Worldsemi WS2801 Schematic

Preliminary WS2801

3-Channel Constant Current LED Driver With Programmable

PWM Outputs

　 Features 　 Applications

• Supports both constant voltage and constant current drive mode

• Programmable constant LED drive current

• Wide constant output current range 5~150mA

• Build in PWM dimming scheme for each output channel,

supports free-run, especially suitable for low cost controller

application

• PWM free-run capability(refresh rate(2.5KHz)

• Build in buffers to cascading data and clock to the next driver

• Output polarity reverse function

• Support hot swap

• Maximum input clock frequency 25MHz

• Power supply voltage 3.3~5.5V

　 General Description

The WS2801 is a constant current LED driver. It is designed for indoor/ outdoor LED displays and decorative LED lighting system.

It is suitable for LED cascading applications. The WS2801ownes 3 output channels, each channel can drive a constant current up

to 30mA. WS2081 contains serial shift registers, data latches, output registers, band gap reference voltage generator, internal

oscillator, and programmable constant output current drivers. The serial data is read into the shift registers at the rise edge of the

external clock. The data and clock output buffers are designed for cascading another chip. The output polarity reverse function is

designed for driving high power LED by adapting the application circuitry. The WS2801 adopts the reliable 2-wire scheme, which

features low EMI transport, very strong anti-interference ability, and support hot-swap. The 2-wire control scheme can reduce the

system cost; it is very suitable for low cost LED decorative LED lighting systems.

WS2801 is available in both SOP-14 and DIP-14 packages, the operating temperature is -40~85℃

　 Pin Configurations

• LED decorative lighting

• Indoor/Outdoor LED video or massage display

• PWM signal generator

• LCD TV back lighting

　 Ty pical Application Circuit

Fig1.a SOP-14 package Fig1.b DIP-14 package

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Preliminary WS2801

3-Channel Constant Current

LED Driver With Programmable

PWM Outputs

Absolute Maximum Ratings

Parameter Symbol Ratings Unit

Power Supply Voltage VCC -0.3 to 6V V

Input Voltage V

Output Voltage V

Output Pin Voltage V

Output Current

Constant Current Drive Mode Constant Voltage Drive Mode

Output Current Deviation (Constant Current Driving Mode)

Between output channels Between chips

Input Clock Frequency F

Maximum Power Dissipation P

OUT

XOUT

I

OUTCC

I

OUTCV

D D

CLK

IN

IOI

IOE

D

Operating Junction Temperature Topr -40 to + 150

Storage Temperature Range Tstg -55 to + 150

Lead Temperature (Soldering, 10 seconds)

Tsolder 300

ESD susceptibility 4000 V

Note: If the voltage on the pins exceeds the maximum ratings may cause permanent damage to the device.

Electrical Characteristics (VCC=5V, TA= 25℃, unless otherwise specified.)

Parameter Symbol Conditions Min Typ Max Units

Power Supply Voltage Range V

Output Voltage VOUT IOUT=1uA -0.3 -- 7.0 V

I

outH

Output Current

Standby Supply Current

Minimum Constant Current Output Time I

I

outL

I

SOURCE

I

SINK

I

STB

OH

Input Current I

Input Voltage Level

V

Constant Current Feed Back Voltage V

Output Saturation Voltage V

XFB

SAT

3.3 -- 5.5 V

CC

Constant Current Output 5 -- 30 mA

Constant Voltage Output -- -- 50 mA

Output Cut Off -- 0.1 1 uA

Other Output -- 1 -- mA

Other Output -- -1 -- mA

B

R/G/BOUT Floating -- 1 1.5 mA

VIN＝V I

OUT

or VIL,

IH

=20mA

PIN：CKI，SDI

＝VDD or GND

V

IN

IH

IL

IN

PIN：CKM，POL

＝VDD or GND

V

IN

TA＝-40～125℃

B R

R/G/BFB

=20Ω B

IOUT=20mA -- 0.4 0.6 V

-0.3 to VCC+0.3V V

-0.4 to 7V V

-0.3 to 7V V

0 to 50

mA

0 to 100

±1

%

±3

25 MHz

600 mW

℃

-- 14 -- uS

-- --

--

±10 ±20

±1

uA

0.8*VDD -- VDD V

GND -- 0.2*VDD

0.582 0.6 0.618

V

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Preliminary WS2801

3-Channel Constant Current

LED Driver With Programmable

PWM Outputs

Output Voltage Regulation %dV

Line Regulation %dV

Pull High Resistance R

OUTVOUT

CC

INHIGH

Switching Characteristics (VCC=5V, TA=25℃)

Parameter Symbol Conditions Min Typ Max Units

Propagation Delay

(‘L’ to ‘H’)

Propagation Delay

(‘L’ to ‘H’)

