MAX17129/MAX17149: 6-String WLED Drivers

The MAX17129/MAX17149 are high-efficiency drivers for white light-emitting diodes (LEDs). They are designed for LED arrays as light sources for small to medium-sized liquid crystal displays (LCDs). With an internal switch boost and a fast PWM control architecture, the controllers drive LED arrays that can be configured with up to six strings in parallel and 11 LEDs (MAX17129) or six LEDs per string in series (MAX17149). Each string is a ballast that achieves ±2% current regulation accuracy, ensuring uniform LED brightness, and provides an adjustable 10mA to 45mA full-scale LED current. The IC has a wide input voltage range of 6V to 26V. The MAX17129 integrates an LDO to simplify applications with a high-voltage power supply. These devices also have a low-input voltage mode for applications with a 3V to 5.5V supply voltage.

These devices support PWM dimming mode. External PWM signal directly controls the brightness of LED. Dimming frequency ranges from 100Hz to 25kHz with a minimum time of 400ns.

The IC has several features to protect the controller from fault conditions. A separate voltage feedback loop limits the output voltage for safe operation. Open and shorted LED detection shuts down the problematic string while maintaining normal operation of the other strings.

These devices feature cycle-by-cycle internal switch current limiting to provide consistent operation and soft-start capability. If the device is in current limit condition, the boost converter is internally latched off after the timer expires. A thermal shutdown circuit provides another protection to prevent damage to the IC.

The IC's boost controller features an internal 0.245Ω (typ), 48V (max) lossless current sense and accurate cycle-by-cycle current limit power MOSFET. The Quick-PWM control architecture provides fast load transient response without external loop compensation components, simplifying peripheral circuits and saving board area. The fast PWM control scheme features a quasi-fixed frequency with adjustable constant off-time, thus providing a wide variety of applications that can trade off operating frequency against component size. The low feedback voltage per LED string (275mV typical at 20mA LED current) helps reduce power losses and improve efficiency.

The IC is available in a 16-pin, thin QFN package with a pin pitch of 0.5mm. The package is designed for ultra-thin LCD panels of 3mm x 0.8mm with a maximum thickness of 3mm2.

Key Features

● 3V to 26V input supply voltage

● Up to six LED series in parallel

● Boost regulator and fast PWM control scheme

● Dual level selectable switching frequency

● 0.245Ω internal high voltage power MOSFET (48V max)

● Low string feedback voltage: 275mV, 20mA LED current

● Full-scale LED current regulation, from 10mA to 45mA

● String current regulation accuracy within ± 2%

● Support PWM dimming mode

● Dimming ratio: 100:1

● 100Hz to 25kHz dimming frequency for PWM dimming mode

● Open circuit and short circuit LED protection

● Output overvoltage protection

● Small, 16-pin 3mm x 3mm thin QFN package

application

● Automotive system

● Handheld terminal

● Laptop, subnotebook and tablet computer monitors