3-1/2 DIGIT A/D CONVERTERS
TC14433
TC14433A
Figure 14 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 seg-
ment drive and the 75492 or 1413 provides sink for digit
current. Display is blanked during the overrange condition.
APPLICATIONS INFORMATION
Figure 10 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
1.999Vor199.9mV.Inputoverrangeisindicatedbyflashing
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 (see recommended operating conditions,
page 2).
The circuit in Figure 11 shows a 3-1/2 digit LCD voltme-
ter. 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
TRUTH TABLE
Coded Condition
of MSD
BCD to 7-Segment
Decoding
Q3 Q2 Q1 Q0
+0
–0
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
Blank
Blank
+0 UR
–0 UR
+1
Blank
Blank
4–1 Hook up
0–1 only
7–1 segments
3–1 b and c
to MSD
above VEE
.
–1
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-
rangingcircuits,occurswhenthecountislessthan180;e.g.,
0.180V for a reference of 2V.
+1 OR
–0 OR
NOTES: 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.
CAUTION
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.
MULTIPLEXED
BCD
DS
DS
DS
DS
3
DS
DS
1
1
2
2
4
V
DD
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
2 3
0
1
2
3
0
1
2
3
0
1
2
3
0
1
V
V
DD
DD
POL 14042B
C
C
14042B POL
POL 14042B
C
C
14042B POL
Q
Q
Q
Q
Q
Q
Q
Q
Q
Q
Q
Q
D
Q
Q
Q
Q
0
1
2
3
0
1
2
3
0
1
2
3
3
0
1
2
3
D
D
D
D
D
D
D
D
D
D
D
D
0
D
D
D
0
1
2
3
0
1
2
3
0
1
2
1
2
3
V
V
V
V
DD
DD
DD
DD
R
14175B
C
POL 14175B
C
POL 14175B
C
POL 14175B
C
Q
Q
Q
Q
Q
Q
Q
Q
Q
Q
Q
Q
Q
Q
Q
Q
0
1
2
3
0
1
2
3
0
1
2
3
0
1
2
3
EOC
Figure 13. Demultiplexing for TC14433 BCD Data
3-134
TELCOM SEMICONDUCTOR, INC.
TELCOM [ TELCOM SEMICONDUCTOR, INC ]
