It's time to say goodbye to discrete solutions for automotive lighting!

Major automakers are using light-emitting diodes (LEDs) extensively , in addition to traditional headlights, taillights, daytime running lights, parking lights and turn signals to make their cars stand out in the market . Currently, LEDs are found in clearance lights, license plates, brand logos, welcome lights and ambient lights .

To drive these LEDs to emit light, the following issues must be considered:

• The accuracy of current and the homogeneity of LEDs will be significantly improved ;

• The brightness change of LED requires some kind of dimming function;

• LED open / short circuit diagnosis and protection, as well as thermal protection, because safety issues have always been the focus of automobiles.

• How to improve energy efficiency.

Traditionally, LEDs have been driven by discrete solutions. Figure 1 shows three typical solutions: an operational amplifier (op amp) (solution 1 ), a power source directly connected to the car battery (solution 2 ), or a bipolar configuration with some kind of current-shunt regulation (solution 3 ).

Figure 1: Typical discrete solution for driving LEDs

Let's first look at solution 1 , an op amp driven from the low side. With an op amp, relatively high accuracy (<10%) can be achieved, and the LED can be dimmed. However, it is difficult to diagnose open and short LEDs with this solution . In addition, the input-output voltage difference is as high as 1 volt, which is not very energy-efficient.

Solution 2 is also popular, which consists of a diode and an NPN type ( n -channel p -channel n- channel) transistor. This solution is not only simple and cost-effective, but its accuracy is only about 20% , which is far from enough. Since its input-output voltage difference is as high as 1.2 volts, its energy efficiency is even lower than that of Solution 1. In addition, it cannot diagnose LED open and short circuits, and there is no pulse width modulation (PWM) dimming function. This solution is too backward for today's design .

Solution 3 is popular in applications that require very high output accuracy (<5%) . The input-output voltage difference is very high, reaching 3V . This solution either cannot implement diagnostics or has PWM dimming function; therefore, the application range of this solution is narrow and the cost is high.

Admittedly, each solution has its own advantages and disadvantages, but compared with discrete solutions, a lower-cost overall solution can not only reduce the number of system-level components, but also significantly improve current accuracy and reliability. The TPS9261x-Q1 series shown in Figure 2 is a product designed specifically for this purpose.

Figure 2: TPS9261x-Q1 Simplified Schematic

The TPS92610-Q1 device is a single-channel high-side LED driver driven by an automotive battery . It is a simple and elegant solution to provide a constant current to a single LED string with full LED diagnostics . Its accuracy is up to 7% , which meets the needs of most applications.

TPS9261x-Q1 has a variety of different packaging options, from small outline transistor (SOT)-23, MSOP-8 to thermally enhanced thin small outline package (HTSSOP)-14 , to support different output power levels. With this series of single-channel automotive LED drivers, you can immediately say goodbye to traditional discrete solutions.