Portable Device Information B
Integrated LDO and DC / DC regulator balance between efficiency and size of the program
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Phone's baseband processor to use the traditional LDO linear regulator power supply, the advantage of a variety of conditions, the output of the noise bias is low, fewer external components, small size, easy to use, disadvantage is low efficiency, but efficiency with chips group to reduce voltage drop. With the functions of cell phones increasing demand for power, designers are using DC / DC regulator to replace the LDO, in order to improve efficiency and maintain battery life. Although the DC / DC regulator provides an efficient alternative, but it is to be the ideal power management devices, need to address the size, noise and switching losses larger issues.
Fairchild Semiconductor Bruno Kranzen manager said that as the battery energy or capacity would be difficult with the rising power requirements, and therefore a smaller form factor to provide more efficient DC / DC conversion is a valid approach, in these systems There is a Switching DC / DC Regulators alternative to linear regulators trend. "
For example, Fairchild's high-speed switching DC / DC regulator FAN5350 switching frequency of 3MHz, designed for handheld applications core processors designed to power. ADI's ADP2102 is a 600mA, 3MHz step-down regulator, and micro-ceramic sensors and capacitors can still be co-existence of up to 93% efficiency.
ADI's director of marketing for portable power products Arcadio Leon, said: "improve the frequency can use smaller capacitors and inductors, thereby reducing the footprint area, but because of increased operating frequency also reduces the overall system efficiency, so the next challenge lies in the operating frequency and found between the shape factor of an ideal balance. "With the increase of switching frequency, DC / DC regulator efficiency benefits will be greatly reduced. 2MHz frequency DC / DC switching loss caused by total loss of 20%, but in the 8MHz frequency, switching losses to rise to 40%.
Clearly, a balance between efficiency, size and cost approach is a combination of switch-mode DC / DC regulator and LDO's new power management IC, they have the former high-efficiency, and the latter's small size and ease of use advantages.
For example, Micrel's recently announced power management IC MIC2800 provides three voltage output: a switch-mode DC / DC regulator output, two LDO outputs. On-chip 2MHz DC / DC regulator provides up to 600mA of current efficiency of 93% or more, just miniature 2.2 F output capacitor and a 2.2 H inductor to stabilize the voltage. The company's power products Ralf Muenster, director of markets and applications, for example, in the digital multimedia broadcasting (DMB) applications, the use of a LDO voltage of the lithium-ion battery is converted to 1.8V (for I / O power supply) and 1.2V (for core power supply), effective rates were 50% and 33%, while the use of integrated MIC2800 in the DC / DC regulator will be lithium-ion battery voltage down to 1.8V, the efficiency of 93%; and then integrated into the MIC2800 in the LDO will be 1.8V is converted to 1.2V, the efficiency of 66%. Other LDO provides a third output voltage, such as the RF voltage of 2.8V rail.
Micrel's director of power products markets and applications Ralf Muenster.
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ON Semiconductor's NCP1526 Dual-Output DC / DC regulators are also integrated 3MHz step-down switching regulator and LDO regulator for the digital multimedia broadcasting (DMB) chip set or a WLAN module in the digital core power supply circuits and RF circuits. This has a number of DC / DC regulator and the LDO output power subsystems will help resolve the clamshell or slider phone board layout, reduce the PMU to flip from the motherboard PCB power alignment, reduce the EMI issue.
ON Semiconductor Product Marketing Manager, Jia-Han also said that power management devices should not only significantly improve full load of work (the current benchmark of 90%), the power conversion efficiency, reduce the time needed to standby (the current benchmark for the 1uA) state of the energy consumption. For the DC / DC regulators, the technology development trends will be used more in the PWM mode and pulse mode (to replace the pure PWM mode) between automatic conversion in order to save power consumption under light load of work.
