ml6509 Microsemi Corporation, ml6509 Datasheet - Page 5

• Manufacturer Part Number: ml6509
• Description: Active Scsi Terminator
• Manufacturer: Microsemi Corporation

Thus in an 8-bit wide SCSI bus arrangement (“A” cable),
two ML6509s would be needed at each end of the SCSI
cable in order to terminate the 18 active signal lines.
16-bit wide SCSI would use three ML6509s, while 32-bit
wide SCSI bus would require five ML6509s.
In a typical SCSI subsystem, the open collector driver in
the SCSI transceiver, when asserted, pulls low and when
negated, the termination resistance serves as the pull-up.
Shown in figure 2 is a typical cable response to a pulse.
The receiving end of the cable will exhibit a single time
delay. When negated, the initial step will reach an
intermediate level defined as V
data rates, sampling could occur during this step portion.
In order to get the most noise margin, the step needs to be
as high as possible to prevent false triggering. For this
reason the regulator voltage and the resistor defining the
MOSFETs characteristic is trimmed to ensure that the I
as close as possible to the SCSI max current specification.
V
where
STEP
V
I
Z
O
OL
O
is current from receiving terminator
is defined as follows :
is characteristic impedance of cable.
is the Driver output low voltage,
0.1µF
10µF
Figure 2. Application Diagram Showing Typical SCSI Bus Configuration with the ML6509
V
STEP
SCSI XCVR
SCSI XCVR
VREF
GND
L9
V
OL
ML6509
. . .
STEP
TERMPWR
(
DISCNKT
I
O
L2 L1
. With the higher SCSI
LPWR
Z
O
TERMPWR LINE
)
V
REG
ASSERTED
LINE
O
is
SCSI CABLE
NEGATED
LINE
285V
0.2V
2.7V
2.5V
V
10µF
Figure 3. V-1 Characteristics of Various
TERMINATOR (SOURCE)
DRIVER (SINK)
V
V
V
REG
STEP
OL
SCSI Termination Schemes
DISCNKT
LPWR
TERMPWR
L1 L2
ML6509
220/330
. . .
GND
VREF
BOULAY
L9
SCSI XCVR
ML6509
20mA
40mA
0.1µF
10µF
ML6509
IDEAL
24mA
48mA
5
I