PT4112 technology characteristics and typical application circuit

Industry leading high TEMPO assessment services segment capacity, high performance patch fuses designed for OEM designers and engineers and product Samtec connector complete signal source new products every day % % 20 times new experience complete 15, 20 a switch mode power supply.

PT4112 is a six channel white LED driver IC, each road up series 10 white LED, so the single chip can drive up to 60 white LED. PT4112 not only has excellent accuracy and current compatibility, ideal conversion efficiency, and wide working voltage range, also integrates the control function of the rich and comprehensive protection function.

PT4112 main functions and technical characteristics are as follows:

1. % 20 ultra-high precision. The patent design technology and advanced simulation technology process, PT4112 current precision as high as + / - 2%, the current matching degree between the 6 channels can be up to + / - 1. 5%, which not only in the domestic original products is second to none, and can completely meet the demands of high-end laptops so high image quality.

　　2. % 20 high conversion efficiency. By adopting the design of the patent technology and advanced process simulation technology, PT4112 conversion efficiency can be as high as 90% above.

　　3. % 20 wide working voltage range. 5 ~ 25 v working voltage range, can let the engineers in more applications easy selection PT4112, without having to worry about the effects of working voltage.

　　4. % 20 support PWM dimming brightness, PWM signal duty ratio range of 0 ~ 100%. The PWM signal is input into the BRT PT4112 port, you can directly control LED lights turned on and off. By keeping the dimming circuit state during shut off, the AC ripple on the output capacitance can be large in PWM duty ratio range is small value, in order to reduce potential audio noise.

　　5. % 20 complete protection function. PT4112 has open circuit over-voltage protection function, by switching cycles of current limiting function, output open circuit protection, over temperature protection function, the input voltage under-voltage lockout, and soft start, etc. In addition, PT4112 also has a unique FAULT protection function, through to provide external PFET drive signal, only need to connect this PFET between input and inductance, when the system is a serious mistake, this PFET power supply (will be For portable applications, is usually a lithium-ion battery pack) And WLED isolation, to avoid the battery damage due to leakage of large current, realize the whole system safe and reliable.

　　6. % 20 unique circuit automatic brightness compensation function. This is PT4112 design does not provide craftsmanship, is an optional features, set by PT4112 IFB port. When dangling IFB port, if the output of a 1 6 road road to stop working, and the remaining 5 current automatically increases by 20%. The IFB port grounding can be shut off this function.

　　7. % 20 good EMI features. By adopting special design techniques, PT4112 EMI effectively suppressed.

the typical application circuit design and matters needing attention

PT4112 circuit design method is as follows:

1. % 20 current output setting

no. 6 current path, each path all the way maximum current can reach 25 ma. Size of the output current can be achieved by external R1 in Iset port setting,

select different R1 resistance can obtain the required output current:

R1 = 1240 / Iset

the R1 is set resistance, unit take K Ω, Iset is required by the current unit for mA. 20 ma of the resistance value is 62 k Ω.

　　2. % 20 inductance selection of

inductance will be decided to work the whole system's stability, the important factors of inductance characteristics mainly have three: the sense of value, DCR and saturation current, PT4112 recommended range of inductance of 4. 7 - 10 mu H, under the condition of the size and encapsulation allows recommended 10 mu H inductors, because such choice system can get a higher efficiency and smaller ripple. In addition, the output current limiting cases, 10 mu H inductor also helps to get a larger output current. Booster circuit, the calculation of inductance are usually calculated according to the following formula:

fengfeng value of the inductor current ripple can be calculated this way:

as a result, the inductance current peak is:

to ensure system stable work, usually 1 saturation current shall be the peak current. 5 times.

　　3. PWM dimming

by PWM chip PT4112 BRT port on, can realize PWM dimming. PWM adjustable light is effective for all channels at the same time, PT4112 does not support of PWM dimming all the way alone. The frequency of the PWM signal at 100 hz ~ 1 KHZ range is more appropriate, as shown in figure 2.

is shown in figure 1, PT4112 efficiency under different frequency PWM dimming of duty ratio curve

in figure 2, the different frequency PWM dimming curve adjustable GuangXianXing degree under the

in figure 3, the typical application of PT4112 circuit

4. PCB layout considerations

to high frequency and high current power supply system, PCB layout is very important link, so you also should follow the following considerations:

1, try to close to the chip Iset end resistance, to effectively reduce the impact of noise on the current setting;

2, input capacitance Cin and output capacitance Cout should be close to the chip, as far as possible to ensure the system's stability.

3, input to the SW side, as well as the SW output end to go online will have the biggest 3 amperes of current, so it need to make sure that the corresponding current density