Description
The A8507 is a multi-output WLED/RGB driver for
backlighting LCD monitors and televisions. The A8507
integrates a boost controller to drive external MOSFET and
six internal current-sinks. The boost converter is constant
frequency current mode converter.
PWM dimming allows LED currents to be controlled in 500:1
ratio. The LED sinks are capable of sinking up to 80 mA
each, and can be paralleled together to achieve even higher
currents.
The A8507 provides protection against overvoltage, open or
shorted LED string, and overtemperature. A dual level cycle-
by-cycle current limit function provides soft start and protects
against overloads.
The device is provided in a 24-pin SOICW package (LB), with
internally fused pins for enhanced thermal dissipation, and a
24-pin TSSOP package (LP), with an exposed thermal pad
for enhanced thermal dissipation. Both packages are lead (Pb)
free, with 100% matte tin leadframe plating.
A8507-DS, Rev. 2
Features and Benefits
Fixed frequency current mode control with integrated
gate driver
Each individual current sink is capable of 80 mA
Adjustable overvoltage protection (OVP)
Active current sharing between LED strings for ±0.6%
accuracy and matching
250 kHz to 1 MHz adjustable switching frequency
Open or shorted LED string protection
Overtemperature, cycle-by-cycle current limit, and
undervoltage protection
No audible MLCC noise during PWM dimming
No pull-up resistors required for LED modules that use
ESD capacitors
SOIC 24-pin package for easy single-side PCB
manufacturing or TSSOP 24-pin package with exposed
thermal pad for better thermal performance
LED Backlight Driver for LCD Monitors and Televisions
Packages:
Functional Block Diagram
Not to scale
A8507
24-pin SOICW
with internally fused pins
(LB package)
24-pin TSSOP
with exposed thermal pad
(Package LP)
LED1
OSC Current Mode
Boost
Controller
EN
FSET
PWM
VIN
FAULT
TSD
OVP
OCP
DRIVER SENP SENN
10 H2.2 F4.7 F
VBAT
OVP
Overvoltage
Protection
LED2
LED3
LED4
LED5
LED6
Control and
Feedback
Reference
Current
LED Select
Logic
Open/Short
LED Detect
6
6
6
COMP
Ref
OCP SS
ISET
100 k
RSC
RFSET
RISET
CCOMP
ROVP
10 k0.1 F
Control
Logic/
UVLO
+5 V
PGND LGNDPAD
LP Only LB Only
LGNDGND GND
P
PP
P
Figure 1. Functional block diagram
showing 6 parallel strings with 9 series
LEDs per channel
LED Backlight Driver for LCD Monitors and Televisions
A8507
2
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Absolute Maximum Ratings
Characteristic Symbol Notes Rating Unit
LED Output Voltage VLEDx –0.3 to 40 V
OVP Pin Input Voltage VOVP –0.3 to 50 V
SENP and SENN Pin Input Voltage VSENx –0.3 to 1 V
Remaining Pins Input Voltage VIN –0.3 to 7 V
Operating Ambient Temperature TARange E –40 to 85 ºC
Maximum Junction Temperature TJ(max) 150 ºC
Storage Temperature Tstg –55 to 150 ºC
Selection Guide
Part Number Packing Package
A8507ELBTR-T 1000 pieces per 13-in. reel 24-pin SOICW, with internally fused pins for enhanced
thermal dissipation
A8507ELPTR-T 4000 pieces per 13-in. reel 24-pin TSSOP, with exposed thermal pad for enhanced
thermal dissipation
Thermal Characteristics may require derating at maximum conditions, see application information
Characteristic Symbol Test Conditions* Value Unit
Package Thermal Resistance RJA
Package LB, on 2-layer PCB, 1-in.
