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Smart drive transfers processor tasks
The solution based on the ADP5520 smart backlight driver can obtain significant energy savings from the LED driver, which can work under the control of a microcontroller configuration or automatically manage the display lighting. The ADP5520 consists of a non-synchronous boost converter, a programmable ambient light management PCB circuit, a state machine and a configurable port expander that can further save system resources.
Boost converter can supply power to up to 6 white LEDs connected in series, the series voltage can be as high as 24.5V, and the drive current can be as high as 30mA. The ambient light measurement part provides all signal conditioning functions for the ambient light sensor, and together with the on-chip state machine and boost converter, it achieves a total of 128 current levels from 0 to 30 mA.
Because there is a processor that only performs light control services that are similar to the control curve, in a test that simulates the usage rate of various mobile phones, the ADP5520 can extend the working time of each charge by 15%. Adding the ambient light detection function to the ADP5520 control method can make the standby time per charge 50% longer than the reference measurement value. These curves simulate mobile interactive applications that do not require radio frequency capabilities, such as games, text and email message reading and writing, or camera applications.
Designers want their products to smoothly transition between different light levels, not just switching. The lighting scheme under the control of the processor requires a large number of processor interactions to achieve a smooth transition. Therefore, compared with simple switch control, this scheme greatly increases the load of the processor. Smart LED drivers, such as the ADP5520, can achieve a variety of fade-in and fade-out current changes, including linearity, square law, and cubic law, which can further reduce the processor load (Figure 2). This configurable driver has 15 discrete and independent fade-in and fade-out times, ranging from 300ms to 5.5s. There is a resettable dimming timer on the chip, which can be programmed to one of 15 time intervals from 10s to 120s.
Two wins: Smart drives provide additional low-bandwidth functions
In addition to energy saving, this smart driver can provide more value by implementing other low-bandwidth peripheral functions. For example, the ADP5520 integrates a configurable port expander, which provides 8 I/O pins.
Two I/O pins can also be connected to the third dedicated pin as an independent current sink pin for LED indicators with programmable dimming, switching and blinking control functions. The remaining pins are programmable and used for keyboard or general I/O.
These auxiliary LED drivers can consume 0-14mA current, and can fade in or fade out in 64 steps. Like the main backlight current consumption, the indicator connected to the auxiliary driver pin can switch the switch state, or realize light adjustment through a linear or non-linear sequence.
Smart driver can reduce the number of PCB traces
In order to allow configuration data to flow from the processor to the smart drive, and to allow status, I/O or keystroke data to flow back to the processor, the ADP5520 implements an I2C interface. This arrangement can reduce the number of devices and traces between the peripheral and the controller, thereby simplifying the PCB (printed PCB circuit board) design in high-density portable electronic equipment.
When a hinge or slider mechanism is used to separate the display, indicator, and keyboard from the processor, the energy saving effect will be more significant. In this case, a smart LED driver with an on-chip port expander can reduce the size and cost of the flexible PCB circuit connected to the other half of the product.
