AP8800AWT-7

AP8800A COST EFFECTIVE 28V BUCK 1-W LED DRIVER Description The AP8800A is a step-down DC/DC converter designed to drive LEDs with a constant current. The device can drive up to 7 LEDs, depending on the forward voltage of the LEDs, in series from a voltage source of 8V to 28V. Series connection of the LEDs provides identical LED currents resulting in uniform brightness and eliminating the need for ballast resistors. The AP8800A switches at frequency up to 600kHz. This allows the use of small size external components, hence minimizing the PCB area needed. Pin Assignments (Top View) SW GND CTRL 1 2 3 TSOT23-5 5 VIN 4 SET N EW PRODUCT Maximum output current of AP8800A 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 switches off the output MOSFET simplifying PWM dimming. Features • • • • • • • • LED driving current up to 370mA Better than 5% accuracy High efficiency up to 95% Operating input voltage from 8V to 28V Simple, versatile solution requiring only 4 components PWM/DC input for dimming control Built-in output open-circuit protection TSOT23-5: Available in “Green” Molding Compound (No Br, Sb) with lead Free Finish/ RoHS Compliant (Note 1) Applications • • MR16 lamps General illumination lamps Notes: 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. Typical Application Circuit VIN AP8800A Document number: DS35100 Rev. 2 - 2 1 of 12 www.diodes.com CTRL GND SW SET January 2011 © Diodes Incorporated AP8800A COST EFFECTIVE 28V BUCK 1-W LED DRIVER Pin Descriptions Pin Name SW GND Pin Number 1 2 Descriptions Switch Pin. Connect inductor/freewheeling diode here, minimizing track length at this pin to reduce EMI. GND Pin 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. An open-drain/collector PWM signal allows the output current to be adjusted 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. • Drive with DC voltage (0.3V < VCTRL < 2.5V) to adjust output current from 24% to 200% of IOUTnom Set Nominal Output Current Pin. Configures the output current of the device. Input Supply Pin. Must be locally decoupled to GND with > 2.2µF X7R ceramic capacitor – see applications section for more information. CTRL 3 N EW PRODUCT SET VIN 4 5 Absolute Maximum Ratings Symbol VIN VSET VSW VCTRL ISW TJ TLEAD TST Caution: Parameter Continuous VIN pin voltage relative to GND Set voltage relative to VIN SW voltage relative to GND CTRL pin input voltage Switch current Junction Temperature Lead Temperature Soldering Storage Temperature Range Ratings -0.3~30 VIN -5 ~ VIN +0.3 -0.3~30 -0.3 ~ 5 0.45 105 300 -55 to +150 Unit V V V V A °C °C °C 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 VIN VCTRLDC VCTRLL ISW DPWM fSW TA Notes: Parameter Operating Input Voltage relative to GND Voltage range for 24% to 200% DC dimming relative to GND Voltage Low for PWM dimming relative to GND Continuous average switch current (Note 2) Duty cycle range applied to CTRL (f < 500Hz) Switching frequency Ambient Temperature Range Min 8.0 0.3 Max 28 2.5 0.2 370 Unit V V V mA kHz °C 0.01 1 600 -40 105 2. Refer to figure 4 for the device derating curve. AP8800A Document number: DS35100 Rev. 2 - 2 2 of 12 www.diodes.com January 2011 © Diodes Incorporated AP8800A COST EFFECTIVE 28V BUCK 1-W LED DRIVER Electrical Characteristics VIN =12V, TA=25 C, unless otherwise specified. o Symbol IQ ISD VTHD VREF Parameter Quiescent Current Shutdown current Internal Threshold Voltage Internal Reference Voltage SET pin input current On Resistance of MOSFET Switch leakage current Switching frequency with L = 100µH Soft start time Internal comparator propagation delay Thermal Resistance Junction-toAmbient VSET=VIN-0.1 Conditions VCTRL = 1.25V, fSW = 250kHz VCTRL = 0V Min Typ. 300 20 Max 650 30 105 Unit µA µA mV V µA 95 100 1.25 1.3 1.5 N EW PRODUCT ISET RDS(ON) ISW-LKG fSW tSS tPD θJA Notes: 2.2 5 Ω µA kHz µs ns °C/W ADJ pin floating L = 100H IOUT = 350mA @ 1 LED (VLED = 3.4V) Time taken for output current to reach 90% of final value after VCTRL = 0.3V 250 500 55 TSOT23-5 (Note 3) 200 3. Test condition for TSOT23-5: Device mounted on FR-4 PCB (25mm x 25mm 1oz 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. AP8800A Document number: DS35100 Rev. 2 - 2 3 of 12 www.diodes.com January 2011 © Diodes Incorporated AP8800A COST EFFECTIVE 28V BUCK 1-W LED DRIVER Typical Characteristics 50 0 TA = 25°C 25 TA = 25°C 400 20 Shutdown Current (µA) Quiescent Current (µA) 300 15 200 10 N