2 2-oz copper exposed area 51 ºC/W
Package LB, on 4-layer PCB, based on JEDEC standard 35 ºC/W
Package LP, 4-layer PCB, based on JEDEC standard 28 ºC/W
*Additional thermal information available on the Allegro website
LED Backlight Driver for LCD Monitors and Televisions
A8507
3
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Package LB Package LP
Pin-out Diagrams
1
2
3
4
5
6
7
8
9
10
11
12
24
23
22
21
20
19
18
17
16
15
14
13
EN
FAULT
LED6
LED5
LED4
LGND
LGND
LED3
LED2
LED1
COMP
FSET
PWM
PGND
NC
NC
SENN
GND
GND
SENP
OVP
DRIVER
VIN
ISET
1
2
3
4
5
6
7
8
9
10
11
12
24
23
22
21
20
19
18
17
16
15
14
13
EN
FAULT
LED6
LED5
LED4
LGND
LED3
LED2
LED1
COMP
FSET
GND
GND
PWM
NC
PGND
NC
SENN
SENP
OVP
NC
DRIVER
VIN
ISET
PAD
Terminal List Table
Number Name Function
LB LP
1 2 PWM PWM LED-current control; apply logic level PWM for dimming
2 4 PGND Power ground for external FET gate driver; connect to common star ground and
RSC ground
3,4 3,5,9 NC No internal electrical connection to these pins
5 6 SENN Connect ground side of current sense resistor RSC
6,7 1,13 GND Connect to common star ground
8 7 SENP Connect high side of current sense resistor RSC
9 8 OVP
Connect this pin to output capacitor +ve node to enable overvoltage protection;
typical OVP level is 36 V, and this level can be increased by connecting through
an external resistor ROVP
10 10 DRIVER Gate driver terminal to drive external MOSFET
11 11 VIN Input supply for the IC; decouple with a 0.1 F ceramic capacitor
12 12 ISET Sets 100% Current through LED strings; connect RISET from ISET to GND
13 14 FSET Sets switching frequency; connect RFSET from FSET to GND
14 15 COMP Compensation pin; connect 1 F capacitor to GND or common star ground
15,16,17 16,17,18 LEDx LED sinks capable of 80 mA sink; connect unused LEDx pins to ground
18,19 19 LGND Connect to common star ground
20,21,22 20,21,22 LEDx LED sinks capable of 80 mA sink; connect unused LEDx pins to ground
23 23 ¯
F
¯
¯
A
¯¯¯
U ¯¯
L
¯
¯
T
¯ During normal operation, this pin is high (high impedance); at a fault event, this
pin pulls low
24 24 EN Device enable
– PAD PAD Exposed pad for enhanced thermal dissipation, connect to common star ground
LED Backlight Driver for LCD Monitors and Televisions
A8507
4
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
ELECTRICAL CHARACTERISTICS Valid at VIN = 5 V; TA = 25°C, RFSET = 52 k, RISET = 12.4 k, except indicates
specifications guaranteed over the full operating temperature range with TA = TJ , unless otherwise noted
Characteristics Symbol Test Conditions Min. Typ.1Max. Unit
Input Voltage Range VIN 4.3 – 5.5 V
Undervoltage Lockout Threshold VUVLO VIN Falling – – 4.0 V
Undervoltage Lockout Hysteresis VUVLOHYS – 0.1 – V
Supply Current2IVIN
Switching at no load – 7 – mA
Shutdown, EN = VIL, TA = 25°C – 0.1 1 A
Standby, EN = VIH, PWM = VIL, soft start
completed –12mA
Boost Controller
Switching Frequency fSW 0.8 1 1.25 MHz
Minimum Switch Off-Time toff(min) Driver output – 72 – ns
Minimum Switch On-Time ton(min) Driver output – 72 – ns
Logic Input Levels (EN and PWM pins)
Input Voltage Level Low VIL – – 0.4 V
Input Voltage Level High VIH 1.5 – – V
Input Leakage Current2I
IN EN = PWM = 5 V – 100 – A
Driver Section
High Side Gate Drive On Resistance RDS(on)H Measured at VGATE = VIN / 2 – 9 –
Low Side Gate Drive On Resistance RDS(on)L Measured at VGATE = VIN / 2 – 10 –
Driver to GND Resistance During Shutdown RSDOFF – 125 – k
Sense Overcurrent Threshold Voltage VSEN VSENP – VSENN 80 95 110 mV
LED Current Sinks
LEDx Pin Regulation Voltage VLEDx ILED = 80 mA – 1 – V
ISET to ILEDx Current Gain AISET ISET = 100 A – 640 – A/A
ISET Pin Voltage VISET – 1.235 – V
ISET Allowable Current Range2ISET 41 – 125 A
LEDx Accuracy3ErrILEDX LED1 through LED6 = 1 V, at 100% Current –3 ±0.6 3 %
LEDx Matching
4ILEDX LED1 through LED6 = 1 V, ISET = 100 A –3 ±0.6 3 %
LEDx Switch Leakage Current2ISL VLEDx = 12 V, EN = 0 – 0.1 – A
Soft Start
Soft Start Sense Threshold Voltage VSENS
Sense voltage for boost switch current
sensing – 28.5 – mV
Soft Start LEDx Current Limit Relative to LED
100% Current ILED(SS)
Current through enabled LEDx pins during
soft start –8–%
Continued on the next page…
LED Backlight Driver for LCD Monitors and Televisions
A8507
5
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Protection Features
Thermal Shutdown Threshold TTSD TJ rising – 165 – °C
Short Circuit Detect Voltage VSC – 18.7 – V
Output Overvoltage Threshold VOVP ROVP = 0 – 36 – V
OVP Pin Leakage Current2IOVPLK VOVP = 22 V, EN = VIL – 0.1 – A
Overvoltage Protection Sense Current2IOVPH – 240 – A
¯
F
¯
¯
A
¯¯¯
U ¯¯
L
¯
¯
T
¯
Pin Output Leakage2IFLT V = 5 V – – 1 A
¯
F
¯
¯
A
¯¯¯
U ¯¯
L
¯
¯
T
¯
Pin Output Voltage VOL I = 500 A – – 0.4 V
1Typical specifications are at TA = 25ºC.
