Portable power system design requirements
Portable Power Supply System-level Design Thinking requires in the Development of Battery-Powered Devices, such as cell phones, MP3 , PDA , PMP , DSC and other Low-Power products, if the Power System Design is unreasonable, IT Will affect the Structure of the Whole System, the Product of the combination of features, Component Selection, Software Design and Power distribution architecture. Similarly, in System Design, but also to Save Battery Power from the perspective of further consideration. For example, Processors are Portable, usually has several different Working conditions, through a Series of different Energy-Saving modes (Idle, Sleep, Deep Sleep, etc.) can reduce the consumption of Battery Capacity. That is, when the User does not need Maximum Processing Capacity of the System, the processor will consume less power into low-power mode.
From the development of portable power management products, trends, need to consider the following questions:
1 ) Start with Power Supply Design must cost, Performance and Time to Market designed to take into account the Whole System;
2 ) Thin Compact Portable products become more, IT is necessary to consider the Power System is Small, Light Weight problem;
3 ) Selection of Power Management Chip to High Integration, High Reliability, Low Noise, interference, Low Power, Breaking the Heat bottlenecks, extend Battery Life;
4 ) The Selection of new products with new Technology Power Chips, Power Chips in the new Program to the new Design is to ensure conditions for the Basic Advanced new products, Portable Power Management is the Eternal Pursuit.
Portable power management chip used
• Low Dropout Voltage Regulator ( LDO Linear Regulators )
LDO
VLDO ;
• Energy Storage INDUCTOR-based DC / DC Converters (Inductor Based Switching Regulators)
Buck
Boost
Buck-Boost ;
• Energy Storage capacitor-based Charge Pumps (Switched Capacitor Regulators) ; ;
• Battery Charge Management Battery Chargers;
• Lithium Battery protection Lithium Battery Protection;
Thinking power management chip select
• Selection of Mature Production Technology, excellent Quality Product Manufacturer;
• High-Frequency Chips used in order to reduce the cost of the cost of the Application of peripheral Circuits;
• use a Small Volume Chip package to Meet the Requirements of Portable products;
• Support a Good Selection of Manufacturers, Easy to solve the problem of Application Design;
• Complete Selection of Product Information, Samples and DEMO Application with Easy availability of Chips in large Numbers;
• Selection of Product Performance / Price ratio of Good Chips;
LDO Low Dropout Linear Regulator
LDO Linear Regulator Low Dropout Linear Regulator is the most Simple, because of its inherent DC Voltage Conversion without Switching, SO IT only can the INPUT Voltage Down to a Lower Voltage. Its Biggest drawback is that in the Thermal Management, is because its Conversion Efficiency approximately equal to the output divided by the INPUT Voltage Voltage value. For example, if a image Processor Driver LDO INPUT Lithium Battery Power from a single nominal 3.6V , the Current is 200mA output 1.8V voltage, then the conversion efficiency of only 50% , Therefore, the phone had some hot spots, and shorten the battery life. Although to a large input and output voltage difference, the existence of these weaknesses, but when the voltage difference is small, the situation is different. For example, if the voltage from 1.5V down to 1.2V , the efficiency becomes 80% .
When using 1.5V main power supply and the need to step-down to 1.2V for the DSP core power supply, the switching regulator to no obvious advantage. In fact, the switching regulator can not be used to 1.5V voltage down to 1.2V , because they can not completely improve MOSFET ( both in the chip or chip ) . Standard low-dropout (LDO) voltage regulator can not accomplish this task, because the pressure is usually higher than 300mV . The ideal solution is to use a very low dropout (VLDO) regulator , input voltage range close to 1V , the pressure is lower than 300mV , an internal reference close to 0.5V . This VLDO regulator can be easily voltage from 1.5V down to 1.2V , conversion efficiency of 80% . Because the power level of this voltage is typically 100mA or so, then 30mW of power loss is acceptable.VLDO output ripple can be less than 1mVP-P . Will VLDO as a step-down switching regulator can be easy after the regulator to ensure low ripple.
Switching DC / DC buck regulator
• When the voltage difference between input and output is high, the switching regulator to avoid all the linear regulator's efficiency. It is through the use of low-resistance switch and the magnetic storage unit by up to 96% efficiency, thus greatly reducing power loss during the conversion process.
• use a high switching frequency DC / DC can greatly reduce the external inductor and capacitor size and capacity, if more than 2MHz high switching frequency.
• disadvantages of small switching regulator can usually be overcome with good design techniques. However, the frequency of leakage inductor is more difficult to avoid interference, the design application of its EMI radiation to consider.
• Switching DC / DC buck regulator according to their functions into Buck Switching DC / DC step-down regulator, Boost switching DC / DC Boost Regulator and in accordance with lithium battery voltage from 4.2V down to 2.5 V can automatically switch buck-boost function of Buck-Boost Switching DC / DC buck regulators.
Charge pump ( Charge Pump )
Capacitive charge pump through the switch array and oscillator, logic circuit, comparing the voltage controller upgrade, using capacitors to store energy. Inductive charge pump is not required, but the need for external capacitors. Work at higher frequencies, so you can use small ceramic capacitors (1 μ F) , so that takes up minimal space, the use of low cost. External capacitor charge pump can only provide ± 2 times the output voltage. The loss mainly from the capacitors ESR ( equivalent series resistance ) and the internal switching transistor of the RDS ( ON ) . Inductive charge pump converter is not used, so the radiation EMI can be ignored. A small input capacitor noise filter available. It is when the output voltage is factory set to the precision , ability to adjust the back-end chip through the realization of the linear regulator, so the charge pump in the design of the switch may need to increase the charge-pump series, in order to provide back-end tuner enough space. Charge pump is very suitable for the design of portable applications. From the point of view the internal structure of capacitive charge pump , it is actually a system on a chip.
Linear regulator and switching regulator comparison
Linear regulator and switching regulator comparison can be clearly seen from the table below.

