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November 2006 P2040A rev 1.3 LCD Panel EMI Reduction IC 4 of 9 Notice: The information in this document is subject to change without notice. Spread Spectrum Selection The Modulation Selection Table defines the possible spread spectrum options. The optimal setting should minimize system EMI to the fullest without affecting system performance. The spreading is described as a percentage deviation of the center frequency. (Note: The center frequency is the frequency of the external reference input on CLKIN, pin1). For example, P2040A is designed for high-resolution, flat panel applications and is able to support an XGA (1024 x 768) flat panel operating at 65MHz (FIN) clock speed. A spreading selection of MRA=0, SR1=1 and SR0=0 provides a percentage deviation of ±0.75% from FIN. This results in the frequency on ModOUT being swept from 64.51MHz to 65.49MHz at a modulation rate of 56.24KHz. Refer Modulation Selection Table. The example in the following illustration is a common EMI reduction method for a notebook LCD panel and has already been implemented by most of the leading OEM and mobile graphic accelerator manufacturers. Application Schematic for Mobile LCD Graphics Controllers Modulated 65MHz signal with ±0.75 deviation and modulation rate of 56.24KHz. This signal is connected back to the spread spectrum input pin (SSIN) of the graphics accelerator. 1 2 3 4 CLKIN MRA SR1 VSS SR0 5 6 7 8 SSON# ModOUT VDD 65MHz from graphics accelerator +3.3V 0.1µF P2040A Digital control for the SS enable or disable |
