TC7106 datasheet(12/34 Pages) MICROCHIP

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TC7106/A/TC7107/A

DS21455D-page 12

6.0

DIGITAL SECTION (TC7107A)

Figure 6-2 shows a TC7106A 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 8 mA. The 1000’s output (Pin 19) sinks

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

capability.

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

negative 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

measurement cycle takes a total of 4000 counts, or

16,000 clock pulses. The 4000-count cycle is indepen-

dent of input signal magnitude.

Each phase of the measurement cycle has the

following 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/TC7107A are drop-in replacements for

the TC7106/TC7107 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.

Where:

FOSC

Externally set clock frequency

OSC

-------------

1000

TC7106A

TC7107A

Crystal

RC Network

EXT

OSC

To TEST Pin on TSC7106A

To GND Pin on TSC7107A

Counter

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