At present, there is a power management IC (PMIC), or power management unit (PMU), in most smartphones. It is a kind of special purpose integrated circuit, whose function is to manage the power supply for the main system. PMU undertakes most of the power supply tasks and some other unit functions, such as interface or audio. Some market leading analog semiconductor manufacturers provide customized, semi customized and / or standard devices of PMU. The structure of a power management IC example is shown in the figure.

 

 

 

1. Low pressure differential linear regulator

 

In most smart phones, 5-12 independent low-voltage differential linear regulators (LDOS) are generally used. Such a large number of LDOS does not mean that the same number of voltage specifications exist in the terminal, but because LDOS are also used as on / off switches with a certain PSRR to prevent noise coupling. Most of the LDOS are integrated in the PMU, but sometimes individual separated LDOS are used. This is mainly due to the layout / wiring of PCB, some special components (such as voltage controlled oscillator) are too sensitive to noise, or used to drive some non-standard units, such as integrated digital camera, etc.

 

For a long time, the 150maldo encapsulated in SOT-23 is the best choice for these discrete (separated) power supplies. At present, some of the latest IC products adopt new packaging, new submicron processing technology and advanced design scheme, which can provide higher performance with smaller size. Now we can get SOT-23 package of single 300maldo or two 150maldo devices, or micro SC-70 package of single 120almado, with standard version and ultra-low noise (RMS value 10 μ V, 85dbpsrr) version devices. In addition, the more advanced chip level package (UCSP ™) provides the smallest possible size, while QFN package allows the largest chip size to be installed in a 3mm × 3mm area plastic package, while providing higher heat transfer capability. QFN package can achieve higher current LDO, and more LDOS can be packaged in each package, which can contain 3-5 LDOS, which reduces the difference between the separation scheme and PMU.

 

Power management has increasingly become a strategic competitive advantage, especially in communication, computing and industrial applications. With the continuous development of FPGA and SOC, designers add a large number of mixed signal functions in the next generation of embedded systems, which can achieve system level performance that previously could not be matched.

 

                

 

 

2. Buck converter for processor core

 

LDO has the characteristics of simplicity and small size, and its main defect is low efficiency, especially when supplying power to low-voltage circuit. Due to the integration of PDA function or internet function in the new generation of smart phones, the data processing ability and computing ability of the processor are required to be more powerful. In order to reduce power consumption, the core voltage of the processor is constantly reduced from 1.8V to 0.9V. In order to reduce the battery loss, an efficient step-down converter should be used to power the processor core. The main factors to be considered in the design are low cost, small size, high efficiency, low static (standby) current and fast transient response. In order to solve these problems, we need not only rich experience in simulation design, but also some creative ability. At present, only a few leading analog semiconductor manufacturers are able to provide suitable, SOT-23 packaged, step-down converters with switching frequency above 1MHz, allowing selection of micro external inductors and capacitors.

 

 

 

3. Buck converter for RFPA

 

Buck converter is also used to drive CDMA RF power amplifier (PA), which dynamically adjusts the VCC power supply voltage of PA as the distance between terminal and base station changes. Considering the transmission probability density function, the buck converter can save 40-65ma battery current on average. The amount of current savings depends on the level of the output voltage, the characteristics of PA, and whether voice or data is sent in urban or suburban areas.

 

The design requires that the buck converter has the characteristics of very small size, low cost, low output ripple and high efficiency. Once again, the SOT-23 encapsulated converter becomes the preferred solution. In order to keep the voltage drop as low as possible, a separate low RDS (on) p-channel MOSFET is usually used, which is directly powered by the

 

Pool driven power amplifier. In order to further reduce the overall size, the latest buck converter integrates this additional FET.

Wendy
2019-11-26

 

 声明： Disclaimer: This article comes from individual, KRECO has the right of final interpretation.