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PDF WS2801 Data sheet ( Hoja de datos )
| Número de pieza | WS2801 | |
| Descripción | 3-Channel Constant Current LED Driver | |
| Fabricantes | Worldsemi | |
| Logotipo |  |
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Preliminary WS2801
3-Channel C onstant Current
LED Driver With Programmable
PWM Outputs
Features
Applications
• 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 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
Typical Application Circuit
Fig1.a SOP-14 package
Fig1.b DIP-14 package
WS-Preliminary-V0.3
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Pin Description
Pin Port
1
2
3
Pin Name
CKI
SDI
POL
4 RFB
5 GFB
6 BFB
7 GND
8 BOUT
9 GOUT
10 ROUT
11 NC
12 SDO
13 CKO
14 VCC
Application Information
Preliminary WS2801
3-Channel C onstant Current
LED Driver With Programmable
PWM Outputs
Pin Description
Data clock input
Serial gray scale data 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
Ground
The output of the B channel
The output of the G channel
The output of the R channel
None connection
The output of the serial gray scale data.
The output of the buffered clock
Power supply input, a capacitor can be connected from this pin to GND to
enhance the noise immunity.
WS-Preliminary-V0.3
Fig4, The typical application circuit of WS2801
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Preliminary WS2801
3-Channel C onstant Current
LED Driver With Programmable
P WM 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
I = I β＋1NPNC
XOUT
--------------------------------------------------------------- (4)
The current flow through the base is:
I = I β1＋1NPNB
XOUT
--------------------------------------------------------------- (5)
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:
RB
= V DD−VXOUT
I NPNB
---------------------------------------------------------------------- (6)
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 edg es, the WS2801 enters rela y 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
=
L[7]* 27
+ L[6]* 26
+ L[5]* 25
+
L[4]* 24 + L[3]* 23
256
+
L[2]* 22
+ L[1]* 21
+
L[0] ----- (7)
Where L[x ]=”0” or “1 ”, which is R 、G、B[x], x=0,1,2……7 in the gra y scale dat a. Gray scale dat a
0000 0000 is for the minimum 0 duty ratio, and 1111 1111 is for the maximum 255/256 duty ratio.
WS-Preliminay-V0.3
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| Páginas | Total 15 Páginas | |
| PDF Descargar | [ Datasheet WS2801.PDF ] | |
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