AP8802_0912

AP8802 1A LED Step-down Converter Features • • • • • • • • LED driving current up to 1A High efficiency up to 92% Operating input voltage up to 48V High switching frequency up to 500kHz PWM/DC input for dimming control Built-in output open-circuit protection SOP-8L, SOP-8L-EP and DFN3030-10 are available in “Green” Molding Compound (No Br, Sb) Lead Free Finish/ RoHS Compliant (Note 1) General Description The AP8802 is a step-down DC/DC converter designed to drive LEDs with a constant current. The device can drive up to thirteen LEDs, depending on the forward voltage of the LEDs, in series from a voltage source of 8V to 48V. Series connection of the LEDs provides identical LED currents resulting in uniform brightness and eliminating the need for ballast resistors. The AP8802 switches at frequency up to 500kHz. This allows the use of small size external components, hence minimizing the PCB area needed. Maximum output current of AP8802 is set via an external resistor connected between the VIN and SET input pins. Dimming is achieved by applying either a DC voltage or a PWM signal at the CTRL input pin. An input voltage of 0.2V or lower at CTRL shuts down the output at SW and puts the device into a low-current standby state. Applications • • • • Commercial & industrial lighting Small LCD panel backlight Appliances interior lighting Architecture Detail lighting Typical Application Circuit Figure 1: Typical Application Circuit AP8802 Rev. 5 DS31766 1 of 16 www.diodes.com DECEMBER 2009 © Diodes Incorporated AP8802 1A LED Step-down Converter Ordering Information AP 8802 XX G - X Package S : SOP-8L SP : SOP-8L-EP FN : DFN3030-10 Green G : Green Packing 7/ 13 : Tape & Reel Device AP8802SG-13 AP8802SPG-13 AP8802FNG-7 Notes: Package Code S SP FN Packaging (Note 2) SOP-8L SOP-8L-EP DFN3030-10 7”/13” Tape and Reel Quantity Part Number Suffix 2500/Tape & Reel 2500/Tape & Reel 3000/Tape & Reel -13 -13 -7 1. EU Directive 2002/95/EC (RoHS). All applicable RoHS exemptions applied. Please visit our website at http://www.diodes.com/products/lead_free.html. 2. Pad layout as shown on Diodes Inc. suggested pad layout document AP02001, which can be found on our website at http://www.diodes.com/datasheets/ap02001.pdf. AP8802 Rev. 5 DS31766 2 of 16 www.diodes.com DECEMBER 2009 © Diodes Incorporated AP8802 1A LED Step-down Converter Pin Assignments (1) SOP-8L (2) SOP-8L-EP ( Top View ) SET 1 GND NC 2 3 AP8802 ( Top View ) 8 7 6 5 CTRL GND SW SW SET 1 GND NC 2 3 AP8802 8 7 6 5 CTRL GND SW SW VIN 4 VIN 4 (3) DFN3030-10 ( Top View ) SET GND NC NC VIN 1 2 3 4 5 10 9 CTRL GND NC SW SW AP8802 8 7 6 Pin Descriptions Pin Name SW GND SET CTRL VIN NC Description Switch Pin. Connect inductor/freewheeling diode here, minimizing track length at this pin to reduce EMI. GND pin Set Nominal Output Current Pin. Configure the output current of the device. Dimming and On/Off Control Input. Input voltage of 0.2V or lower forces the device into low current standby mode and shuts off the output. A PWM signal allows the output current to be adjusted above or below the level set by the resistor connected to SET input pin. The input impedance is about 50kΩ, and if the pin is left open VCTRL = VREF Input Supply Pin. Must be locally bypassed. No connection AP8802 Rev. 5 DS31766 3 of 16 www.diodes.com DECEMBER 2009 © Diodes Incorporated AP8802 1A LED Step-down Converter Block Diagram SET SW VIN Sensing Block Comparator Voltage Regulator 5V CTRL PWM/DC Control VREF 1.25V AP8802 R GND Figure 2: AP8802 block diagram Absolute Maximum Ratings Symbol VIN VSW TJ TLEAD TST VIN pin voltage SW voltage Junction Temperature Lead Temperature Soldering Storage Temperature Range Parameter Rating -0.3~50 -0.3~50 150 300 -65 to +150 Unit V V o o o C C C Caution: The absolute maximum ratings are rated values exceeding which the product could suffer physical damage. These values must therefore not be exceeded under any condition. Semiconductor devices are ESD sensitive and may be damaged by exposure to ESD events. Suitable ESD precautions should be taken when handling