TC7116 View Datasheet(PDF) - TelCom Semiconductor Inc => Microchip
Part Name
Description
Manufacturer
TC7116 Datasheet PDF : 14 Pages
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3-1/2 DIGIT ANALOG-TO-DIGITAL
CONVERTERS WITH HOLD
1 TC7116
TC7116A
TC7117
TC7117A
40
39
38
37
36
35
34
33
32
TC7116 31
TC7116A 30
TC7117 29
TC7117A 28
27
26
25
24
23
22
21
SET VREF = 1V
100 kΩ
100 pF
0.1 µF 25 kΩ
24 kΩ
1MΩ
0.047 µF
0.01 µF
470 kΩ
0.22 µF
TO DISPLAY
V+
+
IN
–
V–
40
39
38
37
36
35
34
33
32
TC7117 31
TC7117A 30
29
28
27
26
25
24
23
22
21
100 kΩ
SET VREF= 100 mV
100 pF
10 k Ω
0.1 pF 1 k Ω
1.2V
0.47 µF
0.01 µF
47 kΩ
10 kΩ
V+
TC9491CZM
+
1 MΩ
IN
–
0.22 µF
TO DISPLAY
2
3
4
Figure 15. Recommended Component Values for 2V Full Scale
(TC7116/TC7116A and TC7117/TC7117A)
Figure 16. TC7117/TC7117A Operated from Single +5V Supply
(An External Reference Must Be Used in This
Application.)
APPLICATIONS INFORMATION
The TC7117/TC7117A sink the LED display current,
causing heat to build up in the IC package. If the internal
voltage reference is used, the changing chip temperature
can cause the display to change reading. By reducing the
LED common anode voltage, the TC7117/TC7117A pack-
age power dissipation is reduced.
Figure 17 is a curve-tracer display showing the relation-
ship between output current and output voltage for typical
TC7117CPL/TC7117ACPL devices. Since a typical LED
has 1.8V across it at 8 mA and its common anode is
connected to +5V, the TC7117/TC7117A output is at 3.2V
(Point A, Figure 17). Maximum power dissipation is 8.1 mA
× 3.2V × 24 segments = 622 mW.
However, notice that once the TC7117/TC7117A's out-
put voltage is above 2V, the LED current is essentially
constant as output voltage increases. Reducing the output
voltage by 0.7V (Point B Figure 17) results in 7.7 mA of LED
current, only a 5% reduction. Maximum power dissipation is
now only 7.7 mA × 2.5V × 24 = 462 mW, a reduction of 26%.
An output voltage reduction of 1V (Point C) reduces LED
current by 10% (7.3 mA), but power dissipation by 38% (7.3
mA × 2.2V × 24 = 385 mW).
5 Reduced power dissipation is very easy to obtain.
Figure 18 shows two ways: Either a 5.1Ω, 1/4W resistor, or
a 1A diode placed in series with the display (but not in series
with the TC7117/TC7117A). The resistor reduces the
TC7117/TC7117A's output voltage (when all 24 segments
are ON) to Point C of Figure 17. When segments turn off, the
output voltage will increase. The diode, however, will result
in a relatively steady output voltage, around Point B.
6 In addition to limiting maximum power dissipation, the
resistor reduces change in power dissipation as the display
changes. The effect is caused by the fact that, as fewer
segments are ON, each ON output drops more voltage and
current. For the best case of six segments (a “111” display)
to worst case (a “1888” display), the resistor circuit will
change about 230 mW, while a circuit without the resistor will
change about 470 mW. Therefore, the resistor will reduce
7 the effect of display dissipation 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 display
brightness remaining steady is very important to the de-
signer, a diode may be used instead of the resistor.
TELCOM SEMICONDUCTOR, INC.
8
3-215
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