6

dc1795af

DEMO MANUAL DC1795A

Dc1795a reconfiguration

table 2. VCo input options: Power settings and board Modifications

DeFAult

oPtion

boArD MoDiFiCAtions

osCillAtor PoWer settings

CoMMents

osCillAtor instAll DePoPulAte

turret

turret

turret

en

turret

l

U4

NA

(Default)

NA

(Default)

[For Active Filters

Only] Determined by

5V for Default U4.

Must be less than 24V

Determined

specification.

5V for Default

U4. Must be

less than 24V

-

Connects to

pin 2 of U4.

Not used with

Default U4

Refer to Table 3: loop

filter component

selections for U4

U3

U3, *C38

0402 0Ω

*R43

[For Active Filters

Only] Determined by

Must be less than 24V

-

Determined

specification.

Must be less

than 24V

-

Refer to Table 4: loop

filter component

selections for U3

Single-Ended

External

*C25

0402 0Ω

*R25, R40,

R41

[For Active Filters

Only] Determined by

External Oscillator

must be less than 24V

-

-

-

Connect signal to

J15. Refer to Table 5:

loop filter component

selections.

Differential

External

*C25, C26

0402 0Ω

C69 0402

~100pF

*R25, R40,

R41

[For Active Filters

Only] Determined by

External Oscillator

must be less than 24V

-

-

-

Connect signals to J14

and J15. [For External

Oscillator Only] Refer

to Table 5: loop filter

component selections.

* General Recommendations: There are several termination and common mode options on the DC1795A for different input signal types. Refer to the

DC1795A schematic, the LTC6950 data sheet and the data sheet for the VCO or clock distribution component used for an optimum termination network.

table 3. loop Filter selection for u4 oscillator (refer to ClockWizard’s loop Design tab)

DeFAult

oPtion

CloCkWizArD AnD boM Cross reFerenCe

other MoDiFiCAtions

CoMMents

looP Filter

tYPe

rz

Ci

CP

r1

C2

l1

instAll DePoPulAte

l

Filter 1 (Passive)

RZ_P

CI1_P + CI2_P

CP_P

-

-

-

-

-

RZ_P, CI1_P, CI2_P, CP_P

populated with default values

Filter 2 (Passive)

RZ_P

CI1_P + CI2_P

CP_P

R12

C22

-

-

-

Filter 3 (Passive)

RZ_P

CI1_P + CI2_P

CP_P

R72

C22

R12

-

-

Filter 4 (Active)

RZ_A

CI1_A + CI2_A

CP_A

R12

C22

-

R69, R71

(0402 0Ω)

R70, R72

Select CPINV under the

ClockWizard System tab

table 4. loop Filter selection for u3 oscillator (refer to ClockWizard’s loop Design tab)

DeFAult

oPtion

CloCkWizArD AnD boM Cross reFerenCe

other MoDiFiCAtions

CoMMents

looP Filter tYPe

rz

Ci

CP

r1

C2

l1

instAll

DePoPulAte

Filter 1 (Passive)

RZ_P

CI1_P + CI2_P

CP_P

-

-

-

R18

(0402 0Ω)

R12

Filter 2 (Passive)

RZ_P

CI1_P + CI2_P

CP_P

R18

C29

-

R12

Filter 3 (Passive)

RZ_P

CI1_P + CI2_P

CP_P

R72

C29

R18

-

R12

Filter 4 (Active)

RZ_A

CI1_A + CI2_A

CP_A

R18

C29

-

R69, R71

(0402 0Ω)

R12, R70,

R72

Select CPINV under the

ClockWizard System tab