HX3248C -AGC

HX1001 HX3248C Boost LED Driver Features Description  Input voltage range: 2.2 to 6V The HX3248C is a step-up DC/DC converter with  Programmable LED Current a constant current to drive white LEDs or similar.  Drives LEDs Up to 27V The device can drive up to eight LEDs in series  Switching Frequency：up to 800KHz from a Li-Ion cell. The LED current is set by the  Wide dimming frequency range: 20KHz~ external resistor (RSET) and is directly regulated 360 KHz by the feedback (FB) voltage (typ: 200mV)  Programmable Overvoltage Protection across the external resistor RSET.  Tiny SOP8/PP Package To ensure maximum safety during operation, the Applications output has integrated overvoltage protection that prevents damage to the device in case of some  PDA fault conditions. The OVP voltage can be  Cellular Phones programmed by two external resistors.  Handheld Devices  MP3 Players  GPS Receivers The HX3248C is available in a tiny SOP8/PP package. Typical Application Circuit ﹡ILED=200mV/ RSET w w w. h x s e m i . c o m 1 HX3248C ﹡This application circuit is applied to PWM dimming. ﹡This application circuit is applied to PWM dimming. Absolute Maximum Ratings (Note1) Supply Voltage……………………………………………………………………….……………………….... 7V SW Voltage………………………………………………………………………………………………….... 36V FB Voltage………………………………………………………………………….. …………………….... 7V EN Voltage………………………………………………………………………….. …………………….... 7V OVP Voltage………………………………………………………………………….. …………………….... 7V Operating Temperature Range (Note 2) ………………………………………………………–40°C to 85°C Maximum Junction Temperature………………………………………………………….……………..125°C Storage Temperature Range ………………………………………………………………….−65°C to 150°C Lead Temperature (Soldering, 10 sec)... ……………………………………………………............... 300°C Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: The HX3248C is guaranteed to meet performance specifications from 0°C to 85°C. Specifications over the –40°C to 85°C operating temperature range are assured by design, characterization and correlation with statistical process controls. www.hxsemi.com 2 HX3248C Pin Assignment Top View PIN NAME FUNCTION 1 OVP Overvoltage protection Pin 2 VIN Input Supply Pin 3,4,9 SW Switch Output Pin 5,6 GND Ground 7 FB Feedback Pin 8 EN ON/OFF Control （High Enable） SOP8/PP *EXPOSED PAD (PIN 9) IS SW, MUST BE SOLDERED TO PCB. Electrical Characteristics Operating Conditions: VIN = 3V, TA = 25°C, unless otherwise specified. SYMBOL VIN PARAMETER CONDITIONS Operating Voltage MIN TYP 2.2 Range MAX UNITS 6 V VFB Feedback Voltage TA = 25℃, ILOAD = 1mA 200 mV IFB FB Pin Bias Current EN=GND 60 nA IOUT = 0 mA, not switching 100 uA Shutdown current 20 uA FSW Switching Frequency 800 KHz VSW Maximum switch voltage 30 V Rds(ON) MOSFET on-resistance 50 mΩ Maximum Duty Cycle 90 % 1.212 V IQ ISD(OUT) DC VOVP Operating quiescent current into VIN Output overvoltage protection VOUT rising VENL EN Falling Threshold 0.5 V VENH EN Rising Threshold 0.7 V www.hxsemi.com 3 HX3248C Typical Performance Characteristics Operating Conditions: TA = 25℃, VIN=5V, RSET=0.68Ω, 8PCS LED Series, unless otherwise specified. LED Current vs. Input Voltage Efficiency vs. Input Voltage 0.35 90% 0.3 86% LED Current(A) Efficiency 88% 84% 82% 80% 0.25 0.2 0.15 78% 0.1 76% 3 3.5 4 4.5 5 Input Voltage (V) www.hxsemi.com 5.5 6 3 3.5 4 4.5 5 Input Voltage (V) 4 5.5 6 HX3248C Block Diagram FB SW 2 7 3,4,9 VREF 1.25V 200mV _ VIN + _ A1 A2 RC + CC R S Q1 Q DRIVER ENABLE CONTROL LOGIC + OVP 1 _ EN 8 _ COMPARATOR Σ 0.2Ω SHUTDOWN + RAMP GENERATOR OSCILLAOR VREF 5,6 GND Pin Functions PIN NAME FUNCTION 1 OVP Overvoltage protection Pin. Programs VOUT overvoltage protection level (OVP) to protect device. 2 VIN Input Supply Pin. Must be locally bypassed. 