As portable products become increasingly smaller and thinner, higher demands are placed on power management chips, such as high integration, high reliability, low noise, interference resistance, and low power consumption. This article discusses various issues that need to be considered in the practical application of power supply design for portable products. Power supply design for portable products requires a system-level approach. When developing low-power products powered by batteries, such as mobile phones, MP3 players, PDAs, PMPs, and DSCs, an unreasonable power system design can affect the entire system architecture, product feature combinations, component selection, software design, and power distribution architecture. Similarly, system design should also consider saving battery energy. For example, processors in modern portable products typically have several different operating states, and a series of different energy-saving modes (idle, sleep, deep sleep, etc.) can reduce battery consumption. When the user's system does not require maximum processing power, the processor enters a low-power mode with lower power consumption. From the development trend of power management in portable products, the following issues need to be considered: 1. Power design must consider the entire system design, including cost, performance, and product time-to-market; 2. Portable products are becoming increasingly smaller and lighter, necessitating consideration of power system size and weight; 3. Power management chips should be selected with high integration, high reliability, low noise, strong anti-interference, and low power consumption, overcoming heat dissipation bottlenecks and extending battery life; 4. Using new power chips with advanced technologies in the design is a fundamental condition for ensuring product advancement and a perpetual pursuit in portable product power management. Commonly used power management chips in portable products include: low dropout regulators (LDOs), very low dropout regulators (VLDOs), DC/DC converters based on inductor energy storage (Buck, Boost, Buck-Boost converters), charge pumps based on capacitor energy storage, battery charging management chips, and lithium battery protection ICs. When selecting power management chips, the following should be considered: choose products from manufacturers with mature manufacturing processes and excellent quality; choose chips with high operating frequencies to reduce the application cost of peripheral circuits; choose chips with small packages to meet the size requirements of portable products; choose manufacturers with good technical support to facilitate the resolution of problems in application design; choose chips with complete product documentation, easy access to samples and demos, and large-scale supply; and choose chips with good cost performance. LDO linear low-dropout regulators are the simplest linear regulators. Due to their inherent DC-DC switching-free voltage conversion, they can only reduce the input voltage to a lower level. Their biggest drawback is in thermal management, as their conversion efficiency is approximately equal to the output voltage divided by the input voltage. Internally, the LDO's main current channel consists of a MOSFET and an overcurrent detection resistor. A Schottky diode provides reverse phase protection. The output voltage divider resistor provides feedback to control the MOSFET's current flow. The EN enable pin allows external control of its operating state. Internally, it also includes overcurrent protection, overtemperature protection, signal amplification, power-OK, and a reference source circuit. In effect, the LDO is a multi-circuit integrated system-on-a-chip (SoC). LDOs have an ESD > 4KV, while HBMs have an ESD > 8KV. Applying low-dropout regulators is as simple and convenient as three-terminal regulators; generally, adding a filter capacitor to both the input and output terminals is sufficient. The capacitor material significantly affects the filtering effect; low-ESR X7R & X5R ceramic capacitors must be selected. The key to LDO wiring design is reducing noise and ripple on the PCB. Proper wiring is a delicate process requiring skill and experience, and is one of the keys to successful product design. Figure 1 illustrates how to design the wiring circuit diagram, mastering the current return nodes to effectively control and reduce noise and ripple. Optimizing the wiring scheme is worth considering. [img=500,475]http://cms.cn50hz.com/files/RemoteFiles/20090204/576438001.jpg[/img] Figure 1: LDO wiring circuit scheme. If an LDO driving an image processor draws its input power from a nominal 3.6V lithium-ion battery and outputs 1.8V at 200mA, its