tc7107a Microchip Technology Inc., tc7107a Datasheet - Page 18

• Manufacturer Part Number: tc7107a
• Description: 3-1/2 Digit Analog-to-digital Converters
• Manufacturer: Microchip Technology Inc.

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 seg-
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.
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:
Package Power Dissipation
DS21455C-page 18
TP5
40
100
kΩ
1
5.1Ω 1/4W
100
pF
1N4001
24kΩ
TP1
TP2
1kΩ
+5V
0.1
μF
1MΩ
TP3
TC7107A
+
10
Display
0.01
μF
Diode or Resistor Limits
IN
30
–
kΩ
0.47
47
μF
TP
0.22
4
μ F
-5V
Display
20
21
150Ω
© 2006 Microchip Technology Inc.