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A6268 Schematic ( PDF Datasheet ) - Allegro MicroSystems

Teilenummer A6268
Beschreibung Automotive High Current LED Controller
Hersteller Allegro MicroSystems
Logo Allegro MicroSystems Logo 




Gesamt 19 Seiten
A6268 Datasheet, Funktion
A6268
Automotive High Current LED Controller
Features and Benefits
▪ AEC Q100 Grade 0 Automotive Qualified
▪ Constant current LED drive
▪ 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 A6268 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.
TheA6268 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
VIN and VREG 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, LED overcurrent and
shorted LED string protection. 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 12VVBAoTr 1224 VV (o5r02V4 Vm(a5x0) V max)
Power nPeot wer net
Buck Boost Mode
VBAT(min)
(V)
Maximum
Quantity of
LEDs
57
68
7 10
8 11
9 13
Vf of each LED = 3.5 V,
D(max) = 85%
VIN VIN
VREG VREG LN
LP
LN
LP
Fault Fault FF1 FF1
Flags Flags FF2 FF2
A6268A62LF68 LF
Enable Enable EN EN SG SG
IREF IREF SP
CKOUTCKOUT
SP
OSC OSC SN SN
GND GLNAD LA
VBAT 12VVBAoTr 1224 VV (o5r02V4 Vm(a5x0) V max)
Power nPeot wer net
VIN VIN
Boost Mode
VBAT(min)
(V)
Maximum
Quantity oFf ault
LEDs Flags
Fault
Flags
VREG VREG LN
LP
FF1 FF1
FF2 FF2
58
A6268A6L2F68
6
7
10
12
Enable Enable EN
EN
SG
8 13
9 15
IREF IREF SP
CKOUTCKOUT
Vf of each LED = 3.5 V,
D(max) = 85%
OSC OSC SN
GND GLNAD
LN
LP
LF
SG
SP
SN
LA
Buck-Boost Mode
(Supply-referenced boost)
A6268-DS, Rev. 3
Boost Mode






A6268 Datasheet, Funktion
A6268
Automotive High Current LED Controller
ELECTRICAL CHARACTERISTICS1 (continued) Valid at TJ = –40°C to 150°C, VIN = 5 to 40 V; unless otherwise noted
Characteristics
Symbol
Test Conditions
Min. Typ. Max.
Oscillator
Oscillator Frequency
Minimum Oscillator Frequency3
OSC Pin Voltage
CKOUT Output Delay
OSC Input Low Voltage
OSC Input High Voltage
OSC Input Hysteresis
OSC Watchdog Period
CKOUT Output High Voltage
CKOUT Output Low Voltage
LED Current Sense
fOSC
fMIN
VOSC
tDC
VOIL
VOIH
VOihys
tOSWD
VCOH
VCOL
ROSC = 43 kΩ
ROSC = 62 kΩ
ROSC = VREG
ROSC = 62 kΩ
OSC input rise to CKOUT rise
Between successive rising edges
IOH = –1 mA
IOL = 1 mA
315
90
1.15
3.5
300
7
VREG – 1
500
350
350
1.2
150
600
385
1.25
0.8
VREG
0.4
Input Bias Current LN (BB mode)4
Input Bias Current LP (BB mode)4
Input Bias Current LN (B mode)1,4
Input Bias Current LP (B mode)1,4
Differential Input Voltage (Active)
Input Common-Mode Range (BB mode)4
Input Common-Mode Range (B mode)4
Current Error
Switch Current Sense
ILN
ILP
ILN
ILP
VIDL
VCMLH
VCMLL
EISL
LP = LN = 12 V
LP = LN = 12 V
LP = LN = 0 V
LP = LN = 0 V
EN = High, VIDL = VLP – VLN
VLP = VLN
VLP = VLN
[(10 × ILED × RSL) – 1] × 100
– 130 –
– 125 –
– –1.0 –
– –12 –
– 100 –
VIN – VIN + 1
0– 1
–5 –
5
Input Bias Current
Maximum Differential Input Voltage3
Input Source Current
Input Common-Mode Range
Diagnostics and Protection
IBIASS
VIDS
IINS
VCMS
SP = SN = 0 to 2 V
VIDS = VSP – VSN with D = 50%
VIDS = 120 mV
VSP = VSN
–30 –
110 150 200
– 120 –
0– 2
Fault Blank Timer5
VIN Undervoltage Turn-Off
VIN Undervoltage Hysteresis
VREG Undervoltage Turn-Off
VREG Undervoltage Hysteresis
tFB
VINUV
VINUVhys
VREGUV
VREGUVhys
Start-up
Decreasing VIN
Decreasing VREG
–3–
– – 4.6
200 – 400
2.9 3.65 4.4
170 300 400
Unit
kHz
kHz
kHz
kHz
V
ns
V
V
mV
μs
V
V
μA
μA
μA
μA
mV
V
V
%
μA
mV
μA
V
ms
V
mV
V
mV
Continued on the next page…
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
6

