ACT6359 Rev 1, 14-Feb-11 High-Efficiency, 40V Step-Up WLED Bias Supplies FEATURES GENERAL DESCRIPTION • High-Efficiency DC/DC WLED Bias Supply The ACT6359 step-up DC/DC converter drives white LEDs with an externally programmable constant current. This device features an integrated, 40V power MOSFET that is capable of driving up to ten white LEDs in series, providing inherent current matching for uniform brightness. WLED brightness adjustment is easily achieved via simple external circuitry, which accepts either a PWM or an analog dimming control signal. • Internal 40V, 0.55Ω Power MOSFET • Up to 10 WLEDs per String • 500mA Peak Current • Supports Analog and PWM LED Dimming • Integrated Over-Voltage Protection (OVP) • Thermal Shutdown • Tiny SOT23-6 Package The ACT6359 features a variety of protection circuits, including integrated over voltage protection (OVP), cycle-by-cycle current limiting, and thermal shutdown protection circuitry. APPLICATIONS The ACT6359 has a 500mA current limit, and is available in a small 6-pin SOT23-6 package. • Cycle-by-Cycle Over Current Protection • TFT LCD Displays • Smart Phones • Portable Media Players • GPS/Personal Navigation Devices SIMPLIFIED APPLICATION CIRCUIT L1 D1 VIN IN Up to 10 WLEDs SW VOUT ROV2 CIN ACT6359 OV ROV1 ON OFF Innovative PowerTM EN FB G -1- RFB COUT www.active-semi.com Copyright © 2011 Active-Semi, Inc. ACT6359 Rev 1, 14-Feb-11 ORDERING INFORMATION PART NUMBER CURRENT LIMIT TEMPERATURE RANGE ACT6359US-T 0.5A -40°C to 85°C PACKAGE PINS PACKAGING SOT23-6 6 TAPE & REEL TOP MARK WJFR PIN CONFIGURATION SW 1 G 2 OV 3 ACT6359 6 IN 5 EN 4 FB SOT23-6 PIN DESCRIPTIONS PIN NAME 1 SW 2 G 3 OV Over Voltage Protection Input. The IC is automatically disabled when the voltage at this pin exceeds 1.21V. Connect OV to the center point of a resistive voltage divider connected across the LED string. 4 FB Feedback Input. Connect this pin to the cathode of the bottom LED, and a current feedback resistor between this pin and G to set the LED bias current. 5 EN Enable Control. Drive to a logic high to enable the device. Connect to a logic low to disable the device. EN should not be left floating; connect EN to IN when unused. 6 IN Supply Input Innovative PowerTM DESCRIPTION Switch Output. Connect this pin to the inductor and the Schottky diode. Ground -2- www.active-semi.com Copyright © 2011 Active-Semi, Inc. ACT6359 Rev 1, 14-Feb-11 ABSOLUTE MAXIMUM RATINGSc PARAMETER VALUE UNIT SW to G -0.3 to 42 V IN, EN to G -0.3 to 6 V FB, OV to G -0.3 to VIN + 0.3 V Continuous SW Current Internally Limited Junction to Ambient Thermal Resistance (θJA) 200 °C/W 0.727 W Operating Junction Temperature -40 to 150 °C Storage Temperature -55 to 150 °C 300 °C Maximum Power Dissipation Lead Temperature (Soldering, 10 sec) c: Do not exceed these limits to prevent damage to the device. Exposure to absolute maximum rating conditions for long periods may affect device reliability. Innovative PowerTM -3- www.active-semi.com Copyright © 2011 Active-Semi, Inc. ACT6359 Rev 1, 14-Feb-11 ELECTRICAL CHARACTERISTICS (VIN = VEN = 3.3V, TA = 25°C, unless otherwise specified.) PARAMETER TEST CONDITIONS MIN TYP Power Switch Voltage Rating Input Voltage Under Voltage Lockout Threshold 2.6 VIN Rising 2.1 Under Voltage Lockout Hysteresis 2.25 MAX UNIT 40 V 5.5 V 2.45 V 80 mV Not Switching 0.1 0.25 Switching 0.25 0.5 Supply Current in Shutdown EN = G 0.1 10 µA Maximum On Time VIN = 3.3V 4.0 5.8 µs Maximum On Time Constant (K) K = tMAXON × VIN Supply Current 2.6 13.2 Minimum Off Time FB Feedback Voltage VEN ≥ 1.8V FB Input Current