A Product Line of Diodes Incorporated PAM2845 40V HIGH POWER BOOST CONVERTER with 6 CHANNEL CONSTANT CURRENT SOURCE Description Pin Assignments The PAM2845 is a high-efficiency boost type LED driver. It is designed for large LCD panel that employs an array of LEDs as back light source. The PAM2845 employs a current-mode step-up converter that drives six parallel strings of LEDs connected in multiple series. This built-in string current-control circuit achieves ±1% typical current matching between strings, which ensures even brightness for all LEDs. Separate feedback loops limit the output voltage if one or more LEDs open or short. The PAM2845 has features cycle-by-cycle current limit to provide consistent operation and soft-start capability. A thermalshutdown circuit provides another level of protection. The PAM2845 has a wide +4.8V to +28V input voltage range and provides adjustable full-scale LED current. The switching frequency of this device can be selected among 500kHz, 1MHz and 1.6MHz according to the application requirements. Applications Features • Six Constant-Current Output Channels • Parallel Channels Allow Higher Current per LED String • Maximum 40V Continuous Voltage Output Limit for Each • White or RGB Backlighting for LCD, TV, LCD Monitor, Notebook, Handy Terminals, and Avionics Displays Panels • LED Lighting Devices Channel • Adjustable Constant Output Voltage • Adjustable Constant LED Current • Drives 10 or more LEDs Each String as Long as the String Voltage Less Than 40V • Internal 2.5A Power MOSFET • Allows Digital PWM and Analog Dimming • Wide (100:1) PWM Dimming Range without Color Shift • Independent Dimming and Shutdown Control of the LED Driver • ±1% Typical Current Matching between Strings • Short LED Protection • 3 Frequencies Selection: 1.6MHz/1MHz/500kHz • Wide Input Voltage Range: 4.8V to 28V • Over Temperature Protection • Available in 24-pin 4mmx4mm QFN Package • Pb-free Package PAM2845 Document number: DSxxxxx Rev. 1 - 2 1 of 14 www.diodes.com October 2012 © Diodes Incorporated A Product Line of Diodes Incorporated PAM2845 Typical Applications Circuit Pin Descriptions Pin Number 1 Pin Name QFN4x4-24 VIN 2 3 4 5 6 7 8 9 10 11 12 13 VCC-Driver GND ENA PWMD LED1 LED2 LED3 GND GND LED4 LED5 LED6 14 ISET 15 VCC-5V VC 5V Linear Regulator FSEL FB PGND PGND PGND SW SW SW Oscillator Frequency Selection Pin 16 17 18 19 20 21 22 23 24 PAM2845 Document number: DSxxxxx Rev. 1 - 2 Function Supply Input 5V Linear Regulator Output for Power MOS Driver Ground Enable Input PWM Dimming Control LED1 Cathode Terminal LED2 Cathode Terminal LED3 Cathode Terminal Ground Ground LED4 Cathode Terminal LED5 Cathode Terminal LED6 Cathode Terminal LED Current Adjustment Pin Boost Stage Compensation Pin Feedback Power Ground Power Ground Power Ground Power MOS Drain Power MOS Drain Power MOS Drain 2 of 14 www.diodes.com October 2012 © Diodes Incorporated A Product Line of Diodes Incorporated PAM2845 Functional Block Diagram Absolute Maximum Ratings (@TA = +25°C, unless otherwise specified.) These are stress ratings only and functional operation is not implied. Exposure to absolute maximum ratings for prolonged time periods may affect device reliability. All voltages are with respect to ground. VIN, ENA SW, LED Parameter Rating -0.3 to +30 -0.3 to +40 VCC -5V, VCC–Driver, VC -0.3 to +6.0 PWMD. FSEL, FB, ISET Storage Temperature Maximum Junction Temperature Soldering Temperature -0.3 to +6.0 PAM2845 Document number: DSxxxxx Rev. 1 - 2 -65 to +170 170 300, 5sec 3 of 14 www.diodes.com Unit V °C October 2012 © Diodes Incorporated A Product Line of Diodes Incorporated PAM2845 Recommended Operating Conditions (@TA = +25°C, unless otherwise specified.) Parameter Supply Voltage Range Operation Temperature Range Junction Temperature Range Rating 4.8 to 28 -40 to +85 -40 to +150 Unit V °C Thermal Information Parameter Package Symbol Max Thermal Resistance (Junction to Case) QFN4x4-24 θJC 12 Thermal Resistance (Junction to Ambient) QFN4x4-24 θJA 30 Unit °C/W Electrical Characteristics (@TA = +25°C, VIN = ENA = 12V, L = 22µH, RSET = 10kΩ, unless otherwise specified.) Parameter Input Voltage Range Quiescent Current Test Conditions Min 4.8 Typ Max 28 2 Units V E NA = high (no switching frequency) 1 FSEL = high (1.6M switching frequency) 10 FSEL = high (1M switching frequency) 6 FSEL = high (500k switching frequency) E NA = low LDO Stage 5 20 µA 5 74 4.2 40 5 74 4.2 70 5.5 90 4.5 V mA V mV V mA V mV VDD_5V VDD_5V Current Limit VDD_5V UVLO Threshold VDD_5V UVLO Hysteresis VDD_Driver VDD_Driver Current_Limit VDD_Driver UVLO Threshold VDD_Driver UVLO Hysteresis mA 3 4.5 14 3.9 4.5 14 3.9 5.5 90 4.5 Boost Stage Feedback Voltage Switch RDS(ON) VCC_5V = 5V Switch Current Limit Switch Leakage Current Switching Frequency Minimum Duty Cycle Ω 2.5 1 A µA 1.6 MHz FSEL = Open 1.0 MHz kHz FSEL = GND 500 FSEL = VCC_5V 20 % FSEL = Open 10 % FSEL = GND Document number: DSxxxxx Rev. 1 - 2 V 0.2 FSEL = VCC_5V Maximum Duty Cycle VC Source Current VC Sink Current PAM2845 1.2 4 of 14 www.diodes.com 5 % 90 60 60 % µA µA October 2012 © Diodes Incorporated A Product Line of Diodes Incorporated PAM2845 Electrical Characteristics (cont.) (@TA = +25°C, VIN = ENA = 12V, L = 22µH, RSET = 10kΩ, unless otherwise specified.) Parameter Full-Scale LED_Output Current Test Conditions LED Controller Stage Min Max Units I = 190*1.2V/RISET, RISET = 7.68k 30 mA I = 190*1.2V/RISET, RISET = 11.3k 20 mA 10 I = 190*1.2V/RISET, RISET = 22.6k LED Current Matching ISET Voltage Minimums LED Voltage Analog Dimming Range Typ -3 I = 190*1.2V/RISET PWM Dimming Frequency 1 1.2 400 mA +3 % V mV I/32 I mA 100 1k Hz 5.1 V V °C °C Fault Protection LED_Overvoltage Threshold LED_Overvoltage Hysteresis Thermal-Shutdown Thermal-Shutdown Hysteresis 4.6 4.9 1 150 30 Control Interface EN High EN Low PWMD High PWMD Low 1.5 0.4 1.5 0.4 VCC_5V 0.5 1 FSEL High FSEL Midlevel FSEL Low EN Min Pulse Width EN Max Pulse Width EN Off Delay PAM2845 Document number: DSxxxxx Rev. 1 - 2 V 2 0.5 0.5 10 10 5 of 14 www.diodes.com V V V V V V µs µs µs October 2012 © Diodes Incorporated A Product Line of Diodes Incorporated PAM2845 Typical Performance Characteristics (@TA = +25°C, VIN = ENA = 12V, L = 22µH, RSET = 10kΩ, unless otherwise specified.) PAM2845 Document number: DSxxxxx Rev. 1 - 2 6 of 14 www.diodes.com October 2012 © Diodes Incorporated A Product Line of Diodes Incorporated PAM2845 Typical Performance Characteristics (cont.) (@TA = +25°C, VIN = ENA = 12V, L = 22µH, RSET = 10kΩ, unless otherwise specified.) PAM2845 Document number: DSxxxxx Rev. 1 - 2 7 of 14 www.diodes.com October 2012 © Diodes Incorporated A Product Line of Diodes Incorporated PAM2845 Typical Performance Characteristics (cont.) (@TA = +25°C, VIN = ENA = 12V, L = 22µH, RSET = 10kΩ, unless otherwise specified.) PAM2845 Document number: DSxxxxx Rev. 1 - 2 8 of 14 www.diodes.com October 2012 © Diodes Incorporated A Product Line of Diodes Incorporated PAM2845 Application Information The inductance, peak current rating, series resistance, and physical size should all be considered when selecting an inductor. These factors affect the converter's operating mode, efficiency, maximum output load capability, transient response time, output voltage ripple, and cost. The maximum output current, input voltage, output voltage, and switching frequency determine the inductor value. Very high inductance 2 minimizes the current ripple, and therefore reduces the peak current, which decreases core losses in the inductor and I R losses in the entire 2 power path. However, large inductor values also require more energy storage and more turns of wire, which increases physical size and I R copper losses in the inductor. Low inductor values decrease the physical size, but increase the current ripple and peak current. Finding the best inductor involves the compromises among circuit efficiency, inductor size, and cost. When choosing an inductor, the first step is to determine the operating mode: continuous conduction mode (CCM) or discontinuous conduction mode (DCM). When CCM mode is chosen, the ripple current and the peak current of the