2For input and output current specifications, negative current is defined as coming out of the node or pin (sourcing), positive current is defined as going
into the node or pin (sinking).
3LED accuracy is defined as (ISET × 640 – ILED(av)) / (ISET × 640), ILED(av) measured as the average of ILED1 through ILED6.
4LED current matching is defined as (ILEDx – ILED(av)) / ILED(av), with ILED(av) as defined in footnote 3.
ELECTRICAL CHARACTERISTICS (continued) Valid at VIN = 5 V; TA = 25°C, RFSET = 52 k, RISET = 12.4 k, except indicates
specifications guaranteed over the full operating temperature range with TA = TJ , unless otherwise noted
Characteristics Symbol Test Conditions Min. Typ.1Max. Unit
LED Backlight Driver for LCD Monitors and Televisions
A8507
6
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
0
10
20
30
40
50
60
0 20 40 60 80 100 120
Average LED Current (mA)
PWM Duty Cycle(%)
VBAT (V)
21
16
12
8
54.9
55.0
55.1
55.2
55.3
55.4
55.5
-4 0 -2 0 0 2 0 4 0 6 0 8 0 1 0 0
LED Current (mA)
Temperature (°C)
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
10 12 14 16 18 20 22 24 26 28
Efficiency (%)
V
BAT
(V)
6 parallel strings, 12 serial LEDs each, ILED = 55 mA
6 parallel strings, 9 serial LEDs each, ILED = 55 mA
6 parallel strings, 12 serial LEDs each, ILED = 80 mA
6 parallel strings, 9 serial LEDs each, ILED = 80 mA
75
80
85
90
95
100
0 10203040506070809010
0
Efficiency (%)
PWM Duty Cycle (%)
VBAT= 21 V VBAT= 16 V
VBAT= 8 V
0.999
1.000
1.001
1.002
1.003
1.004
1.005
1.006
1.007
10 12 14 16 18 20 22 24 26 28 30
Normalized Current Gain
RISET (k)
VBAT= 12 V
Characteristic Performance
Figure 3. Efficiency versus PWM Duty Cycle at various VBAT levels,
5 parallel strings with 9 series LEDs each, I
LED = 55 mA per channel
Figure 2. Efficiency versus Battery Voltage at various LED configurations, R
FSET = 105 k
(500 kHz), RISET = 14.3 k (55 mA) or 10 k (80 mA), Q1 = FQB17N08L, L1 = 10 H
Figure 4. Normalized Current Gain versus RISET , normalized to 1 for
RISET = 12.4 k
Figure 5. LED Current versus Ambient Temperature, RISET = 14.3 kFigure 6. Average LED Current versus PWM Duty Cycle at various
VBAT levels, 6 parallel strings with 9 series LEDs each, I
LED = 55 mA
per channel, fPWM = 200 Hz
LED Backlight Driver for LCD Monitors and Televisions
A8507
7
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
40
50
60
70
80
90
100
0.1 1 10 100
LED Current Accuracy (%)
LED Current Matchiing Error (%)
PWM Duty Cycle (%)
Uncompensated
Compensated (3 s)
0.50
0.55
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0.95
1.00
10 20 30 40 50 60 70 80 90 100
PWM Duty Cycle (%)
50 60 70 80 90 100 110 120 130 140 150 160 170
Switching Frequency (kHz)
RFSET(k)
250
350
450
550
650
750
850
950
1050
180
0
10
20
30
40
50
60
70
80
90
LED Current (mA)
1.027
1.028
1.029
1.030
1.031
1.032
1.033
1.034
fSW (MHz)
Ambient Temperature (°C)
10 15 20 25 30
RISET (k)
--35 -20 0 20 40 6 0 80
Figure 7. LED Current versus RISET Figure 8. Switching Frequency versus Ambient Temperature
