DATA SHEET AAT1407 Six-Channel LED Backlight Driver with Integrated Boost and High Frequency Direct PWM Dimming General Description Features The AAT1407 is a highly integrated, high efficiency LED backlight solution for notebook computers, monitors and portable TVs. The device operates from DC inputs, cigarette lighter adapters, or multi-cell Li-ion batteries over the 4.5V to 26V voltage range. • • • • • • An integrated boost (step-up) converter provides up to 45V output for driving series LEDs. Six precision current sinks are programmed up to 30mA per string through one external RSET resistor, supporting up to 661 white LEDs at 180mA total output current. LED strings may be disabled or operated in parallel for increased drive capability. The boost output voltage is set by the LED string with the highest voltage requirement, allowing a wide range of LED characteristics. • • • The PWM dimming range at 100Hz is up to 1,000:1. The boost switching frequency is selectable (up to 1.3MHz) to allow optimum efficiency and the smallest external L/C filtering components. Alternatively, the device may be synchronized to an external clock. Boost current mode control provides fast response to line and load transients. Integrated Light-Load mode ensures highest efficiency across the entire load range. Fault tolerant circuitry extends system life by disabling open LED strings. The unique high voltage current sinks prevent damage resulting from shorted LEDs. The AAT1407 is available in the Pb-free, thermally enhanced 24-pin 3x4 TQFN package. • • • • • • • VIN Range: 4.5V to 5.5V / 5.0V to 26.0V LX Rated to 50V Maximum IOUT: 180mA Up to 92% Efficiency High Efficiency Light-Load Mode 6 LED Current Sinks up to 30mA/each ▪ ±2% Accuracy (21mA) ▪ ±2% Matching (21mA) Flexible Configurations ▪ Disable or Parallel Switching Frequency Options ▪ 675kHz or 1.3MHz ▪ Synchronize to System Clock PWM Direct Dimming Input ▪ Up to 100kHz Prevents Audio Interference ▪ Fast Turn-On/Off ▪ Wide 1,000:1 Dimming Range (100Hz) Fault Tolerant: Open/Shorted LED(s) Current Limit Protection Over-Voltage Protection Over-Temperature Protection Soft-Start Minimizes Inrush Current TQFN34-24 Low Profile Package -40°C to +85°C Temperature Range Applications •Monitors • Notebook Computers • Portable TV • Portable DVD Players • White LED Backlight 1. The maximum number of LEDs in each string is dependent upon the maximum VF of the diodes in that string. Under no event should the voltage at LX be exceeded. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202117A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 29, 2012 1 DATA SHEET AAT1407 Six-Channel LED Backlight Driver with Integrated Boost and High Frequency Direct PWM Dimming Typical Application VIN: 4.5V–26V C1 2.2µF 50V 0805 L1 4.7µH C2 2.2µF D1 EN VIN VCC R2 R1 2 COMP RSET FSET VOUT: 45V at 180mA R3 C4 2.2µF 50V 0805 OVP AAT1407 TQFN34-24 PWM SYNC C3 LX Up to 66 WLED Backlight R4 CS1 CS2 CS3 CS4 CS5 CS6 PGND GND SGND Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202117A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 29, 2012 DATA SHEET AAT1407 Six-Channel LED Backlight Driver with Integrated Boost and High Frequency Direct PWM Dimming Pin Descriptions Pin # Symbol Function 1 SYNC I 2 FSET I 3, 4, 13, 14, 18, 21 GND GND 5 PWM I 6 7 8 9 10 11 12 15 16 CS1 CS2 CS3 CS4 SGND CS5 CS6 RSET COMP O O O O GND O O I I 17 OVP I 19 LX O 20 PGND GND 22 VCC I/O 23 EN I 24 IN I EP GND Description Synchronizes switching frequency to external system clock. Tie to GND to disable this feature. Connect logic high to set internal oscillator to 1300kHz. Connect logic low to set internal oscillator to 675kHz. Connect to GND. Direct PWM input pin. Connect logic level PWM input signal in the frequency range 100Hz100kHz to this pin to enable PWM dimming. Output current sink 1. Connect to SGND to disable channel 1. Output