A8509
Wide Input Voltage Range, High Efficiency
4-Channel Fault Tolerant LED Driver
Features and Benefits
Description
• 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
VIN = 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)
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.
Packages
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 ¯¯ ¯ ¯ ¯ pin to disconnect the
FAULT
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.
(Not to scale)
24-pin TSSOP with
Exposed Thermal Pad
(LP package)
24-pin SOICW with
Four Internally-Fused Pins
(LB package)
Typical Application
VIN
RISET Value versus LED Current
RISET (kΩ)
30.00
L1
VDD
25.00
VIN
FAULT
15.00
10.00
60
100
140
180
220
260
GATE SENP
ILED (mA)
Figure 1. Typical application circuit
showing 4 channels of LEDs; RZ-CZ
optional (component list shown in the
Typical Applications section)
CDR
CDD
RFSET
RISET
SENN
A8509
OVP
MODE
LED2
LED3
LED4
PAD
RZ
CZ CP
ROVP
LED1
EN
VDR
VDD
FSET/SYNC
ISET
COMP
300
VOUT
RSENSE
PWM
5.00
A8509-DS
COUT
Q1
R1
20.00
D1
CIN
AGND PGND
