FC1360 FS | Alldatasheet
Document overview
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Technical content
Features
Built in thermal and over current protection Internal 32V Power MOSFET Switch 1A output current Single pin on/off and dimming control using DC voltage or PWM at ADJ pin. Internal PWM filter Soft-start High efficiency (up to 90%) Wide input voltage range : 7V to 32V 40V transient capability LX Output shutdown Up to 1MHz switching frequency Inherent open-circuit LED protection Typical 5% output current accuracy
Applications
MR16 and general lighting Automotive lighting Low voltage industrial lighting LED back lighting Illuminated signs General Description The FC1360 is a continuous mode inductive step-down converter, designed for driving single or multiple series connected LEDs efficiently from a voltage source higher than the LED voltage. The device operates from an input supply between 7V and 30V and provides an externally adjustable output current of up to 1A. Depending upon supply voltage and external components, this can provide up to 24 watts of output power. The FC1360 includes the output switch and a high-side output current sensing circuit, which uses an external resistor to set the nominal average output current. Output current can be adjusted above, or below the set value, by applying an external control signal to the 'ADJ' pin. The PWM filter provides a soft-start feature by controlling the rise of input/output current. The soft-start time can be increased using an external capacitor from the ADJ pin to ground. Applying a voltage of 0.2V or lower to the ADJ pin turns the output off and switches the device into a low current standby state. Typical Application circuit
Ordering Information
FC1360PRG SOT-89-5 1,000pcs/reel & tape SEMICO NDUCTOR TECH NICAL DATA FC1360 2009. 07. 10 1/7Revision No : 0
Pin Assignment Pin Function Pin No. Pin Name Description SOT-23-5
1 LX Switching Output
2 VSS Ground
3 ADJ Current Adjustment
4 ISENSE Current Sense
5 VIN Input
Parameter Symbol Ratings Units Input Voltage VIN 30 V LX Output Current ILX 1.25 A I/O Pin Voltage VIO VSS-0.3 ~ VIN+0.3 V Power Dissipation SOT-89-5 Pd 1 W Operation Ambient Temperature Topr -40 ~ +125 ˚C Storage Temperature Tstg -55 ~ +125 ˚C FC1360 2009. 07. 10 2/7Revision No : 0
Electrical Characteristics
Test Condition: VIN = 12V DC, Ta = 25 oC Parameter Symbol Conditions Ta=25C UnitsMin Typ Max Input Voltage VIN 7 32 V Internal regulator start-up threshold voltage VSU VIN rising from 0V until VADJ 1.25V 5.65 V Quiescent supply current with LX output off IINQoff VADJ= 0V, VIN = 12V 55 90 AVADJ= 0V, VIN = 30V 65 130 Quiescent supply current with LX output switching IINQon VSENSE = VIN & VIN – 0.125V at frequency of 250 kHz, ADJ pin floating 1.9 5.2 mA Mean current sense threshold voltage (1) VSENSE Measured on ISENSE pin with respect to VIN, ADJ pin floating 95 100 105 mV Sense threshold hysteresis VSENSEHYS ±15 % Internal reference voltage VREF Measured on ADJ pin with pin floating 1.15 1.25 1.35 V External control voltage range on ADJ pin for dc brightness control (2) VADJ 0.3 2.0 V LX switch On Resistance RLX V SENSE = VIN = 12V, ADJ pin floating 1.3 3.5 Ohm LX switch Output Current ILX 1.25 A LX switch Leakage Current ILX_Leakage VSENSE = VIN = 12V, VADJ= 0V, VLX = 30V 5 A Note (NOTE 1) VSENSE defines LED current setting accuracy LED shall switch off. FC1360 2009. 07. 10 3/7Revision No : 0
Setting nominal average output current with external resistor RS The nominal average output current in the LED(s) is determined by the value of the external current sense resistor (RS) connected between VIN and ISENSE and is given by: IOUT = 0.1/RS (A) The table below gives values of nominal average output current for several preferred values of current setting resistor (RS) in the typical application circuit: RS (ohm) Nominal Average Output Current (mA) 0.1 1000 0.13 760 0.15 667 The above values assume that the ADJ pin is floating and at a nominal voltage of VREF (1.25V).Note that RS = 0.1 ohm is the minimum allowed value of sense resistor under these conditions to maintain switch current below the specified maximum value. Output current adjustment by external DC control voltage The ADJ pin can be driven by an external dc voltage (V ADJ), to adjust the