NEC mPD780208 Subseries User Manual page 327

By placing the above conditions in calculations <1> to <3>, the total dissipation can be worked out.
<1> CPU power dissipation: 5.5 V × 21.6 mA = 118.8 mW
<2> Output pin power dissipation:
Grid
Segment (V
<3> Pull-down resistor power dissipation:
Grid
Segment
Total power dissipation = <1> + <2> + <3> = 118.8 + 25.8 + 2.9 + 50.9 + 155.8 = 354.2 mW
In this example, the power dissipation problem is cleared because the total power dissipation does not exceed
the allowable total power dissipation rating shown in Figure 15-22.
CHAPTER 15 VFD CONTROLLER/DRIVER
Total current value of each grid
) ×
(V – V
DD OD
No. of grids + 1
15 mA × 11 grids
2 V ×
11 grids + 1
Total segment current value of illuminated dots
) ×
– V
DD OD
3 mA × 31 dots
0.4 V ×
11 grids + 1
2
(V – V )
OD LOAD
×
Pull-down resistor value No. of grids + 1
2
(5.5 V – 2 V – (–35 V))
×
25 kΩ 11 grids + 1
2
(V – V ) No. of illuminated dots
OD LOAD
×
Pull-down resistor value
2
(5.5 V – 0.4 V – (–35 V))
×
25 kΩ
User's Manual U11302EJ4V0UM
× Digit width (1 – Cut width) =
1
× (1 –
)
16
No. of grids + 1
1
× (1 –
)
16
No. of grids
× Digit width (1 – Cut width) =
11 grids 1
× (1 –
)
16
× Digit width (1 – Cut width) =
No. of grids + 1
31 dots 1
× (1 –
)
11 grids + 1 16
= 25.8 mW
× Digit width (1 – Cut width) =
= 2.9 mW
= 50.9 mW
= 155.8 mW
327