a6260slj-t Allegro MicroSystems, Inc., a6260slj-t Datasheet - Page 7

• Manufacturer Part Number: a6260slj-t
• Description: High Brightness Led Current Regulator
• Manufacturer: Allegro MicroSystems, Inc.

A6260
the short circuit is removed the short circuit source current, I
pulls the voltage at the LC pin above V
regulator are re-enabled.
LC Short to Supply
into the LC pin remains regulated but the power dissipated in
the A6260 increases. This higher dissipation causes the thermal
monitor to reduce the current to protect the regulator. In extreme
cases, or in cases where the thermal monitor is disabled, the
increased dissipation may cause temperature to reach the thermal
shutdown level, at which point the regulator will be disabled.
LC Short to Ground
the high-side switch current exceeds the trip value, I
longer than the overcurrent detection time, t
When a short is detected, the switch and the regulator are both
disabled. When the voltage at LC drops below the short release
voltage, V
then sourced from LA to provide a short circuit monitor. When
the short circuit is removed, I
above V
LA Short to LC
as the LC Short-to-Supply condition. In this condition, the cur-
rent into the LC pin remains regulated but the power dissipated in
the A6260 increases. This higher dissipation causes the thermal
monitor to reduce the current to protect the regulator. In extreme
cases, or in cases where the thermal monitor is disabled, the
increased dissipation may cause temperature to reach the thermal
shutdown level, at which point the regulator will be disabled.
Temperature Monitor
The primary function of the temperature monitor included in the
A6260 is to limit the power dissipation of the A6260 and maintain
the junction temperature below the maximum. However, it can
also be used to reduce LED current as LED temperature increases.
This can be achieved by mounting the A6260 on the same thermal
substrate as the LEDs, so that temperature rise in the LEDs would
also affect the A6260. As the junction temperature of the A6260
increases, the integrated temperature monitor lowers the regulated
current level, reducing the dissipated power in the A6260 and in the
LEDs. As shown in figure 2, from the full 100% current level (see
the LED Current Level section), current is reduced at a rate of 4%
per degree Celsius typically, until the point at which the current drops
to 25% of the full level. The junction temperature at the 25% current
level is defined as T
SCCR
SCCR
, and the switch and regulator are re-enabled.
, a low value current, I
(figure 1e) This condition is effectively the same
JL
. If the temperature continues to rise above
(figure 1c) In this condition, the current
(figure 1d) This condition is detected when
SCU
pulls the voltage at the LC pin
SCU
SCCR
(1.1 mA typical), is
OCD
, and the switch and
(3 μs typical).
High Brightness LED Current Regulator
LAOC
, for
SCU
,
Figure 2. Temperature monitor current reduction
T
at a slower rate, until the temperature reaches the overtemperature
shutdown 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 typically 98°C. The thermal monitor activation temperature,
T
current level.
T
V
where T
The equivalent circuit of the THTH pin is a 1.124 V source with
a series 5 kΩ resistor. A resistor connected between THTH and
GND will reduce V
lowing formula:
where R
A resistor connected between THTH and a reference supply
greater than 2 V will increase V
JL
JM
JM
THTH
100
90
80
60
40
25
20
, the temperature monitor would continue to reduce current, but
, is defined in the Electrical Characteristics table at the 90%
0
can be increased by reducing the voltage at the THTH pin,
70
, and is defined as approximately:
JM
TH
, in kΩ, is the resistor between THTH and GND.
is in °C.
90
THTH
V
Junction Temperature, T
THTH
T
JF
JM
T
and increase T
.
JM
=
110
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
=
. 1
1
124
.
503
THTH
0
.
00363
×
−
5
V
and reduce T
130
T
THTH
+
JL
R
JM
TH
R
J
, according to the fol-
(°C)
TH
150
JM
. For
T
JF
170
(2)
(3)
7