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Selecting an effective decoupling capacitor – KBA238436

Selecting an effective decoupling capacitor – KBA238436

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Question: Which decoupling capacitor is effective for flash memory?

Answer: To stabilize a device's VCC supply from power noise, take the usual precautions for supply rail decoupling. Each device in the system should decouple its VCC rail with appropriate capacitors close to the package supply connection. Many circuit examples use decoupling capacitors between 0.01 μF and 10 μF for this purpose.

The 10-μF decoupling capacitors are often used in low-frequency analog devices to decouple noise at tens of KHz. These capacitors are also used in logic ICs to decouple noise at tens of MHz. The actual capacitor will be an RLC series circuit with an Equivalent Series Inductance (ESL) and an Equivalent Series Resistance (ESR) component. To minimize the effects of these, Multilayer Ceramic Capacitors (MLCCs) with low ESL and ESR are used.

Depending on the power and load supplied, the appropriate decoupling capacitor capacitance and number should be selected; typically, two 0.1-µF 0402 MLCCs and/or two 1-µF 0402 MLCCs are placed. Infineon recommends using X7R or X5R capacitors with a voltage rating of at least twice the maximum VCCs.

Figure 1 shows an example of decoupling capacitors (C1, C2, C3) on flash power supply rails.


Figure 1 Decoupling capacitors on flash power supply rails