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Data Sheet

AD9253

Rev. B | Page 29 of 40

Table 12. PN Sequence

Sequence

Initial

Value

Next Three Output Samples

(MSB First) Twos Complement

PN Sequence Short

0x1FE0

0x1DF1, 0x3CC8, 0x294E

PN Sequence Long

0x1FFF

0x1FE0, 0x2001, 0x1C00

Consult the Memory Map section for information on how to

change these additional digital output timing features through

the SPI.

SDIO/OLM Pin

For applications that do not require SPI mode operation, the

CSB pin is tied to AVDD, and the SDIO/OLM pin controls the

output lane mode according to Table 13.

For applications where this pin is not used, CSB should be

tied to AVDD. When using the one-lane mode, the encode

rate should be ≤62.5 MSPS to meet the maximum output rate

of 1 Gbps.

Table 13. Output Lane Mode Pin Settings

OLM Pin

Voltage

Output Mode

AVDD (Default)

Two-lane. 1× frame, 16-bit serial output

GND

One-lane. 1× frame, 16-bit serial output

SCLK/DTP Pin

The SCLK/DTP pin is for use in applications that do not require

SPI mode operation. This pin can enable a single digital test

pattern if it and the CSB pin are held high during device power-

up. When SCLK/DTP is tied to AVDD, the ADC channel

outputs shift out the following pattern: 1000 0000 0000 0000.

The FCO and DCO function normally while all channels shift out

the repeatable test pattern. This pattern allows the user to

perform timing alignment adjustments among the FCO, DCO,

and output data. This pin has an internal 10 kΩ resistor to GND.

It can be left unconnected.

Table 14. Digital Test Pattern Pin Settings

Selected DTP

DTP Voltage

Resulting

D0±x and D1±x

Normal Operation

10 kΩ to AGND

Normal operation

DTP

AVDD

1000 0000 0000 0000

Additional and custom test patterns can also be observed when

commanded from the SPI port. Consult the Memory Map

section for information about the options available.

CSB Pin

The CSB pin should be tied to AVDD for applications that do

not require SPI mode operation. By tying CSB high, all SCLK

and SDIO information is ignored.

RBIAS Pin

To set the internal core bias current of the ADC, place a

10.0 kΩ, 1% tolerance resistor to ground at the RBIAS pin.

OUTPUT TEST MODES

The output test options are described in Table 11 and controlled by

the output test mode bits at Address 0x0D. When an output test

mode is enabled, the analog section of the ADC is disconnected

from the digital back-end blocks and the test pattern is run

through the output formatting block. Some of the test patterns

are subject to output formatting, and some are not. The PN

generators from the PN sequence tests can be reset by setting

Bit 4 or Bit 5 of Register 0x0D. These tests can be performed

with or without an analog signal (if present, the analog signal is

ignored), but they do require an encode clock. For more

information, see the AN-877 Application Note, Interfacing to

High Speed ADCs via SPI.

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