ADS7891

SLAS410 − DECEMBER 2003

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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.

th2

th3

td1

td2

t(acq)

CS

CONVST

BUSY

Figure 1. Sampling and Conversion Start Control With CONVST Pin

td3

t(acq)

tw3

tw3

td4

tw1

CS

CONVST

BUSY

Figure 2. Sampling and Conversion Start Control With CS Pin

t(acq)

tw4

td2

CS

CONVST

BUSY

th1

tw5

Figure 3. Sampling Start With CS Low and CONVST High (Back-to-Back)