A8509: Wide Input Voltage Range, High Efficiency 4-Channel Fault Tolerant LED Driver

The A8509 is a multi-output white LED driver for backlighting LCD panels. It integrates a current-mode boost controller and four individual current sinks.

The boost controller architecture allows for significant scaling of boost voltage to optimize the solution for the required number of LEDs per string. The FSET/SYNC pin either sets the required boost switching frequency or synchronizes the value in the range of 300 to 800 kHz.

The LED sink current value is set by an external ISET resistor (see figure 1). The four LED sinks can also be combined to achieve even higher current per LED string.

The A8509 provides protection against output shorts and overvoltage, open or shorted LED pins, and overtemperature. A dual-level, pulse-by-pulse current limit function provides soft start and protects the external current switch against high current overloads. As an option, the A8509 can drive an external P-FET interfaced to the FAULT pin to disconnect the input supply from the system in the event of short-to-ground in the boost converter.

Package options are 24-pin TSSOP (suffix LP) and SOICW (LB) packages. The TSSOP has an exposed thermal pad, and the SOICW has four interally-fused pins, for enhanced thermal dissipation. The Both packages are lead (Pb) free, with 100% matte tin leadframe plating.

• Four integrated high current sinks for LED strings; can be tied together for even higher currents
• Fixed frequency current mode control with integrated gate driver / boost controller; powerful gate driver to drive an external N-channel MOSFET allows significant scaling capability on the number of LEDs per string
• Parallel operation with one boost controller (master) and up to three additional slave controllers; can run up to 16 strings of LEDs while populating only a single master boost regulator
• Active current sharing between LED strings for 0.7% accuracy and 0.8% matching
• Wide input voltage range: 9 to 40 V
• Internal bias supply for single-supply operation (typically V_IN = 12 or 24 V)
• Separate Enable and PWM pins as interface for Enable and PWM Dimming functions
• Fset / Sync function to either set the boost converter switching frequency or synchronize at up to 800 kHz
• Protection Features
  • Open or shorted LED pin protection
  • Open Schottky protection
  • Pulse-by-pulse current limit
  • Overtemperature protection (OTP)