CL6807

参考資料 CL6807 SEMICONDUCTOR 35V 1A LED driver with internal switch GENERAL DESCRIPTION The CL6807 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 6V and 35V and provides an externally adjustable output current of up to 1A. Depending upon supply voltage and external components, this can provide up to 35 watts of output power. FEATURES APPLICATIONS ƹ ƹ ƹ ƹ ƹ Low voltage halogen replacement LEDs ƹ Automotive lighting ƹ Low voltage industrial lighting ƹ LED back-up lighting ƹIlluminated signs ƹ ƹ ƹ ƹ ƹ ƹ Simple low parts count Wide input voltage range: 6V to 35V Up to 1A output current Single pin on/off and brightness control using DC voltage or PWM Typical 5% output current accuracy Inherent open-circuit LED protection High efficiency (up to 95%) High-Side Current Sense Soft-start Available in SOT89-5 packages TYPICAL APPLICATIONS PIN ASSIGNMENT PIN DESCRIPTIONS SOP8 1 2ǃ5 PIN NO. SOT89-5 SOT23-5 1 1 2 2 4 3 5 ADJ 6 8 4 5 4 3 ISNS VIN ABSOLUTE MAXIMUM RATINGS SYMBOL VIN SW ISNS ADJ PDMAX PTR TJ TSTG PIN NAMES LX GND ITEMS Supply Voltage Drain of the internal power switch Current sense input (Respect to VIN) Logic level dimming input Power Dissipation (Note 2) Thermal Resistance, SOT89-5 θJA Operation Junction Temperature Range Storage Temperature ESD Susceptibility (Note 3) DESCRIPTION Drain of the internal N-Ch MOSFET switch. Ground. Multi-function On/Off and brightness control pin: Ь Leave floating for normal operation (VADJ was internal pulled up) .average output current IOUTnom = 0.1/RS) Ь Drive to voltage below 0.4V to turn off output current Ь Drive with DC voltage (0.5V < VADJ < 2.5V) to adjust output current from 0% to 100% of IOUTnom Ь Drive with PWM signal from open-collector or open-drain transistor, to adjust output current. Adjustment range 25% to 100% of IOUTnom for f>10kHz and 1% to 100% of IOUTnom for f < 500Hz Ь Connect a capacitor from this pin to ground to increase soft-start time. Current sense input Input Supply Pin. Must be locally bypassed VALUE -0.3~35 -0.3~35 +0.3~(-5.0) -0.3~6 Internally Limited 45 -40 to 150 -55 to 150 2 UNIT V V V V W °C /W °C °C kV RECOMMENDED OPERATING RANGE SYMBOL VIN TOPT ITEMS VDD Supply Voltage Operating Temperature VALUE 0 ~ 35 -40 to +85 UNIT V °C performance. Note 2: The maximum power dissipation must be derated at elevated temperatures and is dictated by TJMAX, θJA,and the ambient temperature TA. The maximum allowable power dissipation is PDMAX = (TJMAX - TA)/ θJA or thenumber given in Absolute Maximum Ratings, whichever is lower. Note 3: Human body model, 100pF discharged through a 1.5kΩ resistor. 5V Regulator VCC is the output of a 5V regulator capable of sourcing 10mA. VCC was bypassed to GND with internal capacitor. ADJ Input The CL6807 allow dimming with a PWM signal at the ADJ input. A logic level below 0.5V at ADJ turns off the LED current. To turn the LED current on, the logic level at ADJ must be at least 2.5V. ELECTRICAL CHARACTERISTICS (Note 4, 5) The following specifications apply for VIN=24V, TA=25 oC, unless specified otherwise. Symbol VIN FSW VISNS VISNS_hys IISNS IOFF IOP VADJ_H VADJ_L VADJ_DC fADJ DPWM_LF DPWM_HF IADJ_H IADJ_L RLX ILXmean ILEAK Parameter Conditions Input Voltage Max. Switching Frequency Mean current sense threshold VIN-VISNS voltage Sense threshold hysteresis Optional 95 Typ. 100 Max. 35 1 105 Unit V MHz mV ±15 ± 30 8 % % μA with 75 μA with 1.8 mA ISNS Pin Input Current Quiescent supply current output off Quiescent supply current output switching ADJ input voltage High ADJ input voltage Low DC brightness control Max. ADJ Frequency Duty cycle range of frequency dimming Brightness control range Duty cycle range of frequency dimming Brightness control range ADJ input leakage high Duty cycle range of frequencydimming LX On Resistance Continuous LX Current LX Leakage Current Min. 6 VIN-VISNS=100mV 2.5 0.5 2.5 20 1 0.5 low fADJ > 100Hz 0.02% V V V kHz APPLICATION DESCRIPTION Selecting RSENSE to Set the LED Current 参考資料 The CL6807 feature a programmable LED current using a resistor connected between VIN and ISNS. Use the following equation to calculate the sense resistor: 0 .1 × V ADJ ( 0 .5V ≤ V ADJ ≤ 2 .5V ) 2 .5 × Rs Current Regulator Operation I out = The CL6807 regulate the LED output current using an input comparator with hysteresis (Figure 1). As the current through the inductor ramps up and the voltage across the sense resistor reaches the upper threshold, turns off the internal MOSFET. The MOSFET turns on again when the inductor current ramps down through the freewheeling diode until the voltage across the sense resistor equals the lower threshold. Use the following equation to determine the operating frequency: f sw = (VIN − n × V LED ) × n × V LED × R SENSE VIN × Δ V × L where n = number of LEDs, VLED = forward voltage drop of one LED, and ΔV = (VSNS_HI VSNS_LO). 