EW PRODUCT 100 5 0 0 0 12 16 20 24 28 Input Voltage (V) Quiescent Current (Switching) vs. Input Voltage 4 8 1.2425 TA = 25°C 12 16 20 24 28 Input Voltage (V) Shutdow n Current (Non-Sw itching) vs. Input Voltage 1.255 V IN = 12V 0 4 8 1.25 Reference Voltage (V) 1.242 V REF (V) 12 16 20 24 Input Voltage (V) Reference Voltage vs. Input Voltage TA = 25°C 1.245 1.24 1.2415 4 8 28 1.235 -40 10 35 60 85 110 Ambient Temperature ( °C) Reference Voltage vs. Ambient Temperature V IN = 12V -15 1.4 1.2 2.4 2.2 2 1.8 1.6 1.4 1.2 1 -40 Reference Voltage (V) 1 0.8 0.6 0.4 0.2 0 0 4 5 6 7 8 9 10 Input Voltage (V) Reference Voltage vs. Input Voltage (Low Voltage) 1 2 3 Power Switch On-Resistance ( Ω) 110 10 35 60 85 Ambient Temperature (°C) Power Switch On-Resistance vs. Ambient Temperature -15 AP8800A Document number: DS35100 Rev. 2 - 2 4 of 12 www.diodes.com January 2011 © Diodes Incorporated AP8800A COST EFFECTIVE 28V BUCK 1-W LED DRIVER Typical Characteristics (Continued) 2 350 V IN = 12V L = 100µH R S = 0.33 Ω R S = 0.3 Ω Deviation From Nominal Set Current(%) 300 RS = 0.56 Ω 1 IOUT Mean (mA) 250 200 150 100 50 0 RS = 1 Ω N EW PRODUCT -1 -2 -40 0 10 35 60 85 110 Ambient Temperature (°C) Change in LED Current vs. Ambient Temperature -15 0 0.5 1.5 2 V CTRL (V) Output Current vs. VCT RL 1 2.5 3 AP8800A Document number: DS35100 Rev. 2 - 2 5 of 12 www.diodes.com January 2011 © Diodes Incorporated AP8800A COST EFFECTIVE 28V BUCK 1-W LED DRIVER Applications Information (TA = 25°C unless otherwise stated) LED Current Control D1 RSET VIN D2 D3 SET U1 N EW PRODUCT AP8800A C1 C3 GND SW Vsupply CTRL C2 D4 D5 L1 Figure 1. MR16 Typical configuration The LED current is controlled by the resistor RSET in Figure 1. With the CTRL pin left floating and the external current sense resistor, RSET (greater than 0.3 Ω) is connected between VIN and SET, the nominal average output current in the LEDs is: ILED = VTHD R SET where VTHD is nominally 1.25V If the CTRL pin is driven by an external voltage (lower than 2.5V), the average LED current in this case is: ILED = VCTRL VTHD VREF R SET The graph in figure 2 gives values of nominal average output current for several values of current setting resistor (RSET) in the typical application circuit shown on Figure 1, for different voltages applied on the CTRL pin. LED current Versus RSET and VCTRL 400 350 300 LED Current [mA] 250 200 150 100 50 0 0 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 RSET value [Ohms] 3 0.3 0.56 0.3 0.33 0.39 0.47 0.56 0.68 0.39 0.47 0.56 0.82 0.68 0.82 1 1.2 1 1.2 1.5 1.5 0.68 0.75 0.82 1 1.2 1.5 2 2 2 3 3 3 LED current @ VCTRL = 1.25V LED current @ VCTRL = 2.5V LED current @ VCTRL = 0.625V Figure 2. LED Current setting Vs RSET and VCTRL AP8800A Document number: DS35100 Rev. 2 - 2 6 of 12 www.diodes.com January 2011 © Diodes Incorporated AP8800A COST EFFECTIVE 28V BUCK 1-W LED DRIVER Applications Information (Continued) (TA = 25°C unless otherwise stated) Inductor Selection A 68μH inductor or higher, is recommended for most AP8800A applications with input voltage at 12V. Figure 3 displays the resulting switching frequency with various main circuit parameters: Supply voltage, Inductor value and number of LEDs to be driven. Switching Frequency N EW PRODUCT 700 600 500 Frequency [kHz] 400 68 300 100 200 100 470 0 0 50 100 150 200 250 300 350 400 450 500 Inductor Value [uH] 150 220 470 220 47 150 12V - 1LED 24V - 3 LEDs 28V - 4LEDs 100 Figure 3. Switching Frequency Vs Supply voltage, Inductor, and number of LEDs Capacitor Selection A low ESR capacitor should be used for input decoupling, as the ESR of this capacitor appears in series with the supply source impedance and lowers overall efficiency. This capacitor has to supply the relatively high peak current to the coil and smooth the current ripple on the input supply. A minimum value of 1μF is acceptable if the DC input source is close to the device, but higher values will improve performance at lower input voltages, especially when the source impedance is high. The input capacitor should be placed as close as possible to the IC. For AC input sources a bigger capacitor ( 300uF in the case of 12C AC) to guarantee the accuracy of the LED current. For maximum stability over temperature and voltage, capacitors with X7R, X5R, or better dielectric are recommended. Capacitors with Y5V dielectric are not suitable for decoupling in this application and should NOT be