Design and application of a high-brightness LED linear driver chip

High-brightness LEDs are widely used in automotive lighting, displays, camera flashes, panel backlights, landscape lighting, and interior decoration due to their high luminous intensity, high luminous efficiency, energy saving, and long life. Since the brightness of LEDs is related to their current, and slight changes in the on-voltage, operating voltage, and ambient temperature have a significant impact on the LED current, it is necessary to design a dedicated driver chip to maintain the consistency of the brightness of the LED array. Linear constant-current LED driver circuits have the advantages of simple structure, low electromagnetic interference, fast response, small size, and low cost, and are therefore often used in battery-powered automotive electronic systems.

AT8803/AT8800 structural diagram and technical features

This article introduces the high-voltage, high-current LED linear driver chips AT8803 and AT8800 developed by Wuhan Xinjing Technology Co., Ltd. for automotive electronics . They are mainly used in automotive taillights, center high-mounted stop lights (CHMSL), map lights, and door-controlled interior lighting. Within the input voltage range of 6.5V to 40V, a total current of up to 350mA can be provided to drive one or more columns of high-brightness LEDs. Compared with AT8800, AT8803 adds a DIM dimming control pin.

Figure 1: AT8803/AT8800 schematic diagram

The output current is adjusted by an external current-sense resistor RSENSE in series with the LED. The enable input EN can achieve a wide range of "pulse" brightness control. The waveform shaping circuit reduces EMI. The differential current detection input improves noise suppression. AT8803 and AT8800 are very suitable for applications requiring high-voltage input and can withstand automotive load dump up to 40V. The integrated power device reduces the number of external components and provides ±3.5% output current accuracy. The chip also provides 5V regulated output as well as short-circuit protection and thermal protection.

AT8803 dimming application

AT8803 provides two dimming modes as shown in Figure 2 and Figure 3. The DIM pin can withstand 40V high voltage and provide a wide range of PWM dimming function. Connecting EN to the VIN pin and inputting a PWM signal to DIM or connecting DIM to the V5 pin and inputting a PWM signal to EN can generate an LED current with an adjustable duty cycle, thereby controlling the brightness of the LED.

Figure 2: AT8803’s EN is connected to VIN, and the DIM pin is used to achieve dimming

Other typical applications of AT8803

In high current applications, the 350mA current output capability of AT8803 may not meet the requirements, so the drive current can be increased by connecting an external BJT as shown in Figure 4. The chip adjusts the base current by detecting the emitter current of the external Q1, thereby maintaining the current flowing through the LED lamp unchanged.

Figure 4: AT8803 uses an external BJT to achieve current expansion

Figure 5: AT8803 implements two-level brightness control of taillights/brake lights

Figure 5 shows an application solution for using AT8803 to achieve two-level brightness control of taillights/brake lights. In the taillight working mode, the external MOS tube Q1 is turned off, and R1 controls the current flowing through the LED light. When the brake mode is activated, Q1 is turned on, and R1 and R2 are connected in parallel to jointly control the current of the LED light.

summary

This article briefly introduces the functional characteristics and application solutions of a high-brightness LED linear driver chip . With the rapid growth of the domestic automobile market, this type of chip will surely be widely promoted and applied.