VFB = 1V Switch Current Limit 320 450 ns 275 290 305 mV 0 200 nA 500 750 mA 0.55 0.9 Ω 0 10 µA 1.21 1.31 V 0 200 nA Switch On Resistance VSW = 38V, EN = G Over Voltage Protection Threshold VOV Rising OV Input Current VOV = 1.5V 1.11 EN Logic High Threshold 1.4 V EN Logic Low Threshold EN Input Current µs × V 220 320 Switch Leakage Current VEN = 0V, 3.3V mA 18 0.4 V 36 µA Thermal Shutdown Temperature 160 °C Thermal Shutdown Hysteresis 20 °C Innovative PowerTM -4- www.active-semi.com Copyright © 2011 Active-Semi, Inc. ACT6359 Rev 1, 14-Feb-11 FUNCTIONAL BLOCK DIAGRAM IN SW EN ENABLE CIRCUIT UVLO THERMAL SHUTDOWN DRIVER CONTROL LOGIC OV COMPARATOR OV + 1.21V G MAXIMUM ON TIME - MINIMUM OFF TIME BANDGAP REFERENCE + ERROR COMPARATOR FB 0.29V ACT6359 MOSFET. The over-voltage protection circuit detects this condition and switching ceases if the voltage at the OV pin reaches 1.21V. Control Scheme The ACT6359 uses a minimum off-time, currentmode control scheme to achieve excellent performance under high duty-cycle operating conditions. This control scheme initiates a switching cycle only when needed to maintain output voltage regulation, resulting in very high efficiency operation. To set the maximum output voltage, connect a resistor divider from the output node to G, with center tap at OV, and select the two resistors with the following equation: ⎡⎛ V ⎞ ⎤ ROV 2 = ROV1 × ⎢⎜ OV ⎟ − 1⎥ ⎣⎝ 1.21V ⎠ ⎦ During each switching cycle, the N-channel power MOSFET turns on, increasing the inductor current. The switching cycle terminates when either the inductor current reaches the current limit (500mA) or when the cycle lasts longer than the maximum ontime of 4µs. Once the MOSFET turns off, it remains off for at least the minimum off-time of 320ns, then another switching begins when the error comparator detects that the output is falling out of regulation again. where VOV is the over voltage detection threshold, ROV1 is the resistor between OV and G, and ROV2 is the resistor from the output to the OV pin. As a first estimate, the OV threshold can often be set to 4V times the number of LEDs in the string. Setting the LED Current The LED current is programmed by appropriate selection of the feedback resistor RFB connected between FB and G. To set the LED current, choose the resistor according to the equation: V R FB = FB I LED Over Voltage Protection The ACT6359 includes internal over-voltage protection circuitry that monitors the OV pin voltage. Over-voltage protection is critical when one of the LEDs in the LED string fails as an open circuit. When this happens the feedback voltage drops to zero, and the control switches at maximum on time causing the output voltage to keep rising until it exceeds the maximum voltage rating of the power Innovative PowerTM where VFB is the FB feedback voltage (typically 290mV at VEN = 3.3V) and ILED is the desired maximum LED current. -5- www.active-semi.com Copyright © 2011 Active-Semi, Inc. ACT6359 Rev 1, 14-Feb-11 Capacitor Selection The ACT6359 requires only a tiny 0.47µF output capacitor for most applications. For circuits driving 6 or fewer LEDs, a 4.7µF input capacitor is generally suitable. For circuits driving more than 6 LEDs, a 10µF input capacitor may be required. When choosing a larger inductor which results in CCM operation, stability and ripple can be improved by adding a small feed forward capacitor from OUT to FB. About 3000pF is a good starting point for most applications, although a larger value can be used to achieve best results in applications with 6 or fewer LEDs. Ceramic capacitors