February 1997
ML6509*
Active SCSI Terminator
GENERAL DESCRIPTION
The ML6509 BiCMOS SCSI terminator provides active
termination in a SCSI system with single ended drivers and
receivers, in full compliance with the SCSI-1, SCSI-2 and
SCSI-3 recommendations. It provides a 2.85V reference
through an internal 1V dropout linear regulator. Active
SCSI termination helps the system designer to effectively
control analog transmission line effects like ringing, noise,
crosstalk, ground bounce, etc. In addition it provides
greater immunity to voltage drops on the TERMPWR line
of the SCSI bus. The desired V-I characteristics for signal
negation requires that the terminator source 0鈥?4mA
while maintaining 2.85V and for signal assertion
preferably follow a linear slope of 110W. The ML6509
attempts to provide a V-I characteristic optimized to
minimize the transmission line effects during both signal
assertion and negation, using a MOSFET based
architecture. The desired V-I characteristic is achieved by
trimming one resistor in the control block. It provides
negative clamping for signal assertion transients and
current sink capability, to handle active negation driver
overshoots above 2.85V, which is currently accomplished
with external components in SCSI subsystems today. It
provides a disconnect mode, where the terminator is
completely disconnected from the SCSI
bus and the output capacitance is < 5pF, typically.
FEATURES
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Fully monolithic IC solution providing active
termination for 9 lines of the SCSI bus
Low dropout voltage (1V) linear regulator, trimmed for
accurate termination current, with 300mA current
source capability
Output capacitance typically <5pF
Disconnect mode 鈥?logic pin to disconnect terminator
from the SCSI bus, <100碌A
Lowpower mode 鈥?for power conscious, portable
system & peripheral applications, using less than 6"
cables. (Equivalent to a 1mA current drive with a
2.5kW termination)
Current sinking 鈥?can sink current >10mA per line to
handle active negation driver overshoots above 2.85V
Negative clamping on all lines to handle signal
assertion transients
Regulator can source 200mA and sink 50mA while
maintaining regulation
Current limit & thermal shutdown protection
Small and low profile package options; 16-pin SOIC
(300 mil), 20-pin TSSOP (1 mil height)
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* Some Packages Are End Of Life As Of August 1, 2000
BLOCK DIAGRAM
TERMPWR
V
REF
DISCNKT
LPWR
2.85V
LINEAR
REGULATOR
1V DROPOUT
2.85V
GND
216mA
(MAX)
R
TRIM
V
REF
CONTROL
BLOCK
MOSFETs WITH I
MAX
= 24mA
NORMAL MODE
MOSFETs WITH I
MAX
= 1mA
LOW POWER MODE
...
NCLAMP
...
NCLAMP
NCLAMP
...
NCLAMP = Negative Clamp
...
9 TERMINATION LINES
1
1
2
3
4
5
6
7
8
9
10