and transporting these devices Recommended Operating Conditions Symbol TA Duty Cycle Notes: Parameter Ambient Temperature Range Using Inductor ≥ 100µH (Note 3) Min -40 0.1 Max 105 0.95 Unit ºC 3. For most applications the LED current will be within 8% over the duty cycle range specified. Duty cycle accuracy is also dependent on propagation delay. Smaller size inductors can be used but LED current accuracy may be greater than 8% at extremes of duty cycle. This is most noticeable at low duty cycles (less than 0.1) or when the input voltage is high and only one LED is being driven. AP8802 Rev. 5 DS31766 4 of 16 www.diodes.com DECEMBER 2009 © Diodes Incorporated AP8802 1A LED Step-down Converter Electrical Characteristics Symbol VIN IOUT IQ FOSC VTHD VREF SET Rds(on) ISW Leakage (VIN =12V, TA=25oC, unless otherwise specified) EN EN Parameter Operating Input Voltage Continuous switch current Quiescent Current Switching Frequency Internal Threshold Voltage Internal Reference Voltage SET pin input current On Resistance of MOSFET Switch leakage current Voltage High Voltage Low Thermal Resistance Junction-to-Ambient Thermal Resistance Junction-to-Case Conditions (Note 4) Min 8.0 184 1.25 - Typ. 75 200 1.25 5 0.65 82 45 38 52 7 24 VSET=VIN-0.2 ISW=0.8A ON OFF SOP-8L (Note 5) SOP-8L-EP (Note 5) DFN3030-10 (Note 5) SOP-8L (Note 5) SOP-8L-EP (Note 5) DFN3030-10 (Note 5) θJA θJC Notes: Max 48 1 120 0.5 216 1.1 8 0.2 - Unit V A μA MHz mV V μA Ω μA V V °C/W °C/W °C/W °C/W °C/W °C/W 4. Refer to figure 8 for the device derating curve. 5. Test condition for SOP-8L, SOP-8L-EP and DFN3030-10: Device mounted on FR-4 PCB, 2”x2”, 2oz copper, minimum recommended pad layout on top layer and thermal vias to bottom layer ground plane. For better thermal performance, larger copper pad for heat-sink is needed. AP8802 Rev. 5 DS31766 5 of 16 www.diodes.com DECEMBER 2009 © Diodes Incorporated AP8802 1A LED Step-down Converter Application Information LED Current Control The LED current is controlled by the resistor RSET in Figure 1 connected between VIN and SET. The nominal average output current in the LED(s) is defined as: ILED = VTHD RSET If the CTRL pin is driven by an external voltage (lower than 2.5V), the average LED current is: ILED = VCTRL VTHD VREF RSET LED current Versus RSET and VCTRL 1200 0.39 0.47 0.56 600 0.2 400 0.33 0.39 0.47 0.56 0.68 0.33 0.47 0.68 0.82 1 0.82 1 1.2 1.2 1.2 1.5 2 1.5 1.5 2 2 3 3 3 3 LED current @ VCTRL = 1.25V LED current @ VCTRL = 2.5V LED current @ VCTRL = 0.625V 1000 LED Current [mA] 0.2 800 200 0.68 0.82 1 0 0 RSET value [Ohms] 0.15 0.3 0.45 0.6 0.75 0.9 1.05 1.2 1.35 1.5 1.65 1.8 1.95 2.1 2.25 2.4 2.55 2.7 2.85 Figure 3: LED Current setting Vs RSET and VCTRL AP8802 Rev. 5 DS31766 6 of 16 www.diodes.com DECEMBER 2009 © Diodes Incorporated AP8802 1A LED Step-down Converter Application Information Inductor Selection (Continued) This section highlights how to select the inductor suitable for the application requirements in terms of switching frequency, LED current accuracy and temperature. Switching Frequency @ ILED = 700mA 500 450 400 350 Frequency [kHz] 300 250 200 150 100 50 0 0 50 100 150 200 250 300 350 400 450 Inductor Value [uH] 47 68 100 150 150 220 220 470 470 470 500 100 47 100 12V - 3 LEDs 24V - 5 LEDs 220 48V - 10 LEDs 68 68 150 Figure 4: Switching Frequency Vs Inductor Value The inductor influences the LED current accuracy that the system is able to provide. The following section highlights how to select the inductor in relation to the device packages and the LED current, while maintaining the chip temperature below 70˚C. AP8802 Rev. 5 DS31766 7 of 16 www.diodes.com DECEMBER 2009 © Diodes Incorporated AP8802 1A LED Step-down Converter Application Information (Continued) Figure 5: DFN3030-10 recommended inductor with 1A LED current Figure 6: SOP8L-EP recommended inductor with 1A LED current AP8802 Rev. 5 DS31766 8 of 16 www.diodes.com DECEMBER 2009 © Diodes Incorporated AP8802 1A LED Step-down Converter Application Information (Continued) AP8802 SOP-8L Minimum Recommended Inductor 8% Accuracy,