This application note describes the selection considerations of output capacitors, based on load transient and output impedance of processors power rails. Presently, there are no specific tools available for non-Intel processor output capacitors selection in multiphase designs.
Presently, there are no specific tools available for non-Intel processor output capacitors selection in multiphase designs. In Part 1, the minimum required output capacitance to meet low repetitive rate load transient specifications is discussed.
The advancement of small size, high CV value, low-voltage MLCCs in commercial systems has raised concerns regarding insulation resistance, IR, degradation, and parametric failures in capacitors due to the migration of oxygen vacancies [3, 4].
Analytical and experimental results show that output capacitors selection is optimized for load transient and output impedance, to fulfill non-Intel processor requirements. D-CAP+ is a trademark of Texas Instruments. High-performance microprocessors require low voltage and high current voltage regulator modules(VRM).
Although Al e-caps have a larger volume and shorter lifespan, to improve the reliability of the entire switched-mode power supply system, it becomes necessary to choose the capacitors with higher rated ripple current, which also means an increase in volume. Therefore, the optimization design of bulk capacitors still poses significant challenges.
In most cases, designers commonly use empirical formulas [ 16 ], as Eq. (1), to design the bulk capacitor for low-power flyback converters based on the principle of keeping the output voltage ripple of rectifier below 20 %. (1) C bulk ≈ 1 μF / W u inrms = 176 V ∼ 264 V C bulk ≈ 2 ∼ 3 μF / W u inrms = 85 V ∼ 264 V