Micrel, Inc.

SY89464/465U Evaluation Board

July 2006

2

M9999-071106-C

Evaluation Board Description

The default configurations for the SY89464/5U boards

are AC-coupled. The choice between AC-coupled and

DC-coupled configurations offers the user flexibility for

specific applications.

AC-Coupled Evaluation Board

The AC-coupled configuration is suited to most

customer applications and is preferred by the majority of

users because of its ease-of-use. It requires only a

single power supply and offers the most flexibility in

interfacing to a variety of signal sources.

The DC-bias levels and AC-coupling capacitors are

supplied on-board for each input, making it unnecessary

to vary the offset voltage or change any components on

the board as the power supply voltage varies over the

+2.5V +5% and +3.3V +10% operating range. The user

needs only to supply a minimum input voltage swing and

the bias voltage will automatically adjust the input to the

correct level as the power supply voltage varies.

DC-Coupled Evaluation Board

For applications that are not suited to AC-coupling, such

as clock that can be turned off for extended periods of

time, the board can be user-configured for DC-coupled

operation.

SY89464U

DC-coupled

operation

can

be

accomplished

by

modifying the board to use two power supplies in a

“split-supply configuration.” Since LVPECL is referenced

2V, split-supply is an easy method to interface to a 50Ω

(to ground) scope. Therefore, a 3.3V supply will be split

into +2V and –1.3V, and a 2.5V supply will be split into a

+2V and -0.5V.

The +2V offset in this two-power supply configuration

then provides the correct terminations for the device by

setting the GND potential on the board to 2 volts below

3.3V devices, or –0.5V for 2.5V devices to ensure

SY89465U

DC-coupled

operation

can

be

accomplished

by

modifying the board to use two power supplies into a

“split-supply configuration.” In order to correctly interface

above the GND level. Therefore, a 2.5V supply will be

voltage difference.

Runt Pulse Eliminator

The SY89464/5U evaluation board allows the user to

test the runt pulse eliminator function. The runt pulse

eliminator function prevents any short cycles or “runt”

pulses during switchover.

To see the effects of the runt pulse eliminator function,

disable it by replacing C18 with a 0Ω resistor. Sweep

the frequency of the function generator to see runt

pulses develop. Enable the runt pulse eliminator

function by restoring C18, and perform the same

frequency sweep.

Any-Input Interface

The unique internal input termination sets the input

common mode voltage. This enables the input to

interface with any differential signal over the supply

voltage without modifying the board.