current sink 2. Connect to SGND to disable channel 2. Output current sink 3. Connect to SGND to disable channel 3. Output current sink 4. Connect to SGND to disable channel 4. Current sink ground tied to return of internal current sinks CS1-CS6. Output current sink 5. Connect to SGND to disable channel 5. Output current sink 6. Connect to SGND to disable channel 6. Connect resistor to ground to set maximum current through the LED strings. Connect an external resistor and capacitor to ground to compensate the boost converter. Over-voltage protection pin. Connect resistive divider between VOUT and GND. Care should be taken to ensure that the voltage at LX does not exceed its maximum rating under extreme operating conditions. Switching node of boost converter. Connect an inductor between this pin and input voltage source. Connect the anode of Schottky diode between this pin and the boost output capacitor. Power ground; tied to source of integrated NMOS switching device. Internal regulated voltage when operating from input voltage range 5.0V to 26.0V. De-couple with a 2.2µF capacitor to ground. Do not source current from this node. Input voltage pin when operating from input voltage range 4.5V to 5.5V. Logic high enable pin. Pull logic high or tie to IN to enable the device. Pull low to disable the device and minimize quiescent current; pulling low also disables the internal linear regulator. Input voltage to IC. Tied to input voltage source and input boost inductor. Exposed paddle. Connect to PCB GND plane. PCB paddle should maintain acceptable junction temperature. Pin Configuration TQFN34-24 (Top View) PGND GND VCC EN IN 24 SYNC FSET GND GND PWM CS1 CS2 23 22 21 20 1 19 2 18 3 17 EP 4 16 5 15 6 14 7 13 8 9 10 11 LX GND OVP COMP RSET GND GND 12 CS6 CS5 SGND CS4 CS3 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202117A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 29, 2012 3 DATA SHEET AAT1407 Six-Channel LED Backlight Driver with Integrated Boost and High Frequency Direct PWM Dimming Absolute Maximum Ratings1 Symbol Description VLX VIN,EN VCSx VCC OVP, COMP, PWM, SYNC, RSET, IOUT TJ TLEAD PD ΘJA Value LX Voltage to GND Input Voltage, EN to GND Output Current Sinks CS1 – CS6 to GND VCC Voltage to GND OVP, COMP, PWM, SYNC, CLK Voltage to GND Maximum DC Output Current Maximum Junction Operating Temperature Maximum Soldering Temperature (at leads, 10 sec.) Maximum Power Dissipation3 Thermal Resistance3,4 2 50 -0.3 to 30 -0.3 to 32 -0.3 to 7.0 Units V -0.3 to VCC + 0.3 195 -40 to +150 300 2 50 mA W °C/W Value Units °C Recommended Operating Conditions Symbol VIN VOUT FPWM IOUT TA TJ Description Input Voltage Range Output Voltage Range PWM Dimming Frequency Range DC Output Current Operating Ambient Temperature Operating Junction Temperature 5 to 26 VIN + 3 to 45 0.1 to 100 120 to 180 -40 to 85 -40 to 125 V kHz mA °C 1. Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at conditions other than the operating conditions specified is not implied. Only one Absolute Maximum Rating should be applied at any one time. 2. Based on long-term current density limitation. 3. Mounted on an FR4 board. 4. Derate 20mW/°C above 25°C. 4 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202117A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 29, 2012 DATA SHEET AAT1407 Six-Channel LED Backlight Driver with Integrated Boost and High Frequency Direct PWM Dimming Electrical Characteristics1 VIN = 12V; CIN = 4.7µF, COUT = 2.2µF; CVCC = 2.2µF; L1 = 10µH; RSET =7.5kΩ (ICSx = 21mA); TA = -40oC to 85oC unless otherwise noted. Typical values are at TA = 25oC. Symbol Description Conditions Min Typ Max Units Power Supply, Current Sinks VIN VUVLO Input Voltage Range Under Voltage Threshold VCC VCC Output Voltage VCX Current Sink Voltage IQ IN Quiescient Current (no switching) ISD IN Pin Shutdown Current ICSx ICSx-Matching VOVP RDS(ON)LO