LED backlight and flash applications, the power demand
Almost all of the portable consumer electronics products are available in color LCD screen to display the users need different types of information and data. LCD's backlight is usually led by a white light to provide. In addition, many mobile phone also has a high resolution can capture still images and video images of the built-in digital cameras, camera performance improvements also had a right for the camera in indoor or dim ambient light conditions, the use of high-power white LED light source demand. These are spawned by a compact, efficient and low-noise way to serve the needs of those LED power supply.
White LED power supply ic usually charge pump and DC / DC regulators, the main difference between the two is the need for an inductor (magnetic components). For the low-load current must be provided in the space-constrained applications, the charge pump is an ideal choice because they use small-outline package, the required external components is very small. Most step-up DC / DC regulator is designed to provide a white LED backlighting for the efficient and designed for constant current drive.
"LED Power Supply IC technology trends is to integrate digital control interface to enhance operational flexibility, such as the LED backlight dimming control." Jia Han said. Semiconductor charge pump NCP5602/5612/5623 support multiple modes of voltage conversion, with a more optimized power conversion, and in lithium-ion battery peak efficiency in the initial stages of the work of up to 90%, the average efficiency of 85%. These devices are integrated into a digital control interface (single or I2C), to achieve LED dimming control. NCP5608 multi-mode charge pump LED drivers, both driving up to four LED in order to support the main screen and sub-screen backlight function, also provides high-current power supply, output current up to 400mA, to drive the 1W of the LED.
Linear Technology's LTC3208 is a non-inductors, high current, the software can be configured to multi-display | Display LED controller capable of driving 17 LED. The device contains a 1A high efficiency, low-noise charge pump may be the main sub-displays for mobile phones, a camera LED display and an LED display of the auxiliary power supply. Because the devices have up to 95% efficiency and an I2C serial interface.
"If you only need a small LED backlight panel can, if the 3.5-inch LCD screen will also need to bias. For small panel applications, LED drivers and can be integrated with the LCD bias, but for large panel applications, integrated LCD bias on the more difficult. "Hsin-Tsung Ho Lung said. TPS65120 converter for portable electronic devices to meet the lcd module all the necessary power requirements. Single-piece four output inductor DC / DC regulator for smart phones, PDA, portable DVD players, digital cameras and other portable applications in the amorphous silicon (a-Si) and low-temperature polysilicon (LTPS) displays provide bias power supply .
High-power LED flash brightness is to obtain high-quality pictures a factor. In some cases, the camera phone is used to drive the LED brightness by the high-power LED step-up DC / DC regulator efficiency limit. This is because the amount of current draw from the battery is limited, so high-efficiency LED would provide a higher power. Arcadio Leon that: At present, the new sensor-based lighting solutions, has a unique dynamic current management capabilities, which makes the system architecture engineers to maximize the supply of LED current, thus increasing the brightness and significantly improve the picture quality.
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ADI's ADP1653 is a dual-sensor-based high-power white LED driver, which can provide efficient than a single or low-intensity white led driver a higher camera flash, which makes them available in low-light conditions to achieve higher picture quality. ADP1653 peak efficiency of 92%, lithium-ion battery full voltage range of the typical efficiency is higher than 80%. Than the charge pump solution 40% efficiency, its efficiency is greatly improved.
The device uses a unique current management techniques, even in the battery to work simultaneously to multiple mobile phone functions (such as PA and LED flash) the case of electricity supply can be guaranteed picture quality. In order to reduce battery current overload, LED flash current is transmitted in the cell phone automatically adjust the RF signal, so that system design engineers to increase the LED drive current, do not have to worry about the system due to transient load the battery to shut down prematurely.
Linear Technology's LTC3454 is a camera designed for the high-current applications to optimize the efficiency of lighting, LED current control accuracy and designed products. LTC3454 is a synchronous buck - boost DC / DC regulator designed for the use of single-cell lithium-ion battery up to 1A of current to a single high power LED driver optimized. According to VIN and LED forward voltage, the device can be synchronous buck, synchronous boost and four-switch buck.