PCB Blog - Portable intelligent driver makes PCB board layout more orderly

Portable intelligent drivers make PCB board layout more orderly, small portable electronic systems have been constantly moving forward, such as mobile phones, PMP(personal media player), DSC(digital camera), DVC(digital camera), PME(portable medical equipment) and GPS(positioning system), functional features more than the next generation. As a result, the requirements of some peripheral circuits tend to be similar, because their power supplies, ports, and MMI(human-machine interface) all use similar technologies.

Three-level strategy for low-power full-function products
With the increase of functions and performance of portable systems, the demand for power management is also increasing. As a result, the strategies oems use to address power consumption are evolving. The first level of strategy focuses on the efficiency of the energy management subsystem, including minimizing losses on DC/DC converters, LDO, battery management, and battery protection circuits. This is a power subsystem-centric approach that largely depends on the ability of semiconductor suppliers to produce components and integrated devices that consume less power than devices with similar architectures on the market. This leaves the OEM engineer's primary task as component selection, balancing energy efficiency, component cost, and package size. While this strategy has worked well and the component market is aware of the benefits, most analog and mostly analog mixed signal IC vendors have not benefited significantly from the shrinking process size.

The focus of the second level strategy shifts from power supply to certain parts of the system, even those parts of large-scale ASics that are not working at certain times. This strategy is particularly effective when applied to high-power users such as wireless link hardware and display backlighting, and can extend the operating time per charge by turning off even low-power loads such as audio subsystems, I/O ports, or non-volatile configuration memory. Today's mobile phones, for example, have 20 or more power areas. In addition to saving on idle current in high-power circuits such as RF components and display backlights, this strategy can effectively reduce static power consumption as long as the system can turn off a clock-driven part of the circuit. With the development of IC manufacturing technology to ever smaller size, this strategy can effectively replace clock gating to achieve the purpose of reducing idle current. This power reduction strategy relies on the technical contributions of system architects, hardware and software implementers, and ASIC vendors. While this strategy was successful, it was also limited by the amount of load on the application processor, and these additional features forced designers to consume more and more powerful computing resources. For example, mobile phones have shifted from ARM7 to ARM9 and ARM11 processors as optional basebands and secondary processing resources. Other portable electronics have followed a similar trend, though to a lesser extent.

Level 3 strategies focus on reducing power consumption for various functions without sacrificing performance. One possible technique is to make use of distributed intelligent management, which does not require the powerful processing power and speed of the baseband or application processor. This strategy allows the processor to hand over all functionality to semi-automatic peripheral controllers. The result is a mode in which the processor can go to sleep during human activities rather than data processing or communication tasks that require the full power of the processor, such as the smart display backlit driver.

Backlight scheme under the third level strategy
Users of portable electronics require a screen display that is clearly visible in all ambient light conditions. Current portable devices often use photosensitive diodes or transistors to estimate ambient light intensity and use this as input for backlit driver control. Photosensitive sensors require signal conditioning circuits: excitation in the form of DC bias, amplification and analog-to-digital conversion or at least one or two threshold detection levels. Either through external components or analog I/O pins on the chip, the main processor usually monitors the output of the photosensitive sensor in the form of periodic data conversion. The speed of this conversion ranges from one to several orders of magnitude per second. The controller then evaluates the results and typically grades them into three categories, one for the whole day, for a well-lit indoor environment, or for a poorly lit environment. The processor does this by sending a control signal to a backlit driver, which provides one of three possible current levels to the LED string. But this is not efficient. In effect, this is a way of managing microprocessors: delegating tasks to a part of the system with a lower running cost, under the supervision of a central resource that is powerful and expensive to run. This does not seem to help processor task unload.

1. Intelligent driver transfers processor tasks
Solutions based on the ADP5520 smart Backlight driver derive significant energy savings from LED drivers that can operate under microcontroller configuration control or automatically manage display lighting. The ADP5520 consists of an asynchronous boost converter, a programmable ambient light management circuit, a state machine, and a configurable port extender to further save system resources. Boost converters can power up to six white leds in series, with series voltages up to 24.5V and driving currents up to 30mA. The ambient light measurement unit is divided into ambient light sensors to provide all signal conditioning functions, and together with the on-chip state machine and boost converter to achieve a total of 128 current levels from 0 to 30mA. With one processor performing only light control services similar to the control curve, the ADP5520 was able to increase the operating time per charge by 15% in tests simulating various mobile phone usage (Figure 1). The addition of ambient light detection to the ADP5520 control method resulted in 50% more standby time per charge than the baseline measurement. These curves simulate mobile interactive applications that do not require RF capabilities, such as games, text and email message reading and writing, or camera applications. The designers wanted their products to transition smoothly between different light levels, not just switch. The lighting scheme under processor control requires a large number of processor interactions to achieve smooth transitions, so it increases the load of the processor significantly compared to a simple on-off control. Intelligent LED drivers, such as the ADP5520, can achieve a variety of brightening and dimming current variations, including linear, square, and cubic laws, thus further reducing processor load (Figure 2). This configurable driver has 15 discontinuous and independent fade - out times ranging from 300ms to 5.5s. There is a resettable dimming timer on the chip, which can be programmed for one of 15 time intervals from 10s to 120s.

2. Smart drives provide additional low-bandwidth capabilities
In addition to saving energy, such smart drives can provide more value by enabling other low-bandwidth peripherals. For example, the ADP5520 integrates a configurable port extender that provides eight I/O pins. Two I/O pins can also be connected to a third dedicated pin as an independent current sink pin for LED indicators with programmable dimming, switching, and flicker controls. The remaining pins are programmable for keyboard or general I/O. These auxiliary LED drivers consume 0 to 14mA of current and can be dimmed or dimmed in 64 steps. As with the main backlight current consumption, the indicator connected to the auxiliary driver pin can be switched on or off, or light regulation can be achieved through linear or non-linear sequences.

3. The intelligent driver can reduce the number of PCB cables
To allow configuration data to flow from the processor to the smart drive and for status, I/O, or keystroke data to flow back to the processor, the ADP5520 implements an I2C interface. This setup reduces the number of devices and wires between peripherals and controllers, thus simplifying PCB board design in high-density portable electronic devices.