What is LDO? LDO stands for low dropout regulator, which is a low dropout linear regulator. This is relative to the traditional linear regulator. Traditional linear regulators, such as 78XX series chips, require the input voltage to be at least 2V~3V higher than the output voltage, otherwise it will not work properly. LDO is low dropout regulator, which means low dropout linear regulator, which is relative to traditional linear regulator. For example, 78xx series chips require the input voltage to be higher than the output voltage by more than 2v~3V, otherwise they will not work normally.
But in some cases, such conditions are obviously too harsh, such as 5v to 3.3v, the pressure difference between input and output is only 1.7v, which obviously does not meet the conditions. In response to this situation, there is an LDO type power conversion chip. The quiescent current of the LDO can generally be very small, such as HT7550 and 7530, which can be several uA
DC-DC mainly includes buck (buck), boost (boost), buck-boost (buck-boost) (there are some evolved from these 3)
LDO has a problem in terms of efficiency, that is, its efficiency is approximately equal to the output voltage than the input voltage, so when the output voltage and the input voltage differ greatly, the efficiency is low.
The efficiency of DC-DC is relatively high. It can reach 96% under heavy load and over 80% under light load.
Generally speaking, the ripple of LDO is smaller than DC-DC.
If the voltage of 3.3V is required, what is the difference between the LDO implementation and the DCDC conversion implementation?
As mentioned above, with LDO, the input voltage cannot be lower than 3.3V. The DC-DC depends on what structure you use.
The specific use of LDO, DC-DC, or a combination of both depends on the specific application.
Just like the power management chip of a mobile phone, it uses all three types (LDO, DC-DC, and Charge pump) to provide voltage to different functional modules.
DC/DC and LDO difference and selection
In Electronic products, we often see DC/DC and LDO. What is the difference between them, how to choose in the design of electronic products and how to design to avoid Circuit design defects?
DC/DC is the conversion of a certain DC input voltage into another DC output voltage, and the common ones are boost (Boost), step-down (Buck), buck-boost and inverted structures. LDO is the abbreviation of low dropout voltage regulator, which is low dropout linear regulator. They all stabilize an input voltage to a certain voltage, and the LDO can only be used as a step-down output. Mainly pay attention to the following parameters when selecting the power chip:
1. Output voltage. The DC/DC output voltage can be adjusted by feedback resistance, and the LDO has two types of fixed output and adjustable output;
2. Input and output voltage difference. The input and output voltage difference is an important parameter of the LDO. The output current of the LDO is equal to the input current. The smaller the voltage difference, the smaller the internal power consumption of the chip and the higher the efficiency.
3. The maximum output current. Generally, the maximum output current of LDO is several hundred mA, while the maximum output current of DCDC is several A or more.
4. Input voltage. Different chips have different requirements for input.
5. Ripple/noise. The ripple/noise is worse than LDO due to the DC/DC working in the switch state, so when designing more sensitive circuits, try to choose LDO power supply.
6. Efficiency. If the input and output voltages are close, the LDO is relatively more efficient than the DC/DC. If the voltage difference is large, the DC/DC is selected. Because the output current of the LDO is basically the same as the input current, the voltage drop is too large, and the energy consumed on the LDO is too large. The efficiency is not high.
7. Cost and peripheral circuit. Compared with DCDC, the cost of LDO is lower, and the peripheral circuit is simple.
The above parameters need to be paid attention first during product design to avoid problems such as failure of the product to work, instability, and low efficiency after proofing or later. In reality, I did not read the chip specification carefully when I came into contact with the product design. The selected DC-DC was used as the first-stage voltage regulator and then the LDO voltage stabilized to power the entire system. The DC-DC input voltage is input by the battery, DC-DC The specification requires a minimum input voltage of 3.2V, and a minimum battery consumption of about 3.2V, causing some products to appear abnormal in the low-power state. When choosing a DC-DC chip, avoid getting close to sensitive weak signals, and avoid directly supplying power to such circuits.
The switching frequency of DC-DC operation should also be considered in the design, to avoid direct or indirect interference of the switching frequency to the signal through mixing. Under uncertainty, it is best to connect the synchronization signal SYNC to a controllable PWM to adjust the work in different The switching frequency.