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PDF ( 数据手册 , 数据表 ) A6267

零件编号 A6267
描述 Automotive High Current LED Controller
制造商 Allegro
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A6267 数据手册, 描述, 功能
A6267
Automotive High Current LED Controller
Features and Benefits
AEC Q100 Grade 0 Automotive Qualified
Constant current LED drive
6.5 to 50 V supply
Boost or buck-boost modes
Drives up to 15 LEDs in series
Programmable switching frequency 100 to 700 kHz
Open LED overvoltage indication and protection
Single and multiple LED short indication
LED short to ground and supply protection
PWM dimming control
10 μA shutdown current including LED leakage
Applications:
Automotive high power LED lighting systems
Fog lights, reversing lights, daytime running lights
Headlights
Package: 16-pin TSSOP with exposed
thermal pad (suffix LP)
Not to scale
Description
The A6267 is a DC-to-DC converter controller, providing a
programmable constant current output for driving high power
LEDs in series. Driving the LEDs in series ensures identical
currents and uniform brightness. For automotive applications,
optimum performance is achieved when driving up to 15 LEDs
at currents up to 1 A.
TheA6267 provides a cost-effective solution using an external
logic-level MOSFET and minimum additional external
components. The maximum LED current is set with a single
external sense resistor and can be modified using a current
reference input. Direct PWM control is possible via the Enable
input, which also provides a shutdown mode.
This DC-DC converter can be configured as a ground-referenced
boost converter or as a supply-referenced boost converter
providing buck-boost capability.The buck-boost topology used
ensures that there is no leakage path through the LEDs when
in shutdown and no inrush current at power-up.
Integrated diagnostics and two fault outputs give indication of
undervoltage, chip overtemperature, output open circuit, LED
short circuit and LED undercurrent, and can be configured to
provide short to supply and short to ground protection for the
LED connections. A unique feature is the ability to detect one
or more shorted LEDs.
The device is provided in a 16-pinTSSOPpackage with exposed
thermal pad (suffix LP). It is lead (Pb) free, with 100% matte
tin leadframe plating.
Typical Application Diagrams
VBAT 12 V or 24 V (50 V max)
Power net
Buck Boost Mode
VBAT(min)
(V)
Maximum
Quantity of
LEDs
7 10
8 11
9 13
Vf of each LED = 3.5 V,
D(max) = 85%
Fault
Flags
Enable
VIN
VREG
FF1
FF2
A6267
LN
LP
LF
EN
SG
IREF
CKOUT
SP
OSC
SN
GND LA
VBAT 12 V or 24 V (50 V max)
Power net
Boost Mode
VBAT(min)
(V)
Maximum
Quantity of
LEDs
7 12
8 13
9 15
Vf of each LED = 3.5 V,
D(max) = 85%
Fault
Flags
Enable
VIN
VREG
LN
LP
FF1
FF2
A6267 LF
EN
SG
IREF
CKOUT
SP
OSC
GND
SN
LA
Buck-Boost Mode
(Supply-referenced boost)
A6267-DS, Rev. 3
Boost Mode
Free Datasheet http://www.datasheet4u.com/







