A Product Line of Diodes Incorporated PAM2842 HIGH POWER LED DRIVER Description Pin Assignments The PAM2842 is a high power LED driver, capable of driving up to 10 high power LEDs in series. The PAM2842 supports buck, boost and sepic topology. The PAM2842 features over current protection, over voltage protection, under voltage lockout and over temperature protection, which prevent the device from damage. LED dimming can be done by using a PWM signal to the COMP pin. The PAM2842 is available in TSSOP-20 packages. Features • Output Power up to 30W • Chip Enable with Soft-start • Analog and PWM Dimming • Peak Efficiency up to 97% • Low Quiescent Current • Switching Frequency Adjustable • Support Buck/Boost/Sepic Toplogy • Over Current Protection • Over Voltage Protection • Thermal Protection • UVLO • Tiny Pb-Free Packages: 40-Pin QFN6x6 and TSSOP-20 Applications • Home Lighting • Automotive Lighting • Monitor Backlighting PAM2842 Document number: DSxxxxx Rev. 1 - 2 1 of 17 www.diodes.com October 2012 © Diodes Incorporated A Product Line of Diodes Incorporated PAM2842 Typical Applications Circuit Boost with Low Side Current Sense Boost with High Side Current Sense Buck/Boost (Sepic) with Low Side Current Sense Buck/Boost (Sepic) with High Side Current Sense Buck with High Side Current Sense PAM2842 Document number: DSxxxxx Rev. 1 - 2 2 of 17 www.diodes.com October 2012 © Diodes Incorporated A Product Line of Diodes Incorporated PAM2842 Pin Descriptions Pin Name PGND HVIN EN VDD-DR RT AGND SenseSense+ COMP VDD_5V OV SW NC Pin Number QFN6x6-40 TSSOP-20 1–6 1, 2, 3, 4, 10, 11 8 5 9 6 10 7 12 8 13 9 14 12 15 13 17 14 21 15 23 16 25 – 30 17, 18, 19 7, 11, 16, 18-20, 20 22, 24, 31-40 Function Power Ground Input Chip Enable, Active High Internal LDO Output Frequency Adjustment Pin Analog Ground Sense Resistor Sense Resistor+ Compensation Node Internal LDO Output Over Voltage Drain of Main Switch Not Connected Functional Block Diagram PAM2842 Document number: DSxxxxx Rev. 1 - 2 3 of 17 www.diodes.com October 2012 © Diodes Incorporated A Product Line of Diodes Incorporated PAM2842 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. Parameter Supply Voltage Buck Application Maximum Output Current I/O Pin Voltage Range Maximum Junction Temperature Storage Temperature Soldering Temperature Rating 40 3 Unit V A GND -0.3 to VDD +0.3 150 -40 to +150 300, 5sec V °C Recommended Operating Conditions (@TA = +25°C, unless otherwise specified.) Parameter Supply Voltage Range Operation Temperature Range Junction Temperature Range Rating 5.5 to 40 -40 to +85 -40 to +125 Unit V °C Thermal Information Parameter Thermal Resistance (Junction to Case) Thermal Resistance (Junction to Ambient) Note: Package Symbol TSSOP-20 θJC QFN6x6-40 TSSOP-20 θJA QFN6x6-40 Max Unit 20 7.6 (Note 1) 90 °C/W 18.1 (Note 1) 1. The exposed PAD must be soldered to a thermal land on the PCB. Electrical Characteristics (@TA = +25°C, VEN = VDD = 24V, 1W x 10 LEDs, unless otherwise specified.) Parameter Input Voltage Range Quiescent Current E NA = high (no switching frequency) E NA = high (1M switching frequency) E NA = high (500k switching frequency) E NA = high (200k switching frequency) E NA = low 10 Units V mA mA mA mA µA Feedback Voltage, Low Side VFB = VSENSE+ -AGND, VSENSE- = AGND 95 100 105 mV Feedback Voltage, High Side VFB = VSENSE+ – VSENSE- 95 100 105 LED Current Line Regulation IO = 350mA 0.02 %/V LED Current Load Regulation VDD_DR UVLO Hysteresis No Switching 1.0 200 % mV PAM2842 Document number: DSxxxxx Rev. 1 - 2 Test Conditions 4 of 17 www.diodes.com Min 5.5 Typ 1 6 3 1.6 5 Max 40 2 mV October 2012 © Diodes Incorporated A Product Line of Diodes Incorporated PAM2842 Electrical Characteristics (cont.) (@TA = +25°C, VEN = VDD = 24V, 1W x 10 LEDs, unless otherwise specified.) Parameter Test Conditions LDO Stage Min Typ Max Units 4.5 14 3.7 5 74 4.0 200 5 50 4.0 5.5 90 4.3 V mA V mV V mA V VDD_5V VDD_5V Current Limit VDD_5V UVLO Threshold VDD_5V UVLO Hysteresis VDD_DR VDD_DR Current_Limit VDD_DR UVLO Threshold No Switching No Switching No Switching No Switching No Switching No Switching No Switching Switch RDS(ON) Switch Current Limit Switch Leakage Current VDD_5V = 5V RT Voltage RRT = 71kΩ 1.1 1.2 1.3 V RRT = 30kΩ 800k 1M 1.2M Hz RRT = 71kΩ 400 500 600 kHz RRT = 180kΩ 160 200 240 kHz 4.5 14 3.7 5.5 90 4.3 Switch Stage Switching Frequency (Note 2) Min Duty Cycle 0.1 3.5 50 FSW = 1MHz 10 % FSW = 500kHz 5 % FSW = 200kHz Low Side Sense High Side Sense Feedback Voltage = 0 Feedback Voltage = 0 Fault Protection Max Duty Cycle VC Source Current VC Sink Current Ω A µA OV Threshold Voltage OV Hysteresis Thermal Shutdown Thermal Shutdown Hysteresis 1.1 2.5 % 95 100 30 30 % % µA µA 1.2 70 150 30 1.3 V mV °C °C Control Interface EN High EN Low Note: 1.5 0.4 2. Switching frequency FSW = PAM2842 Document number: DSxxxxx Rev. 1 - 2 1012 24 x(RRT + 12k ) V V , reference value. 