PCB Tech - When designing PCB, how to choose power chip?

When designing PCB board, it is necessary to choose DC/DC or LDO for power supply chip design.

A, simply speaking, in boost occasions, of course, can only use DC/DC, because LDO is a pressure drop type, can not boost.

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

1. High noise and ripple suppression;

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

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

4. The power supply should have the function of instantaneous calibration and output state self-check;

5. Voltage regulator low voltage drop, low power consumption;

6. Low line cost and simple scheme are required;

At this time, LDO is the appropriate choice, and at the same time to meet the various requirements of product design.

Second, moreover, need to look at the main characteristics 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, the conversion efficiency is low.

Therefore, if it is used in the case of relatively 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 relatively small, choose LDO because of its low noise, clean power supply, and simple peripheral circuit, low cost.

LDO is the Low Dropout regulator, which stands for low-voltage differential linear regulator, as opposed to traditional linear regulators. Traditional linear voltage regulators, such as 78XX series of chips are required to input voltage than output voltage 2V ~3V above, otherwise it can 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, it is obviously not meet the conditions. In view of this situation, LDO type of power conversion chip.

LDO linear step-down chip: the principle is equivalent to a resistor voltage division to achieve step-down, the energy loss is large, the lowered voltage into heat, step-down voltage difference and load current is greater, the chip heating is more obvious. This kind of chip package is relatively large, easy to heat.

LDO linear buck chip such as: 2596, L78 series.

DC/DC buck chip: in the process of buck energy loss is relatively small, chip heating is not obvious. Chip package is relatively small, can realize PWM digital control.

DC/DC step-down chips such as TPS5430/31, TPS75003, MAX1599/61,TPS61040/41

In general, when designing PCB, DCDC must be chosen for boost voltage, and DCDC or LDO should be chosen for buck voltage. Cost, efficiency, noise and performance should be compared. The key is application-specific analysis.