LTC6950 datasheet(7/12 Pages) LINER

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dc1795af

DEMO MANUAL DC1795A

Dc1795a reconfiguration

table 5. loop Filter selection for external oscillator (refer to ClockWizard’s loop Design tab)

DeFAult

oPtion

CloCkWizArD AnD boM Cross reFerenCe

other MoDiFiCAtions

CoMMents

looP Filter tYPe

instAll

DePoPulAte

Filter 1 (Passive)

RZ_P

CI1_P + CI2_P

CP_P

R68

(0402 0Ω)

R72

Connect CPOUT turret to VTUNE of

external oscillator

Filter 4 (Active)

RZ_A

CI1_A + CI2_A

CP_A

R67, R69

(0402 0Ω)

R70, R72

Select CPINV under the ClockWizard

System tab. Connect CPOUT turret to

VTUNE of external oscillator

typical Dc1795a reQuirements anD characteristics

PArAMeter

inPut or outPut

PhYsiCAl loCAtion

DetAils

3.3V Power Supply

Input

J2 BNC connector, or

V+ = 3.15V to 3.45V turret

Low-noise and spur-free 3.3V,

500mA default (200mA configured*).

Powers LTC6950, U6, U7, U8 and U9

Charge Pump Power Supply

Input

J1 BNC connector, or

V+ to 5.25V turret

Low-noise and spur-free 5V, 35mA*.

Powers LTC6950 and provides common mode to U2

VCXO/VCSO Power Supply

Input

V+ VCXO turret

Low-noise and spur-free 5V, 20mA*. Powers U4

LVDS/CMOS+, LVDS/CMOS–

Two Outputs

J19 and J18 SMA connectors**

DC coupled, 250MHz, (if enabled)*.

Refer to LTC6950 data sheet for output levels for LVDS and

CMOS option.

PECL0+, PECL0–

Two Outputs

J17 and J16 SMA connectors**

AC coupled, 250MHz, 800mVP differential*.

Must have LTC6950’s IBIAS0 = H with default BOM. DC1795A

has options for an external pull down resistor if IBIAS0 = L.

PECL1+, PECL1–

Two Outputs

J13 and J12 SMA connectors**

AC coupled, 250MHz, 800mVP differential (if enabled)*. Must

have LTC6950’s IBIASX = H with default BOM. DC1795A has

options for an external pull down resistor if IBIASX = L.

PECL2+, PECL2–

Two Outputs

J8 and J7 SMA connectors**

PECL3+, PECL3–

Two Outputs

J11 and J10 SMA connectors**

SYNC

Input

SYNC turret or J9 SMA connector EZSync, 0V to 3.3V control signal, refer to the data sheet

STAT1, STAT2

Output

STAT1 and STAT2 turret

STAT1 GREEN LED, if ON LTC6950 is locked*.

STAT2 RED LED, if ON indicates issue*.

Refer to the troubleshooting section and data sheet

Loop Bandwidth

Set by loop filter component values 4.2kHz*

VCO Power Supply

Input

V+ VCO turret

Board Modifications required for use, see Table 2

Active Loop Filter Supply

Input

V+ OA turret

Board Modifications required for use, see Table 2

REF, External Reference

Input

J4 SMA connector

Board Modifications required for use, see Table 1

VCO+, VCO–, External VCO or

Input for clock distribution

Input

J14 and J15 SMA connectors

Board Modifications required to use External VCO.

See Tables 2 and 5. Clock Distribution, see Table 2 only

CPOUT

Output

CPOUT Turret

Used with External VCO, connect to external VCO’s VTUNE

voltage

* These values are for the “LTC6950_PECL0_250MHz” file and the default on board VCO and Reference.

** Any unused RF output must be powered down or terminated with 50Ω, or poor spurious performance may result.

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