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PDF A6262 Data sheet ( Hoja de datos )
| Número de pieza | A6262 | |
| Descripción | Automotive LED Array Driver | |
| Fabricantes | Allegro MicroSystems | |
| Logotipo |  |
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A6262
Automotive LED Array Driver
Features and Benefits
▪ Total LED drive current up to 400 mA
▪ Current shared equally up to 100 mA by up to 4 strings
▪ 6 to 50 V supply
▪ Low dropout voltage
▪ LED output short-to-ground and thermal protection
▪ On/off toggle switch input
▪ Enable input for PWM control
▪ Current slew rate limit during PWM
▪ Current set by reference resistor
▪ Automotive K-temperature range version (–40°C to 150°C):
contact factory for availability
Applications:
▪ Dome light, map light, space lighting,
mood lighting
Packages
10-pin MSOP with
exposed thermal pad
(suffix LY)
16-pin TSSOP with
exposed thermal pad
(suffix LP)
Not to scale
Description
TheA6262 is a linear, programmable current regulator providing
up to 100 mA from each of four outputs to drive arrays of high
brightness LEDs. The regulated LED current from each output,
accurate to 5%, is set by a single reference resistor. Current
matching in each string is better than 10% without the use of
ballast resistors. Driving LEDs with constant current ensures
safe operation with maximum possible light output.
Output control is provided by an enable input, giving direct
control for PWM applications, and by a debounced switch
input, proving an on/off toggle action.
For automotive applications, optimum performance is achieved
when driving 4 strings with 1 to 3 LEDs in each string, at a
total current of up to 100 mA in each string. Outputs can be
connected in parallel or left unused as required.
Short detection is provided to protect the LEDs and the A6262
during a short-to-ground at any LED output pin. The output
will automatically resume the regulated current when the short
is removed.
A temperature monitor is included to reduce the LED drive
current if the chip temperature exceeds an adjustable thermal
threshold.
The device packages are a 10-pin MSOP (LY) and a 16-pin
TSSOP (LP), both with exposed pad for enhanced thermal
dissipation. They are lead (Pb) free, with 100% matte tin
leadframe plating.
Typical Application Diagram
+
Automotive
12 V power net
PWM dimming
input from LCU
On/Off
VIN
A6262
EN
SW
IREF
THTH
LA1
LA2
LA3
LA4
GND
–
A6262-DS
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1 page  
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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.
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.
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. 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.
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.
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.
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:
Given EN = high,
ILAx = 15
RREF
where ILAx is in mA and RREF is in kΩ.
(1)
The output current may be reduced from the set level by the ther-
mal monitor circuit.
Conversely the reference resistors may be calculated from:
RREF = 15
ILAx
where ILAx is in mA and RREF is in kΩ.
(2)
For example, where the required current is 90 mA the resistor
value will be:
RREF =
15
90
= 167 Ω
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.
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
VIN to disable the regulator for that output.
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
5
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5 Page 
www.DataSheet.co.kr
A6262
Automotive LED Array Driver
always be greater than this value and the minimum specified sup-
ply voltage, that is:
VIN > VDO + VLED, and
VIN > VIN (min)
(10)
As an example, consider the configuration used in figures 6 and
7 above, namely 4 strings of 3 red LEDs, each string running at
50 mA, with each LED forward voltage at 2.3 V. The minimum
supply voltage will be approximately:
VIN(min) = 0.55 + (3 × 2.3) = 7.45 V
Maximum Supply Limit: Thermal Limitation As described
above, when the thermal monitor reaches the activation tempera-
ture, TJM (due to increased power dissipation as the supply volt-
age rises), the thermal foldback feature causes the output current
to decrease. The maximum supply voltage is therefore defined as
the voltage above which the LED current drops below the accept-
able minimum.
This can be estimated by determining the maximum power that
can be dissipated before the internal (junction) temperature of the
A6262 reaches TJM.
Note that, if the thermal monitor circuit is disabled (by connect-
ing the THTH pin to GND), then the maximum supply limit will
be the specified maximum continuous operating temperature,
150°C.
The maximum power dissipation is therefore defined as:
PD(max) =
∆T(max)
RθJA
(11)
where ΔT(max) is difference between the thermal monitor activa-
tion temperature, TJM, of the A6262 and the maximum ambient
temperature, TA(max), and RθJA is the thermal resistance from the
internal junctions in the silicon to the ambient environment.
If minimum LED current is not a critical factor, then the maxi-
mum voltage is simply the absolute maximum specified in the
parameter tables above.
Application Examples
Operation with High-Side PWM Supply In some filament
bulb replacement applications the supply may be provided by a
PWM-driven high-side switch. The A6262 can be used in this
application by simply connecting EN to VIN.
The toggle action of the SW input will be reset to off at each
power-up. In addition, in all cases when EN is high, the EN input
will override the SW toggle status and enable the outputs. At the
high-to-low transition of EN, the SW toggle will always be reset
to the off state.
When power is applied, there will be a short startup delay, tON ,
before the current starts to rise. The rise time of the current will
be limited by the internal current slew rate control.
Figures 9a to 9c show application circuit options, including a
higher voltage supply, and combinations of outputs tied together
and disabled.
Operation with both EN and SW In some applications it
may be required to utilize the functionality of both the EN input
and the SW input. For example in dome lighting, where a manual
switch may be used to turn the light on and the lighting control
unit may dim the light to off (see figure 10). In these cases it is
important to understand the interaction of the two control inputs.
• In all cases, when EN is high the EN input will override the SW
toggle status and enable the outputs.
• When EN is low the SW input can be used to toggle the outputs
on and off.
• The only time there is any interaction between the EN input and
the SW toggle is the high-to-low transition of EN, where the
SW toggle will always be reset to the off state.
• The SW toggle will also be reset to the off state at power-up.
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
11
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| PDF Descargar | [ Datasheet A6262.PDF ] | |
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