ML6509 Datasheet, PDF (1/10 Pages) Micro Linear Corporation – Active SCSI Terminator

February 1997
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 0–24mA
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.
BLOCK DIAGRAM
TERMPWR
ML6509*
Active SCSI Terminator
FEATURES
s Fully monolithic IC solution providing active
termination for 9 lines of the SCSI bus
s Low dropout voltage (1V) linear regulator, trimmed for
accurate termination current, with 300mA current
source capability
s Output capacitance typically <5pF
s Disconnect mode — logic pin to disconnect terminator
from the SCSI bus, <100µA
s Lowpower mode — for power conscious, portable
system & peripheral applications, using less than 6"
cables. (Equivalent to a 1mA current drive with a
2.5kW termination)
s Current sinking — can sink current >10mA per line to
handle active negation driver overshoots above 2.85V
s Negative clamping on all lines to handle signal
assertion transients
s Regulator can source 200mA and sink 50mA while
maintaining regulation
s Current limit & thermal shutdown protection
s Small and low profile package options; 16-pin SOIC
(300 mil), 20-pin TSSOP (1 mil height)
* Some Packages Are End Of Life As Of August 1, 2000
V_REF
DISCNKT LPWR
GND
LINEAR
REGULATOR
1V DROPOUT
2.85V
216mA
(MAX)
NCLAMP
MOSFETs WITH IMAX = 24mA
NORMAL MODE
...
2.85V
RTRIM
V_{REF CONTROL}
BLOCK
MOSFETs WITH IMAX = 1mA
LOW POWER MODE
...
NCLAMP = Negative Clamp
NCLAMP
NCLAMP
...
9 TERMINATION LINES
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