Output Current Rise Time

Maximum Turn ON and OFF time of Drive Current

Output Current Propagation

CKI-to-CKO

　 Switching Characteristics (VCC=3.3V, TA=25℃)

Parameter Symbol Conditions Min Typ Max Units

Propagation Delay

(‘L’ to ‘H’)

Propagation Delay

(‘L’ to ‘H’)

Output Current Rise Time

Output Current Fall Time

Output Current Propagation

CKI-to-CKO

CKI-to-CKO T

　 Circuit for Switching Characteristics Test

=0.9~4, R

VCC＝4～5.5V --

R

POL

T

①T

T

①T

pLH

pHL

T

or

T

of

OP

pLH

pHL

T

or

T

of

OP

VIH=VCC

V

R

RL=180Ω

CL=30pF

VIH=VCC

V

R

RL=180Ω

CL=30pF

RGBFB

, R

CKM

=GND

IL

XFBs

=GND

IL

XFBs

=30Ω

=30

=30Ω

--

±0.1

-- 30 -- KΩ

-- 8 -- ns

-- 8.6 -- ns

-- 50 -- ns

-- -- 3.3 mS

-- 9.0 -- ns

-- 13 -- ns

-- 50 --

-- 50 -- ns

-- -- 3.3 mS

-- %/V

Fig2, Circuit for switching characteristics test

Note:

① Reload the gray scale data at each end of the PWM cycle

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Preliminary WS2801

3-Channel Constant Current

LED Driver With Programmable

PWM Outputs

　 Typical Block Diagram

Fig3, Block Diagram of WS2801

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Preliminary WS2801

3-Channel Constant Current

LED Driver With Programmable

PWM Outputs

　 Pin Description

Pin Port Pin Name Pin Description

1

2 SDI Serial gray scale data input

3 POL

4 RFB

5 GFB

6 BFB

7 GND Ground

8 BOUT The output of the B channel

9 GOUT The output of the G channel

10 ROUT The output of the R channel

11 NC None connection

12 SDO The output of the serial gray scale data.

13 CKO The output of the buffered clock

14 VCC

Application Information

CKI Data clock input

Output polarity control. When this pin is pull to GND, the driver output will be

reversed; when floating or pulled high, the output polarity will not be reversed.

The feed back of the R channel, a resistor connected to this pin can set the

output constant current of the R channel

The feed back of the G channel, a resistor connected to this pin can set the

output constant current of the G channel

The feed back of the B channel, a resistor connected to this pin can set the

output constant current of the B channel

Power supply input, a capacitor can be connected from this pin to GND to

enhance the noise immunity.

Fig4, The typical application circuit of WS2801

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Preliminary WS2801

B

3-Channel Constant Current

LED Driver With Programmable

PWM Outputs

Figures

Iout vs. VCC

VFB vs temp

Iout(mA))

30.1

30.05

29.95

29.9

29.85

29.8

29.75

29.7

29.65

29.6

29.55

30

3455.5 VCC(V)

VF

0.63

0.62

0.61

0.6

0.59

0.58

0.57

-40 - 20 0 20 40 60 80 100 120

Output current vs. Temp (RFB=20Ω) Feed back voltage vs. temp.

IVCC vs. Temp.

IOUT(mA)

30.1

30.05

29.95

29.9

29.85

29.8

29.75

29.7

29.65

29.6

IOUT vs.VOUT

1400

30

1200

1000

800

600

IVCC(uA)

400

200

0

2345

VOUT(V)

-40 -20 0 20 40 60 80 100 120

Temp.

Temp.(℃)

Output current vs. output voltage I

vs. Temp.

VCC

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Preliminary WS2801

3-Channel Constant Current

LED Driver With Programmable

PWM Outputs

CKI to CKO delay time at rising edge(VCC=3.3V)

Channel1: CKI

Channel2: CKO

CKI to CKO delay time at falling edge(VCC=3.3V)

Channel1: CKI

Channel2: CKO

CKI to CKO delay time at rising edge(VCC=5V)

Channel1: CKI

Channel2: CKO

CKI to CKO delay time at falling edge(VCC=5V)

Channel1: CKI

Channel2: CKO

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Preliminary WS2801

3-Channel Constant Current

LED Driver With Programmable

PWM Outputs

Application note: Higher Voltage Applications:

The power supply range of WS2801 is from 3.3 to 6V, when the input power supply voltage is higher than 6V, a zener diode D0

can be used to clamp the voltage to generate the power supply of the chip, see Fig 6.

Fig5, the power supply for high voltage application VDD>6V

As the WS2801 dissipates about 1.5mA current during normal operation, the current limit resistor RS should be about 2 or more

times of the current that dissipated in WS2801, if the power supply VDD=12V, then RS=2KΩ functions well. A capacitor C0 is

necessary to filter the noise on the generated power supply voltage for WS2801, and C0=1uF functions well for most of the

applications.

