Datasheet

CLK
DRDY
SYNC
t
NDR
t
SYN
t
SCSU
t
CSHD
FSYNC
ValidData
DOUT
SYNC
t
NDR
t
SYN
CLK
t
CSHD
t
SCSU
ADS1174
ADS1178
www.ti.com ........................................................................................................................................ SBAS373B – OCTOBER 2007 – REVISED SEPTEMBER 2008
After synchronization, indication of valid data In the Frame-Sync format, DOUT goes low as soon
depends on the whether SPI or Frame-Sync format is as SYNC is taken low; see Figure 14 . After SYNC is
used. returned high, DOUT stays low while the digital filter
is settling. Once valid data are ready for retrieval,
In the SPI format, DRDY goes high as soon as SYNC
DOUT begins to output valid data. For proper
is taken low; see Figure 13 . After SYNC is returned
synchronization, FSYNC, SCLK, and CLK must be
high, DRDY stays high while the digital filter is
established before taking SYNC high, and must then
settling. Once valid data are ready for retrieval,
remain running.
DRDY goes low.
Figure 13. Synchronization Timing for SPI Protocol
Table 7. SPI Protocol
SYMBOL DESCRIPTION MIN TYP MAX UNITS
t
CSHD
CLK to SYNC hold time (to not latch on CLK edge) 10 ns
t
SCSU
SYNC to CLK setup time (to latch on CLK edge) 5 ns
t
SYN
Synchronize pulse width 1 CLK periods
t
NDR
Time for new data to be ready 129 Conversions (1/f
DATA
)
Figure 14. Synchronization Timing for Frame-Sync Protocol
Table 8. Frame-Sync Protocol
SYMBOL DESCRIPTION MIN TYP MAX UNITS
t
CSHD
CLK to SYNC hold time (to not latch on CLK edge) 10 ns
t
SCSU
SYNC to CLK setup time (to latch on CLK edge) 5 ns
t
SYN
Synchronize pulse width 1 CLK periods
t
NDR
Time for new data to be ready 127 128 Conversions (1/f
DATA
)
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