LDO 's internal structure
Figure 1 can be seen, LDO current main channel in its interior is a MOSFET over-current sense resistor plus a composition, Schottky diode for reverse protection resistor divider output fed back to control out MOSFET circulation current size, EN enable clients to control it from outside the working state, the internal also set overcurrent, over temperature protection, signal amplification, POWER-OK , reference and other circuits, in fact, LDO is a multi-integrated circuit SOC .LDO 's ESD4KV , HBM ESD8KV . Figure 2 shows examples of its application.

The internal structure of Figure 1LDO
Low Dropout Regulators (LDOs) of the application
LDO applications as easy as three-terminal regulator, usually in the inputs and outputs, plus a filter capacitor to each. Capacitor materials had a significant effect on the filtering effect, be sure to use low ESR of the X7R X5R ceramic capacitors.
On the low dropout regulator (LDOs) manufacturing process
• LDO LDO used in tandem, it is not a switch, nor pass a higher voltage than the output voltage;
Some LDO using bipolar transistors ( Bipolar ) process, fundamentally speaking, Bipolar and CMOS process there is no difference in function between the two, but there are some inherent differences between the performance and cost are different;

LDO wiring considerations: reducing noise and ripple
LDO wiring design points is to consider how to reduce PCB board noise and ripple, how to take a good line is a skills plus experience in the process of deliberately, is key to the success of design products. Figure 3 shows how to design routing circuit, the current return of the master node, effectively control and reduce noise and ripple.Optimal routing scheme is worth considering.Figure 4 illustrates the PCB board layout ( Layout ) design skills, the recommended cabling solutions to address the current return path leads to poor noise and ripple.

Optimal routing solution
Figure 3, the circuit layout programs take into account

Buck Switching DC / DC buck regulator internal structure
From Figure 5, the Buck switching DC / DC buck regulator topology, the internal point of view, this is a use of a constant frequency, current mode buck architecture with the main ( P -channel MOSFET ) and synchronous ( N -channel MOSFET ) switch.PWM -controlled oscillator frequency determined by its efficiency and the use of cost.

DC / DC application circuit design thinking

Figure 6 Buck Switching DC / DC circuit design applications
Figure 6 shows the Buck Switching DC / DC circuit design applications, you need to note some of the figure thick lines:
Thick line is the high-current channels;
Use MuRata, Tayo-Yuden, TDK AVX quality, low ESR of the X7R X5R ceramic capacitors;
In the application of environmental temperatures are high, or low supply voltage and high duty cycles (such as step-down) work, the section of the device to be considered a moderate heat.

Figure 7 shows the Buck Switching DC / DC application PCB design examples, special attention:
SW vs L1 distance of 4mm
Cout vs L1 distance of 4mm
SW , Vin , Vout , GND line to be chunky.
PCB board design elements
To get a stable and low noise operation of high-frequency switching regulators, arrangements need to be careful PCB layout of board, all the components necessary to close DC / DC , for the PCB board is divided into pieces by function, as shown.
1) maintain the pathway in Vin , Vout between, Cin , Cout earth is very short, to reduce noise and interference;
2 ) R1 , R2 and CF must be kept close to the feedback component VFB feedback pin to prevent noise;
3 ) a large area directly connected to 2 feet and Cin , Cout