FCT806 Clock Driver

Gary Peterson (gdpeter@sandia.gov)
Wed, 15 Jan 1997 13:10:44 -0700

Fabrizio Zanella writes...

Hello SI engineers,
I am having problems with an IDT 49FCT806BT inverting clock driver, 0.5
micron CMOS technology. I measured the rise time on this device to be
800ps, and this is causing excessive reflections and false clocking. Does
anyone know of a vendor who makes a pin compatible FCT806 clock driver,
SSOP package with slew rate control or guaranteed rising edges around 1.5ns
or longer? I don't need subnanosecond edges in my system, the frequency is
below 50MHz.
Thanks in advance for any advice.
Hope to see many of you at Design Supercon next week in Santa Clara.

Regards,

Fabrizio Zanella
Design Engineer
................................. Possible Solution Below...................

We use IDT 807s a lot and have taken to routinely adding series dampers to
all of the outputs to slow down the edges and control over/undershoot. I'm
assuming you have a board in-hand since you are looking for a slower, drop-in
replacement. We have had good luck on prototypes with gently lifting the
output pins from their pads on the board and standing an 0805 resistor on end
in the space between the pad and the lead. Solder the resistor in place and
you're in business. Values between 20 ohms and 52 ohms have worked well
depending on the loading/stubs on the output. 20 ohms should be fine for
a single load w/ no stubs in 50 ohm transmission line.

------------
\ ------------
|__/ \ <-- FCT806 output lead
| \_______
/ |_____|
------------ | | <-- 0805 Resistor (on end)
|_____|
| |
--------------------
| | <-- Solder pad on PWB
==================================================================

Gary P.

---
                                  Gary D. Peterson
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