TC14433/A
4.0
TYPICAL APPLICATIONS
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 4-1
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 4-1 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 V
SS
is connected to V
EE
. In this
case, V
AG
must be at least 2.8V above V
EE
.
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 (Q
3
= 0 and Q
0
= 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 4-1:
Coded
Q
Condition
3
of MSD
+0
-0
+0 UR
-0 UR
+1
-1
+1 OR
-1 OR
Note 1:
TRUTH TABLE
Q
2
Q
1
Q
0
BDC to 7-Segment
Decoding
Blank
Blank
Blank
Blank
4–1
0–1
7–1
3–1
Hook up
only segments
b and c to MSD
1
1
1
1
0
0
0
0
1
0
1
0
1
0
1
0
1
1
1
1
0
0
1
1
0
0
1
1
0
0
1
1
Q
3
- 1/2 digit, low for "1", high for "0".
Q
2
- Polarity: "1" = positive, "0" = negative.
Q
0
- Out of range condition exists if Q
0
= 1.
When used in conjunction with Q
3
, the type of
out of range condition is indicated; i.e., Q
3
= 0
→
OR or Q
3
= 1
→
UR.
Figure 4-2 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.
2002 Microchip Technology Inc.
DS21394B-page 9
©
MICROCHIP [ MICROCHIP TECHNOLOGY ]
