TC14433-ESLASHOG datasheet(10/24 Pages) MICROCHIP

10 / 24 page

TC14433/A

DS21394D-page 10

5.0

TYPICAL APPLICATIONS

The typical application circuit is an example of a 3-1/2

digit voltmeter using the TC14433 with Common-

anode displays. This system requires a 2.5V reference.

Full scale may be adjusted to 1.999V or 199.9 mV.

Input overrange is indicated by flashing a display. This

display uses LEDs with common anode digit lines.

Power supply for this system is shown as a dual ±5V

supply; however, the TC14433 will operate over a wide

voltage range

The circuit in Figure 5-1 shows a 3-1/2 digit LCD

voltmeter. The 14024B provides the low frequency

square wave signal drive to the LCD backplane. Dual

power supplies are shown here; however, one supply

may be used when VSS is connected to VEE. In this

case, VAG must be at least 2.8V above VEE.

When only segments b and c of the decoder are con-

nected to the 1/2 digit of the display, 4, 0, 7 and 3

appear as 1.

The overrange indication (Q3 = 0 and Q0 = 1) occurs

when the count is greater than 1999; (e.g., 1.999V for

a reference of 2V) The underrange indication, useful for

auto-ranging circuits, occurs when the count is less

than 180; (e.g., 0.180V for a reference of 2V).

TABLE 5-1:

TRUTH TABLE

Figure 5-2 is an example of a 3-1/2 digit LED voltmeter

with a minimum of external components, (only 11

additional components). In this circuit, the 14511B

provides the segment drive and the 75492 or 1413

provides sink for digit current. Display is blanked during

the overrange condition.

Note:

If the most significant digit is connected to

a display other than a “1” only, such as a

full digit display, segments other than b

and c must be disconnected. The BCD to

7-segment decoder must blank on BCD

inputs 1010 to 1111 (see Table 5-1).

Coded

Condition

of MSD

BDC to 7-Segment

Decoding

+01

Blank

-01

+0 UR

-0 UR

+10

4 – 1

0 – 1

7 – 1

3 – 1

Hook up

only segments

b and c to MSD

-10

+1 OR

-1 OR

Note 1:

Q3 – 1/2 digit, low for “1”, high for “0”.

Q2 – Polarity: “1” = positive, “0” = negative.

Q0 – Out of range condition exists if Q0 = 1.

When used in conjunction with Q3, the type

of out of range condition is indicated; i.e.,

Q3 = 0 → OR or Q3 = 1 → UR.

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