DMAX TMIN ICSx/IRSET ILIMIT ILEAK Current Sink Accuracy Current Matching Between Any Sink Channel Over-Voltage Threshold Over-Voltage Hysteresis Low Side Switch On Resistance Maximum Duty Cycle Minimum On-Time Current Set Ratio Low Side Switch Current Limit LX Pin Leakage CSx Pin Leakage FOSC Oscillator Frequency FSYNC Sync Frequency FSYNC Sync Duty Cycle Range FPWM(MAX) Maximum Direct PWM Frequency TSS Soft-Start Time Logic Level Inputs: EN Pin VEN(L) Threshold Low VEN(H) Threshold High ILEN Input Leakage Enable Pin Logic Level Inputs: SYNC, PWM, FSET Pins V(H) Threshold Low V(H) Threshold High ILK Input Leakage TPWM(ON/OFF) PWM Turn On/Off Delay Thermal Protection TJ(SD) TJ Thermal Shutdown Threshold TJ(HYS) TJ Thermal Shutdown Hysteresis VIN = VCC VCC = Open VIN Rising Hysteresis VIN Falling EN = Logic High, ICC(OUT) = 0mA EN = Logic High, ICSx = 21mA (RSET = 7.5kΩ) ICSx = 0% , VCSx = 0.5V, EN = Logic High CS1-CS6 = Open, EN = Logic Low, does not include LX leakage current ICSx = 21mA ICSx = 21mA VOUT Rising VOUT Falling VCC = 4.5V 4.5 5.0 5.5 26.0 4.3 500 3.2 4.0 -5 -3 1.1 4.5 6 V 1.5 mA 40.0 µA +5 +3 1.3 6.5 1 10 % % V mV mΩ % ns A/A A µA µA ±2 ±2 1.2 100 200 100 262 3.0 EN = EN = FSET VIN = FSET VIN = Logic Low; VLX = 40V Logic Low; CSx = 30V = Logic Low; VIN = 5.0 to 26.0V; VCC = 4.5 to 5.5V = Logic High; VIN = 5.0 to 26.0V; VCC = 4.5 to 5.5V 550 675 800 kHz 1100 1300 1500 kHz FOSC ±20% FOSC ± 20% 10 50 1 VOUT = 35V, CCOMP = 18nF, RCOMP = 10kΩ kHz 90 100 % kHz ms 0.4 V V µA 2.5 VEN = 5V, VIN = 5V 3 0.4 VSYNC = VPWM = VFSET = 5V PWM transition to 95%/5% IRSET V mV V V 0.5 90 ICSx/IRSET, VRSET = 0.6V V 1 V V µA µs 140 15 °C °C 1.4 -1 1 1. The AAT1407 is guaranteed to meet performance specifications over the -40°C to +85°C operating temperature range and is assured by design, characterization, and correlation with statistical process controls. 2. Output voltage must result in a voltage lower than the LX maximum rating under all operating conditions. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202117A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 29, 2012 5 DATA SHEET AAT1407 Six-Channel LED Backlight Driver with Integrated Boost and High Frequency Direct PWM Dimming Typical Characteristics Boost Efficiency vs. Input Voltage Boost Efficiency vs. Load Current (L = 10µH; VCC = 4.7V; PWM = VCC; FSET = GND) 100 100 90 90 80 80 Efficiency (%) Efficiency (%) (L = 10µH; VCC = 4.7V; PWM = VCC; FSET = GND; IOUT = 180mA) 70 60 50 40 VOUT = 29V VOUT = 36V 30 20 6 8 10 12 14 16 18 20 22 24 70 60 50 40 20 45 26 Input Voltage (V) Total Output Current (mA) Efficiency (%) 80 70 60 50 VIN = 9V, VOUT = 29V VIN = 12V, VOUT = 36V VIN = 24V, VOUT = 45V 10 20 30 40 50 60 70 80 90 100 PWM Duty Cycle (%) 220 40 20 0 0 10 20 30 40 50 60 70 80 4.7 4.6 4.6 4.4 4.55 4.2 4 4.5 4.45 3.8 4.4 3.6 4.35 85°C 25°C -40°C 4.3 Temperature (°C) 60 100 VCC Line Regulation vs. Input Voltage 4.65 35 90 PWM Duty Cycle (%) 5 10 270 60 4.8 -15 245 80 VCC (V) Current Limit (A) 195 100 (VIN = 5V to 26V) 6 170 120 Low Side Switch Current Limit vs. Temperature 3.4 -40 145 (VIN = 12V; IOUT = 20mA/ch) 90 0 120 Output Current vs. PWM Duty Cycle 100 20 95 (L = 10µH; VCC = 4.7V; FSET = GND) 30 70 Output Current (mA) Boost Efficiency vs. PWM Duty Cycle 40 VIN = 9V, VOUT = 28V VIN = 12V, VOUT = 36V VIN = 24V, VOUT = 46V 30 6 85 11 16 21 Input Voltage (V) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202117A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 29, 2012 26 DATA SHEET AAT1407 Six-Channel LED Backlight Driver with Integrated Boost and High Frequency Direct PWM Dimming Typical Characteristics Quiescent Current vs. Input Voltage Shutdown Current vs. Input Voltage (Non-switching; VCSX = 0.5V; ICSX =0mA) (VLX = VCSX = Open) 20 1.3 1.25 1.2 1.15 1.1 85°C 25°C -40°C 1.05 1 6 9 12 15 18 21 Shutdown Current (µA) Quiescent Current (mA) 1.4 