L2042A Datasheet, PDF (3/10 Pages) Alliance Semiconductor Corporation – 2.5V LCD Panel Reduction IC

October 2003
rev 1.0
L2042A
Spread Spectrum
The Modulation Selection Table illustrates 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).
Example:
The L2042A is designed for high-resolution flat panel applications and is able to support panel frequencies from
30 to 75 MHz. For a 65MHz pixel clock frequency, a spreading selection of CP0=0 and CP1=1 and SR0=1 gives
a percentage deviation of TBD%. Refer Modulation Selection Table. This results in frequency on ModOUT being
swept from TBD to TBD MHz. This particular example (See figure below) given here is a common EMI reduction
method for notebook LCD panel and has already been implemented by most of the leading OEM and mobile
graphic accelerator manufacturers.
65 MHz from Graphics Accelerator
1 _CLKIN
2 _CP0
3 CP1
4 VSS
VDD ⁸
SR0 ⁷
ModOUT ⁶
0.1µF
SSON# 5
L2042A
Modulated 65MHz signal
with 1.5% deviation and
modulation rate of
50.77KHz. This signal is
connected back to the
spread spectrum input pin
(SSIN) of the graphics
accelerator
VDD
Digital control for SS
Enable or Disable
2.5V LCD Panel EMI Reduction IC
3 of 10