To minimize standby current, the new LDS8160 also features an additional low-power standby mode, where the supply voltage of the device is switched to 1.8V. The LDS8160 is controlled through a high-speed I2C interface. Targeted at mobile backlighting applications, the LDS8160 will support up to six white LEDs or up to two RGB LEDs, with a maximum current of 25mA per channel.
Mobile phones have evolved from voice-centric devices to multi-media platforms. Whereas before five years, the users would use their mobile phones primarily for voice communication, today users exchange text messages, read and write emails, share photos, connect to the Internet, record videos and activate integrated GPS-Navigation systems from their mobile phones. Consequently, the user expectations in terms of display-performance have increased. For example, users now expect excellent outdoor display readability, which is a challenge given the current required to drive the backlight unit to satisfactory display contrast and color saturation. One solution to this problem is to utilize RGB diodes in the backlight unit. These diodes require temperature compensation in order to keep their white color coordinates constant, a problem that the LDS8160 is designed to solve.
The new LDS8160 will offer superior temperature control through its proprietary LED-Sense Temperature Compensation engine. The existing solutions either place a sensor in the proximity of the LEDs, which increases cost and reduces the available footprint of the phone, or rely on measuring temperature only inside the LED driver chip, which can result in inaccurate current readings. The new LDS8160, however, measures the temperature of each LED at the diode itself. This in-situ measurement doubles the accuracy and does not require extra sensor components on the board. Every few seconds, the measured temperature is fed into Leadis’ proprietary compensation engine that adjusts the current on each LED channel in order to optimize luminosity, color saturation and to prevent system overheating. Sixteen I2C-programmable registers for each of 3 channel banks let users define the compensation curve as a function of the specific LED Diode used in the design.
The new LDS8160 will offer multiple advantages for designers of portable applications. For longer battery life, efficiency is increased up to 98% by the inclusion of the PowerLite Current Regulator and the exclusion of boosting circuits that are not needed with most of today LEDs. The ultra low dropout PowerLite Current Regulator provides a transition threshold of 25mV, allowing customers to adopt any LED with a Vf lower than 3.4V. For improved dynamic brightness control, three 12-bit logarithmic PWM generators are integrated on chip. These generators allow the customers to send a dimming command through the I2C interface without having to keep pulsing a PWM bus. This innovation dramatically will improve the power consumption of the system, especially if frequent dimming is required. The LDS8160 is offered in a tiny 3mm x 3mm 16-pin TQFN package and in an ultra small WCSP 3×4 ball grid package with 0.4mm pitch.
We are pleased to bring to the market our first LED Driver featuring our proprietary Temperature Sensing and Compensation Engine, said Donato Montanari, vice president and general manager at Leadis Technology. Whereas the LDS8160 is tailored specifically for the mobile market, our Temperature Sensing and Compensation Engine is an extremely accurate and flexible IP block that can be ported across different application markets. We are expecting to introduce temperature compensated devices for the notebooks market soon. With increasing customer demand for improved outdoor readability, the ability to control backlight unit temperature in a dynamic, accurate and fast manner gives mobile phone designers more flexibility in tackling this challenging problem.
About the LDS8160
The LDS8160 is a dual-output RGB or 6-channel white LED driver with three integrated temperature compensation circuits for each bank of two LED drivers. The new driver can support both RGB LED and WLED backlighting, keypad, and other lighting functions in portable applications. Three programmable, 8-bit DACs set the current level for each LED bank (A, B, & C) from 0 to 25mA in 0.125mA steps. Each channel contains a linear LDO current regulator (driver) in a common cathode (i.e., current source) topology. The LDO drivers have a typical dropout voltage of 25mV at maximum rated current. This will provide a low power/low EMI solution in Li-ion battery applications without voltage boosting and associated external capacitors and components. Three 12-bit PWM generators with smooth logarithmic control support Temperature versus LED Luminosity adjustments, as well as RGB color correction and dimming. These PWM generators are programmable via an I2C serial interface. The user programmed 8-bit codes are converted to 12-bit resolution logarithmic steps of ~0.17 dB per step. The PWM frequency is ~280 Hz to minimize noise generation.
