20
LTC1417
Using External Clock for Conversion and Data Transfer.
In Figure 18, data from the previous conversion is output
during the conversion with an external clock providing
both the conversion clock and the shift clock. To select an
external conversion clock, apply the clock to EXTCLKIN.
The same clock is also applied to SCLK to provide a data
APPLICATIONS INFORMATION
WUU
U
Figure 18. External Conversion Clock Selected. Data Transferred During Conversion Using
the External Clock (External Clock Drives Both EXTCLKIN and SCLK)
shift clock. To maintain conversion accuracy, the external
clock frequency must be between 50kHz and 9MHz.
Using an external clock to transfer data while an internal
clock controls the conversion process is not recom-
mended. As both signals are asynchronous, clock noise
can corrupt the conversion result.
D12 D11
D11D12
CAPTURE ON
RISING CLOCK
D13
D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0
FILL
ZEROS
D13
1
t
2
t
3
t
7
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1 2 3
D13 D13 D12 D11
Hi-Z
Hi-Z
DATA NDATA (N – 1)
(SAMPLE N)
(SAMPLE N + 1)
D
OUT
EXTCLKIN (= SCLK)
CONVST
t
10
t
CONV
t
5
SAMPLE HOLDHOLD
t
dEXTCLKIN
t
4
t
8
1417 F18
BUSY (= RD)
t
12
t
11
t
LEXTCLKIN
t
HEXTCLKIN
EXTCLKIN
(= SCLK)
V
IL
V
OH
V
OL
D
OUT
CAPTURE ON
FALLING CLOCK
LTC1417
BUSY (= RD)
EXTCLKIN ( = SCLK)
BUSYCONVSTCONVST
RD
EXTCLKIN
SCLK
D
OUT
D
OUT
9
1413
7
6
12
µP OR DSP