Want to solve the problem of overheating and off-board uncertainty of LED driver chips? Let TI’s latest product TPS92633-Q1 help you

Today, linear LED driver chips are increasingly used in automotive body lighting systems, and are especially suitable for use in taillight modules. For many years, TI has been committed to providing the most competitive LED driver solutions for users in the automotive industry and building innovative, reliable and cost-effective automotive lighting systems.

Today, linear LED driver chips are increasingly used in automotive body lighting systems, and are especially suitable for use in taillight modules. For many years, TI has been committed to providing the most competitive LED driver solutions for users in the automotive industry and building innovative, reliable and cost-effective automotive lighting systems.

Have you ever been troubled by heat dissipation and off-board design when designing your body lighting system? TI’s latest C-bit product, the TPS92633-Q1, will bring you a transformative solution. As shown in the figure below, TPS92633-Q1 uses external shunt resistors to share heat on the one hand, and supports off board binning resistors on the other hand, which makes off-board design easier and greatly relieves the pressure at the end of the production line. In addition, the new product supports a voltage input range of 4.5V-40V and three channel outputs, each with an output current of up to 150mA.

Want to solve the problem of overheating and off-board uncertainty of LED driver chips? Let TI’s latest product TPS92633-Q1 help you
TPS92633-Q1 Schematic

Better Thermal Performance: External Shunt Resistors

In the design of the tail light module, the thermal short board of the linear driver chip makes it usually unable to support very high power. To prevent “chip overheating” or “system overheating,” designers often rely on expensive, large-area thermal designs to achieve the required output power.

One of the highlights of the TPS92633-Q1 is that it is equipped with an external shunt resistor that can share the heat, which improves the heat dissipation performance and reduces the system BOM cost.

Want to solve the problem of overheating and off-board uncertainty of LED driver chips? Let TI’s latest product TPS92633-Q1 help you
How a Shunt Resistor Works

The default current source channel (green line) outputs current when the input voltage is low and close to the forward voltage drop required by the LED. When the input voltage is higher than the forward voltage drop required by the LED, another resistive path (red line) is also turned on at the same time, sharing the current and power consumption.

Want to solve the problem of overheating and off-board uncertainty of LED driver chips? Let TI’s latest product TPS92633-Q1 help you
Input Voltage VS. Output Current

The comparison of output current and power consumption under different input voltages is shown in the figure below. Itotalis the total current flowing to the LED and is equal to the flow through the OUT pin and RresThe sum of the currents of the pins. The black line in the figure below is the total power consumption of the system, which is equal to the sum of the power consumption of the chip and the resistor. We can see that with the help of RresThe power consumption of the chip itself is significantly reduced, thus effectively controlling the heat generation.

Want to solve the problem of overheating and off-board uncertainty of LED driver chips? Let TI’s latest product TPS92633-Q1 help you
Input Voltage vs. Power Consumption

The thermal test results of the TPS92633-Q1 are shown in the figure below. Typically, a passenger car battery has a voltage range of 9V to 16V, and the ambient temperature of a car taillight is up to 85°C. We performed simulation tests under these conditions when VinWhen the voltage is 16V, the TPS92633-Q1 uses a shunt resistor to share the heat of the system and can support a current of up to 450mA, while the control chip without a shunt resistor will directly trigger thermal shutdown protection at the same ambient temperature.

Want to solve the problem of overheating and off-board uncertainty of LED driver chips? Let TI’s latest product TPS92633-Q1 help you
Thermal test comparison results

A more convenient and low-cost solution: Off-board Binning Resistor.

In the off-board design, due to the limitation of the LED production process, the LED board must be matched with the chip board to unify the brightness of the LED, which is often a cumbersome step that cannot be omitted. Even in the same batch of LED products, there will be different bins. After purchasing a whole batch of LEDs, users still need to set the current of different bins LEDs through the binning resistor to unify the brightness.

The existing solution is shown in the figure below. Considering the noise immunity of the chip, the binning resistor must be placed on the same board as the driver chip, so different binning resistors must be designed for different driver chip boards. In order to match the LED board with the driver chip board, we need to use barcode or QR code for identification, which greatly increases the design complexity and manufacturing cost.