1.35 18 16 14 12 10 8 6 85°C 25°C -40°C 4 2 0 24 6 10 Input Voltage (V) 3 1.28 2 OVP Voltage (V) Switching Frequency Error (%) 1.3 1 0 -1 -2 FSET = GND FSET = VCC 10 35 60 1.26 1.24 1.22 1.2 1.18 1.16 1.14 1.12 1.1 -40 85 -15 Temperature (°C) Current Sink Matching (%) Current Sink Accuracy (%) 3 2 1 0 -1 -2 -3 35 Temperature (°C) 60 85 (VIN = 12V; VCSX = 0.8V; ICSX = 21mA/Channel) 4 10 35 Current Sink Matching vs. Temperature (VIN = 12V; VCSX = 0.8V; ICSX = 21mA/Channel) -15 10 Temperature (°C) Current Sink Accuracy vs. Temperature -4 -40 26 (VIN = 12V) 4 -15 22 Over-Voltage Threshold vs Temperature (VIN = 12V) -4 -40 18 Input Voltage (V) Switching Frequency vs. Temperature -3 14 60 85 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 -40 -15 10 35 60 85 Temperature (°C) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202117A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 29, 2012 7 DATA SHEET AAT1407 Six-Channel LED Backlight Driver with Integrated Boost and High Frequency Direct PWM Dimming Typical Characteristics Startup Switching Waveforms (VIN = 12V; VOUT = 37V; COUT = 2.2μF; L = 4.7µH; IOUT = 120mA) VIN (AC coupled) (50mV/div) EN/SET (10V/div) VOUT (20V/div) IOUT (50mA/div) (VIN = 12V; VOUT = 37V; COUT = 2.2μF; L = 4.7µH; IOUT = 120mA) VOUT (AC coupled) (200mV/div) 12V ILX (1A/div) ILX (1A/div) Time (100µs/div) Time (500ns/div) PWM Switching Waveforms (VIN = 12V; VOUT = 37V; COUT = 2.2μF; L = 4.7µH; IOUT = 120mA) PWM (5V/div) VOUT (1V/div) 37V IOUT (50mA/div) ILX (1A/div) Time (100µs/div) 8 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202117A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 29, 2012 DATA SHEET AAT1407 Six-Channel LED Backlight Driver with Integrated Boost and High Frequency Direct PWM Dimming Functional Block Diagram IN LX Linear Reg VCC EN OVP CS1 CS2 VREF COMP SYNC FSET CS3 P PWM CS4 Logic CS5 Osc CS6 S P GND S PGND SGND Functional Description The AAT1407 is a highly integrated, high efficiency white LED backlight solution for notebook computers, monitors and portable TVs. The device operates from regulated DC inputs, cigarette lighter adapters, and multi-cell Li-ion batteries over a voltage range from 4.5V to 26V. The integrated boost (step-up) converter provides up to 45V output to drive multiple strings of series LEDs. The maximum number of LEDs is dependent upon the forward voltage of each LED. Six precision current sinks can provide constant current drive for up to 66 white LEDs depending upon LED VF. The LED current is set by a single external resistor up to 30mA per string for a total output current capability of 180mA. The controller derives output feedback from the channel with the lowest current sink voltage while maintaining the programmed current in each LED string. This ensures the lowest possible output voltage, highest efficiency and continuous operation with mismatched LED strings. RSET The AAT1407 is designed for maximum flexibility. The LED strings may be disabled or used in parallel for increased current capability. Thus, the AAT1407 allows operation with fewer than 6 LED strings with the maximum number of LEDs per channel set by the LED VF and the output voltage of the boost converter. A lower number of LEDs can also be used. Unused current sinks are disabled by tying them to ground. The unique high voltage current sinks support non-matching LED strings (LED quantity, type, etc.). For high current applications, such as high-brightness LEDs, multiple current sinks may be connected in parallel providing up to 180mA per LED string. The AAT1407 supports a high input PWM frequency to help eliminate potential audio emissions caused by harmonic/sub-harmonic resonance of the power stage. The PWM dimming range is up to 1,000:1 (see Figure 1). The output voltage is regulated by the string with the highest voltage requirement, allowing a wide range of LED