AD561

–8–

REV. A

OUTLINE DIMENSIONS

Dimensions shown in inches and (mm).

16-Pin Ceramic Package

D-16

16-Pin Plastic Package

N-16

Figure 9. Fast Precision Analog to Digital Converter

A much faster converter can be constructed by using higher

performance external components. Each individual high-order

bit settles in less than 250 ns; the low-order bits in less than

200 ns. Because of this, a staged clock, which speeds up for

lower bits will improve the speed. Also, a faster comparator and

Schottky TTL or ECL logic would be necessary. 10-bit convert-

ers in the 3

µs to 5 µs range could be built around the AD561

with these techniques.

DIGITAL 4-TO-20 mA OR 1-TO-5 VOLT CONVERTER

A direct digital 4-to-20 mA or 1-to-5 volt line driver can be built

with the AD561 as shown in Figure 10. The 2.5 volt reference is

divided to provide 1 volt at the op amp noninverting input – thus a

zero input code results in a 1 volt output at the Darlington emitter

(

± 20%) full-scale output from the AD561 to 4 volts, for a

total output of 5 volts FS. The voltage at the emitter forces a

proportional current through the 250

Ω (which appears at the

line; thus 5 volts full scale gives 22 mA in the current loop. For

exactly 20 mA, trim the 1 k pot for 4.5 V FS. (A single op amp

circuit will not produce both 1 to 5 volt and

4-to-20 mA outputs simultaneously.)

Figure 10. Digital 4-to-20 mA or 1-to-5 Volt Line Driver

DIGITALLY PROGRAMMABLE SETPOINT

COMPARATOR

Figure 11 demonstrates a high accuracy systems-oriented

setpoint comparator. The 2.5 volt reference is buffered and

amplified by the AD741K to produce an exact 10.000 volt

reference which could be used as a primary system reference for

several such circuits. The +10 volt compliance of the AD561

then allows it to generate a zero to +10 volt output swing

through the 5 k

Ω application resistor without an additional op

amp. The digital code for this system will be complementary

binary (all 1s give 0.00 volts out).

Figure 11. Digitally Programmable Set-Point Comparator