AN610 Datasheet, PDF (6/9 Pages) Vishay Siliconix – PolarPAK Solder Joint Reliability Based on Thermal Fatigue IPC-9701

AN610
POTENTIAL PROBLEMS CAUSED BY
NOISE IN A VIDEO SYSTEM
Because the typical application for the 24LC21 is in a
computer monitor where electronic noise is prevalent,
some precautions may need to be made in order for
this device (or any other CMOS device) to work prop-
erly. The diagram below (Figure 4) shows a filter circuit
that can be used to reduce the amount of noise seen
by the device on the SCL and VCLK pins.
FIGURE 4: RECOMMENDED FILTER CIRCUIT FOR MONITOR APPLICATIONS
VCC
CBP
VCLK
24LC21
SCL
RPD
CS
RS
CR1
VSYNC
RPU
CS
RS
SCL
CBP = 1 µF
RS = 100 - 300 Ω
RPD = 4.7 kΩ
CS = 100 - 1000 pF
RPU = 47 kΩ
CBP
Bypass capacitor
RPD
Can be as a termination resistor on VGA
cable. Also will discharge the series capaci-
tor going to the MCU and horizontal/Vertical
processor.
CS and RS on VCLK Acts as low pass filter to clean-up noise on
VSYNC line
CS and RS on SCL
Acts as low pass filter to clean-up noise and
dampen power transient spikes that may
cause accidental mode switching from
DDC1 to DDC2
RPU on SCL
Keeps SCL pulled high, although a high
enough value is used that the host will not
power the 24LC21. Lets the 24LC21 reset
when the monitor power is turned off
CR1
Eliminates undershoot on VSYNC
DS00610A-page 6
© 1995 Microchip Technology Inc.