0.25 μm 1.2 MHz BOOST-PFM-CONTINUOUS triple mode LED driver integrated in analog front end IC for portable application

This paper proposes a triple mode LED driver integrated with 16bit level sensitive analog front end by 0.25 μm CMOS process for portable application. The LED driver needs to regulate single LED current with 0.9–3.6 V input voltage to support several types of battery. The output range is 2.5–4 V which requires voltage step-up and step-down. A step-up/step-down converter can do this with a lot complexity, more components, lower efficiency and requirement of high voltage switches which adds extra manufacture cost. Our proposed topology avoids complicated step-up/step-down topology. It has triple modes: Boost PWM mode, PFM mode, LDO mode to cover different input voltage range. The mode control is implemented by simple circuit and gives smooth mode transition and very stable LED current. The simple topology makes it possible to use two stack 3 V IO devices as internal power switch to tolerate max to 5.7 V. By careful design and layout, LED switching activity only degrades the 16bit level analog front end SNR by 1 dB.