Figure 9. LED Current Accuracy versus PWM Duty Cycle,
LED Current Accuracy normalized to the 100% Current level,
VBAT = 12 V, 6 parallel strings with 9 series LEDs each, I
LED = 55 mA
per channel fPWM = 200 Hz
Figure 10. LED Current Matching Error versus PWM Duty Cycle,
VBAT = 12 V, 6 parallel strings with 9 series LEDs each, I
LED = 55 mA
per channel, fPWM = 200 Hz
Figure 11. Switching Frequency versus RFSET
LED Backlight Driver for LCD Monitors and Televisions
A8507
8
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Fig 12. Alternative Turn-On and Turn-Off sequences: (top) VEN –VPWM –VEN, (bottom) VVPWM –VEN –VPWM, with 6 parallel
strings with 9 series LEDs each, VBAT = 12 V, VPWM = 5 V (100% Current), VIN = 5 V, VEN = 5 V, I
LED = 55 mA per channel
Turn-on sequence
Turn-on sequence
Turn-off sequence
Turn-off sequence
VPWM – VEN – VIN
VIN – VEN – VPWM
VIN – VPWM – VEN VEN – VPWM – VIN
C1: VIN
, 1 V / div.
C2: VPWM , 5 V / div.
C3: VEN , 5 V / div.
C4: IOUT , 200 mA / div.
Time: 2 ms / div.
C2
C3
C4
C1
t
VPWM
VPWM
VIN
VIN
VEN
VEN
IOUT
IOUT
C2
C3
C4
C1
t
VPWM
VPWM
VIN
VIN
VEN
VEN
IOUT
IOUT
VPWM
VIN
VEN
IOUT
t
C2
C3
C4
C1
VPWM
VIN
VEN
IOUT C2
C3
C4
C1
t
VPWM
VIN
VEN
IOUT
VPWM
VIN
VEN
IOUT
Typical Power Sequencing Waveforms
LED Backlight Driver for LCD Monitors and Televisions
A8507
9
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Overview The A8507 is a multi-output WLED/RGB controller
for backlighting medium-size displays. It has a integrated gate
driver for driving an external N-channel boost MOSFET. The
boost controller is fixed frequency current mode converter. The
switching frequency can be set in the range from 250 kHz to
1 MHz, by an external resistor, RFSET
, connected between FSET
and ground.
The external MOSFET switch is protected by pulse-by-pulse cur-
rent limiting. The current limit is independent of duty cycle, and
is set using an external sense resistor, RSC.
The A8507 has six well-matched current sinks that provide regu-
lated current through the LEDs for uniform display brightness.
The boost converter is controlled by monitoring all LEDx pins
simultaneously and continuously.
LED Current Setting The maximum LED current can be set,
at up to 80 mA/channel, through the ISET pin. Connect a resistor,
RISET , between this pin and ground to set the reference current
level, ISET . The value of ISET (mA) is determined by:
I
SET = 1.235 / RISET (k) . (1)
The resulting current is multiplied internally with a gain of 640
and mirrored on all enabled LEDx pins. This sets the maximum
current through each LEDx, referred as the 100% Current. The
LEDx current can be reduced from the 100% Current value by
applying an external PWM signal on the PWM pin.
Boost Switching Frequency Setting Connect an external
resistor between the FSET pin and GND, to set boost switching
frequency, fSW . The value of fSW (MHz) is determined by:
f
SW = 52 / RFSET , (2)
where fSW is in MHz and RFSET is in k.
Enable The IC turns on when a high signal is applied on the EN
pin, and turns off when this pin is pulled low.
