Datasheet

AD7466/AD7467/AD7468
Rev. C | Page 19 of 28
NORMAL MODE
The AD7466/AD7467/AD7468 automatically enter power-
down at the end of each conversion. This mode of operation is
designed to provide flexible power management options and to
optimize the power dissipation/throughput rate ratio for low
power application requirements.
Figure 24 shows the general
operation of the AD7466/AD7467/AD7468. On the
CS
falling
edge, the part begins to power up and the track-and-hold,
which was in hold while the part was in power-down, goes into
track mode. The conversion is also initiated at this point. On
the third SCLK falling edge after the
CS
falling edge, the track-
and-hold returns to hold mode.
For the AD7466, 16 serial clock cycles are required to complete
the conversion and access the complete conversion result. The
AD7466 automatically enters power-down mode on the 16th
SCLK falling edge.
For the AD7467, 14 serial clock cycles are required to complete
the conversion and access the complete conversion result. The
AD7467 automatically enters power-down mode on the 14th
SCLK falling edge.
For the AD7468, 12 serial clock cycles are required to complete
the conversion and access the complete conversion result.
The AD7468 automatically enters power-down mode on the
12th SCLK falling edge.
The AD7466 also enters power-down mode if
CS
is brought
high any time before the 16th SCLK falling edge. The conver-
sion that was initiated by the
CS
falling edge terminates and
SDATA goes back into three-state. This also applies for the
AD7467 and AD7468; if
CS
is brought high before the conver-
sion is complete (the 14th SCLK falling edge for the AD7467,
and the 12th SCLK falling edge for the AD7468), the part enters
power-down, the conversion terminates, and SDATA goes back
into three-state.
Although
CS
can idle high or low between conversions,
bringing
CS
high once the conversion is complete is recom-
mended to save power.
When supplies are first applied to the devices, a dummy conver-
sion should be performed to ensure that the parts are in power-
down mode, the track-and-hold is in hold mode, and SDATA is
in three-state.
Once a data transfer is complete (SDATA has returned to three-
state), another conversion can be initiated after the quiet time,
t
QUIET
, has elapsed, by bringing
CS
low again.
THE PART BEGINS
TO POWER UP
AD7468 ENTERS POWER-DOWN
AD7467 ENTERS POWER-DOWN
AD7466 ENTERS POWER-DOWN
VALID DATA
SCLK
S
DAT
A
123 12 14 16
THE PART IS POWERED UP
AND V
IN
FULLY ACQUIRED
CS
02643-025
Figure 24. Normal Mode Operation