Micrel SY87725L User Manual

2.5Gbps GPON/BPON ONU SERDES

SY87725L Evaluation Board

Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel [phone] • fax + 1 [phone] • http://www.micrel.com

July 2008

M9999-071108-B

General Description

The SY87725L evaluation board is designed for
convenient setup and quick evaluation of the SY87725L
using a single power source. The evaluation board is
optimized to interface directly to 50Ω test equipment since
the evaluation board is configured with AC-coupled inputs
and AC-coupled outputs.

All datasheets and support documentation can be found
on Micrel’s web site at: www.micrel.com.

Features

∑ Single +3.3V power supply
∑ AC-coupled configuration for direct interface with 50Ω

test equipment

∑ 2.5G/1.25G/625M down stream

∑ 1.25G/625M/156M up stream

Related Documentation

∑ SY87725L, 2.5Gbps GPON/BPON ONU Serdes

Datasheet

__________________________________________________________________________________________

Evaluation Board

Micrel, Inc.

SY87725L Evaluation Board

July 2008

2

M9999-071108-B

Evaluation Board Description

AC-Coupled Evaluation Board

The SY87725L is 64-pin EPAD-TQFP package. The
evaluation board is designed to operate with a single 3.3V
±10% power supply and is configured with AC-coupled
inputs and outputs. The high-speed input and output
channels are brought out to SMA connectors through
matched-length AC-coupled differential strip-line traces.

AC-Coupled Input

For ease of use, the AC-coupled inputs are biased on­board. The user need only supply the appropriate input
swing to the board.

AC-Coupled Output

The SY87725L is configured with AC-coupled outputs
allowing the board to interface directly with 50Ω
equipment. AC-coupling allows the board to use a single
power supply.

Unused Output

Single-Ended to Scope

Unused complimentary outputs should be terminated into
50Ω-to-ground to prevent unwanted reflections.

AC-Coupled Evaluation Board Setup

Setting up the SY87725L AC-Coupled Evaluation
Board

1. Set the voltage on a DC supply to +3.3V and
turn off the supply. Connect the GND terminal to
the negative side of a DC power supply.
Connect the VCC terminal to the positive side of
a DC power supply.

2. For a LVPECL input signal, set VT to VCC–2.0V.

3. Signal Generator: Using a differential signal
source, set the amplitude of each side of the
differential pair to 400mV (800mV measured
differentially). Set the offset to a positive value,
the value of the offset is not critical, since the
AC-coupled inputs will be automatically biased.
Turn off the outputs of the signal source.

4. I/O Cable Interface: Using equal length 50Ω

impedance coaxial cables connect the signal
source to the inputs on the evaluation board.
Using equal length 50Ω impedance coaxial
cables connect the outputs of the evaluation
board to the oscilloscope of another
measurement device that has an internal 50Ω
termination. Unequal length cables are not
recommended since they introduce duty cycle
distortion and unwanted signal delays.

5. Connect the trigger input of the scope to the
trigger output of the signal generator.

6. Set the evaluation board dipswitch to the
appropriate input selection.

7. Enable the signal source, turn on the DC source,
and monitor the outputs.

Evaluation Board Layout

PC Board Layout

The evaluation boards are constructed with Rogers 4003
material and are coplanar in design fabricated to minimize
noise, achieve high bandwidth and minimize crosstalk.

L1

GND and Signal

L2

GND

L3

VCC

L4

GND

Table 1. Layer Stack

Micrel, Inc.

SY87725L Evaluation Board

July 2008

3

M9999-071108-B

Evaluation Board Schematic

Micrel, Inc.

SY87725L Evaluation Board

July 2008

4

M9999-071108-B

How to Use this Document

The following pages show the individual test modes built
into the SY87725L. The diagram for each mode shows
the main data flow for that mode. The table of required
switch settings lists the switch settings for that mode;
unlisted switch settings are not used in that mode. The
diagram to the left of the table shows the actual dip switch
settings as they would appear on the evaluation board.
The dip switches are configured with a pull-up resistor on

the output so when the switch is in the “OFF” position the
output is HIGH and when the switch is in the “ON”
position the output is pulled to ground, LOW.

The test flow diagram in the Appendix lists the modes in
order from the minimum functionality to the full
configuration. This allows the user to start with the
simplest configuration and progress to the full
configuration.

Micrel, Inc.

SY87725L Evaluation Board

July 2008

5

M9999-071108-B

Remote Loopback Data

This is the most basic test mode. It loops back the data
from SIN to SOUT and is used to verify the connections to

SIN and SOUT as well as the power supply connections
to the evaluation board. The SOUT output can be
monitored with a scope or a serial BERT.

Figure 1. Switch Settings for Remote Loopback Data

Switch Settings

Function

TESTb = 1

Disables factory test mode
(enables normal operation)

XMT_CTRL0/1 = 00

Selects the remote loopback
mode so SDOUT = SDIN

Table 2. Required Switch Settings for

Remote Loopback Data Flow