5 of 17 www.diodes.com October 2012 © Diodes Incorporated A Product Line of Diodes Incorporated PAM2842 Typical Performance Characteristics Boost Mode, @TA = +25°C, VEN = VDD = 24V, 3W LEDs, FSW = 200kHz, unless otherwise specified.) PAM2842 Document number: DSxxxxx Rev. 1 - 2 6 of 17 www.diodes.com October 2012 © Diodes Incorporated A Product Line of Diodes Incorporated PAM2842 Typical Performance Characteristics (cont.) @TA = +25°C, FSW = 300kHz, unless otherwise specified.) PAM2842 Document number: DSxxxxx Rev. 1 - 2 7 of 17 www.diodes.com October 2012 © Diodes Incorporated A Product Line of Diodes Incorporated PAM2842 Application Information Topology Selection When maximum power supply voltage is below than minimum load voltage, select the boost topology. When minimum power supply voltage is high than maximum load voltage, select buck topology. When load voltage range is small and between the power supply voltage, select sepic topology. Table 1: Voltage Condition vs. Topology Condition Topology VINMAX < VOMIN Boost VINMIN > VOMAX Buck VO<VIN Sepic Inductor Selection 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. Large inductance can minimizes the current ripple, and therefore reduces the peak current, which decreases core losses in the inductor and I2R losses in the entire power path. However, large inductor values also require more energy storage and more turns of wire, which increases physical size and I2R 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. For the large power application, if chose DCM, the peak current will be very large, it will have great electrical stress on the components, so we chose CCM. When work in CCM mode, a reasonable ripple current is chosen to ΔIL = 0.4IL For the boost topology, IL = V − VIN V ( V − VIN) IO , D= O , ΔIL = IN O LF V O 1− D VO D: duty cycle, Io: output current, F: switching frequency. From above equation we can get the inductance: L= 2.5 VIN 2 ( V O − VIN) FIO V O 2 The inductor's current rating should be higher than IL + IO 2 For the buck topology, IL = IO VO VIN ( VIN − V O ) V O ΔIL = LFVIN VIN D= so L= 2.5 VO ( VIN − V O ) FIO V O 2 PAM2842 Document number: DSxxxxx Rev. 1 - 2 8 of 17 www.diodes.com October 2012 © Diodes Incorporated A Product Line of Diodes Incorporated PAM2842 Application Information (cont.) Inductor Selection (cont.) For the sepic topology, L1 = L2 IL1 = IO IO 1− D IL 2 = IO D= VO VIN + VO Δ IL = ΔIL = 0.4IL1 Chose so VIN V O LF( VIN + V O) L= 2 2.5 VIN FIO ( VIN + V O ) Capacitor Selection An input capacitor is required to reduce the input ripple and noise for proper operation of the PAM2842. For good input decoupling, Low ESR (equivalent series resistance) capacitors should be used at the input. At least 10µF input capacitor is recommended for most applications. And close the IC VIN-PIN we should add a bypass capacitor, usually use a 1µF capacitor. 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, 50V voltage rating capacitor is chosen. Consider from discharge aspect: I x Δt = C x ΔV In boost and sepic topology, CO = IO D FVRIPPLE I (1 − D) In buck topology, CO = O FVRIPPLE VRIPPLE : Output voltage allowable ripple. Consider from equivalent series resistance: VRIPPLE-ESR = ICO.RIPPLE x COESR In sepic topology, there is a series capacitor Cs between L1 and L2 (see application schematic), it flows the current: ICS(RMS ) = IO VO VIN The ripple voltage is ΔVCS = IO D FC S The voltage rating must be higher than input voltage. Because the Cs capacitor will flow the large RMS current, so this topology is suitable for small power application. PAM2842 Document number: DSxxxxx Rev. 1 - 2 9 of 17 www.diodes.com October 2012 © Diodes Incorporated A Product Line of Diodes Incorporated PAM2842 Application Information (cont.) Diode Selection PAM2842 is a high switching frequency converter which demands high speed rectifier. It's indispensable to use a Schottky diode rated at 3A, 40V with the PAM2842. Using a Schottky diode with a lower forward voltage drop is better to improve the power LED efficiency. In boost topology, the voltage rating should be higher than VOUT and in