output current to a value above or below the nominal average value defined by RS. The nominal average output current in this case is given by: IOUTdc = (VADJ /1.25) x 100mV x RS (for 0.3< VADJ <2.5V) Note that 100% brightness setting corresponds to V ADJ = VREF. When driving the ADJ pin above 1.25V, RS must be increased in proportion to prevent IOUTdc exceeding 1A maximum. The input impedance of the ADJ pin is 200k_ ±25% for voltages below VREF and 20k_ ±25% for voltages above VREF +100mV. Inherent open-circuit LED protection If the connection to the LED(s) is open-circuited, the coil is isolated from the LX pin of the chip, so the device will not be damaged, unlike in many boost converters, where the back EMF may damage the internal switch by forcing the drain above its breakdown voltage. FC1360 2009. 07. 10 4/7Revision No : 0
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 4.7 uF is acceptable if the 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. Inductor selection Recommended inductor values for the FC1360 are in the range 33 uH to 100 uH. Higher values of inductance are recommended at higher supply voltages in order to minimize errors due to switching delays, which result in increased ripple and lower efficiency. Higher values of inductance also result in a smaller change in output current over the supply voltage range. The inductor should be mounted as close to the device as possible with low resistance connections to the LX and VIN pins. Note that, in practice, the duty cycle and operating frequency will deviate from the calculated values due to dynamic switching delays, switch rise/fall times and losses in the external components. Optimum performance will be achieved by setting the duty cycle close to 0.5 at the nominal supply voltage. This helps to equalize the undershoot and overshoot and improves temperature stability of the output current. Diode selection For maximum efficiency and performance, the rectifier (D1) should be a fast low capacitance Schottky diode with low reverse leakage at the maximum operating voltage and temperature. It is important to select parts with a peak 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 and if close to the load may create a thermal runaway condition. FC1360 2009. 07. 10 5/7Revision No : 0
LX pin The LX pin of the device is a fast switching node, so PCB tracks should be kept as short as possible. To minimize ground 'bounce', the ground pin of the device should be soldered directly to the ground plane. Coil, decoupling capacitors, current sense resistor It is particularly important to mount the coil and the input decoupling capacitor as close to the device pins as possible to minimize parasitic resistance and inductance, which will degrade efficiency. It is also important to minimize any track resistance in series with current sense resistor RS. Its best to connect VIN directly to one end of RS and Isense directly to the opposite end of RS with no other currents flowing in these tracks. It is important that the cathode current of the Schottky diode does not flow in a track between RS and VIN as this may give an apparent higher measure of current than is actual because of track resistance. ADJ pin The ADJ pin is a high impedance input for voltages up to 1.35V so, when left floating, PCB tracks to this pin should be as short as possible to reduce noise pickup. A 100nF capacitor from the ADJ pin to ground will reduce frequency modulation of the output under these conditions. An additional series 10k resistor can also be used when driving the ADJ pin from an external circuit . This resistor will provide filtering for low frequency noise and provide protection against high voltage transients. High voltage tracks Avoid running any high voltage tracks close to the ADJ pin, to reduce the risk of leakage currents due to board contamination. The ADJ pin is soft-clamped for voltages above 1.35V to desensitize it to leakage that might raise the ADJ pin voltage and cause excessive output current. However, a ground ring placed around the ADJ pin is recommended to minimize changes in output current under these conditions. FC1360 2009. 07. 10 6/7Revision No : 0
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Package Information
SOT-89-5 FC1360 2009. 07. 10 7/7Revision No : 0