TC7116_06 datasheet(10/24 Pages) MICROCHIP

10 / 24 page

TC7116/A/TC7117/A

DS21457C-page 10

FIGURE 3-4:

Exclusive “OR” Gate for

Decimal Point Drive

3.2

Digital Section

Figure 3-5 and Figure show the digital section for

TC7116/TC7116A and TC7117/TC7117A, respectively.

For the TC7116/TC7116A (Figure 3-5), an internal dig-

ital ground is generated from a 6V Zener diode and a

large P-channel source follower. This supply is made

stiff to absorb the relative large capacitive currents

when the backplane (BP) voltage is switched. The BP

frequency is the clock frequency 4800. For 3 readings

per second, this is a 60Hz square wave with a nominal

amplitude of 5V. The segments are driven at the same

frequency and amplitude, and are in phase with BP

when OFF, but out of phase when ON. In all cases,

negligible DC voltage exists across the segments.

Figure is the digital section of the TC7117/TC7117A. It

is identical to the TC7116/TC7116A, except that the

regulated supply and BP drive have been eliminated,

and the segment drive is typically 8mA. The 1000’s out-

put (Pin 19) sinks current from two LED segments, and

has a 16mA drive capability. The TC7117/TC7117A are

designed to drive common anode LED displays.

In both devices, the polarity indication is ON for analog

inputs. If VIN- and VIN+ are reversed, this indication can

be reversed also, if desired.

FIGURE 3-5:

TC7116/TC7116A Digital Section

TC7116

TC7116A

Decimal

Point

Select

V+

TEST

GND

4030

To LCD

Decimal

Point

TC7116

TC7116A

LCD Phase Driver

Thousands

Hundreds

Tens

Units

Backplane

OSC2

Internal Digital Ground

V+

V-

TEST

6.2V

500

To Switch Drivers

From Comparator Output

Clock

VTH = 1V

7-Segment

Decode

7-Segment

Decode

7-Segment

Decode

200

Typical Segment Output

Internal Digital Ground

Segment

Output

V+

0.5mA

2mA

Latch

OSC3

OSC1

HLDR

~70k

Logic Control

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