In the DC circuit, more technically non-DC-DCs, which enables the electrical energy of the voltage value to another voltage value. The DC-DC converter module in the power supply is based on this technology, which simplifies the design of the circuit and shorten the development cycle of the product. After combining PWM, DC-DC can better control an analog circuit. So how can I better complete the design of the PWM DC-DC system?
The composition core circuit of the PWM DC-DC is divided into two parts, namely RAMP / PULSE OSCILLATOR and ERROR AMPLIFIER. The difficulty of Ramp / Pulse Oscillator is that a high linear Ramp Waveform, although it is not difficult, but the best is difficult. In order to maintain high linearity, it will add an additional compensation circuit to solve it.
ERROR AMPLIFIER, there are currently two compensation architectures of Type II and TYP III, and how to determine the R and C values in the Type II and Typeiii compensation circuitry, the overall DC-DC is required.
Error Amplifier seems simple, but the value of R and C will determine the stability and efficiency of the entire DC-DC system. Therefore, if you don't know the entire theoretical basis, it is very unwise to set the R and C value.
Before doing the DC-DC circuit, according to the range of Input Voltage, Output Voltage, ILOAD, the inductance, capacitance value, TYPE II or TYPE III compensation R and C values are calculated by the composing Excel. Use SIMPLIS simulation to verify before use spectré to simulate each sub-circuit. However, the time required to use SpecTre as analog is very long.
In the DC-DC circuit, the hardest PWM Error Amplifier, as long as R, C value is not decided, the entire system's Performance will be affected, and the constant adjustment will gradually draw a head, to set out R and C values really have to be familiar with the theoretical architecture of the entire PWM.
The PWM DC-DC GM cannot be too high or too low, but to match the system to use the Type II or Type III compensation network, L and C values and operating frequency. Therefore, the GM value is a specification calculated according to the system specifications, not the value of the free.
For ERROR AMPLIFIER, its consideration points are the three-order Filter of the external inductance, capacitance, and ESR, and then cooperate with the partial voltage resistance Gain, the PWM Gain, Error Amplifier itself Gain, Phase. Therefore, it is not high enough of the ERROR AMPLIFIER, and Phase Margin is wide enough. And to coordinate the entire Loop Gain and Phase to know how much Error Amplifier's Gain and Phase margin values, especially Phase Margin, PWM Stability determines the Phase Margin of Error Amplifier.
In addition errr amplifier, undoubtedly the most troublesome protection circuit, use a lot of protection circuit in the DC-DC circuit, such as the soft-start circuit, under voltage lock out, current liming circuit, thermal shut-down circuit, over current protection, ZERO CURRENT Protection, etc., each has different protection objects and conditions. Improper processing will cause the DC-DC system to be paralyzed, and each Protection mechanism has a distinction between priority, so these Protection Circuit is the most troublesome processed.
Most of the current systems will have two Switch Regulator in PWM and PFM. In normal PWM mode, if the system is power saving mode, it will enter PFM. This is because both PWM and PFM have its advantageous disadvantages under light / heavy load, and the past systems are almost only working under PWM. .
Most of the Metal Bus Width of Power Device is estimated by Average Current, but also carefully avoids the issue of too long of TRANSITENT Peak Current, and the time flowing. Because once the value of Transient Peak Current is too large, it is still possible to burn MEAL for a long time.
From the core circuit, this article gives the overall recommendations for the PWM DC-DC system design. I hope that after reading this article, you can have a further understanding of the system design of PWM DC-DC.
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