3,4,9 SW Switch Pin. Connect inductor/diode here. Minimize trace area at this pin to reduce EMI. 5,6 GND 7 FB Feedback Pin. Reference voltage is 200mV. Connect cathode of lowest LED and resistor here. Calculate resistor value according to the formula: RSET = 200mV/ILED. 8 EN Shutdown Pin. Connect to 1.5V or higher to enable device; 0.5V or less to disable device. Ground Pin. www.hxsemi.com 5 HX3248C Application Information Operation The HX3248C operates in a constant frequency, current mode like a standard boost converter but regulates the voltage across the external resistor (RSET) instead of the output voltage. This gives an accurate regulated LED current independent of the input voltage and number of LEDs connected. With integrated overvoltage protection (OVP), the HX3248C is configured as a current source with overvoltage protection ideally suited to drive LEDs. The device can drive up to eight serial LEDs with the internal switch. LED Current Control The LED current is controlled by the feedback resistor (RSET). The feedback reference is 200mV. The LED current is 200mV/ RSET. In order to have accurate LED current, precision resistors are preferred (1% is recommended). Dimming Control With the PWM signal applied to the FB pin, the HX3248C is turned on or off by the PWM signal. The LEDs operate at either zero or full current. The average LED current increases proportionally with the duty cycle of the PWM signal. A 0% duty cycle will turn off the HX3248C and corresponds to zero LED current. A 100% duty cycle corresponds to full current. The typical frequency range of the PWM signal is 20kHz to 360kHz. These are two kinds of dimming control circuits shown in figure 1 and figure 2. Figure 1: PWM Dimming control circuit Figure 2: PWM Dimming control circuit Diode Selection The high switching frequency of HX3248C demands a high-speed rectifier diode. For most applications, Schottky diodes are recommended because of their fast recovery time and low forward voltage. Moreover, the diode reverse breakdown voltage must exceed VOUT. In general, use a high-speed silicon rectifier diode with adequate reverse voltage. Inductor Selection The selection of the inductor together with the nominal LED current, input, and output voltage of the www.hxsemi.com 6 HX3248C application determines the switching frequency of the converter. Because of the HX3248C’s high switching frequency, inductors with a ferrite core or equivalent are recommended. Powdered iron cores are not recommended due to their high losses at frequencies over 50KHz. Output and Input Capacitors Selection Larger output capacitors reduce noise and improve load-transient response, stability, and power-supply rejection. Since output ripple in boost DC-DC designs is dominated by capacitor equivalent series resistance (ESR), Low-ESR capacitors must be used. The input capacitor (CIN) reduces the current peaks caused by the input supply and reduces noise injection. Its value is largely determined by the source impedance of the input supply. High source impedance requires high input capacitance, particularly at the input voltage falls. At low input voltage, increasing CIN or lowering its ESR can improve efficiency. Using the same capacitance value for CIN as for COUT is a good start. The COUT ESR affects loop stability by introducing a left half-plane zero. A small capacitor C1 between FB and GND forms a pole with the feedback resistance that cancels the ESR zero. This small capacitor C1 and provide sufficient compensation for the loop. Overvoltage Protection (OVP) As with any current source, the output voltage rises as the output impedance increases or is disconnected. To prevent the output voltage from exceeding the maximum main switch (Q1) voltage rating of 36V, an overvoltage protection circuit is integrated. When the output voltage exceeds the OVP threshold voltage, (Q1) turns off. The converter switch remains off until the output voltage falls below the OVP threshold voltage. As long as the output voltage is below the OVP threshold the converter continues its normal operation, until the output voltage exceeds the OVP threshold again. www.hxsemi.com 7 HX3248C Packaging Information SOP8/PP (EXP PAD) Package Outline Dimension Symbol Dimensions In Millimeters Min Max Dimensions In Inches Min Max A 1.350 1.750 0.053 0.069 A1 0.050 0.150 0.004 0.010 A2 1.350 1.550 0.053 0.061 b 0.330 0.510 0.013 0.020 c 0.170 0.250 0.006 0.010 D D1 E E1 E2 4.700 3.202 3.800 5.800 2.313 5.100 3.402 4.000 6.200 2.513 0.185 0.126 0.150 0.228 0.091 0.200 0.134 0.157 0.244 0.099 e 1.270(BSC) 0.050(BSC) L 0.400 1.270 0.016 0.050 θ 0° 8° 0° 8° Subject changes without notice. www.hxsemi.com 8 Information furnished by Hexin Semiconductor is believed to be accurate and reliable. However, no responsibility is assumed for its use.