Datasheet

© 2008 Microchip Technology Inc. DS21455D-page 19
TC7106/A/TC7107/A
In addition to limiting maximum power dissipation, the
resistor reduces the change in power dissipation as the
display changes. This 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 will change about 230 mW, while
a circuit without the resistor will change about 470 mW.
Therefore, the resistor will reduce 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 designer, a diode may be used instead of the
resistor.
FIGURE 9-4: Diode or Resistor Limits
Package Power Dissipation.
TP2
TP5
100
k
Ω
TP1
24 k
Ω
1k Ω
0.1
µ F
TP3
0.01
µ F
+
IN
–
0.22
µ F
Display
Display
100 pF
+5V
1M
Ω
-5V
150
Ω
0.47
µ F
TC7107A
40
TP
4
30
21
20
101
47
k
Ω
1N4001
5.1
Ω
1/4W