A8508 Datasheet, PDF (1/28 Pages) Allegro MicroSystems – Wide Input Voltage Range, High Efficiency

A8508
Wide Input Voltage Range, High Efficiency
8-Channel Fault Tolerant LED Driver
Features and Benefits
• 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
V_IN = 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)
Packages (Not to scale)
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 an
external P-FET interfaced to the ^{¯F¯A¯¯U¯¯L¯¯T¯} pin to disconnect the
input 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.
24-pin TSSOP with
Exposed Thermal Pad
(LP package)
28-contact QFN
with Exposed Thermal
Pad (ET package)
24-pin SOICW
(LW package)
Typical Application
30.00
25.00
20.00
15.00
10.00
5.00
30
RISET Value versus LED Current
50 70 90 110 130 150
I_LED (mA)
Figure 1. Typical application circuit
showing 8 channels of LEDs; RZ-CZ
optional (component list shown in the
Typical Applications section)
RVDR
CDR
CDD
RFSET
RISET
V_IN
V_DD
L1
C_IN
D1
Q1
COUT
VOUT
ROVP
R1
VIN
FAULT
R_SENSE
GATE SENP SENN
PWM
EN
VDR
VDD
FSET/SYNC
ISET
COMP
RZ
A8508
PAD
OVP
LED1
LED2
LED3
LED4
LED5
LED6
LED7
LED8
CZ CP
MODE
AGND PGND
A8508-DS, Rev. 1