Preliminary WS2801
3-Channel Constant Current
LED Driver With Programmable
PWM Outputs
FeaturesApplications• Supports both constant voltage and constant current drive mode

• LED decorative lighting• Programmable constant LED drive current• Indoor/Outdoor LED video or massage display• Wide constant output current range 5~150mA• PWM signal generator• Build in PWM dimming scheme for each output channel,• LCD TV back lighting

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 theexternal clock. The data and clock output buffers are designed for cascading another chip. The output polarity reverse function isdesigned for driving high power LED by adapting the application circuitry. The WS2801 adopts the reliable 2-wire scheme, whichfeatures low EMI transport, very strong anti-interference ability, and support hot-swap. The 2-wire control scheme can reduce thesystem 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

Fig1.a SOP-14 package

Typical Application Circuit

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

SymbolRatings

Unit

Power Supply Voltage

VCC-0.3 to 6V

V

Input Voltage

VIN-0.3 to VCC+0.3V

V

Output Voltage

VOUT-0.4 to 7V

V

Output Pin VoltageVXOUT-0.3 to 7V

V

Output Current
Constant Current Drive Mode
Constant Voltage Drive ModeIOUTCCIOUTCV

0 to 50
0 to 100mA

Output Current Deviation (Constant Current Driving Mode)
Between output channels
Between chips

DIOI
DIOE

±1±3%

Input Clock Frequency

FCLK

25MHz

Maximum Power Dissipation

PD

600mW

Operating Junction TemperatureTopr-40 to + 150

Storage Temperature Range

Tstg-55 to + 150

Lead Temperature (Soldering, 10 seconds)

Tsolder300

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

SymbolMin

TypMax

Units

3.3--

5.5

V

IOUT=1uA

-0.3

--

7.0

V

Constant Current Output

5--30

mA

Constant Voltage Output----50mA

IoutL

Output Cut Off--

0.1

1uA

ISOURCE

Other Output

--1--

mA

ISINK

Other Output---1--mA

Standby Supply Current

ISTB

R/G/BOUT Floating

--

11.5

mA

Minimum Constant Current Output TimeIOH--14--uS----±1uAInput Current

IIN--±10±20

uA

0.8*VDD

--VDD

V

GND

--

0.2*VDDV

Power Supply Voltage Range

VCC

Output Voltage

VOUTIoutH

Output Current

Input Voltage Level

B

Conditions

VIN＝VIH or VIL,IOUT=20mA
PIN：CKI，SDI
VIN＝VDD or GND
PIN：CKM，POL
VIN＝VDD or GND

VIH

TA＝-40～125℃

VIL

Constant Current Feed Back Voltage

VXFB

RR/G/BFB=20Ω

0.582

0.6

0.618

V

Output Saturation Voltage

VSAT

IOUT=20mA

--0.4

0.6

VB

B

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Preliminary WS28013-Channel Constant Current
LED Driver With Programmable
PWM Outputs
Output Voltage Regulation%dVOUT

VOUT=0.9~4, RRGBFB=30Ω--±0.1--%/V

Line Regulation%dVCC

VCC＝4～5.5V--±0.1--%/V

Pull High Resistance

RINHIGH--30--KΩ

Min

TypMaxUnits

RPOL, RCKM

Switching Characteristics (VCC=5V, TA=25℃)
Parameter
Propagation Delay(‘L’ to ‘H’)
Propagation Delay(‘L’ to ‘H’)

SymbolConditions

CKI-to-CKO

TpLH

VIH=VCC--8--ns

CKI-to-CKO

TpHL

VIL=GND--

8.6--ns--50--

ns--50--ns----

3.3mS

Min

TypMaxUnits--

9.0--ns--

13--ns--50----50--ns----

3.3mS

Output Current Rise Time

TorMaximum Turn ON and OFF time of Drive Current

Tof

Output Current Propagation①TOP

RXFBs=30
RL=180ΩCL=30pF

Switching Characteristics (VCC=3.3V, TA=25℃)
Parameter
Propagation Delay(‘L’ to ‘H’)
Propagation Delay(‘L’ to ‘H’)