Want to solve the problem of overheating and off-board uncertainty of LED driver chips? Let TI’s latest product TPS92633-Q1 help you
Existing solution: Binning resistors and driver chips are on the same board

Another highlight of TPS92633-Q1 is that its ICTRL pin supports off-board binning resistor, which perfectly solves the above problems. As shown in the figure below, we can directly place the binning resistor on the LED board during the manufacturing process, so that only one driver chip board needs to be designed to match the LED boards of all bins, which greatly reduces the manufacturing cost.

Want to solve the problem of overheating and off-board uncertainty of LED driver chips? Let TI’s latest product TPS92633-Q1 help you
TPS92633-Q1 solution: off-board binning resistor

In addition to supporting off-board binning resistor, TPS92633-Q1 also supports thermal derating by connecting NTC to ICTRL pin. When the temperature rises, the NTC resistance will decrease, RICTRLThe voltage on the device will decrease, thereby reducing the output current for overheating protection. The following picture shows the test results.

Want to solve the problem of overheating and off-board uncertainty of LED driver chips? Let TI’s latest product TPS92633-Q1 help you
Temperature vs. Output Current

in conclusion

Thermal performance is one of the most critical design considerations when designing body lighting systems. In existing linear LED driving schemes, all voltage drops are borne by the chip, which often causes the chip and system to overheat. The matching of the LED board and the driver board is another difficulty in the design process. If the binning resistor and the driver chip are placed on the same board, additional costs will be added.

The new star product TPS92633-Q1 of Texas Instruments (TI) provides a reliable, efficient and low-cost solution. Its external shunt resistor can effectively share the heat dissipation pressure, while supporting off-board binning resistor for off-board design.

Design example

1. Design example of BCM-controlled taillights with One-Fail-All-Fails function

TPS92633-Q1 can drive car tail lights with different functions, including brake lights, turn signals, fog lights, reversing lights, etc.; in the scenario where multiple TPS92633-Q1s are used together, one can be easily realized by connecting the FAULT pins. Fail-All-Fails feature.

Want to solve the problem of overheating and off-board uncertainty of LED driver chips? Let TI’s latest product TPS92633-Q1 help you
Schematic Design

1.1 Design Requirements

The input voltage range of the passenger car battery is 9V to 16V. Generally, 3 LEDs in each channel are required to realize the brake light function; the maximum forward voltage drop of each LED is VF_MAXis 2.5V, the minimum forward voltage drop VF_MINis 1.9V; current I per LED(LED)The requirement is 140mA; the brightness and switch of the LED are directly controlled by the body control module BCM; in addition, the short-circuit detection function of a single LED is also required, and the One-Fail-All-Fails function of the brake light is realized.

1.2 Detailed design steps

STEP 1: When the ICTRL resistor is placed on the same board as the TPS92633-Q1, TI recommends setting I(IREF)is 100uA; use the following formula to get R(IREF)where V(IREF) = 1.235V, I(IREF) = 100uA (recommended value), at this time R(IREF)is 12.3kΩ.

Want to solve the problem of overheating and off-board uncertainty of LED driver chips? Let TI’s latest product TPS92633-Q1 help you

STEP 2: When the ICTRL pin is not used to drive off-board binning resistor or NTC resistor, TI recommends setting V(CS_REG)is 100mV; use the following formula by designing the ICTRL resistor R(ICTRL)resistance to set V(CS_REG)Voltage (voltage between SUPPLY pin and INx pin), where V(CS_REG) = 100mV (recommended value), I(IREF) = 100uA (recommended value). At this time, R(ICTRL)is 680Ω.

Want to solve the problem of overheating and off-board uncertainty of LED driver chips? Let TI’s latest product TPS92633-Q1 help you

STEP 3: When each output current I(OUTx_Tot) = 140mA, use the following formula to get R(SNSx)Resistance (resistance between SUPPLY pin and INx pin), where V(IREF) = 1.235V, R(ICTRL) = 680Ω, R(IREF) = 12.3kΩ, I(OUTx_Tot) = 140mA. At this time, R(SNSx) = 0.717Ω.

Want to solve the problem of overheating and off-board uncertainty of LED driver chips? Let TI’s latest product TPS92633-Q1 help you

According to the design requirements, the output current of each channel is the same, so R(SNS1) =R(SNS2) =R(SNS3) = 0.717Ω. It should be noted here that 0.717Ω is not a standard resistance value, so two resistors need to be connected in parallel to obtain an equivalent 0.717Ω resistance.

STEP 4: Calculate the shunt resistance R using the following formula(RESx)resistance value. R(RESx)The value of actually determines I(OUTx)and I(RESx)current distribution, the basic design principle is to make R(RESx)It consumes about 50% of the total power consumption at the supply voltage.

