Design and typical application of the hottest high

High brightness LED linear driver chip design and typical application scheme analysis

high brightness LED has the advantages of high luminous intensity, high luminous efficiency, energy conservation and environmental protection, long service life, etc. in order to solve the problem of rapid rise in raw material costs, it is widely used in automotive lighting, displays, camera flash, panel backlight, landscape lighting, interior decoration and other fields. Because the brightness of LED is related to its current, and the small changes of on voltage, working voltage and ambient temperature have a great impact on the LED current, it is necessary to design a special driver chip to maintain the brightness consistency of LED array. Linear constant current LED drive circuit has the advantages of simple structure, low electromagnetic interference, rapid response, small size and low cost, so it is often used in automotive electronic systems powered by batteries

structural block diagram and technical characteristics of at8803/at8800

this paper introduces the high voltage and high current LED linear drive chips at8803 and at8800 developed by Wuhan Xinjing Technology Co., Ltd. for automotive electronics, which are mainly used in automotive tail lights, central high mounted brake lights (CHMSL), map lights and door controlled interior lighting. In the range of 6.5V to 40V input voltage, it can provide a total current of up to 350mA to drive one or more columns of high brightness LEDs. Compared with at8800, at8803 adds dim dimming control pins

figure 1:at8803/at8800 structural schematic diagram

an external current detection resistor RSENSE connected with the electromechanical aspect of the LED string is used to adjust the output current. Enable input en to realize a wide range of "pulse" brightness control. Waveform shaping circuit reduces EMI. The differential current detection input improves the noise suppression ability. At8803 and at8800 are very suitable for applications requiring high voltage input, and can withstand vehicle load rejection up to 40V. Power devices are integrated in the chip, which reduces the number of external components and provides an output current accuracy of ± 3.5%. The chip also provides 5V regulated output, short-circuit protection and thermal protection

at8803 dimming application

at8803 provides two dimming methods as shown in Figure 2 and figure 3 respectively. The dim pin can withstand 40V high voltage and provide a wide range of PWM dimming function. Connecting en with VIN pin and inputting PWM signal to dim or connecting dim with V5 pin and inputting PWM signal to en can generate an LED current with adjustable duty cycle, so as to control the brightness of LED

figure 2:en of at8803 is connected to VIN, dimming is realized by dim pin

figure 3:dim of at8803 is connected to V5, dimming is realized by VIN pin

other typical applications of at8803

in high current applications, the current output capacity of 350mA of at8803 may not meet the requirements, so the drive current can be increased by external BJT in the way shown in Figure 4. The chip adjusts the base current by detecting the emitter current of external Q1, so as to maintain the current flowing through the LED lamp unchanged

figure 4:at8803 uses external BJT to realize the current expansion function

Figure 5 shows the application scheme of using at8803 to realize the two-stage brightness control of tail lamp/brake lamp. In the tail lamp working mode, the external MOS tube Q1 is closed, and R1 controls the current flowing through the LED lamp. When the braking mode is started, Q1 is turned on, and R1 and R2 are connected in parallel to jointly control the current of the LED lamp

figure 5:at8803 realizes two-stage brightness control of tail lamp/brake lamp

summary

this paper briefly introduces the functional characteristics and application scheme of a high brightness LED linear driver chip that meets the requirements of contraction and fatigue. With the rapid growth of the domestic automotive market, such chips will be widely promoted and applied. (end)