Preliminary WS2801 3-Channel Constant Current LED Driver With Programmable PWM Outputs Features Applications • 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 ON LY • Supports both constant voltage and constant current drive mode supports free-run, especially suitable for low cost controller application 司 • PWM free-run capability(refresh rate(2.5KHz) • Build in buffers to cascading data and clock to the next driver 公 • Output polarity reverse function • Support hot swap 限 • Maximum input clock frequency 25MHz 有 • Power supply voltage 3.3~5.5V General Description 技 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 科 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 明 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 裕 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. Pin Configurations 深 圳 WS2801 is available in both SOP-14 and DIP-14 packages, the operating temperature is -40~85℃ FO R Typical Application Circuit Fig1.a SOP-14 package Fig1.b DIP-14 package 1 /15 WS-Preliminary-V0.3 http://www.world-semi.com Preliminary WS2801 3-Channel Constant Current LED Driver With Programmable PWM Outputs Absolute Maximum Ratings Ratings Unit VCC -0.3 to 6V V VIN -0.3 to VCC+0.3V V Output Voltage VOUT -0.4 to 7V V Output Pin Voltage VXOUT -0.3 to 7V V Output Current Constant Current Drive Mode Constant Voltage Drive Mode IOUTCC IOUTCV 0 to 50 0 to 100 mA ±1 ±3 % FCLK 25 MHz PD 600 mW Topr -40 to + 150 Tstg -55 to + 150 Tsolder 300 Input Voltage Output Current Deviation (Constant Current Driving Mode) Between output channels Between chips 公 DIOI DIOE ON Power Supply Voltage LY Symbol 司 Parameter 限 Input Clock Frequency Maximum Power Dissipation 有 Operating Junction Temperature 技 Storage Temperature Range Lead Temperature (Soldering, 10 seconds) 4000 科 ESD susceptibility ℃ V Note: If the voltage on the pins exceeds the maximum ratings may cause permanent damage to the device. 明 Electrical Characteristics (VCC=5V, TA= 25℃, unless otherwise specified.) Min Typ Max Units 3.3 -- 5.5 V -0.3 -- 7.0 V Constant Current Output 5 -- 30 mA Constant Voltage Output -- -- 50 mA Output Cut Off -- 0.1 1 uA ISOURCE Other Output -- 1 -- mA ISINK Other Output -- -1 -- mA Standby Supply Current ISTB R/G/BOUT Floating -- 1 1.5 mA Minimum Constant Current Output Time IOH -- 14 -- uS -- -- ±1 uA Input Current IIN -- ±10 ±20 uA 0.8*VDD -- VDD V GND -- 0.2*VDD V 0.582 0.6 0.618 V 0.6 V Power Supply Voltage Range FO R Output Current 深 圳 Output Voltage Symbol 裕 Parameter Input Voltage Level Conditions VCC VOUT IoutH IoutL B IOUT=1uA 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 Output Saturation Voltage VSAT IOUT=20mA B B -- 0.4 2 /15 WS-Preliminary-V0.3 http://www.world-semi.com Preliminary WS2801 3-Channel Constant Current LED Driver With Programmable PWM Outputs %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 RPOL, RCKM Switching Characteristics (VCC=5V, TA=25℃) Units 8 -- ns ON Max VIH=VCC -- CKI-to-CKO TpHL VIL=GND -- 8.6 -- ns RXFBs=30 -- 50 -- ns -- 50 -- ns -- -- 3.3 mS Min Typ Max Units -- 9.0 -- ns -- 13 -- ns -- 50 -- -- 50 -- ns -- -- 3.3 mS Tor RL=180Ω 公 Tof Output Current Propagation CL=30pF ①TOP Symbol CKI-to-CKO 技 TpLH TpHL 科 CKI-to-CKO Output Current Rise Time 明 Output Current Fall Time Output Current Propagation 有 Switching Characteristics (VCC=3.3V, TA=25℃) Parameter Tor Tof ①TOP Conditions VIH=VCC VIL=GND RXFBs=30Ω RL=180Ω CL=30pF 裕 Circuit for Switching Characteristics Test FO R 深 圳 Typ TpLH Maximum Turn ON and OFF time of Drive Current Propagation Delay (‘L’ to ‘H’) Propagation Delay (‘L’ to ‘H’) Min CKI-to-CKO Output Current Rise Time Conditions 限 Propagation Delay (‘L’ to ‘H’) Propagation Delay (‘L’ to ‘H’) Symbol 司 Parameter LY Output Voltage Regulation Fig2, Circuit for switching characteristics test Note: ① Reload the gray scale data at each end of the PWM cycle 3 /15 WS-Preliminary-V0.3 http://www.world-semi.com Preliminary WS2801 3-Channel Constant Current LED Driver With Programmable PWM Outputs Typical Block Diagram Fig3, Block Diagram of WS2801 FO R 深 圳 裕 明 科 技 有 限 公 司 ON LY 4 /15 WS-Preliminary-V0.3 http://www.world-semi.com Preliminary WS2801 3-Channel Constant Current LED Driver With Programmable PWM Outputs Pin Description Pin Name 1 CKI Data clock input 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 12 SDO 13 CKO 14 VCC ON 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 司 output constant current of the R channel The feed back of the G channel, a resistor connected to this pin can set the 公 output constant current of the G channel 限 The feed back of the B channel, a resistor connected to this pin can set the 技 有 output constant current of the B channel 科 None connection The output of the serial gray scale data. 明 The output of the buffered clock Power supply input, a capacitor can be connected from this pin to GND to enhance the noise immunity. FO R 深 圳 Application Information Pin Description LY Pin Port 裕 Fig4, The typical application circuit of WS2801 5 /15 WS-Preliminary-V0.3 http://www.world-semi.com Preliminary WS2801 3-Channel Constant Current LED Driver With Programmable PWM Outputs Figures VFB vs temp 30.1 LY Iout vs. VCC 0.63 30.05 30 ON 0.62 29.95 0.61 29.8 0.59 29.75 29.7 0.58 公 29.65 0.57 29.6 -40 -20 29.55 4 VCC(V) 5 5.5 限 3 有 Output current vs. Temp (RFB=20Ω) 技 IOUT vs.VOUT 科 30 29.95 明 29.9 29.85 29.8 裕 29.75 29.7 29.6 深 2 圳 29.65 3 VOUT(V) 0 20 40 60 80 100 120 Temp. Feed back voltage vs. temp. IVCC vs. Temp. 1400 IVCC(uA) 30.1 30.05 IOUT(mA) 0.6 司 VFB Iout(mA)) 29.9 29.85 1200 1000 800 600 400 200 0 4 -40 -20 0 20 40 60 80 100 120 Temp.