are recommended for most applications. For best performance, use X5R and X7R type ceramic capacitors, which possess less degradation in capacitance over voltage and temperature. Diode Selection The ACT6359 requires a Schottky diode as the rectifier. Select a low forward voltage drop Schottky diode with forward current (IF) rating that exceeds the peak current limit (500mA) and a peak repetitive reverse voltage (VRRM) rating that exceeds the maximum output voltage, typically set by the OV threshold. Shutdown The ACT6359 features a low-current shutdown mode. In shutdown mode, the control circuitry is disabled and the quiescent supply current drops to less than 1µA. To disable the IC, simply drive EN to a logic low. To enable the ICs, drive EN to a logic high or connect it to the input supply. Low Input Voltage Applications In applications that have low input voltage range, such as those powered from 2-3 AA cells, the ACT6359 may still be used if there is a suitable system supply (such as 3.3V) available to power the controller. In such an application, the inductor may be connected directly to the battery, while the IC power is supplied by the system supply. Innovative PowerTM -6- www.active-semi.com Copyright © 2011 Active-Semi, Inc. ACT6359 Rev 1, 14-Feb-11 TYPICAL PERFORMANCE CHARACTERISTICS (VVIN = 3.6V, TA = 25°C, unless otherwise specified.) Efficiency vs. Load Current Efficiency (%) 90 L = 22µH L = 33µH VIN = 5V 90 Efficiency (%) L = 33µH ACT6359-002 VIN = 3.6V Efficiency vs. Load Current 100 ACT6359-001 100 80 70 60 VIN = 3.6V VIN = 3.2V 80 70 60 4 LEDs 4 LEDs 50 50 0 5 10 15 20 25 30 0 5 Load Current (mA) 25 L = 22µH L = 33µH VIN = 5V 90 Efficiency (%) 90 70 VIN = 3.6V 80 VIN = 3.2V 70 60 60 6 LEDs 6 LEDs 50 50 0 5 10 15 20 25 0 30 5 Efficiency vs. Load Current 20 25 30 90 L = 22µH L = 33µH VIN = 5V 90 Efficiency (%) L = 33µH ACT6359-006 VIN = 3.6V 80 15 Efficiency vs. Load Current 100 ACT6359-005 100 10 Load Current (mA) Load Current (mA) Efficiency (%) 30 ACT6359-004 100 ACT6359-003 L = 33µH Efficiency (%) 20 Efficiency vs. Load Current VIN = 3.6V 80 15 Load Current (mA) Efficiency vs. Load Current 100 10 70 60 VIN = 3.6V 80 VIN = 3.2V 70 60 8 LEDs 8 LEDs 50 50 0 5 10 15 20 25 30 0 Load Current (mA) Innovative PowerTM 5 10 15 20 25 30 Load Current (mA) -7- www.active-semi.com Copyright © 2011 Active-Semi, Inc. ACT6359 Rev 1, 14-Feb-11 PACKAGE OUTLINE SOT23-6 PACKAGE OUTLINE AND DIMENSIONS D θ b SYMBOL L E E1 c e A A2 A1 e1 DIMENSION IN INCHES MIN MAX MIN MAX A - 1.450 - 0.057 A1 0.000 0.150 0.000 0.006 A2 0.900 1.300 0.035 0.051 b 0.300 0.500 0.012 0.020 c 0.080 0.220 0.003 0.009 L1 0.2 DIMENSION IN MILLIMETERS D 2.900 BSC 0.114 BSC E 1.600 BSC 0.063 BSC E1 2.800 BSC 0.110 BSC e 0.950 BSC 0.037 BSC e1 1.900 BSC 0.075 BSC L 0.300 0.600 0.012 0.024 θ 0° 8° 0° 8° Active-Semi, Inc. reserves the right to modify the circuitry or specifications without notice. Users should evaluate each product to make sure that it is suitable for their applications. Active-Semi products are not intended or authorized for use as critical components in life-support devices or systems. Active-Semi, Inc. does not assume any liability arising out of the use of any product or circuit described in this datasheet, nor does it convey any patent license. Active-Semi and its logo are trademarks of Active-Semi, Inc. For more information on this and other products, contact [email protected] or visit http://www.active-semi.com. ® is a registered trademark of Active-Semi. Innovative PowerTM -8- www.active-semi.com Copyright © 2011 Active-Semi, Inc.