ICL7135CSLASHD datasheet(6/13 Pages) MAXIM

6 / 13 page

the rising edge of the RUN/HOLD input and the BUSY

output. A RUN/HOLD pulse during the unused portion of

deintegrate phase will be ignored, but when in the auto-

zero phase a positive pulse of only 300ns (typical) will

start the conversion. Figure 5 shows a simple method

of obtaining one, and only one, conversion for each

measurement request.

BUSY

BUSY is a status output that goes high at the beginning

of signal integrate and stays high until the first clock

pulse after zero crossing during De-integrate (or end of

De-Integrate if overranged).The internal data latches are

loaded during the next clock cycle after the falling edge

of BUSY. Since BUSY is high for the 10,000 counts of

signal integrate + number of counts during De-Integrate

+1 clock cycle, a simple way of sending conversion data

down a single pair of wires is to logically ‘AND’ BUSY with

the clock and to subtract 10,001 counts from the number

received. Figure 6 shows a system using this method to

remotely display data.

Figure 3. ICL7135 Digital Section

Figure 4. Timing Diagram

Figure 5. External RUN/HOLD Latch

ICL7135

41/2 Digit A/D Converter with

Multiplexed BCD Outputs

www.maximintegrated.com

Maxim Integrated │ 6

MSB

POLARITY

ANALOG

SECTION

ZERO

CROSS.

DET.

DIGITAL

GND

CLOCK

OVER

RANGE

UNDER

RANGE

BUSY

CONTROL LOGIC

MULTIPLEXER

COUNTERS

LATCH

STROBE

RUN/

HOLD

LSB

V+

POLARITY

ICL7135

INTEGRATOR

OUTPUT

BUSY

OVER-RANGE

WHEN APPLICABLE

UNDER-RANGE

WHEN APPLICABLE

NORMAL DIGIT SCAN

1000*

COUNTS

AUTO ZERO

DIGIT SCAN

FOR OVER-RANGE

*FIRST D5 OF AZ AND

DE-INTEGRATE ARE ONE COUNT LONGER

DE-INTEGRATE

SIGNAL

INTEGRATE

*STROBE

AUTO-

ZERO

INTEGRATOR

10,0001

COUNTS

SIGNAL

INT.

10,000

COUNTS

FULL MEASUREMENT CYCLE

40,002 COUNTS

DE-INTEGRATE

20,001

COUNTS MAX.

RUN/HOLD

FLIP-FLOP

START

PULSE

ICL7135

BUSY

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