
4.7
F
0.1
F
.
3
36
35
10
34
35
34
10
3
DISCNCT 36
DIFFSENSE
DIFFSENSE
REG
TRMPWR
DISCNCT
DIFF B
4.7
F
.
3
36
10
34
DATA LINES (15)
TRMPWR
REG
DIFF B
4.7
F
34
10
DATA LINES (15)
3
DISCNCT 36
4.7
F
.
20k
270k
20k
SCSI CONTROLLER
DIFFSENS
4.7
F
CONTROL LINES (9)
L1+
L1
L9+
L9
L1+
L1
L9+
L9
4 BITS OF THE HIGH BYTE
L10+
L10
L15+
L15
L10+
L10
L15+
L15
HIGH BYTE 4 BITS
PLUS PARITY
L1+
L1
L5+
L5
L1+
L1
L5+
L5
LOW BYTE 8+ PARITY
L6+
L6
L14+
L14
L6+
L6
L14+
L14
TYPICAL APPLICATION
Note: A 220k resistor is added to ground to insure the transceivers will come up in single-ended mode when no terminator is en-
abled. The controller DIFFSENS ties to the DIFFB pin on the terminators, only one RC network should be on a device.
UDG-98064
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