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Preliminary Technical Data

AD7794

REV.PrE 6/04 | Page 9

TIMING CHARACTERISTICS8, 9

Table 2. (AVDD = 2.7 V to 5.25 V; DVDD = 2.7 V to 5.25; GND = 0 V, Input Logic 0 = 0 V, Input Logic 1 = DVDD, unless otherwise

noted.)

Parameter

Limit at TMIN, TMAX

(B Version)

Unit

Conditions/Comments

100

ns min

SCLK High Pulsewidth

100

ns min

SCLK Low Pulsewidth

Read Operation

ns min

CS Falling Edge to DOUT/RDY Active Time

ns max

DVDD = 4.75 V to 5.25 V

ns max

DVDD = 2.7 V to 3.6 V

t210

ns min

SCLK Active Edge to Data Valid Delay11

ns max

DVDD = 4.75 V to 5.25 V

ns max

DVDD = 2.7 V to 3.6 V

t512, 13

ns min

Bus Relinquish Time after CS Inactive Edge

ns max

100

ns max

SCLK Inactive Edge to CS Inactive Edge

ns min

SCLK Inactive Edge to DOUT/RDY High

Write Operation

ns min

CS Falling Edge to SCLK Active Edge Setup Time11

ns min

Data Valid to SCLK Edge Setup Time

t10

ns min

Data Valid to SCLK Edge Hold Time

t11

ns min

CS Rising Edge to SCLK Edge Hold Time

8 Sample tested during initial release to ensure compliance. All input signals are specified with tR = tF = 5 ns (10% to 90% of DVDD) and timed from a voltage level of 1.6 V.

9 See Figure 2 and Figure 3.

10 These numbers are measured with the load circuit of

Figure 1 and defined as the time required for the output to cross the VOL or VOH limits.

11 SCLK active edge is falling edge of SCLK.

12 These numbers are derived from the measured time taken by the data output to change 0.5 V when loaded with the circuit of

Figure 1. The measured number is then extrapolated back to remove the effects of charging or discharging the 50 pF capacitor. This means that the times quoted in the

timing characteristics are the true bus relinquish times of the part and, as such, are independent of external bus loading capacitances.

RDY returns high after a read of the ADC. In single conversion mode and continuous conversion mode, the same data can be read again, if required, while RDY is high,

although care should be taken to ensure that subsequent reads do not occur close to the next output update. In continuous read mode, the digital word can be read

only once.

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