Automotive LED Array Driver
A6269
5
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Functional Description
The A6269 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 two matched programmable current outputs at
up to 200 mA, with low minimum dropout voltages below the
main supply voltage. For 12 V power net applications, optimum
performance is achieved when driving 2 strings of 1 to 3 LEDs,
at current up to 200 mA per string.
The A6269 is specifically designed for use in internal illumina-
tion applications where the LED activity is controlled by a PWM
signal, by a logic signal, or by a push-to-make, ground-connected
switch.
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 until the
short is removed. Open load on any output will be ignored.
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.
EN Logic input to enable LED current output. This provides a
direct on/off action and can be used for direct PWM control. Note
that PWM dimming can only be applied when the LED is initially
in the off state. If the LED is already turned on using SW input, it
will remain on regardless of EN.
SW Logic input to toggle LED current output on and off. A
single push-to-make switch between SW and GND will provide
push-to-make/push-to-break, on/off toggle action. The SW input
is debounced by typically 30 ms and is internally pulled to typi-
cally 3 V, with approximately 100 A.
IREF 1.2 V reference to set current reference. Connect resistor,
R
REF
, to GND to set reference current.
THTH Sets the thermal monitor threshold, T
JM
, where the output
current starts to reduce with increasing temperature. Connecting
THTH directly to GND will disable the thermal monitor function.
LA1, LA2 Current source connected to the anode of the first
LED in each string. Connect directly to VIN to disable the
respective output. In this document “LAx” indicates any one of
the outputs.
LED Current Level
The LED current is controlled by a matching linear current regu-
lator between the VIN pin and each of the LAx outputs. The basic
equation that determines the nominal output current at each LAx
pin is:
Given EN = high,
I
LAx
=
R
REF
K
(1)
where I
LAx
is in mA and R
REF
is in k; K is 30.
The output current may be reduced from the set level by the ther-
mal monitor circuit.
Conversely the reference resistors may be calculated from:
I
LAx
=
R
REF
K
(2)
where I
LAx
is in mA and R
REF
is in k.
For example, where the required current is 180 mA for both chan-
nels the resistor value will be:
180
==
R
REF
167
30
It is important to note that because the A6269 is a linear regu-
lator, the maximum regulated current is limited by the power
dissipation and the thermal management in the application. All
current calculations assume adequate heatsinking for the dissi-
pated power. Thermal management is at least as important as the
electrical design in all applications. In high current high ambient
temperature applications the thermal management is the most
important aspect of the systems design. The application section
below provides further detail on thermal management and the
associated limitations.
Operation with Fewer LED Strings or Higher Currents
The A6269 may be configured to use fewer than the maximum
quantity of LED strings: by connecting outputs together for
higher currents, by leaving the outputs open, or by connecting the
output directly to VIN to disable the regulator for that output.
