How to select power supply chip in PCB design?

When designing PCB, it is required to select DC/DC or LDO for power chip design.

1、 To put it simply, in the case of boosting, of course, only DC/DC can be used, because LDO is voltage drop type and cannot boost.

Selection of LDO

When the designed circuit has the following requirements for shunt power supply

1. High noise and ripple suppression;

2. Small PCB area, such as mobile phones and other handheld electronic products;

3. Inductors, such as mobile phones, are not allowed to be used for circuit power supply;

4. The power supply shall have the functions of instantaneous calibration and output state self-test;

5. The voltage regulator is required to have low voltage drop and low power consumption;

6. It is required that the line cost is low and the scheme is simple;

At this time, LDO is an appropriate choice to meet various requirements of product design.

2、 Furthermore, we need to look at their main characteristics:

DC/DC: high efficiency and high noise; The advantage is that the conversion efficiency is high and the current can be large, but the output interference is large and the volume is relatively large.

LDO: low noise, low static current; Small size, small interference, low conversion efficiency when the difference between input and output voltage is large

Therefore, if it is used in the case of large voltage drop, DC/DC is selected because of its high efficiency, while LDO will lose most of its efficiency due to large voltage drop;

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

LDO is a low dropout regulator, which means a low dropout linear regulator. It is relative to the traditional linear regulator. Traditional linear regulators, such as 78xx series chips, require the input voltage to be more than 2v~3V higher than the output voltage, otherwise they will not work normally. However, in some cases, such conditions are obviously too harsh, such as 5v to 3.3v, and the differential pressure between input and output is only 1.7v, which 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 resistor voltage divider to realize step-down. The energy loss is large, and the reduced voltage is converted into heat. The greater the step-down voltage difference and load current, the more obvious the chip heating. The package of such chips is relatively large, which is convenient for heat dissipation.

LDO linear step-down chip, such as 2596, L78 series, etc.

DC/DC buck chip: The energy loss is relatively small during the buck process, and the chip does not generate heat obviously. The chip package is small and can realize PWM digital control.

DC/DC buck chip, such as TPS5430/31, TPS75003, MAX1599/61, TPS61040/41

In general, when designing PCB, DCDC must be selected for boosting, DCDC or LDO must be selected for reducing voltage, and cost, efficiency, noise and performance must be compared. The key is specific application analysis.