AD7352 datasheet(15/17 Pages) AD

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Preliminary Technical Data

AD7357

Rev. PrD | Page 15 of 17

POWER-UP TIMES

The AD7357 has two power-down modes, partial power-down

and full power-down, which are described in detail in the

previous sections. This section deals with the power-up time

required when coming out of either of these modes.

To power up from partial power-down mode, one dummy cycle

is required. The device is fully powered up after approximately

TBD µs from the falling edge of CS has elapsed. Once the

partial power-up time has elapsed, the ADC is fully powered up

and the input signal is acquired properly. The quiet time, tQUIET,

must still be allowed from the point where the bus goes back

into three-state after the dummy conversion to the next falling

edge of CS.

To power up from full power-down, approximately TBD μs

should be allowed from the falling edge of CS, shown in Figure

18 as tPOWER-UP2.

Note that during power-up from partial power-down mode, the

track-and-hold, which is in hold mode while the part is powered

down, returns to track mode after the first SCLK edge that the

part receives after the falling edge of CS.

When power supplies are first applied to the AD7357, the ADC

can power up in either of the power-down modes or in normal

mode. Because of this, it is best to allow a dummy cycle to

elapse to ensure that the part is fully powered up before

attempting a valid conversion. Likewise, if the part is to be kept

in partial power-down mode immediately after the supplies are

applied, then two dummy cycles must be initiated. The first

dummy cycle must hold CS low until after the 10th SCLK falling

edge; in the second cycle, CS must be brought high between the

second and 10th SCLK falling edges (see Figure 15).

Alternatively, if the part is to be placed into full power-down

mode when the supplies are applied, three dummy cycles must

be initiated. The first dummy cycle must hold CS low until after

the 10th SCLK falling edge; the second and third dummy cycles

place the part into full power-down mode (see Figure 17). See

the Modes of Operation section.

AD7352 Datasheet(PDF) 15 Page - Analog Devices