MC14549B, MC14559B

http://onsemi.com

7

Q7 Q6 Q5

MR

SC

C

MC14549B

Q4 Q3 Q2 Q1 Q0 EOC

TO DAC

Q7 Q6 Q5

SC

MC14559B

Q4 Q3 Q2 Q1 Q0

EOC

TO DAC

FF

EOC

Figure 4. Continuously Cycling 12−Bit ADC

Externally Controlled 12−Bit ADC (Figure 5)

In this circuit the external pulse starts the first SAR and

simultaneously resets the cascaded second SAR. When Q4 of

the first SAR goes high, the second SAR starts conversion,

and the first one stops conversion. EOC indicates that the

parallel data are valid and that the serial output is complete.

Updating the output data is started with every external control

pulse.

Additional Motorola Parts for Successive

Approximation ADC

Monolithic digital−to−analog converters — The

MC1408/1508 converter has eight−bit resolution and is

available

with

6,

7,

and

8−bit

accuracy.

The

amplifier−comparator block — The MC1407/1507

contains a high speed operational amplifier and a high speed

comparator with adjustable window.

With these two linear parts it is possible to construct

SA−ADCs with an accuracy of up to eight bits, using as the

register one MC14549B or one MC14559B. An additional

CMOS block will be necessary to generate the clock

frequency.

Additional information on successive approximation ADC

is found in Motorola Application Note AN−716.

Figure 5. Externally Controlled 12−Bit ADC

Q7 Q6 Q5

MR

SC

C

MC14549B

Q4 Q3 Q2 Q1 Q0 EOC

TO DAC

Q7 Q6 Q5

SC

MC14559B

Q4 Q3 Q2 Q1 Q0

EOC

TO DAC

FF

EOC