UPD78044F datasheet(38/74 Pages) RENESAS

38 / 74 page

mPD78042F, 78043F, 78044F, 78045F

The following total power consumption calculation example assumes the case where the characters shown in the

figure on the next page are displayed.

Example: The operating conditions are as follows:

VDD = 5 V ±10 %, operating at 5.0 MHz

Supply current (IDD) = 21.6 mA

Display outputs: 11 grids

¥ 10 segments (cut width is 1/16)

It is assumed that up to 15 mA flows to each grid pin, and that up to 3 mA flows to each segment pin.

It is also assumed that all display outputs are turned off at key scan timings.

Display output voltage: grid

VO3 = VDD – 2 V (Voltage drop of 2 V is assumed.)

segment

VO3 = VDD – 0.4 V (Voltage drop of 0.4 V is assumed.)

Voltage applied to fluorescent indication panel (VLOAD) = –30 V

Mask-option pull-down resistor = 25 k

Ω

The total power loss is calculated by determining power consumption

under the above

conditions.

Power consumption of CPU: 5.5 V

¥ 21.6 mA = 118.8 mW

Power consumption at output pins:

total current for all grids

Grid:

(VDD – VO3)

¥ digit width (1 – cut width) =

number of grids + 1

15 mA

¥ 11 grids

2 V

¥ (1 – 1/16) = 25.8 mW

11 grids + 1

total segment current for all dots to be lit

Segment: (VDD – VO3)

number of grids + 1

3 mA

¥ 31 dots

0.4 V

= 3.1 mW

11 grids + 1

Power consumption at pull-down resistors:

Grid:

(VO3 – VLOAD)2

number of grids

¥ digit width =

pull-down resistance

number of grids + 1

(5.5 V – 2 V – (–30 V))2

11 grids

¥ (1 – 1/16) = 38.6 mW

25 k

Ω

11 grids + 1

Segment:

(VO3 – VLOAD)2

number of dots to be lit

pull-down resistance

number of grids + 1

(5.5 V – 0.4 V – (–30 V))2

31 dots

= 127.3 mW

25 k

Ω

11 grids + 1

Total power consumption =

= 118.8 + 25.8 + 3.1 + 38.6 + 127.3 = 313.6 mW

In this example, the total power consumption does not exceed the rated value for the permissible total power loss

shown in the graph on the previous page. Therefore, the calculation result in this example (313.6 mW) satisfies the

requirement. If the total power consumption exceed the rated value for the permissible total power loss, the power

consumption must be reduced, by reducing the number of built-in pull-down resistors.

UPD78044F Datasheet(PDF) 38 Page - Renesas Technology Corp

UPD78044F Datasheet(HTML) 38 Page - Renesas Technology Corp

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