6 Page









A6268 pdf, datenblatt
A6268
Automotive High Current LED Controller
threshold provided by the specified hysteresis.
LED Diagnostics The voltage with respect to ground at the
three pins LP, LF, and LA, namely VLP , VLF , and VLA , determine
the status of the LEDs in the load. These voltages provide two
differential voltage measurements:
• the voltage across a single reference LED:
VLED = VLF VLP
(7)
• the ratio of the voltage across all LEDs in a single string:
VSTR = VLA VLP (8)
These measurements are used to determine if there is an open
circuit, if one or more LEDs are shorted, if the output is shorted,
or if there is a short across the LED string.
The voltage, VSTR , is derived from the voltage across all LEDs in
the string, by an external resistor divider with a ratio equal to the
quantity of LEDs in the string. To minimize the effects of the bias
currents introducing an offset voltage, it is recommended that the
resistor between LP and LA should be approximately 560 Ω.
So for example, if eight LEDs were used, the ratio required
would be an eighth, therefore the resistor connected between LA
and the anode end of the LED string would be 3.9 kΩ;
560 / [560 + 3900] = 1/8 .
Open LED–An open circuit is evaluated when:
VSTR > VOP (9)
where VOP is the LED open circuit voltage defined in the Electri-
cal Characteristics table.
Because the output is current-controlled it is possible for an open
circuit on the output to cause extremely high voltages to be pres-
ent. Therefore, to prevent any hazardous voltages or damage to
the circuits, the gate drive output, SG, is immediately driven low
when an open circuit is detected. After an open circuit fault has
been detected, FF2 will become high impedance, and the open
circuit fault state will remain until the open fault time-out period,
tOTO , expires.
Note that the open fault time-out period is derived from the oscil-
lator period by a ratio of 32,768:1, so any variation in the oscilla-
tor frequency will change the open fault time-out period. For the
default switching frequency of 350 kHz, this means the open fault
time-out period would be:
tOTO = 32,768 × ( 1 / 350 × 103 ) = 94 ms
(10)
When the gate drive output is re-enabled at the end of the open
fault time-out period, the output is again monitored for an open
circuit. If the open circuit is still present, then the fault will again
be flagged and the switch drive disabled. This cycle will con-
tinue, as long as the open circuit condition is present.
Shorted LED – A short circuit on one or more LEDs is detected
when:
• for the first (reference) LED:
VSTR > VLED + VSCOR (11)
• for other than the first (reference) LED:
VLED > VSTR + VSCO (12)
where VSTR and VLED are as defined above, VSCO is the nonrefer-
ence LED short offset voltage, and VSCOR is the reference LED
short offset voltage. VSCO and VSCOR are defined in the Electrical
Characteristics table.
When a short is present, the fault flag FF2 is high impedance, but
the regulator continues to operate and drives the remaining LEDs
with the correct regulated current. FF2 will remain high imped-
ance while the short circuit condition is present.
A short circuit on one or more LEDs will not cause a hazard
because the output is current-controlled. If one LED fails and
becomes a short circuit, then the remaining LEDs will continue
to be lit with the same current through, and voltage across,
each LED.
Note—Accuracy: The output status monitor relies on all the
LEDs in the load having a similar forward voltage drop. Where
possible all the LEDs forming the load for a single controller
should be taken from the same voltage bin. The selection of
LEDs from the same bin is more critical when higher numbers of
LEDs are used in a single string. With only two or three LEDs a
wider variation in forward voltage is acceptable.
LED Undercurrent – Under some circuit conditions, particu-
larly during a low input voltage condition, it is possible that there
could be insufficient drive to maintain the current to the LEDs
at the required level. If the voltage across the LED current sense
resistor, RSS , falls below the target sense voltage, VIDL , by an
amount that is more than the LED undercurrent voltage differ-
ence, VUCL , the A6268 will indicate an LED undercurrent condi-
tion by setting FF2 to high impedance. However, the A6268 will
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
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