A6262
Automotive LED Array Driver
Functional Description
The A6262 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.
LA[1:4] 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 four
outputs.
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 equation that determines the nominal output current at each
LAx pin is:
The A6262 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.
Given EN = high,
15
(1)
ILAx
=
RREF
where ILAx is in mA and RREF is in kΩ.
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.
The output current may be reduced from the set level by the ther-
mal monitor circuit.
Conversely the reference resistors may be calculated from:
Integrated thermal management reduces the regulated current
level at high internal junction temperatures to limit power dis-
sipation.
15
RREF
(2)
=
ILAx
where ILAx is in mA and RREF is in kΩ.
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.
For example, where the required current is 90 mA the resistor
value will be:
GND Ground reference connection. Should be connected directly
to the negative supply.
15
RREF
167 ꢀ
=
=
90
EN Logic input to enable LED current output. This provides a
direct on/off action and can be used for direct PWM control. The
EN input overrides the SW input when EN is high. When EN
transitions from high to low, SW input logic is reset to off.
It is important to note that because the A6262 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.
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 μA.
IREF 1.2 V reference to set current reference. Connect resistor,
RREF, to GND to set reference current.
Operation with Fewer LED Strings or Higher Currents
The A6262 may be configured to use fewer than four LED
strings: by connecting outputs together for higher currents, by
leaving the outputs open, or by connecting the output directly to
THTH Sets the thermal monitor threshold, TJM, where the output
current starts to reduce with increasing temperature. Connecting
THTH directly to GND will disable the thermal monitor function. VIN to disable the regulator for that output.
Allegro MicroSystems, Inc.
115 Northeast Cutoff
5
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
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