E749BPJ Datasheet, PDF (7/14 Pages) Semtech Corporation – Octal Pin Electronics Driver/Receiver

EDGE HIGH-PERFORMANCE PRODUCTS
Application Information (continued)
Edge749
Window Comparator
Trinary Driver
Certain applications require a dual threshold window
comparator to distinguish between the DUT being high,
low, or floating. To support this application, two Edge749
channels can be combined to create one channel with a
window comparator (see Figure 7). Notice that
connecting two DUT pins ties together the positive inputs
of both receivers. The result is a difference in polarity
between the digital outputs reporting the high and low
status of the DUT.
At times, there is a need for a three-level driver. Typically,
two levels are required for the standard digital “1” and
“0” pattern generation. The third level provides a higher
voltage to place the device under test (DUT) into a
programming or test mode. By controlling the DATA IN
and DVR EN* inputs, a trinary driver with tristate is
realizable (see Figure 8).
Driver with Pull Up/Pull Down
–
DUT HIGH
+
+
DUT LOW*
–
High Threshold
DUT
Low Threshold
Figure 7. Edge749 as a
Window Comparator
Once two receivers are connected as window
comparators, the two drivers also get connected in
parallel. This dual driver configuration supports a
multitude of applications that have traditionally been
difficult to accommodate.
As the drivers are unbuffered, paralleling two drivers for
one DUT node provides a means for adding pull up or
pull down capability. By connecting the V_HIGH and V_LOW
inputs of one driver through a resistor to a voltage,
additional functionality that would normally require an
external relay on the DUT transmission line to engage
and disengage these functions is realizable.
One common application for the pull up feature is testing
open collector devices. The pull down satisfies open
emitter DUTs (typically ECL). Either the pull up or down
could be used to establish a default high impedance
voltage on a bidirectional bus. Notice that in all
applications, the resistors can be switched dynamically
or statically.
VHIGH A
VLOW A
DATA IN A
DVR EN*A
DATA IN B
DVR EN*B
 2000 Semtech Corp.
VHIGH B
DUT
VHIGH B
VHIGH A
VLOW A
Figure 8. Trinary Driver
7
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