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Temperature compensating LED driver targets mobile phone backlights

Responding to the need to maximise display performance in today's multimedia enabled mobile phones, Leadis Technology has launched an LED driver that combines temperature control and current regulation features.

The LDS8160 integrates Leadis' LED-Sense Temperature Compensation engine and its patent-pending PowerLite current regulator ” the former monitors the in-situ temperature on each LED and independently optimises the LED current for best luminosity vs. temperature performance. The latter ensures a low drop out voltage on each LED channel of typically 25mV across the full operating current range.

According to Leadis, existing solutions for temperature control 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. In contrast, the LDS8160 measures the temperature of each LED at the diode itself, doubling the accuracy of the measurement and obviating the need for extra sensor components, it is claimed.

Every few seconds, the measured temperature is fed into the compensation engine, which adjusts the current on each LED channel in order to optimise luminosity, colour 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. Notably, RGB diodes require temperature compensation in order to keep their white colour coordinates constant, one of the key challenges that the LDS8160 is designed to solve.

Leadis says that the inclusion of a low dropout current regulator and the exclusion of boosting circuits within the LDS8160 contribute to an increase in battery efficiency of up to 98%. The 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 customers to send a dimming command through the I2C interface without having to keep 'pulsing' a PWM bus, a very power intensive option, especially if frequent dimming is required.

The LDS8160, which supports up to six white LEDs or up to two RGB LEDs, is available in a 3mm x 3mm 16-pin TQFN package and in an ultra small WCSP 3×4 ball grid package with 0.4mm pitch.

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