conversion efficiency is only 50%. This generates heat in the phone and reduces battery life. While these drawbacks do exist for larger input-output voltage differences, the situation changes when the difference is smaller. For example, if the voltage is stepped down from 1.5V to 1.2V, the efficiency becomes 80%. When using a 1.5V mains supply and needing to step down to 1.2V to power the DSP core, switching regulators offer no significant advantage. In fact, switching regulators cannot be used to step down 1.5V to 1.2V because they cannot fully boost the MOSFETs (whether on-chip or off-chip). LDO regulators also cannot accomplish this task because their dropout is typically higher than 300mV. The ideal solution is a VLDO regulator with an input voltage range close to 1V, a dropout below 300mV, and an internal reference close to 0.5V. Such a VLDO regulator can easily step down the voltage from 1.5V to 1.2V with a conversion efficiency of 80%. Since the power stage at this voltage is typically around 100mA, a power loss of 30mW is acceptable. The output ripple of the VLDO can be less than 1mV P-P. Using the VLDO as a post-regulator for a buck switching regulator easily ensures low ripple. Switching DC/DC Buck-Buck Regulators Switching DC/DC buck-boost regulators are classified by function into Buck switching DC/DC buck regulators, Boost switching DC/DC boost regulators, and Buck-Boost switching DC/DC buck-boost regulators that automatically switch between buck and boost functions based on the lithium battery voltage, from 4.2V to 2.5V. When the input-output voltage difference is high, switching regulators avoid the efficiency problems of all linear regulators. They achieve efficiencies of up to 96% by using low-resistance switches and magnetic storage units, thus greatly reducing power losses during conversion. Buck switching DC/DC step-down regulators employ a constant-frequency, current-mode step-down architecture with integrated master (P-channel MOSFET) and synchronous (N-channel MOSFET) switches. The PWM-controlled oscillator frequency determines its efficiency and operating cost. Using a high-frequency DC/DC converter, such as those exceeding 2MHz, can significantly reduce the size and capacitance of external inductors and capacitors. The disadvantages of switching regulators are relatively minor and can usually be overcome with good design techniques. However, frequency leakage interference from inductors is difficult to avoid, and EMI radiation must be considered during application design. Figure 2 shows a Buck switching DC/DC application circuit design. Note the thick lines in the figure: these represent high-current paths; use high-quality, low-ESR X7R & X5R ceramic capacitors from Murata, Tayo-Yuden, TDK & AVX; and consider device cooling and heat dissipation when operating in high-temperature environments or under low supply voltage and high duty cycle conditions (such as step-down). Important notes: SW vs. L1 distance < 4mm; Cout vs. L1 distance < 4mm; the wires for SW, Vin, Vout, and GND must be thick and short. [img=500,241]http://cms.cn50hz.com/files/RemoteFiles/20090204/576438002.jpg[/img] Figure 2: Buck switching DC/DC application circuit design. To obtain a stable and low-noise high-frequency switching regulator, the PCB layout needs careful arrangement. All components must be close to the DC/DC converter. The PCB can be divided into several functional sections, as shown in Figure 3. 1. Keep the path between Vin and Vout, and keep Cin and Cout ground very short to reduce noise and interference; 2. The feedback components of R1, R2, and CF must be kept close to the VFB feedback pin to prevent noise; 3. Directly connect pin 2 to the negative terminals of Cin and Cout over a large area. Examples of DC/DC applications: 1. APS1006 powers MCU/DSP cores; 2. APS1006 is used in electronic mining lamps (Figure 3); 3. APS1046 powers 0.8-1.8" micro hard drives (Figure 4); 4. APS1006 and APS4070 are used in smartphones (Figure 5). [img=580,278]http://cms.cn50hz.com/files/RemoteFiles/20090204/576438003.jpg[/img] Figure 3: APS1006 used in electronic mining lamps. [img=500,233]http://cms.cn50hz.com/files/RemoteFiles/20090204/576438004.jpg[/img] Figure 4: APS1046 powered by 0.8-1.8" micro hard drives. [img=580,301]http://cms.cn50hz.com/files/RemoteFiles/20090204/576438005.jpg[/img] Figure 5: Application of APS1006 and APS4070 in Smartphones: Charge Pumps and Their Application Techniques Capacitive charge pumps achieve voltage boosting through a switching array, oscillator, logic circuit, and comparator controller, using capacitors to store energy. Charge pumps do not require inductors but do require external capacitors. Operating at higher frequencies, small