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AD976ARS Datasheet(PDF) 8 Page - Analog Devices |
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AD976ARS Datasheet(HTML) 8 Page - Analog Devices |
8 / 16 page AD976/AD976A –8– REV. C DATA VALID t 6 t 3 t 1 t 10 t 9 CONVERT CONVERT ACQUIRE MODE DATA BUS NOT VALID HI-Z DATA VALID BUSY R/ C t 7 t 8 t 11 t 13 ACQUIRE t 2 t 4 PREVIOUS DATA VALID t 5 PREVIOUS DATA VALID t 14 HI-Z Figure 2. Conversion Timing with Outputs Enabled After Conversion (CS Tied Low) MODE BUSY R/ C DATA BUS CS t 6 t 12 t 1 CONVERT ACQUIRE HI-Z DATA VALID t 7 ACQUIRE t 9 t 12 t 12 t 12 t 1 t 3 t 4 t 14 HI-Z Figure 3. Using CS to Control Conversion and Read Timing CONVERSION CONTROL The AD976/AD976A is controlled by two signals: R/C and CS, as shown in Figures 2 and 3. To initiate a conversion and place the sample/hold circuit into the hold state, both the R/C and CS signals must be brought low for no less than 50 ns. Once the conversion process begins, the BUSY signal will go Low until the conversion is complete. At the end of a conversion, BUSY will return High, and the resulting valid data will be available on the data bus. On the first conversion after the AD976/AD976A is powered up, the DATA output will be indeterminate. The AD976/AD976A exhibits two modes of conversion. In the mode demonstrated in Figure 2, conversion timing is controlled by a negative-going R/C signal, at least 50 ns wide. In this mode the CS pin is always tied low, and the only limit placed on how long the R/C signal can remain low is the desired sampling rate. Less than 83 ns after the initiation of a conversion, the BUSY signal will be brought low and remain low until the conversion is complete and the output shift registers have been updated with the new Binary Twos Complement data. Figure 3 demonstrates the AD976/AD976A conversion timing, using CS to control both the conversion process and the reading of output data. To operate in this mode, the R/C signal should be brought low no less than 10 ns before the falling edge of a CS pulse (50 ns wide) is applied to the ADC. Once these two pulses are applied, BUSY will go low and remain low until a conver- sion is complete. After a maximum of 4 µs (AD976A only), BUSY will again return high, and parallel data will be valid on the ADC outputs. To achieve the maximum 100 kHz/200 kHz throughput rate of the part, the negative going R/C and CS control signals should be applied every 5 µs (AD976A). It should also be noted that although all R/C and CS commands will be ignored once a conversion has begun, these inputs can be asserted during a conversion; i.e., a read during conversion can be performed. Voltage transients on these inputs could feed through to the analog circuitry and affect conversion results. |
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