“Currently on the market, the light sources of car headlights mainly include halogen, xenon and LED headlights. Halogen car lights. Halogen is the main element of car lamp fillings. Among them, iodine or bromine is mainly used in car lights. Its advantage lies in low manufacturing cost, but its disadvantage lies in excessive heat and short service life.
Author: Hong, Holly
Currently on the market, the light sources of car headlights mainly include halogen, xenon and LED headlights. Halogen car lights. Halogen is the main element of car lamp fillings. Among them, iodine or bromine is mainly used in car lights. Its advantage lies in low manufacturing cost, but its disadvantage lies in excessive heat and short service life.
Xenon car lights, xenon gas is an inert gas that is filled in the car lights, and then pressurized by the supercharger inside the car. The pressure generated can instantly ionize the xenon gas to produce light. Its advantages are low price, illuminance and brightness Higher than halogen; the disadvantage is that in some extreme weather, the emitted light is not enough to penetrate the fog, which may cause safety hazards.
LED car lights, as a new type of lighting source, LED has excellent performance this year, and its application is growing rapidly. Its main advantages are long life, high efficiency and low energy consumption. The disadvantages are high cost and poor heat dissipation. In terms of the development status and trends of LED car light technology, its price is steadily declining, and LED car lights are developing in a personalized and artistic direction. At the same time, LED intelligent control systems will also develop rapidly.
Features of TPS92633-Q1
TPS92633-Q1 is a newly launched LED driver from TI, which can be used in automotive taillights and internal/external small lights. TPS92633-Q1 is a linear driver that can withstand a wide voltage input from 4.5V to 40V, with an output current of 150mA per channel. The chip’s diagnostic functions include LED open circuit, LED short circuit to ground and single LED short circuit detection. The one-fails-all-fail function of TPS92633-Q1 can be used with other LED drivers (such as TPS9261x-Q1, TPS92630/8-Q1 and TPS92830-Q1). In addition, TPS92633-Q1 has three unique designs.
1. Unique thermal management design to avoid high temperature of equipment.
Each channel of TPS92633-Q1 provides two current output paths, and current flows from the power supply through R(SNSx)Enter the integrated current regulation circuit and flow to the LED through the OUTx pin and the Resx pin. The current output on the OUTx pin and the Resx pin are independently adjusted to achieve the required total current. The sum current of output OUTx and Resx is equal to flowing through R(SNSx) 的current.
OUTx is connected to the anode of the LED load, but Resx is connected to the LED through an external resistor, and the external resistor is used to realize heat sharing, as shown in Figure 1. When the supply voltage is lower than or close to the forward voltage required by the LED, the current mainly passes through the red path in Figure 1; when the supply voltage is higher than the forward voltage required by the LED, the current path turns to green and passes through R(SHUNT)Partial pressure to achieve heat dispersion. Figure 2 shows R (resx) The power consumption distribution curve when it is 68.5 Ω, it can be seen from the figure that the distribution of output power consumption mainly depends on the supply voltage.
Figure 1 Schematic diagram of current flow
Figure 2 The relationship between output power distribution and supply voltage
2. Adjust the brightness of the LED across the board.
TPS92633-Q1 has an analog dimming function. It can be seen from Equation 1 that the output current can be adjusted by adjusting the resistance on the ICTRL pin, thereby realizing the brightness adjustment of the LED. In order to suppress noise, it is recommended to use two resistors. One of the fixed resistors is placed as close to the ICTRL pin as possible, and the other dimming resistor can be placed on the other PCB board where the LED is placed, as shown in Figure 3.
Figure 3 Schematic diagram of span board adjustment
3. NTC thermistor adjusts the output current.
The analog current control function also allows an NTC thermistor to be connected to the ICTRL pin to adjust the output current according to the measured PCB board temperature or LED unit temperature. The NTC thermistor decreases as the temperature increases. It causes R on the ICTRL pin(ICTRL) The equivalent resistance decreases. According to Equation 1, it can be concluded that as R(ICTRL)Reduce the output current to reduce. In Figure 4, the resistance values of R1 and R2 are used in conjunction with NTC thermistors to adjust the output current at high temperatures. The specific output current change curve with temperature is shown in Figure 5.
Figure 4 Application schematic diagram of external NTC thermistor
Figure 5 Output current change curve with temperature
Typical application and PCB Layout
TPS92633-Q1 can be used to drive taillights and internal small lights of automobiles, and its typical application is shown in Figure 6. Figure 7 is an example of the PCB layout of TPS92633-Q1, which mainly considers two major elements:
Heat dissipation is the main consideration in the layout of the TPS92633-Q1.
It is recommended to have a larger heat dissipation area on the top and bottom layers of the PCB. Because R(RESx)It has the same power consumption as TPS92633-Q1. It is recommended to set R(RESx)The resistor is placed at a distance of more than 20 mm from the TPS92633-Q1 device. In R(RESx)A larger copper pouring area is also needed around to help dissipate heat.
Noise immunity is a secondary consideration in the layout of the TPS92633-Q1.
Place the noise decoupling capacitors on the SUPPLY, ICTRL, and IREF pins as close to the pins as possible. R(RESx)Place the resistor as close as possible to the INx pin and connect it to the SUPPLY pin through the shortest PCB.
Figure 6 Typical application of TPS92633-Q1
Figure 7 PCB layout example of TPS92633-Q1