(℃) IVCC vs. Temp. FO R Output current vs. output voltage 5 6 /15 WS-Preliminary-V0.3 http://www.world-semi.com 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 Channel2: CKO Channel2: CKO 技 有 限 公 司 ON LY Channel1: CKI CKI to CKO delay time at rising edge(VCC=5V) 科 Channel1: CKI Channel1: CKI Channel2: CKO FO R 深 圳 裕 明 Channel2: CKO CKI to CKO delay time at falling edge(VCC=5V) 7 /15 WS-Preliminary-V0.3 http://www.world-semi.com Preliminary WS2801 3-Channel Constant Current LED Driver With Programmable PWM Outputs Application note: Higher Voltage Applications: LY 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 技 有 限 公 司 ON can be used to clamp the voltage to generate the power supply of the chip, see Fig 6. 科 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 明 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 裕 applications. Constant Driving Current Mode 圳 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 FO R 深 the current feed back pin(R/G/BFB), see Fig7. Fig6, The schematic of constant current drive mode 8 /15 WS-Preliminary-V0.3 http://www.world-semi.com Preliminary WS2801 3-Channel Constant Current LED Driver With Programmable PWM Output The output constant current can be set by the following equation: VREF RXFB ---------------------------------------------------------------------------- (1) LY I XOUT = ON Where VREF=0.6V, which is the current setting reference voltage, RXFB is the current feed back resistor connected on R/G/BFB pin, B 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 司 then the drive can output a high precision current over whole operation range, meanwhile there would be not too much power 公 dissipated on WS2801. Constant Voltage Driving Mode 限 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 有 current up to 50mA. Connecting R/G/BFB directly to ground, then WS2801 can operate at constant voltage driving mode. See Fig Fig7, The schematic of constant voltage driving mode FO R 深 圳 裕 明 科 技 8. 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 I LED ---------------------------------------------------------------- (2) 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. 9 / 15 WS-Preliminay-V0.3 http://www.world-semi.com Preliminary WS2801 有 限 公 司 ON LY 3-Channel Constant Current LED Driver With Programmable PWM Output Fig8, Constant Voltage Driving with External Power Switches. 技 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 明 科 resistor RL, RL can be derived by the following equation: RL = V DD − VLED − VCE I LED ------------------------------------------------------------- (2) 裕 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. 圳 Constant Current Driving Mode with External Switches 深 This driving mode makes WS2801 can drive the cascading LED lamps with extreme low cost, at this mode, POL=’HIGH’ or FO R floating, see Fig10. Fig9, Constant current drive with external switches 10 / 15 WS-Preliminay-V0.3 http://www.world-semi.com 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: LY β --------------------------------------------------------------- (4) β＋1 ON I NPNC = I XOUT The current flow through the base is: 1 --------------------------------------------------------------- (5) β＋1 司 I NPNB = I XOUT 公 During normal operation, to avoid too much power dissipating on WS2801, the voltage at R/G/BOUT should be set around 1.2 V DD−V XOUT I NPNB ---------------------------------------------------------------------- (6) 有 RB = 限 volts; the value of RB can be derived by the following equation: 技 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 科 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 明 (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. 裕 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 圳 data shift register is the LSB of the BOUT channel. 深 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 R 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 FO 0000 0000 is for the minimum 0 duty ratio, and 1111 1111 is for the maximum 255/256 duty ratio. 11 / 15 WS-Preliminay-V0.3 http://www.world-semi.com Preliminary WS2801 FO R 深 圳 裕 明 科 技 有 限 公 司 ON LY 3-Channel Constant Current LED Driver With Programmable PWM Output Fig 10, WS2801 data format and timing 12 / 15 WS-Preliminay-V0.3 http://www.world-semi.com Preliminary WS2801 3-Channel Constant Current LED Driver With Programmable PWM Output The Connection and Driving of Cascading Operation capability which enables the data and clock can be transmitted up to 6 meters at 2MHz clock frequency. LY The transmit the data over long distance by cascading, the WS2801 integrates push-pull output stage with strong driving FO R 深 圳 裕 明 科 技 有 限 公 司 ON To prevent the reflection, it is necessary to connect a 50Ω resistor at the data input or output port for impedance match. 13 / 15 WS-Preliminay-V0.3 http://www.world-semi.com Preliminary WS2801 3-Channel Constant Current LED Driver With Programmable PWM Output Package Information LY SOP-14 Package (Unit: mm) FO R 深 圳 裕 明 科 技 有 限 公 司 ON 14 / 15 WS-Preliminay-V0.3 http://www.world-semi.com Preliminary WS2801 3-Channel Constant Current LED Driver With Programmable PWM Output FO R 深 圳 裕 明 科 技 有 限 公 司 ON LY 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 15 / 15 WS-Preliminay-V0.3 http://www.world-semi.com