characteristics. The boost switching frequency is Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202117A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 29, 2012 9 DATA SHEET AAT1407 Six-Channel LED Backlight Driver with Integrated Boost and High Frequency Direct PWM Dimming adjustable up to 1300kHz for optimum efficiency and the smallest external filtering components. Alternatively, the device may be synchronized to an external clock. Current mode control provides fast response to line and load transients. Integrated light load mode ensures highest efficiency across the entire input voltage and load range. Fault tolerant circuitry extends system life by disabling open LED strings. The high voltage current sinks maintain normal operation with non-matched strings while also preventing damage due to shorted LEDs. The AAT1407 is available in a Pb-free, thermally enhanced 24-pin 3x4mm TQFN package. PWM Dimming The AAT1407 provides direct PWM dimming. After initial power-up or when EN is cycled, the device is enabled with brightness controlled by the PWM duty cycle and the RSET resistor value. The ultra-fast 1µs turn-on and turn-off time of the boost regulator and current sinks ensures high performance and excellent dimming range in applications requiring high frequency PWM dimming. The high PWM dimming frequency eliminates audio interference. The integrated current sinks ensure good timing between strings (PWM matching) while the fast response yields a linear PWM duty-cycle versus LED current characteristic. PWM inputs from 100Hz to 100kHz are recommended. AAT1407 Dimming Range vs. PWM Pin Frequency The AAT1407 device is protected from faults arising from LED opens and/or shorts. An LED open condition will be detected by the controller at startup and during normal operation. The low voltage on the current sink is detected by the controller, which disables the feedback to the boost converter from that current sink. The remaining LED strings continue to operate normally. The controller re-enables the disabled current sink feedback if the LED open condition is removed during a power or EN cycle. This feature extends backlight life and reliability, which is otherwise limited by intermittent conditions in the LED string(s) and/or circuit board interconnections. Under all conditions, the over-voltage protection circuitry prevents the switching node (LX) from exceeding the maximum operating voltage prior to disabling the current sink. Over-voltage protection (OVP) disables boost switching while maintaining the programmed LED current. Boost switching is re-enabled when OVP hysteresis is satisfied. A LED short condition results in a higher voltage appearing on the affected channels' current-sink pin. The affected current sink automatically compensates for the additional voltage. The current sink can withstand a high voltage indefinitely. However, the increased voltage across the current sink causes an increase in power dissipation. The channel will continue to operate until the over-temperature protection activates. Integrated over-current protection is provided. Overcurrent protection prevents inductor saturation and any resulting damage to the switching device occurring during an overload fault condition. 100000 Dimming Range Fault Tolerant Operation 10000 1000 100 10 1 1 10 100 1000 10000 100000 PWM Frequency (Hz) Figure 1: PWM Input Frequency vs. Dimming Range. 