5000:1 high fADJ < 20KHz 4% 1 25:1 high VADJ = 5V -1 +1 VADJ = 0 0.2 1 ILX=1A 0.5 0.5 1 5 uA Ω A μA Note 4: Typical parameters are measured at 25°C and represent the parametric norm. Note 5: Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis. SIMPLIFIED BLOCK DIAGRAM Figure 1. Current Regulator Operation REGULATOR VIN Freewheeling Diode Selection LX + Current Sense COMPARATOR ISNS BANDGAP REF ADJ 1.25V + UVLO COMPARATOR The forward voltage of the freewheeling diode should be as low as possible for better efficiency. A Schottky diode is a good choice as long as the breakdown voltage is high enough to withstand the maximum operating voltage. The forward current rating of the diode must be at least equal to the maximum LED current. LED Current Ripple The LED current ripple is equal to the inductor current ripple. In cases when a lower LED current ripple is needed, a capacitor can be placed across the LED terminals. DRIVER LOGIC PCB Layout Guidelines GND ADJ BUFFER OPERATION DESCRIPTION Careful PCB layout is critical to achieve low switching losses and stable operation. Use a multilayer board whenever possible for better noise immunity. Minimize ground noise by connecting high-current ground returns, the input bypass-capacitor ground lead, and the output-filter ground lead to a single point (star ground configuration). In normal operation, there are two power loops. One is formed when the internal MOSFET is on and the high current flows through IN—RSENSE— LEDs—Inductor—MOSFET—GND. The other loop is formed when the internal MOSFET is off when the high current circulates through RSENSE—LEDs—Inductor—freewheeling diode. To minimize noise interaction, each loop area should be as small as possible. Place RSENSE as close as possible to the input filter and VIN. For better noise immunity, a Kelvin connection is strongly recommended between ISNS and RSENSE. Connect the exposed paddle to a large-area ground plane for improved power dissipation. PACKAGE INFORMATION SOT89-5 Package The CL6807 are step-down, constant current,high-brightness LED (HB LED) drivers. These devices operate from a 6V to 35V input voltage range and provide up to 1A souring LEDs. A highside current-sense resistor sets the output current and a dedicated PWM dimming input (ADJ) allows for a wide range of independent pulsed dimming. The high-side current-sensing scheme and on-board current-setting circuitry minimize the number of external components while delivering LED current with a f5% accuracy˄below 30V input˅, using a 1% sense resistor. The device, in conjunction with the coil (L1) and current sense resistor (RS), forms a self oscillating continuous-mode buck converter. When input voltage VIN is first applied, the initial current in L1 and RS is zero and there is no output fromthe current sense circuit. Under this condition, the output of CS comparator is high. This turns MN on and switches the LX pin low, causing current to flow from VIN to ground, via RS, L1 and the LED(s). The current rises at a rate determined by VIN and L1 to produce a voltage ramp (VISNS) across RS. When (VIN-VISNS) >115mV, the output of CS comparator switches low and MN turns off. The current flowing on the RS decreases at another rate. When (VIN-VISNS) < 85mV, the MN turns on again and the mean current on the LED is determined by ((85+ 115)/2 mV) / RS = 100mV / RS . The high-side current-sensing scheme and on-boardcurrent-setting circuitry minimize the number of external components while delivering LED current with ±5% accuracy, using a 1% sense resistor. The CL6807 allow dimming with a PWM signal at the ADJ input. A logic level below 0.3V at ADJ forces CL6807 to turn off the LED and the logic level at ADJ must be at least 2.5V to turn on the LED current. The ADJ pin can be driven by an external dc voltage(VADJ) to adjust the output current to a value belowthe nominal average value defined by RS. High luminance LEDs often need to be supplied with atemperature compensated current in order to maintainstable and reliable operation at all drive levels. The LEDs are usually mounted remotely from the device so,for this reason, the temperature coefficients of theinternal circuits for the CL6807 have been optimized tominimize the change in output current when nocompensation is employed. If output currentcompensation is required, it is possible to use anexternal temperature sensing network - normally using Negative Temperature Coefficient (NTC) thermistors and/or diodes, mounted very close to the LED(s). Theoutput of the sensing network can be used to drive the ADJ pin in order to reduce output current with increasing temperature. Symbol A b b1 c D D1 E E1 e e1 L Min 1.400 Millimeters 0.320 0.360 0.350 4.400 1.400 2.300 3.940 Max 1.600 0.520 0.560 0.440 4.600 1.800 2.600 4.250 1500 TYP 2.900 0.900 3.100 1.100