Decoupling Capacitor for a PCB Track

In summary, the conversation is about reducing the voltage to 1 LSB using capacitance across X1/Q1. The voltage of 1 LSB is calculated to be 0.8507 mV and the voltage across the PCB track is 10 + 64pi mV. The capacitance can be calculated using the equation C = I/(Vripple x f) or by calculating the parallel impedance of the PCB track with a capacitor. The value of C needed for the voltage to be less than 0.8507 mV with 100 mA is 37uF.
  • #1
Weaver
70
6

Homework Statement


Q1.jpg

Q2.jpg

Homework Equations


3. The Attempt at a Solution [/B]
Currently stuck on the question relating to the value of capacitance across X1/Q1 to reduce the voltage to 1 LSB

I have calculated the voltage of the 1LSB to be 0.8507 mV

ADC Range/Resolution 3.3V/2^12

I have also calculated the voltage across the PCB track to be 10 + 64pi mV

Z = 0.1 + j2pi(1.6 x 10^6)(0.2 x 10^-6)
= 0.1 + j16/25 pi

V = IZ
V = (100 x 10^-3)(0.1) + j16/25 pi)
V = 10 + j64pi mV

For the capacitance, can I just used an equation I have seen before,

C = I/(Vripple x f)

with Vripple as 0.8507 mV
or

Do I have to calculate the parallel impedance of a the PCB track with a capacitor and find a value for C such that the magnitude of the voltage with 100 mA is less than 0.8507 mV?
 

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  • #2
C=(Iripple*Ton)/Vmax=0.1A*(1/3.2)*1us/0.85mV=37uF
 
  • #3
trurle said:
C=(Iripple*Ton)/Vmax=0.1A*(1/3.2)*1us/0.85mV=37uF

Great! Thank you very much!
 

Related to Decoupling Capacitor for a PCB Track

1. What is the purpose of a decoupling capacitor for a PCB track?

A decoupling capacitor is used in electronic circuits to reduce noise and improve the stability of the power supply. It acts as a temporary energy storage device, providing a stable voltage to the circuit and preventing fluctuations or spikes in the power supply from affecting the performance of the circuit.

2. How does a decoupling capacitor work?

When a PCB track experiences a sudden increase or decrease in current, the decoupling capacitor absorbs the excess energy and releases it back into the circuit when needed. This helps to maintain a steady voltage and prevent voltage drops and fluctuations, which can cause malfunctions or damage to the circuit.

3. How do I choose the right decoupling capacitor for a PCB track?

The size and capacitance of the decoupling capacitor will depend on the specific needs and requirements of the circuit. Factors such as the maximum current and frequency of the circuit should be considered when selecting a decoupling capacitor. It is recommended to consult with a professional or refer to the circuit's specifications for guidance.

4. Where should a decoupling capacitor be placed on a PCB track?

A decoupling capacitor should be placed as close as possible to the power supply and the circuit it is protecting. Placing the capacitor near the power supply reduces the length of the PCB track and minimizes the inductance, which increases the effectiveness of the capacitor in reducing noise and voltage fluctuations.

5. Can multiple decoupling capacitors be used for a single PCB track?

Yes, multiple decoupling capacitors can be used for a single PCB track, especially in high-frequency circuits. Placing multiple capacitors with different capacitance values in parallel can provide a wider range of noise reduction and better stability for the circuit. However, care should be taken to ensure that the capacitors do not interfere with each other and cause disruptions in the circuit.

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