10 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202117A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 29, 2012 DATA SHEET AAT1407 Six-Channel LED Backlight Driver with Integrated Boost and High Frequency Direct PWM Dimming Application Information VOUT(MIN) > VCSX + N · VFLED(MAX) OVP Protection with Open LED Failure The AAT1407's OVP protection consists of a resistive divider network (R3 and R4) as shown in Figure 2. The resistor divider must be selected so that the voltage at the OVP pin exceeds the OVP rising threshold when the output is at VOUT(MAX). VOUT(MAX) -1 R3 = R4 · VOVP(MAX) When the OVP rising threshold is exceeded, the converter stops switching. The open LED channel is removed from the boost converter feedback loop. When the voltage at the OVP pin falls below the OVP hysteresis voltage, the boost converter can resume switching. It is important that during normal operation the current sinks are given enough headroom that the OVP threshold is not exceeded. The output voltage at the minimum OVP threshold is VOUT(MIN) = VOVP(MIN) · R3 +1 R4 The maximum voltage of each LED string including the current sink headroom should not exceed VOUT(MIN). VCC VOVP(MIN) · R3 + 1 > VCSX + N · VFLED(MAX) R4 R3 > R4 · VCSX + N · VFLED(MAX) - VOVP(MIN) VOVP(MIN) Where: N is the number of LEDs in each string VOVP(MIN) = 1.1V is minimum over-voltage threshold VCSX = 0.5V is the current sink voltage VFLED(MAX) is the maximum forward LED voltage at 20mA. Another factor in setting the OVP voltage using the resistive divider is that the maximum voltage at the LX pin should not exceed VLX(MAX) = 50V. VLX(MAX) = VOUT(MAX) + VD1 + VRING VD1 is the forward voltage of the Schottky diode D1 VRING is the voltage spike at the LX node caused by the delay of D1 at turn on. Measurements should confirm that the maximum switching node voltage VLX(MAX) is less than 50V under worst case conditions. L1 D1 VOUT VIN C4 C1 LX R3 OVP I R2 VRSET = 0.6V 262 .I R2 R4 1.2V R2 Figure 2: Over-Voltage Protection and Current Sink Setting Circuit. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202117A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 29, 2012 11 DATA SHEET AAT1407 Six-Channel LED Backlight Driver with Integrated Boost and High Frequency Direct PWM Dimming For example, if the number of white LEDs in each string is N =11, the resistor divider R3 can be calculated by selecting R4 = 12.1kΩ: R3 > 12.1kΩ · 0.5V + 11 · 3.7V - 1.1 = 441.1kΩ 1.1 choose R3 = 442kΩ. The maximum output voltage with the selected values of R4, R3 is R3 442kΩ + 1 = 1.3V · + 1 = 48.8V R4 12.1kΩ VOUT(MAX) = VOVP(MAX) · LED Current Sink Setting The current sink is controlled by the RSET voltage (0.6V) and the RSET resistor (R2). For maximum accuracy, a 1% tolerance resistor is recommended. The RSET resistor (R2) value can be calculated as follows: R2 = 262 · 0.6V ICSX(MAX) To ensure minimum forward voltage drop, high voltage Schottky diodes are considered the best choice for the White LED boost converter. The output diode is sized to maintain acceptable efficiency and reasonable operating junction temperature under full load operating conditions. Forward voltage (VF) and package thermal resistance (θJA) are the dominant factors to consider in selecting a diode. The diode non-repetitive peak forward surge current rating (IFSM) should be considered for high pulsed load applications. IFSM rating drops with increasing conduction period. Manufacturers’ datasheets should be consulted to verify reliability under peak loading conditions. The diode’s published current rating may not reflect actual operating conditions and should be used only as a comparative measure between similarly rated devices. During the on-time, the output voltage on the output cap is applied to the cathode of the external Schottky diode. The rectifier's reverse breakdown voltage rating should be greater than the maximum output voltage rating of the Boost. 40V rated Schottky diodes are recommended for outputs less than 30V, while 60V rated Schottky diodes are recommended for outputs greater than 35V. The average diode current is equal to the output current. Where VRSET = 0.6V. For example, if the maximum current for each string LEDs is 30mA, this corresponds to a minimum resistor value of 5.23kΩ. 262 · 0.6V R2 = = 5.23kΩ 30mA IAVG = IOUT The approximate power loss on the Schottky diode can be determined: PLOSS-DIODE = IAVG · VF = IOUT · VF Maximum ILED Current (mA) R2 (kΩ) 30 25 20 15 10 5 5.23 6.19 7.87 10.5 15.8 31.6 Table 2: Maximum LED Current Sink vs. RSET Resistor (R2) Values. 