2002 Microchip Technology Inc.
DS21455B-page 17
TC7106/A/TC7107/A
ments (a “111” display) to worst case (a “1888” display),
the resistor will change about 230mW, while a circuit
without the resistor will change about 470mW. There-
fore, the resistor will reduce the effect of display dissi-
pation on reference voltage drift by about 50%.
The change in LED brightness caused by the resistor is
almost unnoticeable as more segments turn off. If dis-
play brightness remaining steady is very important to
the designer, a diode may be used instead of the
resistor.
FIGURE 9-4:
DIODE OR RESISTOR
LIMITS PACKAGE POWER
DISSIPATION
10.0
TYPICAL APPLICATIONS
10.1
Liquid Crystal Display Sources
Several manufacturers supply standard LCDs to inter-
face with the TC7106A 3-1/2 digit analog-to-digital
converter.
Note:
Contact LCD manufacturer for full product listing and
specifications.
10.2
Light Emitting Diode Display
Sources
Several LED manufacturers supply seven segment
digits with and without decimal point annunciators for
the TC7107A.
10.3
Decimal Point and Annunciator
Drive
The TEST pin is connected to the internally generated
digital logic supply ground through a 500
resistor. The
TEST pin may be used as the negative supply for exter-
nal CMOS gate segment drivers. LCD display annunci-
ators for decimal points, low battery indication, or
function indication may be added without adding an
additional supply. No more than 1mA should be sup-
plied by the TEST pin; its potential is approximately 5V
below V+ (see Figure 10-1
).
FIGURE 10-1:
DECIMAL POINT DRIVE
USING TEST AS LOGIC
GROUND
Manufacturer
Address/Phone
Representative
Part Numbers*
Crystaloid
Electronics
5282 Hudson Dr.
Hudson, OH 44236
216-655-2429
C5335, H5535,
T5135, SX440
AND
720 Palomar Ave.
Sunnyvale, CA 94086
408-523-8200
FE 0201, 0701
FE 0203, 0701
FE 0501
Epson
3415 Kashikawa st.
Torrance, CA 90505
213-534-0360
LD-B709BZ
LD-H7992AZ
Hamlin, Inc.
612 E. Lake St.
Lake Mills, WI 53551
414-648-236100
3902, 3933, 3903
TP2
TP5
100
k
TP1
24k
1k
0.1
F
TP3
0.01
F
+
IN
–
0.22
F
Display
100
pF
+5V
1M
-5V
150
0.47
F
TC7107A
40
TP
4
30
21
20
10
1
47
k
1N4001
5.1
1/4W
Manufacturer
Address/Phone
Display
Hewlett-Packard
Components
640 Page Mill Rd.
Palo Alto, CA 94304
LED
AND
720 Palomar Ave.
Sunnyvale, CA 94086
408-523-8200
LED
TC7106A
BP
TEST
37
21
V+
GND
To LCD
Decimal
Point
To LCD
Decimal
Point
To LCD
Backplane
4049
TC7106A
Decimal
Point
Select
V+
TEST
GND
4030
BP