AD9786BSV datasheet(46/60 Pages) AD

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AD9786

Rev. 0 | Page 46 of 60

DATA INPUTS

Digital data inputs to the AD9786 are accessed on the

evaluation board through connectors J1 and J2. These are 40 pin

right angle connectors that are intended to be used with

standard ribbon cable connectors. The input levels should be

either 3.3 V or 2.5 V CMOS, depending on the setting of the

DRVDD jumper JP1. The data format is selectable through

the AD9786 assumes that the input data is in twos complement

format. With this bit set to 1, data should be input in offset

binary format.

When the evaluation board is first powered up and the clock

and data are running, it is recommended that the proper

operating current is verified. Depress reset switch SW1 to

ensure that the AD9786 is in the default mode. The default

mode for the AD9786 is for the interpolation set to 1×. The

modulator is turned off in the default mode. The nominal

operating currents for the evaluation board in the power-up

default mode are shown in Table 39.

Additionally, the DRVDD power supply on the AD9786 is used

to supply power for the digital input bus. DRVDD can be run

from 2.5 V or 3.3 V. On the evaluation board, DRVDD is jumper

selectable by JP1, just to the left of the chip on the evaluation

board. With the jumper set to the 3.3 V position, DRVDD chip

receives its power from VDD3IN. With the jumper set to the

2.5 V position, DRVDD receives its power from AVDIN.

SERIAL PORT

SW1 is a hard reset switch that sets the AD9786 to its default

state. It should be used every time the AD9786 power supply is

cycled or the clock is interrupted, or if new data is to be written

via the SPI port. Set the SPI software to read back data from the

AD9786 and verify that when the software is run, the expected

values are read back.

Table 39. Nominal Operating Currents in Power-Up Default Mode

Nominal Current @ Speed (mA)

Evaluation Board Power Supply

50 MSPS

100 MSPS

150 MSPS

200 MSPS

DVDD

CLKVDD

ACVDD and ADVDD

AVDD1

AVDD2

Table 40. SPI Registers

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 0

01h

INTERP[1]

INTERP[0]

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