Symbol

CKI-to-CKO

TpLH

CKI-to-CKO

TpHL

Output Current Rise TimeTor

Output Current Fall Time

Tof

Output Current Propagation①TOPConditions
VIH=VCC
VIL=GNDRXFBs=30Ω
RL=180ΩCL=30pF

Circuit for Switching Characteristics Test

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

1CKI

Data clock input

2SDI

Serial gray scale data input

3POL

4RFB

5GFB

6BFB

7

GNDGround

8BOUT

The output of the B channel

9GOUT

The output of the G channel

10ROUT

The output of the R channel

11NC

None connection

12SDO

The output of the serial gray scale data.

13CKO

The output of the buffered clock

14

VCC

Output polarity control. When this pin is pull to GND, the driver output will bereversed; 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 theoutput constant current of the R channel
The feed back of the G channel, a resistor connected to this pin can set theoutput constant current of the G channel
The feed back of the B channel, a resistor connected to this pin can set theoutput constant current of the B channel

Power supply input, a capacitor can be connected from this pin to GND toenhance the noise immunity.

Application Information

Fig4, The typical application circuit of WS2801

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3-Channel Constant Current
LED Driver With Programmable
PWM Outputs
Figures
VFB vs temp

Iout vs. VCC

30.1

0.63

30.05
300.62

29.95

0.61
VFB

Iout(mA))

29.9
29.85
29.8

0.6
0.59

29.75
29.7

0.58

29.65

0.57

29.6

-40 -20

29.55
34

VCC(V)

55.5

20406080 100 120

Temp.

Output current vs. Temp (RFB=20Ω)

Feed back voltage vs. temp.
IVCC vs. Temp.

IOUT vs.VOUT

30.1

1400

30.05
30

IVCC(uA)

29.95
IOUT(mA)

029.9
29.85
29.8
29.75
29.7
29.65

12001000800600400200029.623VOUT(V)45-40 -20020406080100 120Temp.(℃)

Output current vs. output voltage

IVCC vs. Temp.

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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)

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

Channel1: CKI

Channel1: CKI

Channel2: CKO

Channel2: CKO

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

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

Channel1: CKI

Channel1: CKI

Channel2: CKO

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 moretimes 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 theapplications.

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:I XOUT =VREF
RXFB ---------------------------------------------------------------------------- (1)Where VREF=0.6V, which is the current setting reference voltage, RXFB is the current feed back resistor connected on R/G/BFB pin,Bfor 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, andthen 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 withcurrent up to 50mA. Connecting R/G/BFB directly to ground, then WS2801 can operate at constant voltage driving mode. See Fig8.

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:

RL =VDD − VLED − VOUT---------------------------------------------------------------- (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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Preliminary WS2801
3-Channel Constant Current
LED Driver With Programmable
PWM Output

Fig8, Constant Voltage Driving 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 theexternal 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:RL =V DD − VLED − VCE------------------------------------------------------------- (2)I LED

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’ orfloating, see Fig10.

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

I NPNC = I XOUT

β--------------------------------------------------------------- (4)β＋1The current flow through the base is:

I NPNB = I XOUT

1--------------------------------------------------------------- (5)β＋1During 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:

RB =V DD−V XOUT---------------------------------------------------------------------- (6)I NPNB

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 datain 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 thedata shift register is the LSB of the BOUT channel.
The duty cycle of the LED driving current can be calculated as:

D XOUT =L[7 ] * 2 7 + L[6] * 2 6 + L[5] * 2 5 + L[4] * 2 4 + L[3] * 2 3 + L[2] * 2 2 + L[1] * 2 1 + L[0]----- (7)256

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 for the maximum 255/256 duty ratio.

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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 tokeep 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 toattempt to supply the best product possible.

World Semiconductor, IncNov. 200815 / 15
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