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What is the principle of selecting DC/DC or LDO for the power chip in the design of the PCBQuick?

What is the principle of selecting DC/DC or LDO for the power chip in the design of the PCBQuick?
Issue Time:2019-01-11
What is the principle of selecting DC/DC or LDO for the power chip in the design of the PCBQuick?
In PCB design, power chip design selection DC/DC or LDO is required.

First, simply speaking, in the booster occasions, of course, can only use DC/DC, because LDO is the pressure drop type, can not boost.
LDO's choice
When the designed circuit has the following requirements for the shunt power supply
1. High noise and ripple suppression;
2. Small area of PCB board, such as mobile phones and other handheld electronic products;
3. Inductors, such as mobile phones, are not allowed to be used in circuit power supply.
4. The power supply needs to have instantaneous calibration and output state self-check function;
5. Voltage regulator low pressure drop, low power consumption;
6. Low cost and simple scheme are required.

At this time, the choice of LDO is the most appropriate choice, while meeting the various requirements of product design.
Secondly, we need to look at the main features of each:

DC/DC: high efficiency, high noise; The advantage is high conversion efficiency, can be large current, but the output interference is large, the volume is relatively large.
LDO: low noise, low static current; Small volume, small interference, when the input and output voltage difference is large, conversion efficiency is low.

Therefore, if it is used in the case of large pressure drop, DC/DC is selected because of its high efficiency, while LDO will lose a large part of its efficiency due to large pressure drop.

If the voltage drop is small, choose LDO, because of its low noise, clean power supply, and the peripheral circuit is simple, low cost.

LDO is the low dropout regulator, which means the linear voltage regulator with low voltage difference, which is relative to the traditional linear voltage regulator. Traditional linear voltage regulators, such as the 78xx series chip are required to input voltage than the output voltage 2v~3V above, or it will not work properly. 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, obviously does not meet the conditions. In this case, there is a LDO class power conversion chip.

LDO linear step-down chip: the principle is equivalent to a resistance voltage to achieve step-down, large energy loss, the voltage down into heat, step-down voltage differential and load current, the larger the chip heating more obvious. The package of this kind of chip is relatively large, which is convenient for heat dissipation.

DC/DC step-down chip: in the step-down process, the energy loss is relatively small, and the chip does not generate significant heat. Chip package is relatively small, can achieve PWM digital control.

In general, when PCB design, DCDC must be selected for voltage boost, and DCDC or LDO should be selected for voltage reduction. Cost, efficiency, noise and performance should be compared. The key is to apply the specific analysis.
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