A6264 Datasheet, PDF (5/16 Pages) Allegro MicroSystems – The A6264 is a linear, programmable current regulator providing up to 100 mA from each of four outputs to drive arrays of high brightness LEDs.

A6264
Automotive Stop/Tail LED Array Driver
Functional Description
The A6264 is a linear current regulator that is designed to pro-
vide drive current and protection for parallel strings of series-
connected high brightness LEDs in automotive applications. It
provides up to four matched programmable current outputs, at
up to 100 mA, with low minimum dropout voltages below the
main supply voltage. For 12 V power net applications optimum
performance is achieved when driving 4 strings of 1 to 3 LEDs,
at currents up to 100 mA per string.
The A6264 is specifically designed for use in stop/tail applica-
tions where the LED current is switched between a high current
(indicating stop or brake) and a lower current (for normal tail
light operation).
Current regulation is maintained and the LEDs protected during a
short to ground at any point in the LED string. A short to ground
on any regulator output terminal will disable that output and set
the fault flag. An open load on any output will set the fault flag
and disable all outputs. Remaining outputs can be re-enabled
by pulling the fault flag output low. Individual outputs can be
disabled by connecting the output to VIN.
Integrated thermal management reduces the regulated current
level at high internal junction temperatures to limit power dis-
sipation.
Pin Functions
VIN Supply to the control circuit and current regulators. A small
value ceramic bypass capacitor, typically 100 nF, should be con-
nected from close to this pin to the GND pin.
GND Ground reference connection. Should be connected directly
to the negative supply.
FULL Logic input to enable high LED current output. Open or
low sets LED current to the base current level. High sets LED
current to the sum of the base current level, and the additional
high current (see Detailed Description of Regulator Operation
section) . Typically connected through a resistor to the stop switch
input.
IREF 1.2 V base current reference. Used for base (low) level
current output, I_REF . Connect resistor, R_REF , to GND to set this
reference current.
IREFH 1.2 V additional high current reference. Summed with
I_REF for full current output. Connect resistor, R_REFH , to GND to
set this reference current.
LA[1:4] Current source connected to the anode of the first LED in
each string. Connect directly to VIN to disable the respective out-
put. In this document “LAx” indicates any one of the four outputs.
FF Open drain fault flag, used with an external pull-up resistor,
to indicate open, short, or overtemperature conditions. FF is inac-
tive when a fault is present. During an open load condition, FF
can be pulled low to force the remaining outputs on.
LED Current Level
The LED current is controlled by four matching linear current
regulators between the VIN pin and each of the LAx outputs. The
basic equations that determine the nominal output current at each
LAx pin are:
Given FULL = low,
I_LAx = ¹⁵
R_REF
and, given FULL = high,
I_LAx = ¹⁵ + ¹⁵
(1)
R R _REF
REFH
where I_LAx is in mA, and R_REF and R_REFH are in kΩ.
In both cases, the output current may be reduced from the set
level by the thermal monitor circuit.
Conversely the reference resistors may be calculated from:
R_{REF =} ¹⁵
I_LAx(LO)
and
R_{REFH =}
15
I_LAx(HI) – I_LAx(LO)
(2)
where I_LAx(LO) is the required source current when FULL is low
and I_LAx(HI) is the current when FULL is high. I_LAx(x) are in mA,
and R_REF and R_REFH are in kΩ.
Allegro MicroSystems, Inc.
5
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com