工具说明
走线宽度是设计人员指定的一项要求，以确保走线能够处理所需的电流容量。该工具根据以下设计规范计算走线宽度。Trace width is a requirement that designers specify to ensure that the trace can handle the required current capacity. This tool calculates the trace width based upon the following design specifications:
- 最大电流Max Current
- 迹线厚度Trace Thickness
- 最大期望温升Max Desired Temperature Rise
此工具还计算与跟踪相关的以下附加有价值信息。This tool also calculates the following additional valuable information related to the trace:
- 阻抗Resistance
- 压降Voltage Drop
- 线宽功耗Trace Power Dissipation
说明
该工具基于标准文档 [1] 中包含的公式和图表，计算传导给定电流所需的铜印刷电路板走线的厚度，同时保持走线本身的温升低于指定的输入值。
通过提供额外的输入参数（环境温度和走线长度），可以计算走线总温度、电阻、电压降和功耗（功率损耗）。
应该注意的是，由于通过空气对流散热，外部 PCB 层比内部层实现更好的热传递。反过来说，内部电介质不能很好地导热，这就解释了为什么内部走线比外部走线宽。
This tool, based on the formulas and graphs contained in the standard document [1], calculates the thickness of a copper printed circuit board trace required to conduct a given current, keeping the temperature increase of the trace itself below the specified input value.
By providing additional input parameters (ambient temperature and trace length), it is possible to calculate the trace total temperature, resistance, voltage drop and power dissipation (power loss).
It should be noted that external PCB layers achieve better heat transfer than internal layers, due to the heat dissipation through air convection. The other way around, internal dielectric does not conduct heat very well and that explains why internal traces are wider than external traces.
线宽计算
First, calculate the area according to the following formula:
A = (I / (k * TRISEb))1/c (I)
Then, calculate the trace width:
W = A / (T * 1.378 [mils/oz/ft2]) (II)
Where:
A is the cross-section area [mils2], I is the maximum current [A], TRISE is the maximum desired temperature rise [°C], W is the trace width [mils], T is the trace thickness [oz/ft2], k, b and c are constants. According to IPC-2221A Par. 6.2 (“Conductive Material Requirements”), their values for inner layers are as follows: k = 0.048 b = 0.44 c = 0.725
Equation (II) is based on a curve fit to the charts provided in [1] (par. 6.2, Figure B and Figure C).
Trace temperature calculation
The overall trace temperature can be calculated as follows
TTEMP = TRISE + TAMB
Where:
TTEMP is the trace temperature [°C], TRISE is the maximum desired temperature rise [°C], TAMB is the ambient temperature [°C].
Resistance calculation
First, convert the cross-section area from [mils2] to [cm2]:
A’ = A * 2.54 * 2.54 * 10-6
Then, calculate the resistance:
R = (ρ * L / A’) * (1 + α * (TTEMP – 25 °C))
Where:
T is the trace thickness [oz/ft2], W is the trace width [mils], R is the resistance [Ω], ρ is the resistivity parameter, whose value for copper is 1.7E-6 [Ω · cm], L is the trace length [cm], α is the resistivity temperature coefficient, whose value for copper is 3.9E-3 [1/°C], TTEMP is the trace temperature [°C]
Voltage drop calculation
Voltage drop can be calculated as follows:
VDROP = I * R
Where:
VDROP is the voltage drop [V] I is the maximum current [A] R is the resistance [Ω]
Power dissipation calculation
Power dissipation, or power loss, can be calculated according to the following formula:
PLOSS = R * I2
Where: PLOSS is the power loss [W], R is the resistance [Ω], I is the maximum current [A]
Example 1
Inputs
I = 10 A
T = 2 mil
TRISE = 20 °C
TAMB = 25 °C
L = 10 inch
Output
Cross-section Area = 256.27 mils2
Trace Width = 128.13 mil
Additional output
Trace Temperature = 45 °C
Resistance = 0.0282 Ω
Voltage Drop = 0.282 V
Power Dissipation = 2.82 W
Example 2
Inputs
I = 8 A
T = 3 oz/ft2
TRISE = 86 °F
TAMB = 27 °C
L = 10 inch
Output
Cross-section Area = 147.29 mils2
Trace Width = 35.63 mil
Additional output
Trace Temperature = 57 °C
Resistance = 0.0511 Ω
Voltage Drop = 0.409 V
Power Dissipation = 3.27
Reference
[1] IPC-2221A “Generic Standard on Printed Board Design”
