4

dc1795af

DEMO MANUAL DC1795A

Quick start proceDure

troubleshooting

If the green LED does not illuminate, follow the instruc-

tions below:

1. Verify that you are able to communicate with the

DC1795A.ThebottomstatuslineinClockWizardshould

read “LTC6950” and “Comm Enabled.”

VCXO turrets have the correct voltages on them (see

theTypicalDC1795ARequirementsandCharacteristics

table).

3. Select “Status” Output = 2 in ClockWizard’s System

Tab. Click “Read All.” See if the NO_VCO or NO_REF

boxes in the second column are checked.

voltage is set to 3.3V. Verify R73 is installed (0 ohm)

b. IF NO_VCO is checked, verify the components between

U4 and U1 match the default BOM.

Contact the factory for further troubleshooting.

Dc1795a reconfiguration

The DC1795A allows the use of a variety of references,

VCOs and active or passive loop filters. The following

covers the hardware reconfiguration of the DC1795A.

Refer to ClockWizard and the LTC6950 data sheet to bet-

ter understand how to change programmed parameters

on the DC1795A.

ltC6950 Clkset Files

The ClockWizard provides three different clkset files for

evaluation purposes. These files were made for the default

bill of materials. If board modifications are made, these

files or the loop filter may need to be modified for the

LTC6950 to lock correctly.

1. LTC6950_PECL0_250MHz.clkset:Producesa250MHz

output on PECL0. All other outputs are powered down.

2. LTC6950_Figure16_250MHZ.clkset: Matches Figure

16 of the LTC6950 data sheet. To sync outputs, refer

to the EZSync Function section.

3. LTC6950_ALL_CHAN_250MHz.clkset: Produces a

250MHz output on all five outputs. To sync outputs,

refer to the EZSync Function section.

ezsync FunCtion

Apply a 1ms or longer high pulse to the SYNC SMA con-

nector to take advantage of the EZSync function. Refer

to the LTC6950 data sheet for SYNC timing and level

requirements.

lVPeCl outPut oPtions

The DC1795A has four AC coupled LVPECL outputs.

Internal biasing (IBIASx = H) is required with this default

termination network. The DC1795A has options for pull

downorseriesresistorstoaccommodatetheotherLVPECL

termination networks described in the data sheet.

lVDs/CMos outPut oPtions

The LVDS/CMOS output is DC coupled without on-board

termination by default. The DC1795A provides pull down,

series and a differential termination resistor options to

accommodate other termination networks described in

the data sheet.