PWM Dimming The A8507 has a very wide range for PWM
signal input. It can accept a PWM signal from 100 Hz to 5 kHz.
When a PWM high signal is applied, the LEDx pins sink
100% Current. When the PWM signal is low, the LED sinks
turn off.
Referring to figure 13, there is a ramp-up delay between when
the PWM signal is applied and when the current reaches the
90% level. To improve current dimming linearity for PWM pulse
widths less than 100 s, increase the applied PWM pulse-width
by 3 s to compensate for this delay.
Startup Sequence When EN is pulled high, the IC enters
soft start. The IC first tries to determine which LEDx pins are
being used, by raising the LEDx pin voltage with a small current.
After a duration of 512 switching cycles, the LEDx pin voltage
is checked. Any LEDx channel with a drain voltage smaller then
100 mV is removed from the control loop.
After the first PWM positive trigger, the boost current is limited
to 35% of normal value and all active LEDx pins sink 1/12 of
the set current until output voltage reaches sufficient regulation
level. When the device comes out of soft start, boost current and
the LEDx pin currents are set to normal operating level. Within
a few cycles, the output capacitor charges to the voltage required
to supply full LEDx current. After output voltage, VOUT , reaches
the required level, LEDx current toggles between 0% and 100%
with each PWM command signal.
In case of a heavy overload on VOUT at startup, the device will
stay in soft start mode indefinitely, as the output voltage cannot
rise to the LED regulation level.
LED Short Detect Any LEDx pins that have a voltage exceed-
ing the Short Circuit Detect Voltage, VSC , cause the device to
shut down and this condition is latched. This faults occurs when
multiple LEDs short. In case only a few LEDs short, the IC will
continue to work as long as power dissipation in the IC is limited.
Overvoltage Protection The A8507 has an adjustable over-
voltage protection feature to protect the external MOSFET
against output overvoltage. The overvoltage level can be set,
from 36 V to a higher voltage, with an external resistor, ROVP
.
When the current though the OVP pin exceeds 240 A, internal
OVP comparator goes high and the device shuts down. The OVP
Functional Description
t
D
PWM
I
LED
Figure 13. Propagation delay from the PWM signal rising edge to ILEDx
reaching the 90% level
LED Backlight Driver for LCD Monitors and Televisions
A8507
10
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
fault disables all LEDx strings that are below regulation, thus pre-
venting them from controlling the boost output voltage.
Calculate the value for ROVP () as follows:
R
OVP = (VOVP – 36) / 240 A , (3)
where VOVP is the required OVP level in V.
Open LED Protection Unused LEDx pins should be connected
to GND. During normal operation, if any enabled LED string
opens, voltage on the corresponding LEDx pin goes to zero. The
boost loop operates in open loop till the OVP level is reached.
The A8507 identifies the open LED string when overvoltage is
detected. Open strings are then removed from the regulation loop.
Afterwards, the boost controller operates in normal manner, and
the output voltage is regulated to drive the remaining strings. If
the open LED string is reconnected, it will sink current up to the
programmed current level.
Note: Open strings are removed from boost regulation, but not
disabled. This keeps the string in operation if LEDs open for only
a short length of time, or reach OVP level on a transient event.
The disconnected string can be restored to normal mode by reen-
abling the IC. It can also be restored to normal operation if the
fault signal is removed from the corresponding LEDx pin, but an
OVP event occurs on any other LEDx pin.
Overcurrent Protection The IC provides pulse-by-pulse
current limiting for the boost MOSFET. The current limit level,
ISC (A), can be set by selecting the external resistor, RSC ():
R
SC = 0.095 / ISC . (4)
If the boost output voltage is unable to reach the regulation target
even when the switch is operating at maximum current limit, the
boost control loop will force the compensating capacitor, CCOMP
,
to rise in voltage until it reaches the overcurrent fault level
(3.4V approximately). The overcurrent fault forces the device
into soft start.
Channel Selection The A8507 can be used to drive 1 to 6 LED
channels. During startup, the IC detects LED sink pins which are
shorted to ground, and disables the corresponding LED channel.
Therefore, any unused LED pins must be connected to ground,
otherwise the IC will go into overvoltage protection fault during
startup. LED pins can be paralleled together for higher cur-
rent. For example for a 3 parallel string configuration, connect
LED1-2, LED3-4, and LED5-6 together to deliver up to 160 mA
per LED.
