A6261KLPTR-T Allegro Microsystems Inc, A6261KLPTR-T Datasheet - Page 7

• Manufacturer Part Number: A6261KLPTR-T
• Description: A6261/2/4 Four Channel Constant Current LED Drivers
• Manufacturer: Allegro Microsystems Inc

A6261
ing LEDs will remain in regulation and the LEDs will be pro-
tected. The current will be summed and shared by the affected
strings. Current matching in the strings will then depend on the
LED forward voltage differences.
Open Load Detection An open load condition is detected
when the voltage across the regulator, V
the open load detect voltage, V
disable threshold voltage, V
for more than the open load detect time, t
will be disabled and the fault flag allowed to go high.
The regulators will remain disabled until either the power is
cycled off and on, the EN input is taken low then high, or the
fault flag, FF, is pulled low. If the power is cycled or EN is pulsed
low, the regulators will start in the enabled state, unless disabled
by tying the output to VIN, and the open load detection timer will
be reset. If the open load is still present the regulators will again
be disabled after the open load detect time.
Pulling the fault flag low will override the open load fault action
and all enabled regulators will be switched on. This state will
be maintained while the fault flag is held low. If the fault flag is
allowed to go high the A6261 will return to the open load fault
condition and will disable all regulators.
Each of the four regulators includes a limiter to ensure that
the output voltage will not rise higher than the output disable
threshold voltage below V
means that the voltage across the regulator will not be less than
the output disable voltage, unless it is forced by connecting the
LAx pin to VIN. However if a load becomes disconnected, the
regulator will pull the LAx pin up to the limit, which will ensure
that the voltage across the regulator, V
open load detect voltage, V
Note that an open load may also be detected if the sum of the for-
ward voltages of the LEDs in a string is close to or greater than
the supply voltage on VIN.
Temperature Monitor A temperature monitor function,
included in the A6261, reduces the LED current as the silicon
junction temperature of the A6261 increases (see figure 2). By
mounting the A6261 on the same thermal substrate as the LEDs,
this feature can also be used to limit the dissipation of the LEDs.
As the junction temperature of the A6261 increases, the regulated
current level is reduced, reducing the dissipated power in the
IN
OCD
ODIS
when driven by the regulator. This
OCD
.
. When this condition is present
, but greater than the output
IN
IN
– V
OCD
– V
LAx
, then all regulators
LAx
, is less than the
, is less than
A6261 and in the LEDs. The current is reduced from the 100%
level at typically 4% per degree Celsius until the point at which
the current drops to 25% of the full value, defined at T
this temperature the current will continue to reduce at a lower
rate until the temperature reaches the overtemperature shutdown
threshold temperature, T
The temperature at which the current reduction begins can be
adjusted by changing the voltage on the THTH pin. When THTH
is left open the temperature at which the current reduction begins
is defined as the thermal monitor activation temperature, T
is specified, in the characteristics table, at the 90% current level.
T
reduced and is defined as approximately:
A resistor connected between THTH and GND will reduce V
and increase T
ence supply greater than 1 V will increase V
Figure 2. Temperature monitor current reduction.
JM
100
80
60
40
20
90
25
will increase as the voltage at the THTH pin, V
0
70
Protected LED Array Driver
JM
. A resistor connected between THTH and a refer-
90
Junction Temperature, T
T
JM
T
JF
JM
.
=
110
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
1.46 –V
0.0039
T
JL
THTH
J
130
(°C)
THTH
(°C)
and reduce T
150
THTH
T
JL
JF
. Above
, is
JM
THTII
170
(3)
, and
JM
.
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