A8507 LED Backlight Driver for LCD Monitors and Televisions Features and Benefits Description 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 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 cycleby-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. Packages: 24-pin TSSOP with exposed thermal pad (Package LP) Not to scale 24-pin SOICW with internally fused pins (LB package) Functional Block Diagram VBAT 10 H 4.7 F 2.2 F P RSC P ROVP P SENP DRIVER RFSET OSC FSET OVP Overvoltage Protection Ref OCP SS CCOMP SENN Current Mode Boost Controller COMP Control and Feedback LED1 6 RISET LED2 ISET Reference Current PWM LED3 100 k EN +5 V 10 k VIN Control Logic/ UVLO LED Select Logic 6 Open/Short LED Detect 6 LED4 TSD OVP OCP LED5 0.1 F LED6 FAULT LB Only LP Only PGND P A8507-DS, Rev. 2 GND GND PAD LGND LGND Figure 1. Functional block diagram showing 6 parallel strings with 9 series LEDs per channel A8507 LED Backlight Driver for LCD Monitors and Televisions Selection Guide Part Number Packing Package A8507ELBTR-T 1000 pieces per 13-in. reel A8507ELPTR-T 4000 pieces per 13-in. reel 24-pin SOICW, with internally fused pins for enhanced thermal dissipation 24-pin TSSOP, with exposed thermal pad for enhanced thermal dissipation Absolute Maximum Ratings Characteristic Rating Unit 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 LED Output Voltage Symbol -0.3 to 7 V -40 to 85 C TJ(max) 150 C Tstg -55 to 150 C Remaining Pins Input Voltage VIN Operating Ambient Temperature TA Maximum Junction Temperature Storage Temperature Notes Range E Thermal Characteristics may require derating at maximum conditions, see application information Characteristic Package Thermal Resistance Symbol RJA Value Unit Package LB, on 2-layer PCB, 1-in.2 2-oz copper exposed area Test Conditions* 51 C/W Package LB, on 4-layer PCB, based on JEDEC standard 35 C/W Package LP, 4-layer PCB, based on JEDEC standard 28 C/W *Additional thermal information available on the Allegro website Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 2 A8507 LED Backlight Driver for LCD Monitors and Televisions Pin-out Diagrams PWM 1 PGND 2 24 EN GND 1 24 EN 23 FAULT PWM 2 23 FAULT NC 3 22 LED6 NC 3 22 LED6 NC 4 21 LED5 PGND 4 21 LED5 SENN 5 20 LED4 NC 5 GND 6 19 LGND SENN 6 GND 7 18 LGND SENP 7 18 LED3 SENP 8 17 LED3 OVP 8 17 LED2 OVP 9 16 LED2 NC 9 16 LED1 DRIVER 10 15 LED1 DRIVER 10 20 LED4 PAD 19 LGND 15 COMP VIN 11 14 COMP VIN 11 14 FSET ISET 12 13 FSET ISET 12 13 GND Package LB Package LP 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 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 10 10 DRIVER No internal electrical connection to these pins 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 Gate driver terminal to drive external MOSFET 11 11 VIN 12 12 ISET Input supply for the IC; decouple with a 0.1 F ceramic capacitor 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 AULT F 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 Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 3 A8507 LED Backlight Driver for LCD Monitors and Televisions ELECTRICAL CHARACTERISTICS Valid at VIN = 5 V; TA = 25C, RFSET = 52 k, RISET = 12.4 k, except specifications guaranteed over the full operating temperature range with TA = TJ , unless otherwise noted Characteristics Input Voltage Range Min. Typ.1 Max. Unit 4.3 - 5.5 V VIN Falling - - 4.0 V - 0.1 - V Switching at no load - 7 - mA Shutdown, EN = VIL, TA = 25C - 0.1 1 A Standby, EN = VIH, PWM = VIL, soft start completed - 1 2 mA 0.8 1 1.25 MHz Symbol Test Conditions VIN Undervoltage Lockout Threshold VUVLO Undervoltage Lockout Hysteresis VUVLOHYS Supply Current2 IVIN indicates Boost Controller Switching Frequency fSW 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 Current2 IIN 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 VSEN VSENP - VSENN 80 95 110 mV 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 41 - 125 A Sense Overcurrent Threshold Voltage LED Current Sinks ISET Allowable Current Range2 LEDx Accuracy3 ErrILEDX LED1 through LED6 = 1 V, at 100% Current -3 0.6 3 % LEDx Matching4 ILEDX LED1 through LED6 = 1 V, ISET = 100 A -3 0.6 3 % VLEDx = 12 V, EN = 0 - 0.1 - A LEDx Switch Leakage Current2 ISL 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... Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 4 A8507 LED Backlight Driver for LCD Monitors and Televisions ELECTRICAL CHARACTERISTICS (continued) Valid at VIN = 5 V; TA = 25C, RFSET = 52 k, RISET = 12.4 k, except specifications guaranteed over the full operating temperature range with TA = TJ , unless otherwise noted Characteristics Symbol Test Conditions indicates Min. Typ.1 Max. Unit - 165 - C Protection Features Thermal Shutdown Threshold TTSD TJ rising Short Circuit Detect Voltage VSC - 18.7 - V Output Overvoltage Threshold VOVP ROVP = 0 - 36 - V IOVPLK VOVP = 22 V, EN = VIL - 0.1 - A - 240 - A OVP Pin Leakage Current2 Overvoltage Protection Sense Current2 IOVPH AULT Pin Output Leakage2 F IFLT V=5V - - 1 A AULT Pin Output Voltage F VOL I = 500 A - - 0.4 V 1Typical specifications are at TA = 25C. 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 (I SET x 640 - ILED(av)) / (ISET x 640), ILED(av) measured as the average of ILED1 through ILED6. 4LED current matching is defined as (I LEDx - ILED(av)) / ILED(av), with ILED(av) as defined in footnote 3. 2For Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 5 A8507 LED Backlight Driver for LCD Monitors and Televisions Efficiency (%) Characteristic Performance 99 98 97 96 95 94 93 92 91 90 89 88 87 86 85 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 10 12 14 16 18 20 VBAT (V) 22 24 26 28 Figure 2. Efficiency versus Battery Voltage at various LED configurations, RFSET = 105 k (500 kHz), RISET = 14.3 k (55 mA) or 10 k (80 mA), Q1 = FQB17N08L, L1 = 10 H 100 1.007 Normalized Current Gain Efficiency (%) 1.006 VBAT= 16 V VBAT= 21 V 95 VBAT= 12 V 90 VBAT= 8 V 85 80 1.005 1.004 1.003 1.002 1.001 1.000 75 0 10 20 30 40 50 60 70 80 90 100 0.999 10 12 14 Figure 3. Efficiency versus PWM Duty Cycle at various VBAT levels, 5 parallel strings with 9 series LEDs each, ILED = 55 mA per channel 20 22 24 26 28 30 60 Average LED Current (mA) LED Current (mA) 18 Figure 4. Normalized Current Gain versus RISET , normalized to 1 for RISET = 12.4 k 55.5 55.4 55.3 55.2 55.1 55.0 54.9 -40 16 RISET (k) PWM Duty Cycle (%) -20 0 20 40 60 80 100 Temperature (C) Figure 5. LED Current versus Ambient Temperature, RISET = 14.3 k 50 40 30 VBAT (V) 20 21 16 12 8 10 0 0 20 40 60 80 100 120 PWM Duty Cycle(%) Figure 6. Average LED Current versus PWM Duty Cycle at various VBAT levels, 6 parallel strings with 9 series LEDs each, ILED = 55 mA per channel, fPWM = 200 Hz Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 6 A8507 LED Backlight Driver for LCD Monitors and Televisions 90 1.034 80 1.033 1.032 60 50 fSW (MHz) LED Current (mA) 70 40 30 20 1.030 1.029 1.028 10 1.027 --35 0 10 1.031 15 20 25 30 -20 RISET (k) LED Current Matchiing Error (%) LED Current Accuracy (%) 90 80 70 Uncompensated Compensated (3 s) 50 40 1 10 60 80 1.00 0.95 0.90 0.85 0.80 0.75 0.70 0.65 0.60 0.55 0.50 10 100 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, ILED = 55 mA per channel fPWM = 200 Hz 20 30 40 50 60 70 80 90 100 PWM Duty Cycle (%) PWM Duty Cycle (%) Switching Frequency (kHz) 40 Figure 8. Switching Frequency versus Ambient Temperature 100 0.1 20 Ambient Temperature (C) Figure 7. LED Current versus RISET 60 0 Figure 10. LED Current Matching Error versus PWM Duty Cycle, VBAT = 12 V, 6 parallel strings with 9 series LEDs each, ILED = 55 mA per channel, fPWM = 200 Hz 1050 950 850 750 650 550 450 350 250 50 60 70 80 90 100 110 120 130 140 150 160 170 180 R F S E T (k) Figure 11. Switching Frequency versus RFSET Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 7 A8507 LED Backlight Driver for LCD Monitors and Televisions Typical Power Sequencing Waveforms Turn-on sequence VIN - VEN - VPWM Turn-off sequence VPWM - VEN - VIN VIN VIN VEN VEN VEN VPWM VPWM C2 C1 C4 VEN C3 C3 VPWM IOUT VIN C2 VIN C1 IOUT IOUT C4 t t Turn-on sequence VIN - VPWM - VEN C3 Turn-off sequence VEN - VPWM - VIN VIN VIN VEN VEN VEN C1 VPWM IOUT VIN VPWM C2 VPWM IOUT VIN C1 IOUT C4 VEN C3 VPWM C2 VPWM IOUT IOUT C4 t t C1: VIN , 1 V / div. C2: VPWM , 5 V / div. C3: VEN , 5 V / div. C4: IOUT , 200 mA / div. Time: 2 ms / div. 