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dc1954af

DEMO MANUAL DC1954A

Troubleshooting

If the board is not functioning as expected, follow the

instructions below:

1. Verify that you are able to communicate with the

DC1954A. The bottom status line in LTC6954_GUI

should read LTC6954 and Comm Enabled.

2. Verify that V+ 3.15V-3.45V turret has the correct

voltage. (see the Typical DC1954A Requirements and

Characteristics table).

3. Ensure JP1, JP2, and JP3 are set to desired position.

4. IftheoutputtypeisLVPECLandtheoutputisAC-coupled,

OUTxSEL must be high for proper signal swing.

The DC1954A allows for a variety of input and output

configurations. The following covers the hardware recon-

figuration of the DC1954A.

LVPECL Output Options

TheDC1954ALVPECLoutputsareAC-coupledandrequire

internalbiasing(OUTxSEL=H)withthedefaulttermination

network. The DC1954A provides pull-down, series and a

differential termination resistor options to accommodate

the other LVPECL termination networks described in the

data sheet.

LVDS/CMOS Output Options

The LVDS/CMOS outputs are DC-coupled and have an on

boarddifferential100Ωresistorterminationbydefault.The

DC1954A provides pull-down, series and a differential ter-

minationresistoroptionstoaccommodatetheotherLVDS/

CMOS termination networks described in the data sheet.

Table 1. DC1954A Assembly Options

ASSEMBLY VERSION

U1 PART NUMBER

OUT0+/–

OUT1+/–

OUT2+/–

DC1954A-A

LTC6954IUFF-1

LVPECL

LVPECL

LVPECL

DC1954A-B

LTC6954IUFF-2

LVPECL

LVPECL

LVDS/CMOS

DC1954A-C

LTC6954IUFF-3

LVPECL

LVDS/CMOS

LVDS/CMOS

DC1954A-D

LTC6954IUFF-4

LVDS/CMOS

LVDS/CMOS

LVDS/CMOS

5. IftheoutputtypeisLVDS,theoutputsmustbeAC-coupled

intosingle-ended,50Ωinputtestequipment.Additionally,

the unconnected output must be AC-coupled into a 50Ω

load to ground to provide a balanced output load. If the

LVCSx bit is low, the signal amplitude at the instrument

will be approximately half of the data sheet value due to

the existing 100Ω termination on the demo board.

6. If the output is CMOS, a 200Ω series resistor must be

included to limit the output current when connecting

to the 50Ω input on test equipment. The signal swing

at the instrument is then approximately 20 percent of

the data sheet value.

Contact the factory for further troubleshooting.

Input Options

The inputs have a 50Ω termination resistor to GND and are

AC-coupled by default. The DC1954A provides pull-down,

pull-up and a differential termination resistor options to

accommodate the other input termination networks de-

scribed in the data sheet.

Clock Follower Input Network

When using the DC1954A as a clock follower, EZSync

requires the LTC6954 inputs to be taken to a low state

while the SYNC pin is high. To meet this requirement, the

DC1954AmustbemodifiedtosupportDC-coupling.Refer

to the EZSync Function section and to the data sheet for

more details on using the LTC6954 as a clock follower.

EZSync Function

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

nector to take advantage of the EZSync function. Refer

to the LTC6954 data sheet for SYNC timing and level

requirements.

Quick start proceDure

Dc1954a reconfiguration

assembly options