AD7357 datasheet(16/20 Pages) AD

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AD7357

Preliminary Technical Data

Rev. PrF | Page 16 of 20

FULL POWER-DOWN MODE

This mode is intended for use in applications where throughput

rates slower than those in the partial power-down mode are

required, as power-up from a full power-down takes

substantially longer than that from a partial power-down. This

mode is more suited to applications where a series of

conversions performed at a relatively high throughput rate are

followed by a long period of inactivity and thus, power-down.

When the AD7357 is in full power-down, all analog circuitry is

powered down. Full power-down is entered in a similar way as

partial power-down, except that the timing sequence shown in

Figure 25 must be executed twice. The conversion process must

be interrupted in a similar fashion by bringing CS high

anywhere after the second falling edge of SCLK and before the

10th falling edge of SCLK. The device enters partial power-down

mode at this point.

To reach full power-down, the next conversion cycle must be

interrupted in the same way, as shown in Figure 27. Once CS

has been brought high in this window of SCLKs, the part

completely powers down.

Note that it is not necessary to complete the 16 SCLKs once CS

has been brought high to enter a power-down mode.

To exit full power-down mode and power-up the AD7357,

perform a dummy conversion, such as powering up from partial

power-down. On the falling edge of CS, the device begins to

power up, as long as CS is held low until after the falling edge of

the 10th SCLK. The required power-up time must elapse before

a conversion can be initiated, as shown in Figure 28.

SCLK

DOUTA

DOUTB

INVALID DATA

VALID DATA

110

THE PART BEGINS

TO POWER UP.

THE PART IS FULLY

POWERED UP; SEE

POWER-UP TIMES

SECTION.

tPOWER-UP1

Figure 26. Exiting Partial Power-Down Mode

THREE-STATE

110

SCLK

DOUTA

DOUTB

THREE-STATE

110

INVALID DATA

THE PART BEGINS

TO POWER UP.

THE PART ENTERS

PARTIAL POWER DOWN.

THE PART ENTERS

FULL POWER DOWN.

Figure 27. Entering Full Power-Down Mode

SCLK

DOUTA

DOUTB

INVALID DATA

VALID DATA

THE PART BEGINS

TO POWER UP.

THE PART IS FULLY POWERED UP,

SEE POWER-UP TIMES SECTION.

tPOWER-UP2

Figure 28. Exiting Full Power-Down Mode

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