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A6261 Schematic ( PDF Datasheet ) - Allegro MicroSystems

Teilenummer A6261
Beschreibung Protected LED Array Driver
Hersteller Allegro MicroSystems
Logo Allegro MicroSystems Logo 




Gesamt 14 Seiten
A6261 Datasheet, Funktion
www.DataSheet.co.kr
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/






A6261 Datasheet, Funktion
www.DataSheet.co.kr
A6261
Protected LED Array Driver
Operation with Fewer LED Strings or Higher Currents
The A6261 may be configured to use fewer than four LED
strings, either by connecting outputs together for higher cur-
rents, or by connecting the output directly to VIN to disable the
regulator for that output. When a regulator is disabled it will
not indicate an open load and will not affect the fault flag or the
operation of the remaining regulator outputs.
VIN
A6261
LA1
LA2
LA3
LA4
A. Any LED cathode short-to-ground.
Current remains regulated in
non-shorted LEDs. Matching may be
affected. FF is low.
Sleep Mode
When EN is held low the A6261 will be in shutdown mode and
all sections will be in a low power sleep mode. The input current
will be typically less than 10 μA. This means that the complete
circuit, including LEDs, may remain connected to the power sup-
ply under all conditions.
Safety Features
The circuit includes several features to ensure safe operation and
to protect the LEDs and the A6261:
• The current regulators between VIN and each LAx output pro-
vide a natural current limit due to the regulation.
• Each LAx output includes a short-to-ground detector that will
disable the output to limit the dissipation.
• An open circuit on any output will disable all outputs.
• The thermal monitor reduces the regulated current as the tem-
perature rises.
• Thermal shutdown completely disables the outputs under ex-
treme overtemperature conditions.
Short Circuit Detection A short-to-ground on any LED
cathode (figure 1A) will not result in a short fault condition. The
current through the remaining LEDs will remain in regulation and
the LEDs will be protected. Due to the difference in the voltage
drop across the LEDs, as a result of the short the current match-
ing in the A6261 may exceed the specified limits.
GND
VIN
A6261
LA1
LA2
LA3
LA4
GND
VIN
A6261
LA1
LA2
LA3
LA4
GND
B. Any LAx output short-to-ground.
Shorted output is disabled. Other
outputs remain active. FF is high.
C. Shorted LEDs.
Current remains regulated.
Matching may be affected.
Only the shorted LED is inactive.
FF is low.
Any LAx output that is pulled below the short detect voltage
(figure 1B) will disable the regulator on that output and allow
the fault flag, FF, to go high. A small current will be sourced
from the disabled output to monitor the short and detect when
it is removed. When the voltage at LAx rises above the short
detect voltage the fault flag will be removed and the regulator
re-enabled.
A shorted LED (figure 1C) will not result in a short fault condi-
tion. The current through the remaining LEDs will remain in
regulation and the LEDs will be protected. Due to the difference
in the voltage drop across the LEDs, as a result of the short, the
current matching in the A6261 may exceed the specified limits.
VIN
A6261
LA1
LA2
LA3
LA4
GND
D. Short between LEDs in different
strings. Current remains regulated.
Current is summed and shared by
affected strings. Intensity match
dependent on voltage binning.
FF is low.
A short between LEDs in different strings (figure 1D) will not
result in a short fault condition. The current through the remain-
Figure 1. Short circuit conditions.
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
6
Datasheet pdf - http://www.DataSheet4U.net/

6 Page









A6261 pdf, datenblatt
www.DataSheet.co.kr
A6261
Protected 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
A6261 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 determined by the specified maximum continuous operating
temperature, 150°C.
The maximum power dissipation is therefore defined as:
+
12 V PWM
high-side drive
VIN
A6261
EN
FF
IREF
THTH
LA1
LA2
LA3
LA4
GND
A. High brightness (HB) LED incandescent lamp replacement
+
24 V
VIN
PWM dimming
input
Fault output
A6261
LA1
EN
LA2
LA3
FF LA4
IREF
THTH
PD(max) =
T
RθJA
(11)
where ΔT is difference between the thermal monitor activa-
tion temperature, TJM, of the A6261 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
In some filament bulb replacement applications the supply may
be provided by a PWM-driven, high-side switch. The A6261 can
be used in this application by simply connecting EN to VIN.
If neither fault action nor fault reporting is required, then FF
should be tied to ground.
When power is applied there will be a short startup delay, tON,
before the current starts to rise. The current rise time will be lim-
ited by the internal current slew rate control.
The application circuit options in figure 9 show operation with
a higher voltage supply and with combinations of outputs tied
together and disabled.
+
12 V
PWM dimming
input
GND
B. Higher voltage operation
VIN
A6261
EN
FF
IREF
THTH
LA1
LA2
LA3
LA4
GND
C. Mix of output combinations
Figure 9. Typical applications with various supply and output options.
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
12
Datasheet pdf - http://www.DataSheet4U.net/

12 Page





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