ceramic capacitors (1μF) can be used, minimizing space requirements and reducing operating costs. Charge pumps can provide ±2 times the output voltage using only external capacitors. Their losses mainly come from the equivalent series resistance (ESR) of the capacitor and the RDS(ON) of the internal switching transistor. Charge pump converters do not use inductors, so their radiated EMI is negligible. Input noise can be filtered out with a small capacitor. Its output voltage is precisely preset during factory production, and its adjustment capability is achieved through an on-chip linear regulator at the back end. Therefore, the number of switching stages of the charge pump can be increased as needed during design to provide sufficient flexibility for the back-end regulator. Charge pumps are well-suited for portable applications. From an internal structure perspective, a capacitive charge pump is essentially a system-on-a-chip. A charge pump is a radiation-free, efficient boost device that uses capacitors as energy storage instead of inductors. When designing applications, attention must be paid to the impact of capacitor capacitance and material on output ripple. The capacitance of the external capacitor affects the output ripple; at a fixed operating frequency, too small a capacitance will increase the output ripple. The magnitude of the output ripple is related to the capacitor's dielectric material; the type of external capacitor material directly affects the output ripple. For the same charge pump, using capacitors of the same capacitance and size but different material types will result in different output ripple. At a fixed operating frequency and with the same capacitor capacitance, a superior dielectric material will effectively reduce ripple. Using low-ESR X7R & X5R ceramic capacitors is a good choice. LCD Modules (LCMs) are currently in high demand for consumer electronics (CPs), MP3/MP4 players, and PMPs. Within a limited PCB area, they need to house components such as LCD screens, digital camera lenses and flashes, and audio DACs. Therefore, they require small, multi-chip power modules (MCMs) to reduce the PCB area occupied by the power ICs. Furthermore, mobile phone products require these power ICs to have virtually no RF interference. Battery charging management chips and lithium battery protection ICs are also important. A lithium battery charging IC is a System-on-a-Chip (SoC), integrating over ten different ICs on a single chip, including a read-enable microcontroller, a 2x trickle charge controller, a current loop error amplifier, a voltage loop error amplifier, a voltage comparator, a temperature sensing comparator, a loop selector and multiplexer driver, a charging state logic controller, a state generator, a multiplexer, an LED signal generator, MOSFETs, a reference voltage, power-on reset, undervoltage lockout, and overcurrent/short-circuit protection. It is a highly integrated and intelligent chip. The intelligent charging process of lithium batteries is: trickle charging → constant current charging → constant voltage charging → voltage detection. Therefore, the key to circuit design is to achieve: sufficient protection, sufficient charging, automatic monitoring, and automatic control. The lithium battery protection circuit is packaged inside the lithium battery pack and consists of a lithium battery protection IC and two MOSFETs. In Figure 6, OD represents over-discharge control; OC represents over-charge control; P+ and P- are connected to the charger; B+ and B- are connected to the lithium battery. The simple working principle of the lithium battery protection circuit is as follows: In normal operation, both M1 and M2 are conducting; during overcharging, the OC pin of M2 changes from high potential to low potential, the circuit breaker closes, and charging is stopped, achieving overcharge protection; the charging current direction is P+ → -; during over-discharge, the OD pin of M1 changes from high potential to low potential, the circuit breaker closes, and charging and discharging are stopped, achieving over-discharge protection; the discharging current direction is P- → +. [img=500,315]http://cms.cn50hz.com/files/RemoteFiles/20090204/576438006.jpg[/img]Figure 6: Lithium battery protection circuit. The PCB board for the lithium battery protection circuit is very small, and the following must be noted during design: 1. MOSFETs should be placed as close as possible to B- and P-; 2. ESD protection capacitors should be placed as close as possible to P+ and P-; 3. The spacing between adjacent lines should be >0.25mm, and the spacing should be wider for lines carrying high current, and the ground line should be widened. [tr][/tr][td] [/td]