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, ILED = 55 mA per channel Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 8 A8507 LED Backlight Driver for LCD Monitors and Televisions Functional Description 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 current 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 regulated 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: ISET = 1.235 / RISET (k) . (1) 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. 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. LED Short Detect Any LEDx pins that have a voltage exceeding 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. 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: Overvoltage Protection The A8507 has an adjustable overvoltage 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 fSW = 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 PWM tD ILED Figure 13. Propagation delay from the PWM signal rising edge to ILEDx reaching the 90% level Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 9 A8507 LED Backlight Driver for LCD Monitors and Televisions fault disables all LEDx strings that are below regulation, thus preventing them from controlling the boost output voltage. Calculate the value for ROVP () as follows: ROVP = (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 reenabling 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 (): RSC = 0.095 / ISC . 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 current. 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 165C. It will recover automatically when the junction temperature falls below 125C. 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 AutoRestart Overvoltage Protection Yes Fault occurs when OVP pin exceeds the VOVP threshold. Used to protect the output voltage from damaging the part. 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-bypulse 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. Overtemperature Protection Yes Fault occurs when the die temperature exceeds the over-temperature threshold, 165C 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. Pulseby-Pulse Current Limit (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. Description Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 10 A8507 LED Backlight Driver for LCD Monitors and Televisions Application Information 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. Connect all these grounds at the common ground plane under the A8507, serving as a star ground. * Place the resistors RFSET and RISET, and the compensation components (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 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 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. VOUT L1 VBAT 8 to 21 V C1 P 10 RSC 7 C3 6 P DRIVER SENP SENN VBIAS 4.5 to 5.5 V ROVP 8 OVP C4 P 11 VIN R1 R2 Q1 C2 8 LEDs per string D1 C5 RFSET 23 FAULT EN 24 PWM 2 COMP 15 FSET 14 RISET R3 12 Rz1 Cz1 3 5 9 A8507 (LP package) LED1 LED2 LED3 LED4 ISET LED5 NC NC PAD NC GND GND 1 13 LED6 16 17 18 20 21 22 LGND PGND 19 4 P R2, R3 optional (A8507 has internal pull-down resistors) Figure 14. Typical application circuit Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 11 A8507 LED Backlight Driver for LCD Monitors and Televisions VOUT L1 C1 Q1 C2 P 10 RSC 7 C3 6 P DRIVER SENP SENN VBIAS 4.5 to 5.5 V 8 LEDs per string D1 ROVP 8 OVP C4 P 100 11 VIN R1 R2 C5 RFSET 23 FAULT EN 24 PWM 2 COMP 15 FSET 14 RISET R3 12 Rz1 3 5 Cz1 9 A8507 (LP package) LED1 16 LED2 17 LED3 GND GND 1 13 21 0 20 21 LED6 NC 12 85 20 LED5 PAD VBAT (V) 90 80 LED4 NC 95 18 ISET NC Efficiency (%) VBAT 8 to 21 V 40 60 80 100 PWM duty cycle (%) 22 RISET = 10.0 k, RFSET = 51 k, ROVP = 0 , Q1=FQB17N08L LGND PGND 19 4 P R2, R3 optional (A8507 has internal pull-down resistors) Figure 15. Typical Application with 6 parallel strings, 8 series LEDs each, 80 mA per channel 12 LEDs per string VOUT L1 C1 P 10 D1 RSC 7 C3 6 P DRIVER SENP SENN VBIAS 4.5 to 5.5 V ROVP 8 OVP C4 P 100 11 VIN R1 R2 Q1 C2 C5 RFSET 23 FAULT EN 24 PWM 2 COMP 15 FSET 14 RISET R3 12 Rz1 Cz1 3 5 9 A8507 (LP package) LED1 LED2 LED3 LED4 ISET LED5 NC NC PAD