SSD1811_ Просмотр технического описания (PDF) - Solomon Systech
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SSD1811_ Datasheet PDF : 14 Pages
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APPLICATION NOTE 5: VF PROTECTION
FOR POTENTIAL HIGH RF INTERFERENCE SITUATIONS
There are situations when the design of the LCD driver circuits is in close proximity with the RF components/circuits,
and noise generated from the RF circuit, will potentially affect the general performance of the LCD. There are cases
where interference may cause distortion to VF circuit operation, thus it may have an unexpected effect on the LCD dis-
play.
Function of the VF circuit: Circuit design which is using external resistor network (IRS pulled low), the VF pin is the volt-
age feedback of the built-in voltage regulator for generating VL6. In order to generate the LCD
driving level, VL6, two external resistors, R1 and R2 should be connected between VDD and
VF, and VF and VL6, respectively.
Further study needs to be done in a very careful manner, but there are a few precautions that can be done during the
PCB design stage:
1) Layout consideration: PCB design should be carefully designed, so that VF circuit can be placed as far as possible
from the RF circuit. The placement of the external components in VF circuit should be avoided to form a close loop an-
tenna, so as to reduce the chance of RF interference. Reducing the total length of the external circuit from the VF pin
will help improve the immunity to RF signal.
2) VF circuit: If external resistor network is used, the noise immunity of VF can be further improved by an additional fil-
tering capacitor as indicated in the circuit below:
VL6
VF
VDD
0.01uF
R2
R1
0.1uF
This circuit will act as a feedback path which reduce the RF interference.
3) Selection of R1& R2: It is recommended in some of the designs using the values of R1+R2 - less than 1.5 Mohm.
4) Shielding: Shielding is the most effective way to resist RF noise. By covering up the VF pin and other external com-
ponents with a metal foil connected to GND, will provide the best result.
Application of SSD181X/SSD1815A/SSD1815B to Existing LCD Modules
8
SOLOMON
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