ST2225A

點晶科技股份有限公司

SILICON TOUCH TECHNOLOGY INC.

LED Display Driver

-6-

Version：A.025

Operating Ratings

Supply Voltage (V

DD

– V

SS

) ..............................+4.75V to 11V

Ambient Temperature Range (T

A

Functional Description

The ST2225A display driver can drive either 4- or 5-digit alphanumeric LED displays. One of

its advantages is its minimal interface requirement with the display or data source.

Data transfer is accomplished by sending clock and serial data signals, without any need of an

external load signal. This method provides a non-multiplexed, direct drive to the LED display. The

data transfer format uses a leading “1” followed by 35 data bits. These 35 data bits are latched after

changes only if the serial data bits differ from those previously transferred.

Display brightness is controlled by the output current for LED displays. A 1nF capacitor should

be connected to brightness control pin to prevent oscillations.

Figure 1 shows the block diagram of this driver. The output current is set via an external

variable resistor, and is typically 27 times greater than the current in brightness control pin.

transferred, a LOAD signal is generated synchronously with the clock high state, thus, the 35 bits of

data are loaded into the latches. The low state of the clock is used to generate a RESET signal to

clear all shift registers for the next set of data. To allow continuous operation, all shift registers are

static master-slaves, with no clear for the master portion of the first register.