Compiled version: V1.0
Comparison of LDO and DC/DC
According to the above description of LDO and DC/DC parameter selection
1. Comparison of advantages and disadvantages
LDO advantages: less peripheral components, simple circuit, low cost, fast load response, low output ripple and low noise.
DC/DC advantages: high conversion efficiency, wide input voltage range, support for buck and boost circuit design, high output current, high power.
LDO shortcomings: the conversion efficiency is lower than DC/DC, the input and output voltage difference cannot be too large, only the power supply step-down design can be carried out, the load cannot be too large, the current largest LDO is 8A (but there are many more to ensure that the 8A output limitation factor).
DC/DC disadvantages: many peripheral components, complex circuits, high cost, load response is slower than LDO, output ripple is larger than LDO, and switching noise is greater.
Generally, in order to improve the switching DC/DC accuracy, an LDO device is connected to the back end of the DC/DC device.
2. Reference conditions for selection
2.1 Conversion efficiency
If the circuit input voltage is very close to the output voltage, it is recommended to choose LDO devices for efficiency comparison.
The efficiency of the LDO is proportional to the difference between the input and output voltages. The smaller the difference, the higher the conversion efficiency.
However, if the difference between the input and output voltage is relatively large, it is recommended to use DC/DC devices for the following reasons:
The input current of the LDO is basically close to the output current. If the voltage drop difference is too large, the energy loss in the LDO is large, and the efficiency conversion is not high.
The advantages of DC/DC devices are high conversion efficiency, large output current, and low quiescent current.
2.2 Output voltage
Different power input is required in the circuit design, and the power chip also corresponds to different types of voltage output.
DC/DC devices have different output types and support different design circuits, such as boost, buck, buck-boost and other outputs, but LDO can only provide buck conversion.
In applications where the output voltage is required to be higher than the input voltage, or the negative output voltage needs to be converted from a positive input voltage, LDO is obviously not suitable.
2.3 Power noise
DC/DC devices require external inductors and filter capacitors to reduce noise. Compared with LDO, DC/DC devices have larger output pulsation and switching noise, and the cost is relatively high. LDO can estimate how much external signal affects the output signal from the PSRR value of the chip. Especially for noise-sensitive circuit applications, low power supply noise is critical.
2.4 Occupied board area
Generally, LDO devices require few peripheral components, usually only bypass capacitors, and the circuit design is relatively simple, and the area of the circuit board occupied is relatively small.
The peripheral components of DC/DC devices include filter capacitors, inductors and other devices. In addition, circuit design also needs to consider the maximum operating current of the inductor, the ESR of the capacitor under high-frequency switching and other circuit parameters.
So in terms of the selection of peripheral devices and circuit design, DC/DC devices are more load-bearing than LDOs, and the peripheral circuit system of DC/DC devices occupies a relatively large area of the circuit board.