Want to solve the problem of overheating and off-board uncertainty of LED driver chips? Let TI’s latest product TPS92633-Q1 help you

where V(SUPPLY) = 12V, I(OUTx_Tot) = 140mA. When V(OUTx) = 3 x 2.2V = 6.6V, R(RESx)(including R(RES1)R(RES2)R(RES3)) is 75Ω.

STEP 5: Design the threshold voltage for diagnosing a single LED short circuit, and use the following formula to calculate the resistor R used to set the threshold voltage(SLS_REF)resistance value.

The total forward voltage drop of the three LEDs in series is a maximum of 3 × 2.5 V = 7.5V and a minimum of 3 × 1.9 V = 5.7V. Once any of the three LEDs fail short, the total forward voltage drop for the remaining two LEDs in series is 2 × 2.5 V = 5 V (max) and 2 × 1.9 V = 3.8 V (min). Therefore, we can choose 5.3 V as the threshold voltage V for a single LED short circuit(SLS_th_falling).

Want to solve the problem of overheating and off-board uncertainty of LED driver chips? Let TI’s latest product TPS92633-Q1 help you

where V(IREF) = 1.235V, R(IREF) = 12.3kΩ, N(OUT) = 4, N(SLS_REF) = 1. When V(SLS_th_falling) = 5.34V, R(SLS_REF) = 13.3kΩ.

STEP 6: Design the threshold voltage of the SUPPLY pin to set the LED open-circuit and short-circuit diagnostic functions of a single LED, and calculate the resistance values ​​of the voltage divider resistors R1 and R2 on the DIAGEN pin.

The maximum forward voltage drop for 3 LEDs is 3 × 2.5 V = 7.5 V; to avoid false open faults or short circuits of a single LED during slow power-up operation, the minimum voltage between the SUPPLY pin and the OUTx pin needs to be considered. Voltage drop; when the supply voltage is lower than the maximum forward voltage drop of the 3 LEDs, V(OPEN_th_rising)V(CS_REG)When the three are combined, the TPS92633-Q1 must turn off the open-circuit detection and the short-circuit detection of a single LED. The resistance values ​​of the voltage divider resistors R1 and R2 can be calculated by the following formula.

Want to solve the problem of overheating and off-board uncertainty of LED driver chips? Let TI’s latest product TPS92633-Q1 help you

where V(OPEN_th_rising) = 210mV(maximum), V(CS_REG) = 100mV, VIL (DIAGEN) = 1.045V(minimum), R2 = 10kΩ (recommended value). At this time, R1is 64.9kΩ.

STEP 7: Design the threshold voltage of the SUPPLY pin to control the switching of the LED channel, and calculate the voltage dividing resistor R on the PWM input pin3and R4resistance value.

The minimum forward voltage drop of the 3 LEDs is 3×1.9 V = 5.7V; in order to ensure that the current output of each channel is normal, when the SUPPLY pin voltage is lower than the minimum forward voltage drop of the 3 LEDs, the INx pin and the OUTx pin Voltage drop between feet, V(CS_REG)When the sum is reached, each output should be in a closed state. divider resistor R3R4The resistance value can be calculated by the following formula.

Want to solve the problem of overheating and off-board uncertainty of LED driver chips? Let TI’s latest product TPS92633-Q1 help you

where V(DROPOUT) = 300mV, V(CS_REG) = 100mV, VIH(PWM) = 1.26V(maximum), R4 = 10kΩ (recommended value). At this time, R4is 38.3kΩ.

1.3 Simulation curve

Want to solve the problem of overheating and off-board uncertainty of LED driver chips? Let TI’s latest product TPS92633-Q1 help you
80% brightness SUPPLY dimming & 20% brightness SUPPLY dimming

2. Design example of off-board independent PWM-controlled taillights

The TPS92633-Q1 can independently drive the output current of each channel through the PWM inputs on the PWM1, PWM2 and PWM3 pins. The LEDs are placed together with the LED binning resistor on a different PCB than the TPS92633-Q1, and the LED binning resistor is connected to the ICTRL pin to adjust the current through the LED accordingly.