buck topology, the voltage rating higher than VIN, the peak current is ID(MAX ) = IL + ΔIL 2 in sepic topology, the voltage rating should be higher than VIN +VOUT, the peak current is ID(MAX ) = IL1(PEAK ) + IL 2(PEAK ) The average current of the diode equals to IO. Work Frequency Selection PAM2842 working frequency is decided by resistor connect to the RT pin, it can be calculated by follow equation: FSW = 1012 (Hz) 24 x(RT + 12K ) From the equations, we can see when working frequency is high, the inductance can be small. It's important in some size limit application. But we should know when the working frequency is higher, the switching loss is higher too. We must pay attention to thermal dissipation in this application. Methods for Setting LED Current There are two methods for setting and adjusting the LED current: 1) RSENSE only 2) PWM signal with external components a) Use the COMP pin b) Use the Sense pin ● Method 1: LED Current Setting with Resistor RSENSE The most basic means of setting the LED current is connecting a resistor between RSENSE+ and RSENSE-. The LED current is decided by ISET Resistor RSENSE. ILED = 0.1/ RSENSE For flowing the large current, must pay attention to power dissipation on the resistor. RSENSE has two positions to select: high side current sense and low side current sense. In buck topology it just has high side current sense. In other topology we recommend use low side current sense for easier PCB layout. ● Method 2: LED Current Setting with PWM Signal Using COMP Pin This circuit uses resistor Rsense to set the on state current and the average LED current, then proportional to the percentage of off-time when the COMP pin is logic high. Here use a invert component 2N7002 (Q1) to isolate and invert the PWM signal (See Figure 1). Figure 1. PWM Dimming Use COMP Pin Average LED current is approximately equal to: IAVG = TOFF ILED TON + TOFF PAM2842 Document number: DSxxxxx Rev. 1 - 2 10 of 17 www.diodes.com October 2012 © Diodes Incorporated A Product Line of Diodes Incorporated PAM2842 Also, the recommended PWM frequency is between 100Hz and 200Hz. Application Information (cont.) ● Method 2: LED Current Setting with PWM Signal Using COMP Pin (cont.) Frequency <100Hz can cause the LEDs to blink visibly. As the COMP pin connects to a capacitor, it needs rise time. If frequency >200Hz, the average LED current will have a large error when duty cycle is small (<50%). It maybe generate the audible noise in this dimming condition. ● Method 3: LED Current Setting with PWM Signal using Sense Pin This method is turn PWM signal to DC voltage, the output current can be adjusted. Because the LED current is a adjustable DC value, it will cause LED color drift. Low side current sense and high side current sense circuit is different. Please see Figure 2 and 3. It use the internal reference voltage, so PWM dimming signal voltage is not considered, just meet the request of the MOSFET driving voltage. Figure 2. PWM Dimming Use Sense Pin in Low Side Current Sense Figure 3. PWM Dimming Use Sense Pin in High Side Current Sense The RC filter (R1,R2,C1,C2) value is decided by dimming frequency, the divider resistor (R3,R4) is decided by dimming range. Because final adjusted is a DC value, this method can avoid audible noise effectively and achieve better EMI performance than the second method. Setting the Output Limit Voltage The OV pin is connected to the center tap of a resistive voltage divider from the high-voltage output to ground (see application schematic). V OUT −LIMIT = V OV (1 + RUP ) RDOWN The recommend procedure is to choose R3 = 360K and R4 = 12K to set VOUT_LIMIT = 37.2V. In boost and sepic circuit, when LED open or no load, the circuit will have no feedback, if no other measure be taken the switch voltage will be very high and damage the switch, so this OV pin must be set carefully. In buck circuit, the switch voltage is always small than input voltage, so the OV pin setting is not important in this condition. This OV pin is used to limit output voltage to avoid breakdown of the switch other than to regulate output voltage. The setting value must keep the switch voltage below 40V. In sepic circuit, one must notice that the switch voltage equals VIN +VO. This OV pin has a hysteresis voltage detect function, not latch-up function, so output voltage will have a overshoot when no load or load working voltage is high than setting limit voltage. If the component parameter not match appropriately, the overshoot voltage