Datasheet

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SLAS400B − SEPTEMBER 2003 − REVISED NOVEMBER 2005
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8
DESCRIPTION AND TIMING DIAGRAMS
SAMPLING AND CONVERSION START
There are three ways to start sampling. The rising edge of CONVST starts sampling with CS and BUSY being low
(see Figure 1) or it can be started with the falling edge of CS when CONVST is high and BUSY is low (see
Figure 2). Sampling can also be started with an internal conversion end (before BUSY falling edge) with CS
being low and CONVST high before an internal conversion end (see Figure 3). Also refer to the section DEVICE
OPERATION AND DATA READ IN BACK-TO-BACK CONVERSION for more details.
A conversion can be started two ways (a conversion start is the end of sampling). Either with the falling edge
of CONVST when CS is low (see Figure 1) or the falling edge of CS when CONVST is low (see Figure 2). A
clean and low jitter falling edge of these respective signals triggers a conversion start and is important to the
performance of the converter. The BUSY pin is brought high immediately following the CONVST falling edge.
BUSY stays high throughout the conversion process and returns low when the conversion has ended.
t
h2
t
h3
t
d1
t
d2
t
(acq)
CS
CONVST
BUSY
Figure 1. Sampling and Conversion Start Control With CONVST Pin
t
d3
t
(acq)
t
w3
t
w3
t
d4
t
w1
CS
CONVST
BUSY
Figure 2. Sampling and Conversion Start Control With CS Pin
t
(acq)
t
w4
t
d2
CS
CONVST
BUSY
t
h1
t
w5
Figure 3. Sampling Start With CS Low and CONVST High (Back-to-Back)