Thermal Shutdown (TSD) The IC shuts down when junction
temperature exceeds 165°C. It will recover automatically when
the junction temperature falls below 125°C.
VIN Undervoltage Lockout (UVLO) The device is shut down
when input voltage, VIN , falls below VUVLO.
Fault Mode The IC functions in various fault states:
Fault State Auto-
Restart Description
Over-
voltage
Protection
Yes
Fault occurs when OVP pin exceeds the VOVP
threshold. Used to protect the output voltage
from damaging the part.
Pulse-
by-Pulse
Current Limit
Yes
Fault occurs when the current through the
external MOSFET increases exceeds such that
the voltage across the SENP and SENN pins
exceeds 95 mV typical. The MOSFET switch is
turned off on a cycle-per-cycle basis.
Overcurrent
Protection Yes
Fault occurs when the COMP pin exceeds the
overcurrent detect threshold. Multiple pulse-by-
pulse current limits will result in the COMP pin
voltage to rise. After a time period determined
by the COMP pin current and the output
capacitor, COUT
, the COMP voltage will exceed
the overcurrent detect threshold, forcing a fault.
Over-
temperature
Protection
Yes Fault occurs when the die temperature exceeds
the over-temperature threshold, 165°C typical.
LED Short
Protection No Fault occurs when the LED pin voltage exceeds
VSC , 18.7 V typical.
VIN UVLO No Fault occurs when VIN drops below VUVLO,
4.0 V typical. This fault resets all latched faults.
LED Backlight Driver for LCD Monitors and Televisions
A8507
11
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
PCB Layout Guidelines As with any switching power supply,
care should be taken in laying out the board. A switching power
supply has sources of high dv/dt and high di/dt which can cause
malfunction. All general norms should be followed for board
layout. Refer to figure 14 for a typical application schematic. The
A8507 evaluation board provides a useful model for designing
application circuit layouts.
The following guidelines should be observed:
• Place the supply bypass capacitor (C5) close to the VIN pin and
the ground plane.
• Route analog ground, digital signal ground, LED ground
(LGND pin), and power ground (PGND pin) separately. Con-
nect all these grounds at the common ground plane under the
A8507, serving as a star ground.
• Place the input capacitors (C1, C2), inductor (L1), boost diode
(D1), MOSFET (Q1), and output capacitors (C3, C4) so that
they form the smallest loop practical. Avoid long traces for
these paths.
• Place the resistors RFSET and RISET, and the compensation com-
ponents (Rz and Cz) close to the FSET, ISET, and COMP pins,
respectively. Connect the other ends to the common star ground.
• A8507 has 50 k internal pull-down resistors on the EN and
PWM pins to keep these pins low while driving through tri-state
state (for example, shutdown). Add external resistors R2 and
R3 between the EN and PWM pins and ground, for added noise
immunity. Connect these resistors close to the pins and return to
the common star ground.
• Sense voltage across RSC with smaller length traces. Place the
SENP and SENN traces as close to each other as possible to
minimize noise pickup. Connect the SENN trace to the negative
end of the resistor and do not connect it to power ground plane.
• Provide a substantial copper plane near MOSFET Q1 and the
IC, to provide good thermal conduction.
• Place ROVP as close as possible to the OVP pin. A long trace
between ROVP and the OVP pin may pick up switching noises
and cause overvoltage protection to trip prematurely.
