Letter MAX8790 white LED driver for large screen LCD backlight design

Maxim Integrated Products the day before the launch of the MAX8790 high efficiency white light emitting diode (WLED) driver. This device is specially designed for large screen liquid crystal display (LCD) with LED array as the light source. MAX8790 uses current mode boost controller to drive 6 parallel LED strings. The built-in string current control circuit can make the current regulation accuracy of the string to achieve + 1.5%, to ensure that all LED brightness uniformity. The MAX8790 features a wide input voltage range of +4.5V to +26V and can provide fixed (20mA) or adjustable (15mA to 25mA) full-scale LED current.

Boost controller using external MOSFET, can achieve high efficiency, and adjustable output power and maximum operating voltage, used to drive a series of LED. The low feedback voltage (450mV) of each LED string can reduce power consumption and improve the efficiency. Selectable switching frequencies (500kHz, 750kHz or 1MHz) can be used to compromise between external component size and work efficiency.

MAX8790 has two dimming mode, suitable for a variety of applications. In direct DPWM mode, the PWM signal is used to directly turn on / off the LED current. In the analog dimming mode, the internal phase locked loop circuit converts the PWM signal to an analog signal, which controls the LED current to a minimum of 12.5%. Digital dimming can be adjusted to LED average current below 12.5%, as low as 1%. Two control modes can be achieved wide (100:1) dimming range.

MAX8790 has a variety of functions, can provide protection when the fault occurs. When the LED is switched on or off, the independent feedback loop can limit the output voltage. If any of the feedback voltage exceeds the protection threshold, the device will turn off the controller after the internal timer is out of time and the device is in the locked state. The controller also has a cycle by cycle current limit, which ensures stable operation and provides a soft start function. Thermal shutdown circuitry provides additional protection.

MAX8790 uses a small size, thermally enhanced, 4mm x 4mm, 20 pin TQFN package, which can operate in the range of -40 DEG C to +85 DEG C. The price of the device is $1.95 (1000 chips, us FOB). To provide a MAX8790 evaluation board that has been assembled, the evaluation board contains the recommended external components to help shorten the design process.

Source: Electronic Engineering album