Contents
Why are input and output noise in buck converters important?
Abstract: Input and output noise in buck (step-down) converters can concern the system designer. This application note provides a theoretical explanation of the individual contributions of conducted noise on the input and output sides of buck converters. These equations will allow the power-supply designer to optimize components for noise immunity.
What are the components of a buck converter?
Single-Stage Filter Design A synchronous buck converter consists of an input capacitor CIN, two switches (S1 and S2) with their body diodes, an energy storage power inductor (L), and output capacitors (COUT). The input source provides energy to the power inductor (L) and the load when S1 is turned on and S2 is turned off.
What are the waveforms of a buck converter?
Shown are some typical waveforms for a buck converter. Graph A, I (L), shows the current waveform through the inductor. Graph B, I (CIN), shows the current flow through the input capacitor. Graph C, V (CIN1:1) shows the noise at the input of the converter that is due to the ESR of the input capacitor.
Which is the best capacitor for a buck converter?
A .01µF ceramic chip capacitor tends to be ideal in terms of capacitance and low inductance. In addition to placing the .01µF capacitors at the input of the buck converter, placing these capacitors close to sensitive circuits that use the V IN supply will greatly reduce the noise at these circuits.
When does discontinuous current flow occur in a buck converter?
Discontinuous current flow occurs when the current through the inductor tries to go negative (i.e., current flows out of the output capacitor and into ground), but gets clamped at zero. Discontinuous conduction typically, but not always, occurs under light-load conditions.
Why is my DC-DC buck converter unstable?
Cheaper converter chips may be internally compensated to save external parts, but make sure your Cout meets the min and max Cout ESR range in which they will be stable. Other explanations for instability may include bad voltage sense or summing node layout or noise.
What causes high frequency voltage drop in buck converter?
In ideal case, the input and output capacitors would be very low impedance for the buck converter switching currents. But in practice, capacitors will have ESR and ESL, which increases the capacitor impedance and results in extra high frequency voltage drop across the capacitor.