AD7490BCPZ datasheet(21/28 Pages) AD

21 / 28 page

Data Sheet

AD7490

Rev. D | Page 21 of 28

Powering Up the AD7490

When supplies are first applied to the AD7490, the ADC may

power up in any of the operating modes of the part. To ensure

that the part is placed into the required operating mode, the

user should perform a dummy cycle operation, as outlined in

Figure 26.

The three dummy conversion operations outlined in Figure 26

must be performed to place the part into either of the auto modes.

The first two conversions of this dummy cycle operation are

performed with the DIN line tied high, and for the third conver-

sion of the dummy cycle operation, the user should write the

desired control register configuration to the AD7490 to place

the part into the required auto mode. On the third CS rising

edge after the supplies are applied, the control register contains

the correct information and valid data results from the next

conversion.

Therefore, to ensure the part is placed into the correct operating

mode when supplies are first applied to the AD7490, the user

must first issue two serial write operations with the DIN line

tied high. On the third conversion cycle, the user can then write

to the control register to place the part into any of the operating

modes. The user should not write to the Shadow register until

the fourth conversion cycle after the supplies are applied to

the ADC to guarantee that the control register contains the

correct data.

If the user wishes to place the part into either normal mode or

full shutdown mode, the second dummy cycle with DIN tied

high can be omitted from the three dummy conversion

operation outlined in Figure 26.

SCLK

DOUT

DIN

DUMMY CONVERSION

CORRECT VALUE IN CONTROL

NEXT CONVERSION USER CAN

WRITE TO SHADOW REGISTER

IN NEXT CONVERSION

INVALID DATA

DATA IN TO CONTROL

CONTROL REGISTER IS LOADED ON THE

FIRST 12 CLOCK EDGES

KEEP DIN LINE TIED HIGH FOR FIRST TWO DUMMY CONVERSIONS

Figure 26. Placing into the Required Operating Mode After Supplies Are Applied

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