Multimode SCSI 15 Line Terminator
UCC5638
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.
BLOCK DIAGRAM
2.15V
34DIFFB
0.6V
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 0°C to 70°C.
HIGH POWER
DIFFERENTIAL
LOW VOLTAGE
DIFFERENTIAL
SINGLE ENDED
(NOISE LOAD)
REF
1.3V
–15mA ≤ I
50µA ≤ I
SOURCE
SINK
≤ –5mA
≤ 200µA
1.3V
35 DIFFSEN
-
-
-
-
-
REF
2.7V
REF
1.25V
10µA
DISCNCT
36
3TRMPWR
HS/GND
27
GND
4-9
SLUS271A - FEBRUARY 2000
SOURCE/SINK REGULATOR
SE
HS/GND
28-33
ALL SWITCHES
UP
DOWN
OPEN
MODE
LVD
DISCNCT
10
REG
4.7µF .
110
124
110
124
56mV
–+
56mV
+–
SE GND SWITCH
56mV
–+
56mV
+–
SE GND SWITCH
52.5
52.5
52.5
52.5
12
11
2
1
L1–
L1+
L15–
L15+
UDG-98063
UCC5638
ABSOLUTE MAXIMUM RATINGS
TRMPWR Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +6V
Signal Line Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . 0V to 5V
Package Dissipation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2W
Storage Temperature . . . . . . . . . . . . . . . . . . . –65°C to +150°C
Junction Temperature. . . . . . . . . . . . . . . . . . . –55°C to +150°C
Lead Temperature (Soldering, 10 sec.). . . . . . . . . . . . . +300°C
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 . . . . . . . . . . . . . . . . . . . . . . 0°C to +70°C
CONNECTION DIAGRAMS
(TOP VIEW)
FQP Package
HS/GND
HS/GND
HS/GND
REG
L1+
L1–
12
10
8
7
9
27
28
313233
29
30
L8+
L8–
GND
HS/GND
HS/GND
HS/GND
L2+
L2–
L3+
L3–
L4+
L4–
L5+
L5–
L6+
L6–
L7+
L7–
11
13
14
15
16
17
18
19
20
21
22
23
24
25
26
HS/GND
HS/GND
HS/GND
TRMPWR
L15–
L15+
6
4
321
5
35
34
L14–
48
47
L14+
L13–
46
L13+
45
L12–
44
L12+
43
L11–
42
L11+
41
L10–
40
L10+
39
38
L9–
37
L9+
36
DISCNCT
DIFFSENS
DIFFB
HS/GND
HS/GND
HS/GND
ELECTRICAL CHARACTERISTICS
Unless otherwise stated, these specifications apply for TA=TJ= 0°C to 70°C,
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
Regulator Section
1.25V Regulator LVD SCSI Mode 1.15 1.25 1.35 V
1.25V Regulator Source Current V
1.25V Regulator Sink Current V
= 0V –375 –700 –1000 mA
REG
= 3.3V 170 300 700 mA
REG
1.3V Regulator Diff Sense 1.2 1.3 1.4 V
1.3V Regulator Source Current V
1.3V Regulator Sink Current V
= 0V –15 –5 mA
REG
= 3.3V 50 200 A
REG
2.7V Regulator SE SCSI Mode 2.5 2.7 3.0 V
2.7V Regulator Source Current V
2.7V Regulator Sink Curren V
= 0V –375 –700 –1000 mA
REG
= 3.3V 170 300 700 mA
REG
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
A
2
UCC5638
ELECTRICAL CHARACTERISTICS Unless otherwise stated, these specifications apply for T
TRMPWR = 3.3V.
PARAMETER TEST CONDITIONS MIN TYP MAX UNITS
Single Ended Termination Section
Impedance
Termination Current Signal Level 0.2V, All Lines Low –21 –24 –25.4 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
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
Note 1: Guaranteed by design. Not 100% tested in production.
Note 2: Line+ (positive) tied to Line– (negative);
VL V
−(.)02
Z
Signal Level 0.5V –18 –22.4 mA
II
[]
X
=
12.
V
( max) ( min)
VCM VCM
–
IL
X
, (Note 3)
102.3 110 117.7
A=TJ
= 0°C to 70°C,
A
A
Note 3: VLX= Output voltage for each terminator minus output pin (L1– through L15–) with each pin unloaded.
IL
= Output current for each terminator minus output pin (L1– through L15–) with the minus output pin forced to 0.2V.
X
PIN DESCRIPTIONS
DIFFB: Diff sense filter pin should be connected at a
F capacitor.
0.1
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.
LINEn–: Signal line active line for single ended or negative line in differential applications for the SCSI bus.
n
+: Ground line for single ended or positive line for
LINE
differential applications for the SCSI bus.
REG: Regulator bypass pin, must be connected to a
F capacitor.
TRMPWR: V
2.7V to 5.25V supply, bypass near the
IN
terminator with a 4.7 µF capacitor to ground.
3
APPLICATION INFORMATION
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, determine the bus status as follows. Any diff sense signal below 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
terminating resistor connected to a 2.7V termina-
110
tion voltage regulator. The 2.7V regulator is used on all
Unitrode terminators designed for 3.3V systems. This requires the terminator to operate in specification down to
2.7V TRMPWR voltage to allow for the 3.3V supply tolerance, 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
pedance standard, including connector and feed-through.
This is normally done on the outer layers with 4 mil etch
im
UCC5638
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 feedthrough 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
differential systems.
120
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 measured in the typical application, material and components
above and below the circuit board effect the capacitance.
Multi-mode terminators need to consider power dissipation; 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.
rather than
-
-
-
-
-
-
4
TYPICAL APPLICATION
UCC5638
4.7µF
TERMPWR
3
36
TRMPWR
DISCNCT
REG
DIFF B REGDIFF B
10 34
4.7µF
.
DATA LINES (15)
L1+
L1–
L9+
L9–
L10+
L10–
L15+
L15–
L1+
L1–
L5+
L5–
35
0.1µF
.
CONTROL LINES(9)
4 BITS OF THE HIGH BYTE
20k
270k
HIGH BYTE4 BITS
PLUS PARITY
20k
L1+
L1–
L9+
L9–
L10+
L10–
L15+
L15–
35
DIFFSENSEDIFFSENSE
34 10
L1+
L1–
DATA LINES(15)
L5+
L5–
0.1µF
.
TRMPWR
DISCNCT
3
36
4.7µF
TRMPWR
4.7µF
.
TRMPWR
3
36
DISCNCT
REG
10 34
SCSI CONTROLLER
DIFFSENS
4.7µF
.
L14+
L14–
DIFF B
L6+
L6–
L6+
L6–
LOW BYTE 8+ PARITY
L14+
L14–
34 10
TRMPWR
DISCNCT
REGDIFF B
3
36
4.7µF
UDG-98064
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.
UNITRODE CORPORATION
7 CONTINENTAL BLVD.• MERRIMACK, NH 03054
TEL. (603) 424-2410 • FAX (603) 424-3460
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