used. Diode Selection For maximum efficiency and performance, the rectifier (D1) should be a fast low capacitance SBR diode with low reverse leakage at the maximum operating voltage and temperature. The recommended diode for use with this part is the SBR1A40, with a current rating above the peak coil current and a continuous current rating higher than the maximum output load current. It is very important to consider the reverse leakage of the diode when operating above 85°C. Excess leakage will increase the power dissipation in the device. AP8800A Document number: DS35100 Rev. 2 - 2 7 of 12 www.diodes.com January 2011 © Diodes Incorporated AP8800A COST EFFECTIVE 28V BUCK 1-W LED DRIVER Applications Information (Continued) (TA = 25°C unless otherwise stated) LED Current Dimming The LED current can be dimmed in two ways; either by applying a dc signal to the CTRL pin or by applying a Pulse Width Modulated (PWM) signal to the CTRL pin. A dc signal from 0.3V to 2.5V applied to the CTRL pin will vary the LED current from 24% to 200% of nominal LED current. This gives an approximate 8:1 dimming range; care, however, should be exercised when overdriving the CTRL pin to 200% LED current not to exceed the power dissipation of the package. N EW PRODUCT A PWM signal with a max resolution of 8bit can be applied to CTRL regulate the output current to a value below the nominal average value set by resistor RSET. PWM dimming gives a wider average LED current variation and is more accurate at lower average LED currents than by applying dc voltage to the CTRL pin to achieve average LED current dimming. The recommended method of driving the CTRL pin and controlling the amplitude of the PWM waveform is to use a small NPN switching transistor as shown below: This scheme uses the 50k resistor between the ADJ pin and the internal voltage reference as a pull-up resistor for the external transistor eg MMBT3904. AP8800A Document number: DS35100 Rev. 2 - 2 8 of 12 www.diodes.com January 2011 © Diodes Incorporated AP8800A COST EFFECTIVE 28V BUCK 1-W LED DRIVER Applications Information (Continued) (TA = 25°C unless otherwise stated) Thermal Considerations The graph below in figure 4, gives details for the power derating of the AP8800AWT. This assumes the device to be mounted on a 25x25mm PCB with 1oz copper standing in still air. 450 N EW PRODUCT 400 350 Power dissipation (mW) 300 250 200 150 100 50 0 -40 -25 -10 5 20 35 50 65 80 95 110 Ambient temperature (°C) Figure 4. Derating Curve Soft-start An external capacitor from the CTRL pin to ground will provide soft-start delay, by increasing the time taken for the voltage on this pin to rise to the turn-on threshold and by slowing down the rate of rise of the control voltage at the input of the comparator. The soft-start time is 0.5ms/nF. AP8800A Document number: DS35100 Rev. 2 - 2 9 of 12 www.diodes.com January 2011 © Diodes Incorporated AP8800A COST EFFECTIVE 28V BUCK 1-W LED DRIVER Applications Information (Continued) Application example The typical application for the AP8800A is the MR16 application driving 1W rated LEDs from a 12V ac supply. N EW PRODUCT VIN AP8800A Component list QUANTITY 1 1 1 1 1 PCB IDENT U1 D1, D2, D3, D4, D5 R1 C1 C2 VALUE AP8800A SBR1A40 0R15 330uF 20v 1uF >=25v LED Driver IC Input bridge & freewheeling diode Resistor, 0805, +/-1% =25v 100uH AP8800A Document number: DS35100 Rev. 2 - 2 10 of 12 www.diodes.com CTRL GND SW SET January 2011 © Diodes Incorporated AP8800A COST EFFECTIVE 28V BUCK 1-W LED DRIVER Ordering Information (Continued) AP8800A AP8800A WT - 7 Package WT : TSOT23-5 Package Code WT Packaging (Note 4) TSOT23-5 Packing 7 : Tape & Reel 7” Tape and Reel Quantity Part Number Suffix 3000/Tape & Reel -7 N EW PRODUCT Device AP8800AWT-7 Notes: 4. 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. Marking Information (1) TSOT23-5 (Top View) 5 4 7 XX Y W X 1 2 3 XX : Identification code Y : Year 0~9 W : Week : A~Z : 1~26 week; a~z : 27~52 week; z represents 52 and 53 week X : A~Z : Internal code Package TSOT23-5 Identification Code AZ Part Number AP8800AWT-7 Package Outline Dimensions (All Dimensions in mm) (1) Package Type: TSOT23-5 AP8800A Document number: DS35100 Rev. 2 - 2 11 of 12 www.diodes.com January 2011 © Diodes Incorporated AP8800A COST EFFECTIVE 28V BUCK 1-W LED DRIVER 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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