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The PT4112 is a 6-channel white LED driver IC with up to 10 white LEDs in series, so a single chip can drive up to 60 white LEDs. The PT4112 not only has excellent current accuracy and current matching, ideal conversion efficiency, and wide operating voltage range, but also integrates rich control functions and comprehensive protection functions.
The main functions and technical features of the PT4112 are as follows:
1.%20 ultra high precision. Using patented design technology and advanced analog process technology, PT4112's current accuracy is up to ±2%, and the current matching between 6 channels can be as high as ±1.5%, which is not only second to none in local original products, but also fully meets High-end notebooks require such high image quality applications.
2.%20 high conversion efficiency. Through patented design techniques and advanced analog process processes, the conversion efficiency of the PT4112 can be as high as over 90%.
3.%20 wide operating voltage range. The 5 to 25V operating voltage range allows engineers to choose the PT4112 in more applications without worrying about the operating voltage.
4.%20 supports PWM brightness dimming, PWM signal duty cycle range is 0~100%. Input the PWM signal to the BRT port of the PT4112 to directly control the LED light on and off. By maintaining the state of the circuit during dimming off, the AC ripple on the output capacitor can be kept small over a large duty cycle of the PWM to reduce potential audible noise.
5.%20 various protection functions are complete. The PT4112 features open-circuit over-voltage protection, current-by-switch cycle current limiting, output shutdown protection, overtemperature protection, input voltage undervoltage lockout, and soft-start. In addition, the PT4112 has a unique FAULT protection function. By supplying a driving signal to the external PFET, it is only necessary to connect this PFET between the input and the inductor. When a serious error occurs in the system, the PFET can supply power. Portable applications, usually lithium battery packs, are isolated from the WLED to prevent damage to the battery due to leakage of large currents, making the entire system safe and reliable.
6.%20 unique open circuit automatic brightness compensation function. This is an ingenious design of the PT4112, an optional feature that is set via the IFB port of the PT4112. When the IFB port is left floating, if one of the 6 outputs stops working, the remaining 5 currents are automatically increased by 20%. Grounding the IFB port turns off this feature.
7.%20 good EMI characteristics. The EMI of the PT4112 is effectively suppressed by using special design techniques.
Typical application circuit design and precautions
The PT4112 application circuit design method is as follows:
1.%20 current setting
The output of the 6 current paths, the maximum current of each channel can reach 25mA. The output current can be set by externally connected to R1 on the Iset port.
Select the different R1 resistor values ​​to get the required output current:
R1=1240/Iset
Where R1 is the set resistance, the unit is taken as KΩ, Iset is the required current, and the unit is mA. The resistance corresponding to 20 mA is 62 KΩ.
2.%20 inductance selection
The choice of inductors will be an important factor in determining whether the entire system can work stably. There are three main characteristics of inductors: sense, DCR and saturation current. The recommended range of PT4112 is 4.7-10μH, which is recommended when size and package allow. Use a 10μH inductor because such a choice system can achieve higher efficiency and less ripple. In addition, the 10μH inductor also helps to obtain a large output current when the output current limit is constant. In the boost circuit, the calculation of the inductance is usually calculated according to the following formula:
The peak-to-peak value of the inductor current ripple can be calculated as follows:
Thus, the peak value of the inductor current is:
In order to ensure stable operation of the system, the saturation current should be 1.5 times the peak current.
3. PWM dimming
PWM dimming can be achieved by applying a PWM chip to the BRT port of the PT4112. PWM dimming is effective for all channels simultaneously. The PT4112 does not support PWM dimming for a single channel. The frequency of the PWM signal is suitable in the range of 100 Hz to 1 kHz, as shown in Fig. 2.
Figure 1. Efficiency vs. duty cycle curve of PT4112 at different PWM dimming frequencies
Figure 2. Dimming linearity curve at different PWM dimming frequencies
Figure 3. Typical application circuit of PT4112
4. PCB layout considerations
PCB layout is a very important part for high frequency and high current power supply systems, so the following precautions should be followed:
1. The Iset terminal resistance should be as close as possible to the chip to effectively reduce the influence of noise on the current setting.
2. The input capacitor Cin and the output capacitor Cout should be as close as possible to the chip to ensure stable operation of the system.
3. Input to the SW terminal, and the current from the SW terminal to the output will have a maximum current of 3 amps, so the trace needs to ensure the corresponding current density.
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