TC7107RCPL datasheet(19/34 Pages) MICROCHIP

19 / 34 page

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

TP1

24 k

0.1

µF

TP3

0.01

µF

–

0.22

µF

Display

100 pF

+5V

-5V

150

0.47

µF

TC7107A

1N4001

5.1

Ω 1/4W

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