NC GND GND 1 13 LED6 LGND PGND 19 4 16 17 Efficiency (%) VBAT 8 to 21 V 95 VBAT (V) 90 12 21 85 18 80 20 21 22 0 20 40 60 80 100 PWM duty cycle (%) RISET = 10.0 k, RFSET = 51 k, ROVP = 36 k, Q1=FQB17N08L P R2, R3 optional (A8507 has internal pull-down resistors) Figure 16. Typical Application with 2 parallel strings, 12 series LEDs each, 240 mA per channel Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 12 A8507 LED Backlight Driver for LCD Monitors and Televisions VOUT C1 Q1 C2 P RSC 7 10 C3 6 P DRIVER SENP SENN VBIAS 4.5 to 5.5 V 12 LEDs per string D1 ROVP 8 OVP C4 P 100 11 VIN R1 C5 23 FAULT EN A8507 (LP package) 24 2 R2 RFSET 15 14 RISET R3 12 Rz1 3 5 Cz1 9 16 LED1 17 LED2 PWM FSET 95 VBAT (V) 90 12 21 85 18 LED3 COMP Efficiency (%) L1 VBAT 8 to 21 V 80 20 LED4 0 20 ISET 21 LED5 NC NC PAD GND GND 1 13 60 80 100 22 LED6 NC 40 PWM duty cycle (%) RISET = 10.0 k, RFSET = 51 k, ROVP = 36 k, Q1=FQB17N08L LGND PGND 19 4 P R2, R3 optional (A8507 has internal pull-down resistors) Figure 17. Typical Application with 3 parallel strings, 12 series LEDs each, 160 mA per channel 12 LEDs per string VOUT L1 C1 P 10 D1 RSC 7 C3 6 P DRIVER SENP SENN VBIAS 4.5 to 5.5 V ROVP 8 OVP C4 P 100 11 VIN R1 R2 Q1 C2 C5 RFSET 23 FAULT EN 24 PWM 2 COMP 15 FSET 14 RISET R3 12 Rz1 Cz1 3 5 9 A8507 (LP package) LED1 LED2 LED3 LED4 16 17 18 20 ISET LED5 NC NC PAD NC GND GND 1 13 LED6 LGND PGND 19 4 P 21 22 Efficiency (%) VBAT 8 to 21 V 95 VBAT (V) 90 12 21 85 80 0 20 40 60 80 100 PWM duty cycle (%) RISET = 10.0 k, RFSET = 51 k, ROVP = 36 k, Q1=FQB17N08L R2, R3 optional (A8507 has internal pull-down resistors) Figure 18. Typical Application with 4 parallel strings, 12 series LEDs each, 80 mA per channel Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 13 A8507 LED Backlight Driver for LCD Monitors and Televisions VOUT C1 P 10 RSC 7 C3 6 P DRIVER SENP SENN VBIAS 4.5 to 5.5 V D2 8 OVP C4 100 P 11 VIN R1 R2 Q1 C2 18 LEDs per string D1 Efficiency (%) L1 VBAT 8 to 21 V C5 RFSET 23 FAULT EN 24 PWM 2 COMP 15 FSET 14 RISET R3 12 Rz1 Cz1 3 5 9 A8507 (LP package) LED1 LED2 LED3 LED4 16 17 LED5 NC PAD NC GND GND 1 13 LED6 LGND PGND 19 4 12 21 85 0 20 21 40 60 80 100 RISET = 10.0 k, RFSET = 51 k, D2 = 30 V Zener, Q1=FQB17N08L R5 22 20 PWM duty cycle (%) R4 R6 R7 P R2, R3 optional (A8507 has internal pull-down resistors) VBAT (V) 90 80 18 ISET NC 95 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 Figure 19. Typical Application with 4 parallel strings, 18 series LEDs each, 80 mA per channel Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 14 A8507 LED Backlight Driver for LCD Monitors and Televisions Package LB 24-Pin SOICW with Internally Fused Pins 15.40 0.20 8 0 24 24 0.33 0.20 7.50 0.10 2.20 10.30 0.33 9.60 A 1.40 REF 1 2 1.27 0.40 Branded Face 24X SEATING PLANE 0.10 C 0.51 0.31 1.27 BSC 1 2 0.65 1.27 0.25 BSC SEATING PLANE GAUGE PLANE C B PCB Layout Reference View 2.65 MAX 0.30 0.10 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 A Terminal #1 mark area B 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 Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 15 A8507 LED Backlight Driver for LCD Monitors and Televisions Package LP 24-Pin TSSOP with Exposed Thermal Pad 7.800.10 24 0.65 0.45 8 0 0.20 0.09 B 3 NOM 4.400.10 3.00 6.400.20 6.10 0.60 0.15 A 1 2 1.00 REF 4.32 NOM 0.25 BSC 24X SEATING PLANE 0.10 C 0.30 0.19 0.65 BSC SEATING PLANE GAUGE PLANE C 1.65 4.32 C PCB Layout Reference View 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 1.20 MAX 0.15 0.00 A Terminal #1 mark area B Exposed thermal pad (bottom surface); dimensions may vary with device C 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) Copyright (c)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 departures from the detail specifications as may be required to permit improvements in the performance, 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 information included herein is believed to be accurate and reliable. However, Allegro MicroSystems, Inc. assumes no responsibility for its use; nor for any infringement 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 Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 16