TC7106AIJL datasheet(11/26 Pages) MICROCHIP

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DS21455B-page 11

TC7106/A/TC7107/A

6.0

DIGITAL SECTION (TC7107A)

Figure 6-2 shows a TC7107A block diagram.

It is

designed to drive common anode LEDs. It is identical

to the TC7106A, except that the regulated supply and

backplane drive have been eliminated and the segment

drive is typically 8mA. The 1000's output (Pin 19) sinks

current from two LED segments, and has a 16mA drive

capability.

In both devices, the polarity indication is “ON” for neg-

ative analog inputs. If VIN- and VIN+ are reversed, this

indication can be reversed also, if desired.

The display font is the same as the TC7106A.

6.1

System Timing

The oscillator frequency is divided by 4 prior to clocking

the internal decade counters. The four-phase mea-

surement cycle takes a total of 4000 counts, or 16,000

clock pulses. The 4000-count cycle is independent of

input signal magnitude.

Each phase of the measurement cycle has the follow-

ing length:

Auto-zero phase: 1000 to 3000 counts (4000 to

12000 clock pulses).

For signals less than full scale, the auto-zero phase is

assigned the unused reference integrate time period:

Signal integrate: 1000 counts (4000 clock

pulses).

This time period is fixed. The integration period is:

EQUATION 6-1:

Reference Integrate: 0 to 2000 counts (0 to 8000

clock pulses).

The TC7106A/7107A are drop-in replacements for the

7106/7107 parts. External component value changes

are not required to benefit from the low drift internal

reference.

6.2

Clock Circuit

Three clocking methods may be used (see Figure 6-1):

An external oscillator connected to Pin 40.

A crystal between Pins 39 and 40.

An RC oscillator using all three pins.

FIGURE 6-1:

CLOCK CIRCUITS

TSI = 4000

FOSC









Where: FOSC is the externally set clock frequency.

TC7106A

TC7107A

Crystal

RC Network

EXT

OSC

To TEST Pin on TSC7106A

To GND Pin on TSC7107A

Counter

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