will be too high and can demage the switch. PAM2842 Document number: DSxxxxx Rev. 1 - 2 11 of 17 www.diodes.com October 2012 © Diodes Incorporated A Product Line of Diodes Incorporated PAM2842 Application Information (cont.) Setting the Output Limit Voltage (cont.) Several methods can decrease the overshoot voltage: (1) Add a small capacitor (<100pF) parallel with the up divider resistor (See Figure 4). (2) Use external zener to clamp the output peak voltage (See Figure 5). Figure 4. Add Forward Capacitor Figure 5. Use External Zener Note: The output limit voltage must be set higher than working output voltage by a proper value, or it will work abnormal in low temperature or some other conditions. Short LED Function PAM2842 is a constant current driver. When one or more LED shorted, the circuit will still work, the output voltage is decided by LED numbers. In boost topology, make sure the output voltage is higher than input voltage; otherwise the unlimited current will directly go through supply to LED and damage the LED. Power Dissipation As PAM2842 integrates a power MOSFET, the power dissipation must be considered. To a MOSFET the power loss includes 5 sections, turn on loss, turn off loss, conduction loss, drive loss and output capacitor Coss loss. 1 ITURN−ON V OUT Tr f 2 1 PTURN−OFF = ITURN−ON V OUT Tr f 2 PTURN−ON = 2 PRDS( ON) = IRMS RDS(ON) PSWITCH PDRIVE = QG UDRIVE f 1 2 f PCOSS = COSS V OUT 2 = PTURN−ON + PTURNE ff + PRDS(ON) + PDRIVE + PCOSS ΔT = θ JA PSWITCH Tr: switch rise time. Tf: switch fall time. UDRIVE: gate drive voltage. θJA is relative with IC package, heat-sink area and air flow condition etc. Above description does not consider the IC control power, so the total power will be more than calculated value. PAM2842 has over-temperature protection. When junction temperature is over +150°C, it will shut down and auto restart when junction temperature decrease below +120. In high temperature circumstance application, one must pay attention to heat dissipation, or it will shut down and restart. It is recommended to use external heat-sink and placed near to the IC surface. PAM2842 Document number: DSxxxxx Rev. 1 - 2 12 of 17 www.diodes.com October 2012 © Diodes Incorporated A Product Line of Diodes Incorporated PAM2842 Application Information (cont.) PCB Layout Guidelines Careful PCB layout is important for normal operation. Use the following guidelines for good PCB layout: (BOOST) 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-cur rent 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 and 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 highcurrent 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 (AGND) consisting of the output voltage detection-divider ground connection, the Sense-pin connection, VCC-5V and VCC-driver capacitor connections. Connect the device's exposed backside pad to PGND. Make sure no other connections between these separate ground planes. 4) Place the output voltage setting-divider resistors as close to the OV 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. If possible, avoid running the SW node from one side of the PCB to the other. 7) For the good thermal dissipation, PAM2842 has a heat dissipate pad in the bottom side, it should be soldered to PCB surface. As the copper area cannot be large in the component side, we can use multiple vias connecting to other side of the PCB. 8) Refer to the example of a PAM2842 Evaluation board layout below. TSSOP-20 Boost QFN6x6-40 Boost PCB Layout Example PAM2842 Document number: DSxxxxx Rev. 1 - 2 13 of 17 www.diodes.com October 2012 © Diodes Incorporated A Product Line of Diodes Incorporated PAM2842 Ordering Information Part Number PAM2842RGR PAM2842TJR Package Type TSSOP-20 QFN6x6-40 Standard Package 1000 Units/Tape&Reel 1000 Units/Tape&Reel Marking Information PAM2842 Document number: DSxxxxx Rev. 1 - 2 14 of 17 www.diodes.com October 2012 © Diodes Incorporated A Product Line of Diodes Incorporated PAM2842 Package Outline Dimensions (All dimensions in mm.) TSSOP-20 PAM2842 Document number: DSxxxxx Rev. 1 - 2 15 of 17 www.diodes.com October 2012 © Diodes Incorporated A Product Line of Diodes Incorporated PAM2842 Package Outline Dimensions (cont.) (All dimensions in mm.) QFN6x6-40 PAM2842 Document number: DSxxxxx Rev. 1 - 2 16 of 17 www.diodes.com October 2012 © Diodes Incorporated A Product Line of Diodes Incorporated PAM2842 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. 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