Linear Technology DC1795A Demo Manual page 4

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. The bottom status line in ClockWizard should
read "LTC6950" and "Comm Enabled."
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2. Verify that V
VCXO turrets have the correct voltages on them (see
the Typical DC1795A Requirements and Characteristics
table).
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: Produces a 250MHz
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.
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= 3.15V to 3.45V, V to 5.25V and V
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.
a. If NO_REF is checked, verify the "V
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.
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Contact the factory for further troubleshooting.
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
down or series resistors to accommodate the other LVPECL
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.
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XO" test point
dc1795af