Datasheet

Data Sheet AD9637
Rev. A | Page 29 of 40
HARDWARE INTERFACE
The pins described in Table 15 comprise the physical interface
between the user programming device and the serial port of the
AD9637. The SCLK pin and the CSB pin function as inputs
when using the SPI interface. The SDIO pin is bidirectional,
functioning as an input during write phases and as an output
during readback.
The SPI interface is flexible enough to be controlled by either
FPGAs or microcontrollers. One method for SPI configuration
is described in detail in the AN-812 Application Note, Micro-
controller-Based Serial Port Interface (SPI) Boot Circuit.
The SPI port should not be active during periods when the full
dynamic performance of the converter is required. Because the
SCLK signal, the CSB signal, and the SDIO signal are typically
asynchronous to the ADC clock, noise from these signals can
degrade converter performance. If the on-board SPI bus is used for
other devices, it may be necessary to provide buffers between
this bus and the AD9637 to prevent these signals from transi-
tioning at the converter inputs during critical sampling periods.
Some pins serve a dual function when the SPI interface is not
being used. When the pins are strapped to DRVDD or ground
during device power-on, they are associated with a specific
function. Table 13 and Table 14 describe the strappable
functions supported on the AD9637.
CONFIGURATION WITHOUT THE SPI
In applications that do not interface to the SPI control registers,
the SDIO/DFS pin, the SCLK/DTP pin, and the PDWN pin
serve as standalone CMOS-compatible control pins. When the
device is powered up, it is assumed that the user intends to use the
pins as static control lines for the output data format, output
digital test pattern, and power-down feature control. In this
mode, CSB should be connected to AVDD, which disables the
serial port interface.
When the device is in SPI mode, the PDWN pin (if enabled)
remains active. For SPI control of power-down, the PDWN pin
should be set to its default state.
SPI ACCESSIBLE FEATURES
Table 16 provides a brief description of the general features that
are accessible via the SPI. These features are described in detail
in the AN-877 Application Note, Interfacing to High Speed ADCs
via SPI. The AD9637 part-specific features are described in detail
in the Memory Map Register Descriptions section following
Table 17, the external memory map register table.
Table 16. Features Accessible Using the SPI
Feature Name Description
Mode Allows the user to set either power-down
mode or standby mode
Clock Allows the user to access the DCS, set the
clock divider, set the clock divider phase,
and enable the sync
Offset Allows the user to digitally adjust the
converter offset
Test I/O Allows the user to set test modes to have
known data on output bits
Output Mode Allows the user to set the output mode
Output Phase Allows the user to set the output clock polarity
ADC Resolution
and Speed Grade
Scalable power consumption options based
on resolution and speed grade selection