Allegro Microsystems A8508

Description

The A8508 is a multi-output white LED driver for backlighting LCD panels. It integrates a current-mode boost controller and eight 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 eight LED sinks can also be combined to achieve even higher current per LED string.

The A8508 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 A8508 can drive anexternal P-FET interfaced to the ¯ F¯A¯ ¯U¯ ¯ L¯ Tpin to disconnect theinput supply from the system in the event of short-to-ground in the boost converter.

The A8508 is available in a 24-pin TSSOP package (suffix LP) with an exposed thermal pad for enhanced thermal dissipation. Contact factory for additional options, including: a 24-pin SOICW (LW) or a a 5 × 5 mm 28-contact QFN (ET) with exposed thermal pad. All packages are lead (Pb) free, with 100% matte tin leadframe plating.

Features

• Eight 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 capability with one boost controller
• (master) and up to three additional slave controllers; can
• run up to 32 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 VIN = 12 or 24 V)
• 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)

Remarks:L1,L2 Inductor Used In Sepic Config.

More information

• Datasheet
• IC product information