Simplified Block Diagram
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- Synchronous Step-Up Regulator
- Achieves >95% Efficiency
- Internal Switch and Synchronous Rectifier
- Eliminates External MOSFETs and Diodes
- 1MHz Fixed Frequency Minimizes Component Sizes
- Up to 90% Total LED Efficiency
- Accurate LED Current Matching (8% max)
- Adjustable Maximum LED Current
- Multimode Dimming Control
- Digital Pulse-Width Modulation Control
- 2-Bit Parallel Control
- 3-Bit Parallel Control
- Analog Control
- Selectively Enable LEDs
- Open-LED Detection
- Unique 0.5mA LED Test Mode
- 2.7V to 5.5V Input Supply Range
- Small 4mm x 4mm 20-Pin Thin QFN Package
- Cell Phones
- Digital Cameras
- PDAs and Handheld PCs
The individual current regulators allow good current matching between LEDs. Open or shorted LEDs cannot affect the performance of other LEDs.
The step-up regulator achieves high efficiency by using synchronous rectification. The internal N-channel switch and P-channel synchronous rectifier eliminate the need for external MOSFETs and diodes. The 1MHz switching frequency allows the use of low-profile inductors and ceramic capacitors.
The brightness can be easily adjusted using a multi-mode dimming interface, which allows brightness control through a DPWM signal, a 2- or 3-bit parallel control interface, or an analog signal. The DPWM signal can be connected directly to the control pin without the need for an external RC filter if its frequency is 10kHz or above.
The MAX1984 drives up to eight LEDs, the MAX1985 drives up to six LEDs, and the MAX1986 drives up to four LEDs. Each device has an LED select pin (SEL) that allows one subset, the other subset, or all LEDs to be illuminated. All three devices are available in a 4mm x 4mm thin QFN package.