TC7117ACPL datasheet(10/14 Pages) TELCOM

10 / 14 page

3-212

TELCOM SEMICONDUCTOR, INC.

3-1/2 DIGIT ANALOG-TO-DIGITAL

CONVERTERS WITH HOLD

TC7116

TC7116A

TC7117

TC7117A

TC7117

TC7117A

THOUSANDS

HUNDREDS

TENS

UNITS

OSC

DIGITAL

GND

TEST

TO SWITCH DRIVERS

FROM COMPARATOR OUTPUT

CLOCK

7-SEGMENT

DECODE

7-SEGMENT

DECODE

7-SEGMENT

DECODE

OSC3

OSC1

HLDR

CONTROL LOGIC

TYPICAL SEGMENT OUTPUT

DIGITAL GROUND

SEGMENT

0.5 mA

8 mA

500

Ω

LATCH

~70 k

Ω

System Timing

The clocking method used for the TC7116/TC7116A

and TC7117/TC7117A is shown in Figure 9. Three clocking

methods may be used:

(1) An external oscillator connected to pin 40.

(2) A crystal between pins 39 and 40.

(3) An RC network using all three pins.

The oscillator frequency is

4 before it clocks the

decade counters. It is then further divided to form the three

convert-cycle phases: signal integrate (1000 counts), refer-

ence deintegrate (0 to 2000 counts), and auto-zero (1000 to

3000 counts). For signals less than full scale, auto-zero gets

the unused portion of reference deintegrate. This makes a

complete measure cycle of 4000 (16,000 clock pulses)

independent of input voltage. For 3 readings per second, an

oscillator frequency of 48 kHz would be used.

To achieve maximum rejection of 60-Hz pickup, the

signal-integrate cycle should be a multiple of 60 Hz. Oscil-

lator frequencies of 240 kHz, 120 kHz, 80 kHz, 60 kHz, 48

kHz, 40 kHz, etc. should be selected. For 50 Hz rejection,

oscillator frequencies of 200 kHz, 100 kHz, 66-2/3 kHz, 50

kHz, 40 kHz, etc. would be suitable. Note that 40 kHz (2.5

readings per second) will reject both 50 Hz and 60 Hz.

HOLD Reading Input

When HLDR is at a logic HIGH the latch will not be

updated. Analog-to-digital conversions will continue but will

not be updated until HLDR is returned to LOW. To continu-

ously update the display, connect to test (TC7116/TC7116A)

or ground (TC7117/TC7117A), or disconnect. This input is

CMOS compatible with 70 k

Ω typical resistance to TEST

(TC7116/TC7116A) or ground (TC7117/TC7117A).

Figure 9. TC7117/TC7117A Digital Section

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