DC-DC converter circuit design must consider at least the following conditions:
6. Switching Frequency: fsw
Most commonly used switching frequencies are above 500kHz. There are also higher switching frequencies from 1.2M to 2M. Since the high frequency switching loss increases the IC heat dissipation design is better, so it is mainly concentrated on the products with low voltage input of 5V and small current. The switching frequency of DC-DC converters is related to the selection of inductors and capacitors. Other issues such as EMC and noise under light load are also related to it.
7. Feedback Voltage & output accuracy: Vref
The feedback voltage of the DC-DC converter should be compared with the internal reference voltage, and the external feedback voltage divider resistors should be used to output different voltages. The reference voltage of different products will be different, such as 0.6~0.8V, pay attention to adjust the feedback resistance when replacing. The feedback resistor should be selected with 1% accuracy, as long as it is selected according to the manufacturer's recommendation, generally do not choose too large, so as not to affect the stability.
The accuracy of the reference voltage affects the output accuracy. The common accuracy is below 2%, such as 1%~1.5%, and the cost of products with high accuracy will vary. Choose according to your needs.
8. Linear stability and load stability (line/load regulation):
The linear stability of the DC-DC converter reflects the input voltage change and the output voltage stability. The load stability reflects the output load change and the output voltage stability. Generally, 1% is required, and the maximum should not exceed 3%.
9. EN level:
The high and low levels of EN must meet the requirements of the DC-DC converter device specifications, and some ICs cannot exceed the specific voltage range; pay attention to timely shutdown when the resistor divides the voltage, and consider the maximum range of voltage fluctuations. Due to the need of timing control, this pin will increase the capacitance, in order to adjust the level and turn off the discharge, at the same time there must be resistance to ground.
10. Protection performance:
The DC-DC converter must have over-current protection OCP, over-heat protection OTP, etc., and the condition disappears and can be self-recovered after protection.
The DC-DC converter is required to have a soft start; thermal resistance and packaging; the operating temperature range should be able to cover high and low temperatures.
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