WS2801 데이터 시트보기 (PDF) - Unspecified

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WS2801

3-Channel Constant Current LED Driver With Programmable PWM Outputs

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Preliminary WS2801

3-Channel Constant Current

LED Driver With Programmable

PWM Output

The output constant current can be set by the following equation:

I XOUT

=

VREF

RXFB

---------------------------------------------------------------------------- (1)

Where VREF=0.6V, which is the current setting reference voltage, RXFBB is the current feed back resistor connected on R/G/BFB pin,

for example RXFB=30Ω to set IXOUT=20mA,则RXFB=30Ω.

To guarantee the normal operation of the constant current drive, the voltage on R/G/BOUT should be set between 1 to 1.5 V, and

then the drive can output a high precision current over whole operation range, meanwhile there would be not too much power

dissipated on WS2801.

Constant Voltage Driving Mode

WS2801 is a versatile LED driver, it does not only provide user constant current driving mode, but also constant voltage driving

mode, which is compatible with ZQL9712. The constant voltage driving mode (POL=’HIGH’ or floating) can drive the LEDs with

current up to 50mA. Connecting R/G/BFB directly to ground, then WS2801 can operate at constant voltage driving mode. See Fig

8.

Fig7, The schematic of constant voltage driving mode

At constant voltage driving mode, the LED diving current can be set by adjusting RL; the RL can be derived by the following

equation:

V −V −V DD

LED

OUT

R = L

---------------------------------------------------------------- (2)

I LED

Where RL is the current setting resistor, VDD is the LED power supply, VLED is the LED forward conducting voltage drop, VOUT is

the saturation voltage of the output driver(about 0.2~0.4V), ILED is the LED operating current, usually ILED≤20mA.

Constant Voltage Driving Mode with External Switches

WS2801 provides constant voltage driving mode with external switches to drive high brightness LED, and also realize the HB LED

256 gray scales control, when POL is pull to GND, WS2801 can operate at this driving mode, see Fig9.

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WS-Preliminay-V0.3

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