Star vs bus power routing in PCB Design - Formula Comparison Trace

Sample Data

This data shows current and voltage drop values for different loads connected using star and bus power routing methods in a PCB design.

Cell	Value
A1	Node
B1	Current (A)
C1	Voltage Drop (V)
D1	Routing Type
A2	Power Source
B2	10
C2	0
D2	Star
A3	Load 1
B3	3
C3	0.1
D3	Star
A4	Load 2
B4	4
C4	0.15
D4	Star
A5	Load 3
B5	3
C5	0.12
D5	Star
A6	Bus Total
B6	10
C6	0.35
D6	Bus

Formula Trace

Total Voltage Drop Star = SUM(C3:C5) Total Voltage Drop Bus = C6

Step 1: SUM(C3:C5)

Step 2: 0.1 + 0.15 + 0.12

Step 3: Total Voltage Drop Bus = C6

Cell Reference Map

    A          B          C          D
1 | Node     | Current  | Voltage  | Routing
2 | Power    | 10       | 0.00     | Star
3 | Load 1   | 3        | 0.10     | Star
4 | Load 2   | 4        | 0.15     | Star
5 | Load 3   | 3        | 0.12     | Star
6 | Bus Total| 10       | 0.35     | Bus

References:
- Voltage drops C3, C4, C5 used for star sum
- Voltage drop C6 used for bus

Cells C3 to C5 provide voltage drops for star routing loads. Cell C6 provides voltage drop for bus routing total.

Result

    A          B          C          D
1 | Node     | Current  | Voltage  | Routing
2 | Power    | 10       | 0.00     | Star
3 | Load 1   | 3        | 0.10     | Star
4 | Load 2   | 4        | 0.15     | Star
5 | Load 3   | 3        | 0.12     | Star
6 | Bus Total| 10       | 0.35     | Bus
7 | Total Voltage Drop Star: 0.37 V
8 | Total Voltage Drop Bus: 0.35 V

The total voltage drop for star routing is 0.37 V, calculated by summing individual loads. The bus routing voltage drop is 0.35 V, shown directly. This helps compare power routing methods.

Sheet Trace Quiz - 3 Questions

What is the total voltage drop for star routing?

A 0.10 V

B 0.35 V

C 0.37 V

D 0.12 V

Key Result

Sum of individual load voltage drops for star routing vs direct total voltage drop for bus routing

Practice

1. What is the main advantage of star power routing in PCB design?

easy

A. It is cheaper to manufacture than bus routing

B. It simplifies the layout by sharing one power line

C. It reduces noise by connecting power separately to each component

D. It increases voltage drop across components

Solution

1. Step 1: Understand star routing concept

   Star routing connects power from a single point directly to each component separately.

2. Step 2: Identify the benefit of separate connections

   This reduces electrical noise and interference between components.

3. Final Answer:

   It reduces noise by connecting power separately to each component -> Option C

4. Quick Check:

   Star routing = noise reduction [OK]

Hint: Star routing means separate power lines to reduce noise [OK]

Common Mistakes:

• Confusing star routing with bus routing
• Thinking bus routing reduces noise
• Assuming star routing is simpler to layout

2. Which of the following correctly describes bus power routing?

easy

A. It is used only for sensitive circuits

B. Each component has its own separate power line

C. It eliminates voltage drops completely

D. Power is shared on a single line among components

Solution

1. Step 1: Recall bus routing definition

   Bus routing shares one power line among multiple components.

2. Step 2: Identify the correct description

   This means power is distributed along a single line to all components.

3. Final Answer:

   Power is shared on a single line among components -> Option D

4. Quick Check:

   Bus routing = shared power line [OK]

Hint: Bus routing shares one power line for all components [OK]

Common Mistakes:

• Thinking bus routing uses separate lines
• Assuming bus routing removes voltage drops
• Confusing bus routing with star routing

3. Consider a PCB with 4 components powered by a bus routing line. If the voltage at the source is 5V and each component causes a 0.1V drop, what is the voltage at the last component?

medium

A. 4.6V

B. 4.7V

C. 5.4V

D. 5.0V

Solution

1. Step 1: Calculate total voltage drop

   Each component causes 0.1V drop, so total drop for 4 components = 0.1V * 4 = 0.4V.

2. Step 2: Subtract total drop from source voltage

   Voltage at last component = 5V - 0.4V = 4.6V.

3. Final Answer:

   4.6V -> Option A

4. Quick Check:

   5V - (4 * 0.1V) = 4.6V [OK]

Hint: Subtract total drops from source voltage for last component [OK]

Common Mistakes:

• Adding voltage drops instead of subtracting
• Multiplying voltage drop by wrong number of components
• Ignoring voltage drop in bus routing

4. A PCB designer used star routing but noticed unexpected voltage drops at some components. What is the most likely cause?

medium

A. The central power point has high resistance

B. Power lines were connected in a bus instead of star

C. Components were connected with separate power lines

D. Noise was reduced by star routing

Solution

1. Step 1: Understand star routing setup

   Star routing connects each component separately from a central power point.

2. Step 2: Identify cause of voltage drop in star routing

   If the central power point has high resistance, voltage drops can occur despite separate lines.

3. Final Answer:

   The central power point has high resistance -> Option A

4. Quick Check:

   High resistance at center causes voltage drop [OK]

Hint: Check central point resistance if star routing shows voltage drop [OK]

Common Mistakes:

• Confusing bus and star routing wiring
• Assuming separate lines always prevent voltage drop
• Ignoring resistance at power source

5. You are designing a sensitive analog circuit and a simple LED indicator circuit on the same PCB. Which power routing strategy should you use for each and why?

hard

A. Use bus routing for analog circuit to reduce voltage drop; star routing for LED to reduce noise

B. Use star routing for analog circuit to reduce noise; bus routing for LED to simplify layout

C. Use bus routing for both circuits to simplify design

D. Use star routing for both circuits to eliminate voltage drops

Solution

1. Step 1: Analyze requirements for analog circuit

   Sensitive analog circuits need low noise, so star routing is best to reduce interference.

2. Step 2: Analyze requirements for LED circuit

   LEDs are less sensitive and simpler, so bus routing is acceptable to simplify layout.

3. Final Answer:

   Use star routing for analog circuit to reduce noise; bus routing for LED to simplify layout -> Option B

4. Quick Check:

   Star for sensitive, bus for simple circuits [OK]

Hint: Star for sensitive, bus for simple circuits [OK]

Common Mistakes:

• Using bus routing for sensitive analog circuits
• Using star routing unnecessarily for simple LEDs
• Ignoring noise and layout complexity trade-offs