inductor can be minimized. If a small-size inductor is required, DCM mode can be chosen. In DCM mode, the inductor value and size can be minimized but the inductor ripple current and peak current are higher than those in CCM. Capacitor Selection An input capacitor is required to reduce the input ripple and noise for proper operation of the PAM2845. For good input decoupling, Low ESR (equivalent series resistance) capacitors should be used at the input. At least 2.2µF input capacitor is recommended for most applications. A minimum output capacitor value of 10µF is recommended under normal operating conditions, while a 22µF or higher capacitor may be required for higher power LED current. A reasonable value of the output capacitor depends on the LED current. The total output voltage ripple has two components: the capacitive ripple caused by the charging and discharging on the output capacitor, and the ohmic ripple due to the capacitor's equivalent series resistance. The ESR of the output capacitor is the important parameter to determine the output voltage ripple of the converter, so low ESR capacitors should be used at the output to reduce the output voltage ripple. The voltage rating and temperature characteristics of the output capacitor must also be considered. So a value of 10µF, voltage rating (50V) capacitor is chosen. Diodes Selection PAM2845 is high switching frequency convertor, which demands high speed rectifier. It's indispensable to use a Schottky diode rated at 2A, 60V with the PAM2845. Using a Schottky diode with a lower forward voltage drop is better to improve the power LED efficiency, and its voltage rating should be greater than the output voltage. Methods for Setting LED Current There are three methods for setting and adjusting the LED current outlined here. The methods are: 1) RSET 2) PWM Input at PWMD 3) PWM Input at ENA Figure 1 PAM2845 Document number: DSxxxxx Rev. 1 - 2 9 of 14 www.diodes.com October 2012 © Diodes Incorporated A Product Line of Diodes Incorporated PAM2845 Application Information (cont.) • Method 1: LED Current Setting with External Resistor RISET The most basic means of setting the LED current is connecting a resistor between RISET and GND. The LED current is decided by ISET Resistor. ILED = 228/ RISET • Method 2: LED Current Setting Using PWM Signal to PWMD Pin This circuit uses resistor RISET to set the on state current and the average LED current, then proportional to the percentage of on-time when the PWMD pin is logic low. Average LED current is approximately equal to: I = (tON*I)/ (tON + tOFF) Also, the recommended PWM frequency is between 100Hz and 1kHz. Frequency <100Hz can cause the LEDs to blink visibly. • Method 3: LED Current Setting with Single Wire Logic to ENA Pin When the LEDs are enabled by high level, the LED current initially goes to ILED. Dimming is done by pulsing ENA low (500ns to 10µs pulse width). Each pulse reduces the LED current by 1/32, so after one pulse the LED current is 31/32*ILED. The 32th pulse sets the LED current back to ILED. Figure 1 shows a timing diagram for EN. Setting the Output Voltage The FB pin is connected to the center tap of a resistive voltage divider (R1 and R2 in Figure 1) from the high-voltage output. VOUT = VFB (1 + R2/R1) The recommend procedure is to choose R2 = 300kΩ and R1 = 9.2kΩ to set VOUT(MAX) = 40V. Generally the VOUT must be higher than total LED voltage. For 10-LED application, R1 = 9.1kΩ, R2 = 270kΩ, VOUT = 36.8V, higher than VLED = 33V. One or more of the LED1 - 6 pins could be floating if not used because the PAM2845 uses external resistor to set the output voltage. One or more LEDx pins floating is just like change of output loadings. LED Short Protection The PAM2845 uses LED FB function to protect devices when one or more LED(s) is/are shorted. VLED = VOUT – VfN Normally VLED is around 0.4V and VOUT is decided by LED numbers. When one or more LED(s) is/are shorted, the PAM2845 will clamp VOUT to make sure all LED pins’ voltage is less then 5V. With this function VOUT will be clamped at (5V+ VfNMIN). Note: VLED: LED pin voltage VOUT: Output voltage Vf: LED forward voltage NMIN: The minimum LED numbers among all strings. PAM2845 Document number: DSxxxxx Rev. 1 - 2 10 of 14 www.diodes.com October 2012 © Diodes Incorporated A Product Line of Diodes Incorporated PAM2845 Application Information (cont.) PCB Layout Guidelines Careful PCB layout is important for proper operation. Use the following guidelines for good PCB layout: 1) Minimize the area of the high current switching loop of the rectifier diode and output capacitor to avoid excessive switching noise. 