Preliminary

WS2803

18-Channel Constant Current LED Driver

With Programmable PWM Outputs

4/8

Pin Description

SOP-28

Pin No.

Pin Name

Pin Description

1

GND

Ground

2

IREF

A resistor connected to this pin can set the output constant current.

3

NC

None connection

4

CKI

Data clock input

5

SDI

Serial gray scale data input

6~23

OUT0~17

Constant current output terminals

24

SDO

Buffered serial data output

25

CKO

Buffered clock output

26

NC

None connection

27

NC

None connection

28

VCC

VCC input

DIP-28

Pin Port

Pin Name

Pin Description

1

GND

Ground

2

IREF

A resistor connected to this pin can set the output constant current.

3

NC

None connection

4

CKI

Data clock input

5

SDI

Serial gray scale data input

6~23

OUT0~17

Constant current output terminals

24

NC

None connection

25

NC

None connection

26

SDO

Buffered serial data output

27

CKO

Buffered clock output

28

VCC

VCC input

Application note:

Output Constant Current

In LED display and decorative applications, WS2803 provides nearly no variations in current from channel to channel

and from IC to IC. This can be achieved by:

1)

The maximum current variation between channels is less than 2%, and between chips is less than 4%.

2)

In addition, the current characteristic of the output stages is flat and users can refer to the figures as shown below.

The output current can be kept constant regardless of the variations of led forward voltages (VF). This performs as a

perfection of load regulation.

Adjusting the output current

The output current of each channel can be set by an external resistor, REXT, the output current can be set by the

following formula:

22

×

=

EXT

REXT

OUT

R

V

I

Where, REXT is the resistance of the external resistor connected to REXT terminal, and VREXT is the voltage of REXT pin

WS-Preliminary-V0.1

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