12 Schottky Diode Selection Diode junction temperature can be estimated. TJ = TAMB + θJA · PLOSS-DIODE Output diode junction temperature should be maintained below 110°C, but may vary depending on application and/or system guidelines. The diode θJA can be minimized with additional PCB area on the cathode. PCB heat-sinking the anode may degrade EMI performance. The reverse leakage current of the rectifier must be considered to maintain low quiescent (input) current and high efficiency under light load. The rectifier reversed current increases dramatically at elevated temperatures. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202117A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 29, 2012 DATA SHEET AAT1407 Six-Channel LED Backlight Driver with Integrated Boost and High Frequency Direct PWM Dimming Inductor Selection The white LED boost (step-up) converter is designed to operate with an inductor with a minimum value of 4.7μH for all input and output voltage combinations. The inductor saturation current rating should be greater than the NMOS current at maximum duty cycle. should confirm that output voltage droop and operating stability are acceptable. Voltage derating can minimize this factor, but results may vary with package size and among specific manufacturers. The output capacitor size can be estimated using the equation: COUT = (VOUT + VF - VIN(MIN)) DMAX = VOUT + VF The inductor (L) is selected to avoid saturation at minimum input voltage, maximum output load conditions. Peak current may be calculated from the following equation, again assuming continuous conduction mode. Worst-case peak current occurs at minimum input voltage (maximum duty cycle) and maximum load. IPEAK = IOUT DMAX · VIN(MIN) + 1 - DMAX 2 · FS · L Output Capacitor The high output ripple inherent in the boost converter necessitates low impedance output filtering. Multi-layer ceramic (MLC) capacitors provide small size and adequate capacitance, low parasitic equivalent series resistance (ESR) and equivalent series inductance (ESL), and are well suited for use with the white LED boost regulator. MLC capacitors of type X7R or X5R are recommended to ensure good capacitance stability over the full operating temperature range. The output capacitor is sized to maintain the output load without significant voltage droop (ΔVOUT) during the power switch ON interval, when the output diode is not conducting. A ceramic output capacitor from 2.2μF to 4.7μF is recommended. Typically, 50V rated capacitors are required for the 42V maximum boost output. Ceramic capacitors sized as small as 0805 or 1206 are available which meet these requirements. MLC capacitors exhibit significant capacitance reduction with applied voltage. Output ripple measurements IOUT · DMAX FS · ∆VOUT To maintain stable operation at full load, the output capacitor should be sized to maintain ΔVOUT between 100mV and 200mV. The WLED boost converter input current flows during both ON and OFF switching intervals. The input ripple current is less than the output ripple and, as a result, less input capacitance is required. Compensation Component Selection The AAT1407 Boost architecture uses peak current mode control to eliminate the double pole effect of the output L&C filter and simplifies the compensation loop design. The current mode control architecture simplifies the transfer function of the control loop to be a one-pole, one left plane zero and one right half plane (RHP) system in frequency domain. The dominant pole can be calculated by: fP = 1 2π · R0 · C4 The ESR zero of the output capacitor (see Figure 3) can be calculated by: fZ_ESR = 1 2π · RESR · C4 Where: C4 is the output filter capacitor RO is the equivalent load resistor value RESR is the equivalent series resistance of the output capacitor. