It should be understood that the DC-DC means that DC changes (to) DC (transitions of different DC power values), as long as this definition can be called DC-DC converters, including LDO. However, the general statement is to call DC-DC to DC Change (to) DC by switching mode.
1 What is LDO
LDO is the meaning of low voltage drop. This is a paragraph: low pressure drop (LDO) linear regulator is low, low noise, low static current, which is its prominent advantage. The external components it need are very small, usually only one or two bypass capacitors. The new LDO linear regulator can reach the following indicators: output noise 30μV, PSRR is 60dB, and the quadrant current is 6μA, and the voltage drop is only 100mV. The performance of the LDO linear regulator can achieve this level. The main reason is that the adjustment tube is used with a P-channel MOSFET, while the normal linear regulator is using a PNP transistor. The P-channel MOSFET is a voltage driven. It does not require a current, which greatly reduces the current consumption of the device itself; on the other hand, in the circuit of the PNP transistor, in order to prevent the PNP transistor from entering the saturation state, the output capacity, input, and output The voltage drop can not be too low; and the voltage drop on the P-channel MOSFET is generally equal to the product of the output current and the on-resistance. Since the on-resistance of the MOSFET is small, it is very low above.
If the input voltage and the output voltage are close, it is best to use the LDO regulator to achieve high efficiency. Therefore, most of the LDO regulator is selected in applications that convert the lithium ion battery voltage to 3V output voltage. Although the energy of the battery is not used by 10%, the LDO regulator can still ensure that the battery has a long working time and the noise is low.
If the input voltage and output voltage are not very close, it is necessary to consider the switch type DC-DC. It should be understood from the principle that the input current of the LDO is substantially equal to the output current, if the pressure drop is too large, consumption Energy is too large in LDO, not high efficiency.
2 What is DC-DC
The DC-DC converters include boost, buck, liter / buck, and reverse phase. The advantage of the DC-DC converter is that the efficiency is high, and the large current can be output, the static current is small. As integration improves, many new DC-DC converters require only several external sensors and filter capacitors. However, the output pulsation and switching noise of such power controllers is relatively high.
In recent years, with the development of semiconductor technology, surface-mounted inductors, capacitors, and high-intensive power control chips have been reduced, and the volume is getting smaller. Since the MOSFET with a small on-resistance can output a lot of power, there is no need to externally high power FET. For example, for 3V input voltages, the output of 5V / 2A can be obtained by using the NFET on the chip. Second, for medium and small power applications, cost low-small packaging can be used. In addition, if the switching frequency is increased to 1 MHz, it is also possible to reduce costs, which can be used in size inductors and capacitors. Some new devices also add a number of new features such as soft start, current limiting, PFM, or PWM mode.
In general, boosting is to select DC-DC, buck, is to choose DC-DC or LDO, to compare cost, efficiency, noise, and performance.
3 LDO compared to DC-DC
First, in terms of efficiency, the efficiency of DC-DC is generally much higher than LDO, which is determined by its working principle.
Second, DC-DC has Boost, Buck, Boost / Buck, (someone collects Charge Pump into such a class). And LDO is only buck.
Again, it is also very important, DC-DC causes its power supply noise because of its switching frequency, far more than LDO, you can pay attention to PSRR parameters. So when considering a relatively sensitive analog circuit, it is possible to sacrifice the efficiency to ensure the purity of the power supply to select LDO.
Also, usually the peripherals needed by LDO, small area, and DC-DC generally require inductors, diodes, large capacitors, and some will have MOSFET, especially Boost circuits, and need to consider the maximum operating current of the inductance. The reverse recovery time of the diode, the ESR, etc. of the large capacitance, so the selection of the peripheral device is complicated than the LDO, and the area is also a lot.
Original link: https://www.eeboard.com/news/ldo/
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