Application Information
Figure 14. Typical application circuit
FSET
DRIVER
VIN
PWM
EN
SENP SENN
LED1
LED2
LED3
LED4
LED5
LED6
VBAT
8 to 21 V
VBIAS
4.5 to 5.5 V
87610
419131
11
23
24
A8507
(LP package)
COMP
ISET
NC
NC
NC
GND GND LGND PGND
RSC
ROVP
OVP
VOUT 8 LEDs per string
R3
R2, R3 optional (A8507 has
internal pull-down resistors)
R2 RFSET
RISET
Rz1
Cz1
2
12
14
15
9
5
3
D1
Q1
L1
FAULT
PAD
P
P
C5
R1
C4C3
P
C2C1
P
17
18
20
21
22
16
LED Backlight Driver for LCD Monitors and Televisions
A8507
12
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Figure 15. Typical Application with 6 parallel strings, 8 series LEDs each, 80 mA per channel
Figure 16. Typical Application with 2 parallel strings, 12 series LEDs each, 240 mA per channel
FSET
DRIVER
VIN
PWM
EN
SENP SENN
LED1
LED2
LED3
LED4
LED5
LED6
VBAT
8 to 21 V
VBIAS
4.5 to 5.5 V
87610
419131
11
23
24
A8507
(LP package)
COMP
ISET
NC
NC
NC
GND GND LGND PGND
RSC
ROVP
OVP
VOUT 8 LEDs per string
R3
R2, R3 optional (A8507 has
internal pull-down resistors)
R2 RFSET
RISET
Rz1
Cz1
2
12
14
15
9
5
3
D1
Q1
L1
FAULT
PAD
P
P
C5
R1
C4
C3
P
C2C1
P
17
18
20
21
22
16
R2, R3 optional (A8507 has
internal pull-down resistors)
FSET
DRIVER
VIN
PWM
EN
SENP SENN
LED1
LED2
LED3
LED4
LED5
LED6
VBAT
8 to 21 V
VBIAS
4.5 to 5.5 V
810
419131
11
23
24
A8507
(LP package)
COMP
ISET
NC
NC
NC
GND GND LGND PGND
RSC
ROVP
OVP
VOUT
12 LEDs per string
R3
R2 RFSET
RISET
Rz1
Cz1
2
12
14
15
9
5
3
D1
Q1
L1
FAULT
PAD
P
P
C5
R1
C4
C3
P
C2C1
P76
17
18
20
21
22
16
12
VBAT (V)
21
80
85
90
95
100
0 20406080100
Efficiency (%)
PWM duty cycle (%)
80
85
90
95
100
0 20406080100
Efficiency (%)
PWM duty cycle (%)
12
VBAT (V)
21
RISET = 10.0 k, RFSET = 51 k,
ROVP = 0 , Q1=FQB17N08L
RISET = 10.0 k, RFSET = 51 k,
ROVP = 36 k, Q1=FQB17N08L
LED Backlight Driver for LCD Monitors and Televisions
A8507
13
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Figure 17. Typical Application with 3 parallel strings, 12 series LEDs each, 160 mA per channel
Figure 18. Typical Application with 4 parallel strings, 12 series LEDs each, 80 mA per channel
R2, R3 optional (A8507 has
internal pull-down resistors)
FSET
DRIVER
VIN
PWM
EN
SENP SENN
LED1
LED2
LED3
LED4
LED5
LED6
VBAT
8 to 21 V
VBIAS
4.5 to 5.5 V
810
419131
11
23
24
A8507
(LP package)
COMP
ISET
NC
NC
NC
GND GND LGND PGND
RSC
ROVP
OVP
VOUT
12 LEDs per string
R3
R2 RFSET
RISET
Rz1
Cz1
2
12
14
15
9
5
3
D1
Q1
L1
FAULT
PAD
P
C5
R1
P
C4C3
P
C2C1
P76
17
18
20
21
22
16
R2, R3 optional (A8507 has
internal pull-down resistors)
FSET
DRIVER
VIN
PWM
EN
SENP SENN
LED1
LED2
LED3
LED4
LED5
LED6
VBAT
8 to 21 V
VBIAS
4.5 to 5.5 V
810
419131
11
23
24
A8507
(LP package)
COMP
ISET
NC
NC
NC
GND GND LGND PGND
RSC
ROVP
OVP
VOUT 12 LEDs per string
R3
R2 RFSET
RISET
Rz1
Cz1
2
12
14
15
9
5
3
D1
Q1
L1
FAULT
PAD
P
C5
R1
P
C4C3
P
C2C1
P76
17
18
20
21
22
16
80
85
90
95
100
0 20406080100
Efficiency (%)
PWM duty cycle (%)
12
VBAT (V)
21
80
85
90
95
100
0 20406080100
Efficiency (%)
PWM duty cycle (%)
12
VBAT (V)
21
RISET = 10.0 k, RFSET = 51 k,
ROVP = 36 k, Q1=FQB17N08L
RISET = 10.0 k, RFSET = 51 k,
ROVP = 36 k, Q1=FQB17N08L
LED Backlight Driver for LCD Monitors and Televisions
A8507
14
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Figure 19. Typical Application with 4 parallel strings, 18 series LEDs each, 80 mA per channel
For higher output voltage, the voltage on the LEDx pins during
PWM off-time may exceed the rated voltage. Connect a resistor
from the LEDx pin to GND. Recommended values are:
• C3 = 2.2 F / 100 V ceramic
