AP8800A COST EFFECTIVE 28V BUCK 1-W LED DRIVER Description Pin Assignments (Top View) SW 1 GND 2 CTRL 3 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 Applications • • • • • • • • • • 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) Notes: 5 VIN 4 SET TSOT23-5 MR16 lamps General illumination lamps 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. AP8800A Document number: DS35100 Rev. 2 - 2 SET CTRL 1 of 12 www.diodes.com GND VIN Typical Application Circuit SW NEW PRODUCT 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. January 2011 © Diodes Incorporated AP8800A COST EFFECTIVE 28V BUCK 1-W LED DRIVER NEW PRODUCT Pin Descriptions Pin Name Pin Number SW 1 GND 2 CTRL 3 SET 4 VIN 5 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. Absolute Maximum Ratings Symbol VIN VSET VSW VCTRL ISW TJ Parameter Ratings Unit -0.3~30 V VIN -5 ~ VIN +0.3 V Continuous VIN pin voltage relative to GND Set voltage relative to VIN SW voltage relative to GND -0.3~30 V CTRL pin input voltage -0.3 ~ 5 V 0.45 A Switch current Junction Temperature 105 °C TLEAD Lead Temperature Soldering 300 °C TST Storage Temperature Range -55 to +150 °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 VIN VCTRLDC VCTRLL ISW DPWM Notes: Parameter Min Max Unit Operating Input Voltage relative to GND 8.0 28 V Voltage range for 24% to 200% DC dimming relative to GND 0.3 2.5 V Voltage Low for PWM dimming relative to GND 0.2 V Continuous average switch current (Note 2) 370 mA Duty cycle range applied to CTRL (f < 500Hz) fSW Switching frequency TA Ambient Temperature Range 0.01 -40 1 600 kHz 105 °C 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 o VIN =12V, TA=25 C, unless otherwise specified. NEW PRODUCT Symbol Parameter Conditions Min Typ. Max Unit IQ Quiescent Current VCTRL = 1.25V, fSW = 250kHz 300 650 µA ISD Shutdown current VCTRL = 0V 20 30 µA 100 105 mV VTHD Internal Threshold Voltage VREF Internal Reference Voltage ISET SET pin input current RDS(ON) On Resistance of MOSFET ISW-LKG Switch leakage current fSW Switching frequency with L = 100µH tSS Soft start time tPD Internal comparator propagation delay θJA Thermal Resistance Junction-toAmbient Notes: 95 VSET=VIN-0.1 1.25 V 1.3 µA 1.5 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 TSOT23-5 (Note 3) 2.2 Ω 5 µA 250 kHz 500 µs 55 ns 200 °C/W 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 500 25 TA = 25°C TA = 25°C Shutdown Current (µA) Quiescent Current (µA) 20 300 200 100 0 0 15 10 5 0 4 0 12 16 20 24 28 Input Voltage (V) Shutdow n Current (Non-Sw itching) vs. Input Voltage 1.255 8 12 16 20 24 28 Input Voltage (V) Quiescent Current (Switching) vs. Input Voltage 1.2425 4 TA = 25°C 8 V IN = 12V V REF (V) Reference Voltage (V) 1.25 1.242 1.245 1.24 1.2415 4 8 12 16 20 24 Input Voltage (V) Reference Voltage vs. Input Voltage 28 1.235 -40 1.4 10 35 60 85 110 Ambient Temperature ( °C) Reference Voltage vs. Ambient Temperature V IN = 12V Power Switch On-Resistance ( Ω) 1.2 1 0.8 0.6 0.4 0.2 0 -15 2.4 TA = 25°C Reference Voltage (V) NEW PRODUCT 400 2.2 2 1.8 1.6 1.4 1.2 0 1 2 3 4 5 6 7 8 9 10 Input Voltage (V) Reference Voltage vs. Input Voltage (Low Voltage) AP8800A Document number: DS35100 Rev. 2 - 2 4 of 12 www.diodes.com 1 -40 110 10 35 60 85 Ambient Temperature (°C) Power Switch On-Resistance vs. Ambient Temperature -15 January 2011 © Diodes Incorporated AP8800A COST EFFECTIVE 28V BUCK 1-W LED DRIVER Typical Characteristics (Continued) 350 R S = 0.3 Ω V IN = 12V L = 100µH R S = 0.33 Ω 300 RS = 0.56 Ω 1 250 IOUT Mean (mA) Deviation From Nominal Set Current(%) NEW PRODUCT 2 0 200 RS = 1 Ω 150 100 -1 50 -2 -40 0 -15 10 35 60 85 110 Ambient Temperature (°C) Change in LED Current vs. Ambient Temperature AP8800A Document number: DS35100 Rev. 2 - 2 5 of 12 www.diodes.com 0 0.5 1.5 2 V CTRL (V) Output Current vs. VCT RL 1 2.5 3 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 U1 D3 SET D2 VIN RSET C2 CTRL C3 C1 GND Vsupply SW NEW PRODUCT AP8800A D5 D4 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 0.56 350 0.3 LED Current [mA] 300 0.33 0.39 250 0.47 200 0.3 150 50 LED current @ VCTRL = 2.5V 1 0.56 0.68 0.39 0.47 0.56 100 LED current @ VCTRL = 1.25V 0.68 0.75 0.82 1.2 0.82 0.68 1 1.2 0.82 LED current @ VCTRL = 0.625V 1.5 1 1.2 2 1.5 1.5 2 3 2 3 3 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 3 RSET value [Ohms] 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. 700 600 100 47 500 Frequency [kHz] NEW PRODUCT Switching Frequency 150 400 12V - 1LED 68 24V - 3 LEDs 220 300 28V - 4LEDs 100 200 150 470 220 100 470 0 0 50 100 150 200 250 300 350 400 450 500 Inductor Value [uH] 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. NEW PRODUCT 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. 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. 400 350 Power dissipation (mW) NEW PRODUCT 450 300 250 200 150 100 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 SET CTRL GND SW VIN NEW PRODUCT The typical application for the AP8800A is the MR16 application driving 1W rated LEDs from a 12V ac supply. AP8800A Component list QUANTITY 1 1 PCB IDENT U1 D1, D2, D3, D4, D5 VALUE LED Driver IC Diodes Inc. SBR1A40 Input bridge & freewheeling diode Diodes Inc. Resistor, 0805, +/-1% <+/-300ppm KOA SR732ATTDR150F Kemet R1 0R15 1 C1 330uF 20v 1 C2 1uF >=25v 1 C3 100nF >=25v 1 L1 100uH Document number: DS35100 Rev. 2 - 2 SUGGESTED SOURCE AP8800A 1 AP8800A DESCRIPTION Electrolytic capacitor X7R 1206 Generic Kemet C1206105K5RAC7800 (50v) NIC NMC1206X7R105K50F (50v) X7R 0805 Generic Kemet C0805C104K5RAC (50v) NIC NMC0805X7R104K50TRPF (50v) LPS6235 - series 10 of 12 www.diodes.com Kemet Kemet NIC Components Kemet NIC Components Coilcraft January 2011 © Diodes Incorporated AP8800A COST EFFECTIVE 28V BUCK 1-W LED DRIVER Ordering Information (Continued) Device AP8800AWT-7 Notes: Package Packing WT : TSOT23-5 7 : Tape & Reel Package Code Packaging (Note 4) WT TSOT23-5 7” Tape and Reel Quantity Part Number Suffix 3000/Tape & Reel -7 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 NEW PRODUCT AP8800A WT - 7 XX Y W X 1 2 Part Number AP8800AWT-7 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 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). 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