All Module will include LED drive circuit inductor, are integrated in a surface mount package.

............ Technology company David Ng

The introduction

Once classified as a low cost indicator, LED is once again the focus of attention in the field of lighting. LED lighting can now be seen everywhere, from the car headlights to USB power supply lava lamps, etc.. The automobile headlamp shows high quality available advantages LED -- Application of stable light output, steely robustness and inherent high efficiency - and USB lava lamp shows only LED is suitable for the application. Despite the obvious advantages of the LED, but the stability of the voltage and current requirements so that the complexity of the LED driver circuit is higher than the past. However, some new devices are gradually make up for this gap. For example, LTM Module LED 8040 drive drive circuit are all integrated in a single package, which enables the designer to put their time and energy to focus on the details of the lighting design, which is crucial for the success of the product.

An excellent LED driver

LTM8040 is a complete buck DC/DC switching converter system that can drive up to 1A current through a LED string. The 4V to 36V input voltage range of the device makes it suitable for a variety of power applications, including two lithium ion batteries, 12VAC rectifier and industrial 24V. LTM8040 both analog and PWM dimming function, can provide a 250:1 dimming range. Built in 14V output voltage clamp circuit is used to avoid accidental LED open circuit damage. The default switching frequency of LTM8040 is 500kHz, but can be used to connect a resistor between the RT pin and the GND to set the switching frequency to 2MHz.

Easy to use

The high integration of the LTM8040 reduces the number of external components and simplifies the layout of the circuit board. As shown in Figure 1, the LTM8040 is required to drive a LED string as high as 1A and an input decoupling capacitor. Even in the case of all these built-in features, LTM8040 itself is still very small size, only 15mm x 9mm x 4.32mm.

Figure 1: using LTM8040 to drive a LED string is easy - simply add the input capacitor and connect the LED string

Rich feature set

The LTM8040 features a ADJ pin for accurate LED current amplitude control. The ADJ pin is capable of accepting a full scale input voltage range of 0V to 1.25V and linearly adjusts the output LED current (from 0A to 1A). Figure 2 shows the relationship between the proportional response of the output LED current and the ADJ voltage. In the internal 5.11k through a high precision resistor on the ADJ pin will be pulled to an internal 1.25V reference, so the output current can also LED between the ADJ pin and a single resistor to adjust the layout, as shown in figure 3.

PWM control pin can provide high light ratio. Using an external MOSFET in series with the LED series (as shown in Figure 4), the LTM8040 can achieve a dimming ratio of more than 250:1. As shown in Figure 5, the distortion of the PWM LED current is minimal, even at frequencies as low as 10Hz. The performance of the 10Hz shown in the diagram is intended to illustrate the capability of the LTM8040, which is too low for the actual pulse width modulation and is fully within the range of the human eye.

Figure 5:LTM8040 can be used to minimize the distortion of the LED current pulse width modulation (PWM), even at frequencies as low as 10Hz is no exception

In addition, the LTM8040 also features a low-power shutdown state. When the /SHDN pin is low efficient, static input current is less than 1 A.

Figure 6:LTM8040 LED driver of the board area of only 9mm x x 4.32mm, is a complete system using LGA package

conclusion

LTM8040 Module LED LED driver to drive easy. Its high integration and rich feature set (including open circuit LED protection, analog and PWM dimming) can save a lot of design time and board space.