An LED driver with active EMI mitigation scheme

Addressed in this paper is an active EMI mitigation scheme for the LED driver based on a switching DC-DC boost converter. The EMI mitigation scheme employs the pseudo-random frequency modulation such that the frequency spectrum of the switching clock of the LED driver is spread and the corresponding power spectral density is mitigated. Different from most of the solutions where either DSP or MCU are used, the EMI mitigation scheme is realized by a simple, on-chip mixed-signal circuit in which a 10^th-order LFSR is employed to generate pseudo random vectors for the pseudo-random PWM control. The four out of the ten bits of the LFSR are used for the control of the PWM. Thorough analysis is performed and the results show promising. The system is designed in the TSMC 0.35um CMOS process and will meet EMI standard for LED drivers without sacrificing the stability and the efficiency. The measurement results showed that the proposed mitigation scheme can reduce the EMI by 14 dB while maintaining a LED constant current of 120mA.