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202117A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 29, 2012 13 DATA SHEET AAT1407 Six-Channel LED Backlight Driver with Integrated Boost and High Frequency Direct PWM Dimming The right half plane (RHP) zero can be calculated by: C3 is the compensation capacitor R1 is the compensation resistor REA is the output resistance of the error amplifier (2.97MΩ). VIN2 fZ_ESR = 2π · L1 · IOUT · VOUT It is recommended to design the bandwidth decade lower than the frequency of RHP zero to tee the loop stability. A series capacitor and network (R1 and C3) connected to the COMP pin pole and zero which are given by: fP_COM = fZ_COM = Where: to one guaranresistor sets the A 15nF (C3) capacitor and a 5kΩ (R1) resistor in series are chosen for optimum phase margin and fast transient response. 1 2π · REA · C3 1 2π · R1 · C3 VIN L1 VOUT D1 ESR RO I OUT C4 Figure 3: AAT1407 Equivalent Output Stage. 14 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202117A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 29, 2012 DATA SHEET AAT1407 Six-Channel LED Backlight Driver with Integrated Boost and High Frequency Direct PWM Dimming VIN 5V - 26V D1 L1 4.7μH JP1 C1 10µF 35V C2 2.2µF 10V C3 15nF 5 JP5 16 R1 4.99k JP3 MSS1P6 R3 442k U1 TQFN34-24 19 23 24 22 R2 7.5k 2 1 OVP R4 12.1k VCC PWM COMP 17 C4 2.2µF 50V 0805 AAT1407 RSET FSET SYNC 6 CS1 7 CS2 8 CS3 CS4 9 CS5 11 12 CS6 13 GND 14 GND EP 20 PGND 21 GND 18 GND 4 GND 3 GND 10 SGND JP2 15 LX EN IN 10 LEDs in series VOUT L1 Sumida, CDRH5D28RHPNP-4R7N, 4.7μH, 3.7A, DCR = 43.1mΩ D1 Vishay, Schottky Barrier Diode, MSS1P6, 1A, 60V C1 Taiyo Yuden, GMK325BJ106KN-T, 10μF, 35V, X5R,1210; OR Murata GRM32ER71H106K, 10μF, 50V, X7R, 1210 C2 2.2μF, 10V, 0603 C3 Cap, 15nF, 10V, 0603 C4 Murata, GRM31CR71H225KA88L, 2.2μF, 50V, X7R, 1206 R1, R2, R3, R4 Carbon Film resistors, 1%, 0603 Figure 4: AAT1407IMK Evaluation Board Schematic. Figure 5: AAT1407IMK Evaluation Board Top Side Layout. Figure 6: AAT1407IMK Evaluation Board Bottom Side Layout. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202117A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 29, 2012 15 DATA SHEET AAT1407 Six-Channel LED Backlight Driver with Integrated Boost and High Frequency Direct PWM Dimming Ordering Information Package Marking1 Part Number (Tape and Reel)2 TQFN34-24 K2XYY AAT1407IMK-T1 Skyworks Green™ products are compliant with all applicable legislation and are halogen-free. For additional information, refer to Skyworks Definition of Green™, document number SQ04-0074. Package Information TQFN34-243 3.000 ± 0.050 1.700 ± 0.050 Index Area 0.400 ± 0.050 R(5x) 2.700 ± 0.050 4.000 ± 0.050 0.210 ± 0.040 0.400 BSC Detail “A” Bottom View Detail “A” 0.750 ± 0.050 Top View 0 + 0.10 - 0.00 0.203 REF Side View All dimensions in millimeters. 1. XYY = assembly and date code. 2. Sample stock is generally held on part numbers listed in BOLD. 3.The leadless package family, which includes QFN, TQFN, DFN, TDFN and STDFN, has exposed copper (unplated) at the end of the lead terminals due to the manufacturing process. A solder fillet at the exposed copper edge cannot be guaranteed and is not required to ensure a proper bottom solder connection. Copyright © 2012 Skyworks Solutions, Inc. All Rights Reserved. Information in this document is provided in connection with Skyworks Solutions, Inc. (“Skyworks”) products or services. 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Additional information, including relevant terms and conditions, posted at www.skyworksinc.com, are incorporated by reference. 16 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202117A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 29, 2012