LTC6946 datasheet(41/54 Pages) LINER

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LTC2000A

2000afb

For more information www.linear.com/LTC2000A

APPLICATIONS INFORMATION

Table 13. Adjusting Latency in Single-Port Mode

PHASE COMPARATOR OUTPUTS

SYNC_PH (REG 0x06)

DELAY FROM DCKIP/N RISING

EDGE TO NEXT CKP/N FALLING

EDGE (CKP/N CYCLES)

SYNC_PS SETTING

(DEFAULT)

(ADJUSTED TO REDUCE LATENCY

BY 1 CYCLE)*

0x03

0.5 to 0.6

N/A

0x04

0.6 to 0.7

0x05

0.7 to 0.8

0x15

0.8 to 0.9

0x25

0.9 to 1.0

0x35

0 to 0.1

N/A

0x45

0.1 to 0.2

N/A

0x55

0.2 to 0.3

N/A

0x54

0.3 to 0.4

N/A

0x53

0.4 to 0.5

N/A

0x52

0.5 to 0.6

N/A

0x51

0.6 to 0.7

0x50

0.7 to 0.8

0x40

0.8 to 0.9

0x30

0.9 to 1.0

0x20

0 to 0.1

N/A

0x10

0.1 to 0.2

N/A

0x00

0.2 to 0.3

N/A

0x01

0.3 to 0.4

N/A

0x02

0.4 to 0.5

N/A

*N/A indicate SYNC_PH values that should not occur if the timing mismatch requirements described above are met. If such a case occurs,

keep SYNC_PS as the default value.

PCB Layout Considerations

The close proximity of high frequency digital data lines

and high dynamic range, wideband analog signals make

clean printed circuit board design and layout an absolute

necessity. Figures 16 and 17 show a schematic and PCB

layers for an evaluation circuit for the LTC2000A. A single,

solid ground plane should be used, while separate supply

planes for AVDD18, DVDD18, AVDD33, and DVDD33 should

be kept all the way to the individual supply or LDO. All

LVDS input (DCKIP/N, DAP/N, DBP/N) board traces must

be carefully matched to ensure proper phase alignment.

These LVDS inputs should be kept far away from both the

IOUTP/N and CKP/N traces to avoid any data dependent

coupling into the analog output and DAC sample clock.

The CKP/N traces should be routed either over the analog

groundplaneorovertheirownsectiononthegroundplane.

Thesetracesalsoneedtohaveaccuratelycontrolledimped-

ance and should be well terminated near the LTC2000A.

The IOUTP/N traces should also be carefully matched to

each other, routed over the ground plane, away from the

LVDS inputs and CKP/N signals.

BypasscapacitorsarerequiredonAVDD18,DVDD18,AVDD33,

and DVDD33, and should all be connected to the analog

ground plane. 2.2µF ceramic capacitors with low ESR

are recommended to be placed close to the LTC2000A

with minimum trace lengths. A sample PCB layout and

schematic can be found below.

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