參數(shù)資料
型號(hào)： μPD78P0208
廠商： NEC Corp.
英文描述： 8 Bit Single Chip Microcontrollers(8位單片微控制器)
中文描述： 8位單片機(jī)微控制器（8位單片微控制器）
文件頁(yè)數(shù)： 32/72頁(yè)
文件大小： 424K
代理商： ΜPD78P0208
32
m
PD78P0208
How to calculate total power dissipation
The total power dissipation of the μPD78P0208GF is the sum of the values at the following three parts. Design
your application set so that the sum is lower than the total power dissipation P
T
. (The recommended operating
condition is 80% or lower of the rated value.)
<1>
CPU: the power consumed by CPU and calculated with V
DD
(max.)
￥
I
DD1
(max.)
<2>
Output pins: the power consumption when the maximum current flows at all output pins (normal output and
display output).
<3>
Pull-down resistors: the power dissipated at the on-chip pull-down resistors connected to display output
pins
The calculation example of the total power dissipation is provided below. The following total power dissipation
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:
V
DD
= 5 V ±10%, operating at 5.0 MHz
Supply current (I
DD1
) = 21.6 mA
FIP 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
V
OD
= V
DD
– 2 V (Voltage drop of 2 V is assumed.)
segment V
OD
= V
DD
– 0.4 V (Voltage drop of 0.4 V is assumed.)
Voltage applied to fluorescent indication panel (V
LOAD
) = –35 V
On-chip pull-down resistor = 25 ky
<1>
Power consumption of CPU: 5.5 V
￥
21.6 mA = 118.8 mW
<2>
Power consumption at output pins
11 grids
12 timings
Grid:
2 V
￥
15 mA
￥
￥
(1 – 1/16) = 25.8 mW
31 segments
12 timings
Segment:0.4 V
￥
3mA
￥
￥
(1 – 1/16) = 2.9 mW
<3>
Power consumption at pull-down resistors
Grid:
(35 V + (5.5 V – 2 V))
2
￥
￥
(1 – 1/16) = 50.9 mW
25 k
W
12 timings
(35 V + (5.5 V – 0.4 V))
2
31 segments
￥
(1 – 1/16) = 155.8 mW
25 k
W
12 timings
11 grids
Segment:
Total power dissipation =
<1>
+
<2>
+
<3>
= 118.8 + 2.9 + 25.8 + 155.8 + 50.9 = 354.2 mW ( < P
T
= 600 mW)
According to the graph shown on the previous page,the total power dissipation in the temperature range
of T
A
= –40 to +85 °C must be lower than 600 mW. Therefore, the calculation result in this example
(354.2 mW) satisfies the requirement. If the calculation result for the total power dissipation becomes
higher than the rated value, the power consumption must be reduced.
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