SSD1821 datasheet(36/43 Pages) ETC1

36 / 43 page

SSD1820A/21

REV 1.4

01/03

SOLOMON

APPLICATION NOTE 1: ESD PROTECTION CIRCUIT

For SSD1820A/21 IC, it is recommended to design a simple protection circuit to prevent from unexpected external interference.

This is useful especially the designed product has to go through unexpected electrostatic discharge. Figure 1 is an example of

the common circuit used.

Figure 9: Additional ESD protection circuit

Figure 9 shows one of the most common connection design of the LCD driver IC and the main Microprocessor (MCU) unit, the

RES pin of the driver is connected directly to one of the port of the MCU. When external charge is brought near the device, or

electrostatic charge (a spike), the charge will be induced inside the device and it will discharge by finding its way to the shortest

path to ground.

This discharge sometimes will affect the normal operation of the device, causing data disruption inside RAM or internal register s,

or even re-initialize / reset the device. The IC design is in-built with a protection circuit (or a diode circuit to the power a nd ground

rails), to protect the I/O pins from external charge or spike. Since the diode circuit in the IC is very small, the protection of the

circuit is limited. Therefore, it is very useful to build an external device to help prevent the disturbance. it is easy to add a capacitor

across the RES pin, this will have a big improvement on the stability of the driver IC.

In addition, more protection can be done by adding a resistor in series, directly in between the RES pin of the driver IC and the

port of the MCU. This will create a filter (R-C circuit) effect, that will be able to eliminate external noises entering the RES pin of

the driver IC.

The value of the capacitor and resistor used largely depend on the application printed circuit board design. It is recommended to

test and evaluate to find out the best capacitor value for a particular design application. However, for mobile communication de-

vices (eg mobile phones), a lot of applications there is a 1nF capacitor placed across the RES pin and ground.

(Port output pin)

Microproesscor

unit

RES

Typical value:

C = 1000nF;

R = 3 ~ 10K ohm;

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