PDA System Power Supply Design

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PDA System Power Supply Design [Copy link]

The power system of a PDA is one of the most important indicators related to the performance of the PDA , followed by the area and space occupied by the solution and the cost of implementation. For low-end PDAs or notebook products, cost is the most important issue for designers.

In this topic, we have designed several system power solutions for PDAs based on information provided by several semiconductor manufacturers for your reference. This solution can also be used in portable products.

First, let's study the power supply source of the PDA and possible output requirements. As shown in Figure 1, the left side of the dotted line is the external power supply terminal, and the right side is the PDA or portable device.

Figure 1

External power sources usually include AC adapters. On high-end PDAs , there is also a USB interface. When connected to a PC , the PDA can obtain power from the USB port. In addition to powering the device, it can also charge the battery. When two power sources are connected at the same time, the PDA must control which one to connect.

In the PDA system, there will be various peripherals depending on the designer's requirements, which require different operating voltages. In designs with high power management requirements, manageable control functions will be added to each power supply channel. The CPU and memory are indispensable parts of each PDA . The CPU power management usually uses the CPU 's own sleep, stop and other functions to save power. Faced with such complex requirements, each PDA requires the power system to provide more than two voltage sources. As the hardware functions increase, the special voltage requirements will also increase.

The usual design is to use a main DC-DC to provide a stable, high-current voltage source for the entire machine. All requirements different from this voltage are converted to the required voltage value using step-up or step-down devices, such as Step-Up/Down DC -DC or LDO . For example, the DC-DC in Figure 1 is connected to various voltage conversion devices to provide various voltages.

We can also separate the power supply of infrequently used peripherals from the main DC-DC . This is entirely up to the designer and the actual situation, and whether there are corresponding device support. The purpose of separation is to reduce the output power of the main DC-DC . For example, if we want to expand the application of PDA by adding modules, we do not want the main DC-DC to be the backup power of the modules when the modules are not used . We can add a DC-DC ( as shown in Figure 2 ) specifically for the modules or those infrequently used devices.

Figure 2

We can obtain devices that can meet this requirement from many semiconductor companies. Below we will introduce several practical devices for your reference.

Analogic Power Management IC integrates fast response buck converter and LDO

Advanced Analogic Technologies Incorporated has announced the launch of the latest addition to its SystemPower family of power management ICs , the AAT2505 , which combines an instantaneous 600mA step-down converter with an instantaneous 300mA low dropout (LDO) linear regulator to provide a highly compact solution for popular Global System for Mobile Communications (GSM) mobile phone applications.

　　" Power supplies supporting GSM handset baseband chipsets must reach full load within microseconds, " said Bill Weiss , product line director at Analog Logic . "By combining an instantaneous 600mA step-down converter with a 300mA LDO , the AAT2505 is a complete high-performance power solution for GSM handset baseband cores and input / outputs. In addition, the AAT2505 requires less than half the printed circuit board (PCB) area of discrete solutions, eliminating the need for the extensive PCB layout expenses associated with ' million-dollar ' power management units . "

　　The low RDS(ON) power switch integrated on the AAT2505 step-down converter extends battery life and mobile phone talk time by supporting power levels up to 98% . With an output voltage range from 0.6V to VIN , the 600mA converter also maintains a no-load quiescent current as low as 27μA . Its 1.4MHz switching frequency helps minimize the size and cost of external parts. Typically, the turn-on time is 150μs .

　　The LDO generates up to 300mA and has a separate input pin. Optimized to support the fast line / load transient requirements of GSM chipsets, the LDO has low quiescent current and a power-OK (POK) output function for signaling when the output voltage is in control .

　　The AAT2505 also adds internal soft-start, over-temperature and current limit protection.

　　AAT2505 is suitable for the following temperature ranges:-40℃To +85℃The device is available in a lead-free 12 -pin TDFN33 package and is priced at $ 1.14 in 1,000- unit quantities .