17
LTC1609
1609fa
APPLICATIO S I FOR ATIO
WUUU
DATA
SYNC
BUSY
R/C
B1B14
B15
(MSB)
B0
1606 F11
t
17
t
18
t
3
t
2
t
1
t
21
t
22
t
15
012 1516
EXTERNAL
DATACLK
t
13
t
14
t
12
To minimize the possible external disturbances that can
occur while a conversion is in progress, the data needs to
be shifted out within 1.2µs from the start of the conver-
sion. Using the maximum data clock frequency of 20MHz
will ensure this condition is met.
External Data Clock Data Read During the Conversion
Figure 12 shows how the result from the previous conver-
sion can be read out during the current conversion. The
externally supplied data clock is running continuously. CS
and R/C are used to initiate a conversion and read the data
from the previous conversion. The conversion starts on
the falling edge of CS after R/C is low. A pulse on the SYNC
pin will be generated on the first rising edge of DATACLK
#1 after R/C has returned high. The SYNC output can be
captured on the falling edge of DATACLK #1 or on the
rising edge of DATACLK #2. After the rising edge of
DATACLK #2 the SYNC output will go low and the MSB will
be clocked out on the DATA pin. This bit can be latched on
the falling edge of DATACLK #2 or on the rising edge of
DATACLK #3. The LSB will be valid on the falling edge of
DATACLK #17 or the rising edge of DATACLK #18. After
the rising edge of DATACLK #18 the DATA pin will take on
the value of the TAG pin that occurred at the rising edge of
DATACLK #2.
To minimize the possible external disturbances that can
occur while a conversion is in progress, the data needs to
be shifted out within 1.2µs from the start of the conver-
sion. Using the maximum data clock frequency of 20MHz
will ensure this condition is met. Since there is no through-
put penalty for clocking the data out after the conversion,
clocking the data out during the conversion is not recom-
mended.
Use of the TAG Input
The TAG input pin is used to daisy-chain multiple convert-
ers. This is useful for applications where hardware con-
straints may limit the number of lines needed to interface
to a large number of converters. This mode of operation
works only using the external clock method of shifting out
the data.
Figure 13 shows how this feature can be used. R/C, CS and
the DATACLK are tied together on both LTC1609s. CS can
be grounded if a discontinuous data clock is used. A falling
edge on R/C will allow both LTC1609s to capture their
respective analog input signals simultaneously. Once the
conversion has been completed the external data clock
DCLK is started. The MSB from device #1 will be valid after
the rising edge of DCLK #1. Once the LSB from device #1
has been shifted out on the rising edge of DCLK #16, a null
Figure 11. Conversion and Read Timing Using a Discontinuous Data Clock (EXT/INT Tied High, CS Tied Low).
Read Previous Conversion Result During the Conversion. For Best Performance, Complete Read in Less Than 1.2µs
