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PDF A6261 Data sheet ( Hoja de datos )
| Número de pieza | A6261 | |
| Descripción | Protected LED Array Driver | |
| Fabricantes | Allegro MicroSystems | |
| Logotipo |  |
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A6261
Protected 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
▪ Disable on open LED detection option
▪ 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
Packages
10-pin MSOP with
exposed thermal pad
(suffix LY)
16-pin TSSOP with
exposed thermal pad
(suffix LP)
Description
TheA6261 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. Outputs can be connected in
parallel or left unused as required.
Short detection is provided to protect the LEDs and the A6261
during a short-to-ground at any LED output pin. An open LED
in any of the strings disables all outputs, but can be overridden.
Shorted LED output pins or open LEDs are indicated by a
fault flag.
A temperature monitor is included to reduce the LED drive
current if the chip temperature exceeds a 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.
Not to scale
Typical Application Diagram
+
Power input
PWM dimming input
VIN
A6261
EN
FF
IREF
THTH
LA1
LA2
LA3
LA4
GND
–
A6261A-DS, Rev. 1
Datasheet pdf - http://www.DataSheet4U.net/
1 page  
www.DataSheet.co.kr
A6261
Protected LED Array Driver
Functional Description
The A6261 is a linear current regulator that is designed to provide
drive current and protection for parallel strings of series-con-
nected high brightness LEDs. It provides up to four matched pro-
grammable 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 A6261 is specifically designed for use in applications where
the LED current is controlled by a single logic input or a high-
side switched supply. In addition the A6261 disables all LEDs on
detecting a single open LED.
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.
EN Logic input to enable LED current output. This provides a
direct on/off action and can be used for direct PWM control.
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.
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 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
These equations completely define the output currents with
respect to the setting resistors. However, for further reference, a
more detailed description of the internal reference current calcu-
lations is included below.
It is important to note that because the A6261 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.
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
5
Datasheet pdf - http://www.DataSheet4U.net/
5 Page 
www.DataSheet.co.kr
A6261
Protected LED Array Driver
2.3 V. The graph shows the temperature as the supply voltage
increases from 14 to 17 V. Without the thermal foldback feature
the temperature would continue to increase up to the thermal
shutdown temperature as shown by the dashed line. The solid line
shows the effect of the thermal foldback function in limiting the
temperature rise.
Figures 6 and 7 show the thermal effects where the thermal resis-
tance from the silicon to the ambient temperature is 40°C/W as
described below.
Thermal Dissipation
The amount of heat that can pass from the silicon of the A6261
to the surrounding ambient environment depends on the thermal
resistance of the structures connected to the A6261. The thermal
resistance, RθJA, is a measure of the temperature rise created by
the power dissipated and is usually measured in degrees Celsius
per watt (°C/W).
The temperature rise, ΔT, is calculated from the power dissipated,
PD, and the thermal resistance, RθJA, as:
• For minimum supply voltage the limiting factor is the maximum
drop-out voltage of the regulator, where the difference between
the load voltage and the supply is insufficient for the regulator
to maintain control over the output current.
Minimum Supply Limit: Regulator Saturation Voltage
The supply voltage, VIN, is always the sum of the voltage drop
across the high-side regulator, VREG , and the forward voltage of
the LEDs in the string, VLED, as shown in figure 4.
VLED is constant for a given current and does not vary with
supply voltage. Therefore VREG provides the variable difference
between VLED and VIN . VREG has a minimum value below which
the regulator can no longer be guaranteed to maintain the output
current within the specified accuracy. This level is defined as the
regulator drop-out voltage, VDO.
The minimum supply voltage, below which the LED current does
not meet the specified accuracy, is therefore determined by the
sum of the minimum drop-out voltage, VDO , and the forward
voltage of the LEDs in the string, VLED . The supply voltage must
ΔT = PD × RθJA
(9)
A thermal resistance from silicon to ambient, RθJA, of approxi-
mately 40°C/W can be achieved by mounting the A6261 on a
standard FR4 double-sided printed circuit board (PCB) with a
copper area of a few square inches on each side of the board
under the A6261. Multiple thermal vias, as shown in figure 8,
help to conduct the heat from the exposed pad of the A6261 to the
copper on each side of the board. The thermal resistance can be
reduced by using a metal substrate or by adding a heatsink.
Supply Voltage Limits
In some applications the available supply voltage can vary over
a two-to-one range; for example, emergency lighting systems
using battery backup. In such systems is it necessary to design
the application circuit such that the system meets the required
performance targets over a specified voltage range.
To determine this range when using the A6261 there are two
limiting conditions:
• For maximum supply voltage the limiting factor is the power
that can be dissipated from the regulator without exceeding the
temperature at which the thermal foldback starts to reduce the
output current below an acceptable level.
Figure 8. Board via layout for thermal dissipation: (top) LP package
(bottom) LY package.
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
11
Datasheet pdf - http://www.DataSheet4U.net/
11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet A6261.PDF ] | |
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