Datasheet

POWER-DOWN ( PWDN)
NOTE:(1)InSPIprotocol,thetimingoccursonthefallingedgeof /FSYNC.Poweringdownallchannelsforces /FSYNChigh.DRDY DRDY
CLK
DRDY/FSYNC
(1)
DOUT
(DiscreteDataOutputMode)
· · ·· · ·
PWDN
t
NDR
t
PDWN
P -UpDataostPower
DOUT1
(TDMMode,DynamicPosition)
NormalPosition
NormalPositionDataShiftPosition
NormalPosition
NormalPositionDataRemaininPosition
DOUT1
(TDMMode,FixedPosition)
ADS1174
ADS1178
SBAS373B – OCTOBER 2007 – REVISED SEPTEMBER 2008 ........................................................................................................................................ www.ti.com
2. Wait for 130/f
DATA
(SPI) or 129/f
DATA
(Frame-Sync) after taking the PWDN pins high.
The ADS1174/78 measurement channels can be
3. Detect for non-zero data in the powered-up
independently powered down by use of the PWDN
channel.
inputs. To enter the power-down mode, hold the
respective PWDN pin low for at least two f
CLK
cycles.
After powering up one or more channels, the
To exit power-down, return the corresponding PWDN
channels are synchronized to each other. It is not
pin high. Note that when all channels are powered
necessary to use the SYNC pin to synchronize them.
down, the ADS1174/78 enters a microwatt ( µ W)
When a channel is powered down in TDM data
power state where all internal biasing is powered
format, the data for the powered-down channel are
down. In this event, the TEST[1:0] input pins must be
either forced to zero (fixed-position TDM data mode)
driven; all other input pins can float (the ADS1174/78
or replaced by shifting the data from the next channel
outputs remain driven).
into the vacated data position (dynamic-position TDM
As shown in Figure 15 and Table 9 , a maximum of
data mode).
130 conversion cycles (SPI interface) or 129
In discrete data format, the data are always forced to
conversion cycles (Frame-Sync interface) must
zero. When powering-up a channel in
elapse before reading data after exiting power-down.
dynamic-position TDM data format mode, the channel
Data from channels already running are not affected.
data remain packed until the data are ready, at which
The user software can perform the required delay
time the data frame is expanded to include the
time in the following ways:
just-powered channel data. See the Data Format
1. Count the number of data conversions after
section for details.
taking the PWDN pin high.
Figure 15. Power-Down Timing
Table 9. Power-Down Timing
SYMBOL DESCRIPTION MIN TYP MAX UNITS
t
PDWN
PDWN pulse width to enter Power-Down mode 2 CLK periods
Time for new data to be ready (SPI) 129 130 Conversions (1/f
DATA
)
t
NDR
Time for new data to be ready (Frame-Sync) 128 129 Conversions (1/f
DATA
)
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