Constant Driving Current Mode

In WS2801, a high performance OpAmp is applied to control the pass element M0 to generate a constant output current to drive

the external LED strings. The output current of each channel can be set by adjusting the current feed back resistor connected at

the current feed back pin(R/G/BFB), see Fig7.

Fig6, The schematic of constant current drive mode

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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:

V

R

REF

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

XFB

is the current feed back resistor connected on R/G/BFB pin,

B

XFB

I =

XOUT

Where V

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.

=0.6V, which is the current setting reference voltage, R

REF

Fig7, The schematic of constant voltage driv ing 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:

VVV

=

R

L

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.

I

LED

OUTLEDDD

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

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Preliminary WS2801

−

3-Channel Constant Current

LED Driver With Programmable

PWM Output

Fig8, Constant Voltage Drivin g with External Power Switches.

This driving mode is mainly used in high input voltage, high LED driving current (ILED>300mA). Its operating principle is using the

external power NPN switches to driving the LED lamps. The LED driving current can be adjusted by the external current limiting

resistor RL, RL can be derived by the following equation:

VVV

CELEDDD

R

=

L

The external NPN transistor operates in saturation region, VCE is the saturation voltage, and VCE=0.5~0.8V, the base resistor

RB=2~5K.

Constant Current Driving Mode with External Switches

This driving mode makes WS2801 can drive the cascading LED lamps with extreme low cost, at this mode, POL=’HIGH’ or

floating, see Fig10.

I

LED

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

Fig9, Constant current drive with external switches

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Preliminary WS2801

−

[

[][][

3-Channel Constant Current

LED Driver With Programmable

PWM Output

This mode can be used to drive the LED strings under high input voltage (VIN>6V), the highest application voltage is determined

by the external NPN power switch. The current flows through the collector of the NPN transistor:

β

The current flow through the base is:

II =

XOUTNPNC

--------------------------------------------------------------- (4)

1β＋

1

II =

B

XOUTNPN

β＋

During normal operation, to avoid too much power dissipating on WS2801, the voltage at R/G/BOUT should be set around 1.2

volts; the value of RB can be derived by the following equation:

VV

I

XOUTDD

NPNB

=

R

B

Gray Scale Data Word Format and Timing

CLK pin keeps low more than 500uS will make the WS2801 internal status register reset, and at this moment, the gray scale data

in the data shift registers will be latched. Now WS2801 is ready for gray scale data transport. When the WS2801 receives total 24

clock rising edges, the WS2801 enters relay mode, which relays the input signal got from CKI and SDI with very low distortion

(100pS typical) and very low delay time ( 8 ns typical). The data format and the timing diagram can be seen in Fig 11.

The gray scale data frame is comprised of 3 gray data words, each data word is composed of 8 gray scale data bits, total 24 bits.

The 8bit gray data can easily realize the linear 256 LED gray levels control.

During data transfer, the first bit is the data frame signal, then is the MSB of the ROUT channel, the last one transferred into the

data shift register is the LSB of the BOUT channel.

The duty cycle of the LED driving current can be calculated as:

D

XOUT

Where L[x]=”0” or “1”, which is R、 G 、 B[x], x=0,1,2……7 in the gray scale data. Gray scale data

0000 0000 is for the minimum 0 duty ratio, and 1111 1111 is f o r t h e maxim u m 255/256 duty ratio.

][][]

=

--------------------------------------------------------------- (5)

1

---------------------------------------------------------------------- (6)

][][]

256

1234567

02*12*22*32*42*52*62*7

LLLLLLLL

+++++++

----- (7)

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Preliminary WS2801

3-Channel Constant Current

LED Driver With Programmable

PWM Output

Fig 10, WS2801 data format and timing

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Preliminary WS2801

3-Channel Constant Current

LED Driver With Programmable

PWM Output

The Connection and Driving of Cascading Operation

The transmit the data over long distance by cascading, the WS2801 integrates push-pull output stage with strong driving

capability which enables the data and clock can be transmitted up to 6 meters at 2MHz clock frequency.

To prevent the reflection, it is necessary to connect a 50Ω resistor at the data input or output port for impedance match.

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Preliminary WS2801

3-Channel Constant Current

LED Driver With Programmable

PWM Output

　 Package Information

SOP-14 Package (Unit: mm)

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Preliminary WS2801

3-Channel Constant Current

LED Driver With Programmable

PWM Output

DIP-14 Package (Unit: mm)

IMPORTANT NOTICE

The information in this document has been carefully reviewed and is believed to be accurate.

Nonetheless, this document is subject to change without notice. World-Semi assumes no responsibility

for any inaccuracies that may be contained in this document, and makes no commitment to update or to

keep current the contained information, or to notify a person or organization of any update. World-semi

reserves the right to make changes, at any time, in order to improve reliability, function or design and to

attempt to supply the best product possible.

World Semiconductor, Inc

Nov. 2008

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