2) Connect high-current input and output components with short and wide connections. The high-current input loop goes from the positive terminal of the input capacitor to the inductor, to the SW pin. The high-current output loop is from the positive terminal of the input capacitor through the inductor, rectifier diode, and positive terminal of the output capacitors, reconnecting between the output capacitor and input capacitor ground terminals. Avoid using vias in the high-current paths. If vias are unavoidable, use multiple vias in parallel to reduce resistance and inductance. 3) Create a ground island (PGND) consisting of the input and output capacitor ground and PGND pin. Connect all these together with short, wide traces or a small ground plane. Maximizing the width of the power ground traces improves efficiency and reduces output-voltage ripple and noise spikes. Create an analog ground island (GND) consisting of the output voltage detection-divider ground connection, the I resistor connections, VCC-5V and VCC-driver capacitor connections, and the device's exposed backside pad. Connect the GND and PGND islands by connecting the GND pins directly to the exposed backside pad. Make sure no other connections between these separate ground planes. 4) Place the output voltage setting-divider resistors as close to the OVP pin as possible. The divider's center trace should be kept short. Avoid running the sensing traces near SW Pin. 5) Place the VIN pin bypass capacitor as close to the device as possible. The ground connection of the VIN bypass capacitor should be connected directly to GND pins with a wide trace. 6) Minimize the size of the SW node while keeping it wide and short. Keep the SW node away from the feedback node and ground. If possible, avoid running the SW node from one side of the PCB to the other. 7) Refer to the PAM2845 Evaluation board for an example of proper board layout. PAM2845 Evaluation Board PAM2845 Document number: DSxxxxx Rev. 1 - 2 11 of 14 www.diodes.com October 2012 © Diodes Incorporated A Product Line of Diodes Incorporated PAM2845 Ordering Information Part Number PAM2845KHR Package Type QFN4x4-24 Standard Package 3000 Units/Tape&Reel Marking Information PAM2845 Document number: DSxxxxx Rev. 1 - 2 12 of 14 www.diodes.com October 2012 © Diodes Incorporated A Product Line of Diodes Incorporated PAM2845 Package Outline Dimensions (All dimensions in mm.) QFN4x4-24 PAM2845 Document number: DSxxxxx Rev. 1 - 2 13 of 14 www.diodes.com October 2012 © Diodes Incorporated A Product Line of Diodes Incorporated PAM2845 IMPORTANT NOTICE DIODES INCORPORATED MAKES NO WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, WITH REGARDS TO THIS DOCUMENT, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE (AND THEIR EQUIVALENTS UNDER THE LAWS OF ANY JURISDICTION). Diodes Incorporated and its subsidiaries reserve the right to make modifications, enhancements, improvements, corrections or other changes without further notice to this document and any product described herein. Diodes Incorporated does not assume any liability arising out of the application or use of this document or any product described herein; neither does Diodes Incorporated convey any license under its patent or trademark rights, nor the rights of others. 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Copyright © 2012, Diodes Incorporated www.diodes.com PAM2845 Document number: DSxxxxx Rev. 1 - 2 14 of 14 www.diodes.com October 2012 © Diodes Incorporated