In kinds of electronic devices, the DC-DC converter is a core part that converts the input DC voltage into the kinds of direct current voltages required by the device. DC-DC converters, especially those devices based on switching mode are widely used due to their high efficiency, small size, and small weight. However, it is not easy to design an excellent DC-DC power converter in the PCB. Layout, EMC electromagnetic shielding, working current, and thermal management all require careful consideration and fine adjustment.
1. Introduction of DC-DC converter applications
Introduction to DC-DC converter types
DC-DC converter is the core device for DC voltage conversion, including LDO and other types. Among them, the device implemented by switching mode is often called a DC-DC converter.
2. Working rule of DC-DC converter
The working rule of the DC-DC converter involves voltage conversion and regulation. This step is mainly achieved through the converter of the switching power supply. In general, the working principle of this converter can be divided into three main steps:
1)Filtering: When the mains power is turned on through the input power switch, it first passes through the rectifier electric circuit to become pulse-pulsating DC power, and then passes through the filter electric circuit to filter out the ripple and become a smooth DC power supply, which is supplied to the converter for conversion power.
Conversion: The DC-DC converter generates a certain pulse power through the input voltage through the power switch tube and the energy storage inductor, and then uses the pulse transformer and the rectifier filter electric circuit to get the corresponding output voltage. The voltage conversion is achieved by controlling the switching timing of the switch tube by PWM (pulse width modulation) or PFM (frequency modulation). In the switching power supply, the switching speed of the switch tube is very very very fast, normally completing the switching action within tens of microseconds.
2)Regulation: The steady of the output voltage is implemented through the feedback loop. Then, the conduction time of the switch tube will be reduced through PWM or PFM control, thereby reducing the average power output of the converter and achieving output voltage stability.
3. DC-DC converter layout and wiring suggestions
For the layout and wiring of the converter, you can download the chip datasheet from their original manufacturer’s website in advance, then design it according to the suggested layout and wiring.
But we still have some other suggestions and rules for layout as below:
1)The rule of closeness for the IC power source: For the shift power that provides voltage to the IC Chip. It should be placed as close as possible to the IC chip. This can avoid the low voltage output running too long, this will help reduce the voltage drop.
2)Avoid electromagnetic interference: The shift power supply works under high voltage and big current status, which may cause complex EMC（electromagnetic interference） problems. So sensitive components should be avoided around the DC-DC converter to reduce the impact of electromagnetic interference on the operation of the components.
3)Layout with the power IC chip as the central: When laying out the PCB or designing the PCB, the DC-DC converter IC chip should be organized as the central component. When laying out the input and output ends of the power filter. Ensure enough distance to prevent noise from coupling from the input to the output. The components should be arranged neatly and compactly on the PCB to reduce and make the lines and connections between the components.
When designing the PCB, the wiring process is very important. We have some suggestions and rules for wiring as below:
1) Avoid PCB lines designed in parallel: The input and output lines should be avoided in parallel, so it can reduce unnecessary EMC problems. It is very important when designing the PCB, especially for wiring the DC-DC converter PCB.
2) Big current lines processing rule: big current lines, such as common ground lines, and power input/output lines should be thickened as much as possible. It is very important when designing the PCB, especially for wiring the DC-DC converter PCB. This can reduce resistance and voltage drop for DC-DC converter PCB.
3) Stiffen the ground lines when designing the DC-DC converter PCB: It is very important when designing the PCB, especially for laying the PCB. Stiffen the ground lines between input and output to ensure current fastness, and the components reduce feedback coupling.