A6267 pdf, 数据表
A6267
Automotive High Current LED Controller
LF Single diode forward voltage reference input. Measures the
forward voltage of the first LED. This value is used as a reference
against the voltage on the LA pin to detect possible shorted LEDs
in the LED string.
Circuit Operation
Converter A constant frequency, current mode control scheme
is used to regulate the current through the LEDs. There are two
control loops within the regulator. The inner loop formed by the
amplifier, AS (see the Functional Block Diagram for AS, AC, AE,
and AL), comparator, AC, and the RS bistable, controls the induc-
tor current as measured through the switch by the switch sense
resistor, RSS .
The outer loop including the amplifier, AL, and the integrating
error amplifier, AE, controls the average LED current by provid-
ing a setpoint reference for the inner loop.
The LED current is measured by the LED sense resistor, RSL,
and compared to the internal reference current to produce an
integrated error signal at the output of AE. This error signal sets
the average amount of energy required from the inductor by the
LEDs. The average inductor energy transferred to the LEDs is
defined by the average inductor current as determined by the
inner control loop.
The inner loop establishes the average inductor current by
controlling the peak switch current on a cycle-by-cycle basis.
Because the relationship between peak current and average cur-
rent is non-linear, depending on the duty cycle, the reference
level for the peak switch current is modified by a slope generator.
This compensation reduces the peak switch current measurement
by a small amount as the duty cycle increases (refer to figure 1).
The slope compensation also removes the instability inherent in a
fixed frequency current control scheme.
The control loops work together as follows: the switch current,
sensed by the switch current sense resistor, RSS , is compared
to the LED current error signal. As the LED current increases
the output of AE will reduce, reducing the peak switch current
and thus the current delivered to the LEDs. As the LED current
decreases the output of AE increases, increasing the peak switch
current and thus increasing the current delivered to the LEDs.
Under some conditions, especially when the LED current is set to
a low value, the energy required in the inductor may result in the
inductor current dropping to zero for part of each cycle. This is
known as discontinuous mode operation, and results in some low
frequency ripple. The average LED current, however, remains
regulated down to zero. In discontinuous mode, when the induc-
tor current drops to zero, the voltage at the drain of the external
MOSFET rings, due to the resonant LC circuit formed by the
inductor, and the switch and diode capacitance. This ringing is
low frequency and is not harmful.
Switch Current Limit The switch current is measured by the
switch sense resistor, RSS , and the switch sense amplifier, AS
(see the Functional Block Diagram). The input limit of the sense
amplifier, VIDS, and the maximum switch current, ISMAX , define
the maximum value of the sense resistor as:
RSS = VIDS / ISMAX
(1)
This defines the maximum measurable value of the switch (and
inductor) current.
The maximum switch current is modulated by the on-time of the
switch. An internal slope compensation signal is subtracted from
the voltage sense signal to produce a peak sense voltage which
effectively defines the current limit. This signal is applied at a
rate of –16 mV / μs starting with no contribution (t = 0 μs) at the
beginning of each switching cycle. Figure 1 illustrates how the
peak sense voltage (typical values) changes over a period of 3 μs.
For example, the maximum current (typical) through the switch
at t = 1.5 μs (D = 50%) would be 145 mV/RSS , however, if the
switch remained on for a further 1 μs, the maximum current
through the switch would be 129 mV/RSS .
200
150
100
50
0
012
Period (μs)
Figure 1. Slope compensation for peak switch current control.
3
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
8
Free Datasheet http://www.datasheet4u.com/







A6267 equivalent, schematic
A6267
Automotive High Current LED Controller
Package LP 16-Pin TSSOP with Exposed Thermal Pad
5.00±0.10
16
B
3 NOM 4.40±0.10 6.40±0.20
A
0.20
0.09
0.45
16
1.70
0.60 ±0.15
1.00 REF
0.65
3.00 6.10
12
3 NOM
16X
0.10 C
0.30
0.19
0.65 BSC
Branded Face
SEATING
PLANE
C
1.20 MAX
0.15
0.00
0.25 BSC
SEATING PLANE
GAUGE PLANE
12
3.00
C PCB Layout Reference View
For Reference Only; not for tooling use (reference MO-153 ABT)
Dimensions in millimeters
Dimensions exclusive of mold flash, gate burrs, and dambar protrusions
Exact case and lead configuration at supplier discretion within limits shown
A Terminal #1 mark area
B Exposed thermal pad (bottom surface); dimensions may vary with device
C Reference land pattern layout (reference IPC7351
SOP65P640X110-17M);
All pads a minimum of 0.20 mm from all adjacent pads; adjust as
necessary to meet application process requirements and PCB layout
tolerances; when mounting on a multilayer PCB, thermal vias at the
exposed thermal pad land can improve thermal dissipation (reference
EIA/JEDEC Standard JESD51-5)
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
16
Free Datasheet http://www.datasheet4u.com/










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