Want to solve the problem of overheating and off-board uncertainty of LED driver chips? Let TI’s latest product TPS92633-Q1 help you
Schematic Design

2.1 Design Requirements

The input voltage range of the passenger car battery is 9V to 16V. Generally, 2 total 6 LEDs per channel are required to realize the turn signal function; the maximum forward voltage drop of each LED is VF_MAXis 2.5V, the minimum forward voltage drop VF_MINIt is 1.9V; the LED binning resistor and the LED are placed on another PCB board; the current required by the bins LED of different brightness is 50 mA, 75 mA and 100 mA; the output of each channel is independent and controlled by the MCU.

2.2 Design detailed steps

TI recommends grounding the SLS_REF pin when the single LED short-circuit diagnostic feature is not required.

STEP 1: When the ICTRL resistor and TPS92633-Q1 are placed on two different boards, TI recommends setting I(IREF)is 200uA; use the following formula to get R(IREF)where V(IREF) = 1.235V, I(IREF) = 200uA (recommended value off board), at this time R(IREF)is 6.19kΩ.

Want to solve the problem of overheating and off-board uncertainty of LED driver chips? Let TI’s latest product TPS92633-Q1 help you

STEP 2: When the ICTRL resistor and TPS92633-Q1 are placed on two different boards, use the following formula by designing the ICTRL resistor R(ICTRL1)R(ICTRL2)resistance to set V(CS_REG)voltage (between the SUPPLY pin and the INx pin), where I(IREF) = 200uA (recommended value).

Want to solve the problem of overheating and off-board uncertainty of LED driver chips? Let TI’s latest product TPS92633-Q1 help you

For LEDs with three different bins, TI recommends that the R(SNSx)(resistance between SUPPLY pin and INx pin) 80mV, 120mV and 160mV are applied across the terminals, respectively. The table below lists the R of different brightness bins LEDs(ICTRL1)R(ICTRL2)The calculation result of the resistance value, it is recommended to choose R with the largest resistance value as possible.(ICTRL1)to enhance noise immunity.

Want to solve the problem of overheating and off-board uncertainty of LED driver chips? Let TI’s latest product TPS92633-Q1 help you

STEP 3: Use the following formula to get R(SNSx)resistance, where V(IREF) = 1.235V, R(IREF) = 6.19kΩ.

Want to solve the problem of overheating and off-board uncertainty of LED driver chips? Let TI’s latest product TPS92633-Q1 help you

According to the design requirements, the output current of each channel is the same, so R(SNS1) =R(SNS2) =R(SNS3). R(SNSx)The calculation results are also listed in the table above.

STEP 4: Calculate the shunt resistance R using the following formula(RESx)resistance value. R(RESx)The value of actually determines I(OUTx)and I(RESx)current distribution, the basic design principle is to make R(RESx)It consumes about 50% of the total power consumption at the supply voltage.

Want to solve the problem of overheating and off-board uncertainty of LED driver chips? Let TI’s latest product TPS92633-Q1 help you

where V(SUPPLY) = 12V, I(OUTx_Tot) = 100mA. When V(OUTx) = 2 x 2.2V = 4.4V, R(RESx)(including R(RES1)R(RES2)R(RES3)) has a resistance value of 152Ω.

STEP 5: The design is used to set the SUPPLY voltage threshold of the LED open circuit diagnostic function, and use the following formula to calculate the voltage divider resistor R on the DIAGEN pin1R2resistance value.

The maximum forward voltage drop of 2 LEDs is 2 × 2.5 V = 5V; to avoid false open circuit faults during slow power-on operation, the minimum voltage difference between the SUPPLY pin and the OUTx pin needs to be considered; when the power supply voltage Maximum forward voltage drop below 2 LEDs, V(OPEN_th_rising)V(CS_REG)When the three are added together, the TPS92633-Q1 must turn off the open circuit detection function. The resistance values ​​of the voltage divider resistors R1 and R2 can be calculated by the following formula.

Want to solve the problem of overheating and off-board uncertainty of LED driver chips? Let TI’s latest product TPS92633-Q1 help you

where V(OPEN_th_rising) = 210mV(maximum), V(CS_REG) = 160mV(maximum), VIL (DIAGEN) = 1.045V(minimum), R2 = 10kΩ (recommended value). At this time, R1is 41.2kΩ.

2.3 Simulation curve

Want to solve the problem of overheating and off-board uncertainty of LED driver chips? Let TI’s latest product TPS92633-Q1 help you
80% duty cycle PWM dimming at 200Hz & 20% duty cycle PWM dimming at 600Hz

The Links:   ER057000NM6 EP1C6F256I7N

Author: Yoyokuo