TC835 datasheet(14/24 Pages) MICROCHIP

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TC835

DS21478B-page 14

The clock used should be free from significant phase or

frequency jitter. Several suitable low-cost oscillators

are shown in Section 6.0, Typical Applications. The

multiplexed output means that if the display takes sig-

nificant current from the logic supply, the clock should

have good PSRR.

6.5

Zero Crossing Flip-Flop

The flip flop interrogates the data once every clock

pulse after the transients of the previous clock pulse

and half-clock pulse have died down. False zero cross-

ings caused by clock pulses are not recognized. Of

course, the flip flop delays the true zero crossing by up

to one count in every instance. If a correction were not

made, the display would always be one count too high.

Therefore, the counter is disabled for one clock pulse

at the beginning of the reference integrate (de-inte-

grate) phase. This one-count delay compensates for

the delay of the zero crossing flip flop and allows the

correct number to be latched into the display. Similarly,

a one-count delay at the beginning of auto zero gives

an overload display of 0000 instead of 0001. No delay

occurs during signal integrate, so that true ratiometric

readings result.

FIGURE 6-1:

4-1/2 DIGIT ADC MULTIPLEXED COMMON ANODE LED DISPLAY

9–15

777

DM7447A

Blank MSD On Zero

D1 D2

INT OUT

AZ IN

BUFF

OUT

FIN

+INPUT

–INPUT

ANALOG

COMMON

V –

REF

POL

CREF-

+5V

0.33

µF

200kHz

–

Analog

Input

µF

100k

Ω

µF

4.7k

Ω

µF

–5V

100k

Ω

100k

Ω

RBI

V+

CREF+

TC835

MCP1525

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