The OK4418/6818 development board has a variety of power supply modes to choose from, but because it uses a single DC power supply, when the development board is used as a device, plugging and unplugging the O TG will cause the system to restart. Therefore, the Feiling baseboard chose to use an analog lithium battery for the design. Today, I will talk about my understanding of power inductors based on the inductor selection of the DCDC chip TPS5432 used in the OK4418/6818 development board.
As the power inductor on the DCDC circuit, it maintains a continuous current by accumulating and releasing energy in the circuit. Generally, the inductor value recommended by the DCDC chip specification should be used; the larger the inductance value, the smaller the ripple, but the size will increase; usually to increase the switching frequency, a small inductor can be used, but the increase in the switching frequency will increase the system loss and reduce the efficiency; The DCDC chip's specifications have recommended inductance values. As described in the TPS5432 chip manual.
Rated current: Power inductors generally have two rated currents, namely temperature rise current and saturation current; when current flows through the inductor, due to loss, the inductor heats up and generates temperature rise. The greater the current, the greater the temperature rise; Within the rated temperature range, the maximum allowable current is the temperature rise current.
Regarding the layout: In order to ensure the stability of the DCDC circuit, the following points need to be considered in the PCB layout
1. The freewheeling diode and input capacitor should be close to the IC and on the same layer, directly connected to the IC ground and switch. Prevent noise from wiring inductance;
2. If necessary, drill some heat dissipation holes;
3. The inductor is close to the IC to reduce the noise of the switching node;
4. The output capacitor is close to the inductor, not the input capacitor. Avoid the input high frequency noise from spreading to the output capacitor through the ground;
5. The loop wiring is far away from the noise area (inductance, diode) and the feedback end resistance is close to the IC. The detection voltage needs to collect the back-end voltage of the output capacitor, and the parallel resistance is as close to the line as possible;
6. No wiring is allowed under the inductor, and the copper skin close to the inductor is dug out. Prevent excessive consumption of inductance by the eddy current effect. For details, please refer to the related circuit layout of XX18 backplane.
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