Driver chip increase LED display quality scheme is introduced

Pulse output current, will be the same time the average break up

it is best to more than 4 layer board, PCB, linear part as short as possible

• VLED is separated from VCC for different power supply

• VLED and VCC to end with a large voltage capacitance

now LED display using more and more widely, for financial securities, sports, such as traffic, advertising message transmission can see its footprint, but also because in recent years LED their costs down and brightness and LED display has less power consumption, long life, a large Angle of view, and the advantages of the fast response.

and may, according to different locations and ordering the size of the corresponding to the demand, in the market's rapid emergence as a new generation of media darling, its condition is unmatched by other large display device. This article will further explain how to don't change the circuit design, took advantage of the rapid response of the drive chip to realize high quality LED display. Promotion -

the overall speed Higher refresh frequency and repetition frequency

the LED is driven by flow of electric current, and can be controlled by the pulse width of the LED brightness and gray, simply without consideration to the system design, the refresh rate ( refreshrate) Is the time by addressing ( Tacc) And the speed is determined by the current through the LED; And in the frame frequency ( 帧速率) Improvement in addition to the support of the system more in need of addressing time faster, and the addressing time and transmission frequency ( DCLK) And addressing the number has a strong positive correlation.

for example: a full color outdoor displays its addressing number is 768, if use different frequency of addressing the whole time will be different working frequency of 10 MHZ - > 768 x0。 1us=76. Eight us working frequency of 30 MHZ - > 768 x0。 033us=25. Six us both of addressing three times.

and the speed of the current through the LED to LED display refresh rate, for example, if a LED display its addressing number is 768, the working frequency of 30 MHZ, gray-scale adjustment for eight ( 比特) , brightness adjustment are two ( 比特) , each field of the time interval is 4 us; Traditional driving chip of the display pulse width 250 ns, and pulse width of 50 ns SnapDriveTM driver chips, refresh rate have obvious differences that can be achieved in both the

display gray-scale spend promotion on the market at present the tradition of common drive chip OE response time is about 250 ns, if in the above case its highest gray-scale for eight; Known as R, G, B each has 256 gray-scale degrees. Its colour is 256 x256x256 = 166777216 about 1 six million colors. To gray-scale degrees up to 14 or 16384 x16384x16384 = 4. 3. 9 trillion color; The refresh rate between the two also have obvious differences in

the following rapid for Taiwan jie tech contains drive chip test condition and result of SnapDriveTM technology, shown in figure 1 and figure 3 borrow clear its driver chip in small under the OE pulse width of the output current is still the linear output, while the traditional drive chip could not provide a linear output.

test conditions: the Vcc = 5 v, Iout = 38. 3 ma, RL = 47 Ω, CL = 13 pf

low distortion rate for different output current slope driver chip, using the simulation software ( HSPICE2007) We we get different results in distortion rate

the simulation conditions: traditional driver chip: Ton: 160 ns, Tof: 70 ns SnapDriveTM driver chip: Ton: 15 ns, Tof: 15 ns Vin: 5 v, Iout = 20 ma, LED equivalent circuit RL: 52 Ω, CL: 10 pf OE pulse width is: 250 ns

the problem of the LED heat and increase the service life of the LED as shown in figure 5 to 50% Dutycycle diagram output current, if in the same period of time will be out of the current pulse, on average, break up, not only will not affect the output current and the LED brightness can also avoid the LED long light LED overheating and attenuation of the early life phenomenon.

fast response circuit design using quick response driver chip although can improve the gray-scale and refresh rate of LED display; But according to the inductive effect of formula Δ V = l. di/dt for smaller time t; Relative instantaneous voltage bigger so prone to surge. The author herein several circuit on the improvement of the design pattern for readers reference:

Δ V: voltage variation L: circuit of parasitic inductance di: the current differential dt: the differential of time

there are a few points on the circuit design need to pay special attention to:

1. PCB is best more than 4 layer board, will power and independent layer; Linear part as short as possible.

　　2. VLED and VCC to end with a large voltage capacitance, advice and contact international. like apply SSDS CP1 uf is 1000 ~ 1500.

　　3. VLED is separated from VCC for different power supply.

　　4. In the frequency of input ( 时钟) Plus the RC circuit, its peak is reduced, to reduce the influence of electromagnetic interference; Recommended Rt

scan screen; Suggestions in MOS Gate between client and 74 hc138 string of a resistor, in order to avoid VLED side inductance effect and MOS surge produced by stray capacitance, cause 74 hc138 burned; Suggest Rg

the conclusion that by rapid response, SnapDriveTM) Driver chip can not only improve the whole screen gray-scale display and refresh rate, decrease the rate of output current distortion, but also because of the climb and traditional drive chip due to the current fall time is longer, in the nonlinear fails to reach the set current output will effect on the characteristic of the LED light ( Wavelength) And easy to display color distortion phenomenon. But as a result of transmission and the improvement of working frequency for designers in addition to be more careful on circuit design, selection of high quality, high reliability, driver chip is ideal.

instructions:

OE: can cause foot chip output ( 芯片输出启用) 。

SnapDriveTM: rapid for Taiwan jie technology research and development production of quick response of driver chip, pin is fully compatible with TB62746 etc. Product.