3-1/2 DIGIT A/D CONVERTERS
TC14433
TC14433A
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
1.999V 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 (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 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.
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.
TRUTH TABLE
Coded Condition
of MSD
+0
–0
+0 UR
–0 UR
+1
–1
+1 OR
–0 OR
BCD to 7-Segment
Q
3
Q
2
Q
1
Q
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
Decoding
Blank
Blank
Blank
Blank
Hook up
only
segments
b and c
to MSD
4–1
0–1
7–1
3–1
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.
NOTES: 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.
DS
1
DS
2
MULTIPLEXED
BCD
DS
1
DS
2
DS
3
DS
4
D
0
D
1
D
2
D
3
V
DD
POL 14042B
C
C
D
0
D
1
D
2
D
3
14042B POL
Q
0
Q
1
Q
2
Q
3
D
0
D
1
D
2
D
3
C
V
DD
POL 14175B
Q
0
Q
1
Q
2
Q
3
C
V
DD
D
0
D
1
D
2
D
3
POL 14042B
Q
0
Q
1
Q
2
Q
3
D
0
D
1
D
2
D
3
V
DD
POL 14175B
Q
0
Q
1
Q
2
Q
3
C
V
DD
C
C
D
0
D
1
D
2
D
3
14042B POL
Q
0
Q
1
Q
2
Q
3
D
0
D
1
D
2
D
3
POL 14175B
Q
0
Q
1
Q
2
Q
3
C
V
DD
Q
0
Q
1
Q
2
Q
3
D
0
D
1
D
2
D
3
V
DD
R
14175B
Q
0
Q
1
Q
2
Q
3
EOC
Figure 13. Demultiplexing for TC14433 BCD Data
3-134
TELCOM SEMICONDUCTOR, INC.
TELCOM [ TELCOM SEMICONDUCTOR, INC ]