• C4 = 10 F / 100 V electrolytic
• R4 through R7 = 25 k, 0603
R2, R3 optional (A8507 has
internal pull-down resistors)
FSET
DRIVER
VIN
PWM
EN
SENP SENN
LED1
LED2
LED3
LED4
LED5
LED6
VBAT
8 to 21 V
VBIAS
4.5 to 5.5 V
810
419131
11
23
24
A8507
(LP package)
COMP
ISET
NC
NC
NC
GND GND LGND PGND
RSC
OVP
VOUT 18 LEDs per string
R3
R2 RFSET
RISET
Rz1
Cz1
2
12
14
15
9
5
3
D1
D2
Q1
L1
FAULT
PAD
P
C5
R1
P
R7
R4
R5
R6
C4C3
P
C2C1
P76
17
18
20
21
22
16
80
85
90
95
100
0 20406080100
Efficiency (%)
PWM duty cycle (%)
12
VBAT (V)
21
RISET = 10.0 k, RFSET = 51 k,
D2 = 30 V Zener, Q1=FQB17N08L
LED Backlight Driver for LCD Monitors and Televisions
A8507
15
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Package LB 24-Pin SOICW with Internally Fused Pins
C
SEATING
PLANE GAUGE PLANE
SEATING PLANE
ATerminal #1 mark area
B
B
PCB Layout Reference View
21
24
C
SEATING
PLANE
C0.10
24X
0.25 BSC
1.40 REF
2.65 MAX
Pins 6, 7, 18, and 19 internally fused for enhanced thermal dissipation
For Reference Only; not for tooling use (reference MS-013AD)
Dimensions in millimeters
Dimensions exclusive of mold flash, gate burrs, and dambar protrusions
Exact case and lead configuration at supplier discretion within limits shown
15.40 ±0.20
7.50 ±0.10 10.30 ±0.33
0.30
0.10
0.33
0.20
1.27
0.40
8°
0°
A
1.27 BSC
0.51
0.31
21
24
Reference pad layout (reference IPC SOIC127P1030X265-24M)
All pads a minimum of 0.20 mm from all adjacent pads; adjust as necessary
to meet application process requirements and PCB layout tolerances
2.20
0.65
9.60
1.27
Branded Face
LED Backlight Driver for LCD Monitors and Televisions
A8507
16
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Copyright ©2009-2010, Allegro MicroSystems, Inc.
The products described here are manufactured under one or more U.S. patents or U.S. patents pending.
Allegro MicroSystems, Inc. reserves the right to make, from time to time, such de par tures from the detail spec i fi ca tions as may be required to per-
mit improvements in the per for mance, reliability, or manufacturability of its products. Before placing an order, the user is cautioned to verify that the
information being relied upon is current.
Allegro’s products are not to be used in life support devices or systems, if a failure of an Allegro product can reasonably be expected to cause the
failure of that life support device or system, or to affect the safety or effectiveness of that device or system.
The in for ma tion in clud ed herein is believed to be ac cu rate and reliable. How ev er, Allegro MicroSystems, Inc. assumes no re spon si bil i ty for its use;
nor for any in fringe ment of patents or other rights of third parties which may result from its use.
For the latest version of this document, visit our website:
www.allegromicro.com
Package LP 24-Pin TSSOP with Exposed Thermal Pad
A
1.20 MAX
0.15
0.00
0.30
0.19
0.20
0.09
8º
0º
0.60 ±0.15
1.00 REF
C
SEATING
PLANE
C0.10
24X
0.65 BSC
0.25 BSC
21
24
7.80±0.10
4.40±0.10 6.40±0.20
GAUGE PLANE
SEATING PLANE
ATerminal #1 mark area
B
For Reference Only; not for tooling use (reference MO-153 ADT)
Dimensions in millimeters
Dimensions exclusive of mold flash, gate burrs, and dambar protrusions
Exact case and lead configuration at supplier discretion within limits shown
B
Exposed thermal pad (bottom surface); dimensions may vary with device
4.32 NOM
3 NOM
0.65
6.103.00
4.32
1.65
0.45
Reference land pattern layout (reference IPC7351
TSOP65P640X120-25M); 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)
PCB Layout Reference View
C
C
