ACT6359

ACT6359 Rev0, 13-May-08 High-Efficiency, 40V Step-Up WLED Bias Supplies FEATURES • High-Efficiency DC/DC WLED Bias Supply • 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 • Cycle-by-Cycle Over Current Protection • Tiny SOT23-6 Package GENERAL DESCRIPTION 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. The ACT6359 features a variety of protection circuits, including integrated over voltage protection (OVP), cycle-by-cycle current limiting, and thermal shutdown protection circuitry. The ACT6359 has a 500mA current limit, and is available in a small 6-pin SOT23-6 package. APPLICATIONS • TFT LCD Displays • Smart Phones • Portable Media Players • GPS/Personal Navigation Devices SIMPLIFIED APPLICATION CIRCUIT L1 Up to 10 WLEDs VOUT ROV2 D1 VIN CIN IN SW ACT6359 ON OFF OV ROV1 EN G FB RFB COUT Innovative PowerTM -1- www.active-semi.com Copyright © 2008 Active-Semi, Inc. ACT6359 Rev0, 13-May-08 ORDERING INFORMATION PART NUMBER ACT6359US-T CURRENT LIMIT 0.5A TEMPERATURE RANGE -40°C to 85°C PACKAGE PINS PACKAGING SOT23-6 6 TAPE & REEL TOP MARK WJFR PIN CONFIGURATION 6 SW 1 IN G 2 ACT6359 5 EN OV 3 4 FB SOT23-6 PIN DESCRIPTIONS PIN 1 2 3 4 5 6 NAME SW G OV FB EN IN Ground DESCRIPTION Switch Output. Connect this pin to the inductor and the Schottky diode. 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. 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. 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. Supply Input Innovative PowerTM -2- www.active-semi.com Copyright © 2008 Active-Semi, Inc. ACT6359 Rev0, 13-May-08 ABSOLUTE MAXIMUM RATINGS PARAMETER SW to G IN, EN to G FB, OV to G Continuous SW Current Junction to Ambient Thermal Resistance (θJA) Maximum Power Dissipation Operating Junction Temperature Storage Temperature Lead Temperature (Soldering, 10 sec) VALUE -0.3 to 42 -0.3 to 6 -0.3 to VIN + 0.3 Internally Limited 200 0.727 -40 to 150 -55 to 150 300 UNIT V V V °C/W W °C °C °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 © 2008 Active-Semi, Inc. ACT6359 Rev0, 13-May-08 ELECTRICAL CHARACTERISTICS (VIN = VEN = 3.3V, TA = 25°C, unless otherwise specified.) PARAMETER Power Switch Voltage Rating Input Voltage Under Voltage Lockout Threshold Under Voltage Lockout Hysteresis Supply Current Supply Current in Shutdown Maximum On Time Maximum On Time Constant (K) Minimum Off Time FB Feedback Voltage FB Input Current Switch Current Limit Switch On Resistance Switch Leakage Current Over Voltage Protection Threshold OV Input Current EN Logic High Threshold EN Logic Low Threshold EN Input Current Thermal Shutdown Temperature Thermal Shutdown Hysteresis VEN ≥ 1.8V VFB = 1V VIN Rising TEST CONDITIONS MIN 2.6 2.1 TYP MAX 40 5.5 UNIT V V V mV 2.25 80 2.45 Not Switching Switching EN = G VIN = 3.3V K = tMAXON × VIN 220 275 2.6 0.1 0.25 0.1 4.0 13.2 320 290 0 320 500 0.55 0.25 0.5 10 5.8 mA µA µs µs × V 450 305 200 750 0.9 10 1.31 200 ns mV nA mA Ω µA V nA V VSW = 38V, EN = G VOV Rising VOV = 1.5V 1.4 1.11 0 1.21 0 0.4 VEN = 0V, 3.3V 18 160 20 36 V µA °C °C Innovative PowerTM -4- www.active-semi.com Copyright © 2008 Active-Semi, Inc. ACT6359 Rev0, 13-May-08 FUNCTIONAL BLOCK DIAGRAM IN SW EN ENABLE CIRCUIT UVLO DRIVER THERMAL SHUTDOWN OV COMPARATOR OV 1.21V + - CONTROL LOGIC MAXIMUM ON TIME MINIMUM OFF TIME G BANDGAP REFERENCE + ERROR COMPARATOR 0.29V FB ACT6359 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. 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. MOSFET. The over-voltage protection circuit detects this condition and switching ceases if the voltage at the OV pin reaches 1.21V. 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 ⎠ ⎦ 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 where VFB is the FB feedback voltage (typically 290mV at VEN = 3.3V) and ILED is the desired maximum LED current. -5www.active-semi.com Copyright © 2008 Active-Semi, Inc. 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 ACT6359 Rev0, 13-May-08 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 © 2008 Active-Semi, Inc. ACT6359 Rev0, 13-May-08 TYPICAL PERFORMANCE CHARACTERISTICS (VVIN = 3.6V, TA = 25°C, unless otherwise specified.) Efficiency vs. Load Current 100 VIN = 3.6V 100 ACT6359-001 L = 33µH Efficiency vs. Load Current ACT6359-002 L = 33µH VIN = 5V 90 90 Efficiency (%) L = 22µH 80 Efficiency (%) VIN = 3.6V 80 VIN = 3.2V 70 70 60 4 LEDs 50 0 5 10 15 20 25 30 60 4 LEDs 50 0 5 10 15 20 25 30 Load Current (mA) Load Current (mA) Efficiency vs. Load Current 100 VIN = 3.6V L = 33µH 90 100 ACT6359-003 Efficiency vs. Load Current ACT6359-004 L = 33µH VIN = 5V 90 Efficiency (%) Efficiency (%) 80 L = 22µH VIN = 3.6V 80 VIN = 3.2V 70 70 60 6 LEDs 50 0 5 10 15 20 25 30 60 6 LEDs 50 0 5 10 15 20 25 30 Load Current (mA) Load Current (mA) Efficiency vs. Load Current 100 VIN = 3.6V L = 33µH 90 100 ACT6359-005 Efficiency vs. Load Current ACT6359-006 L = 33µH VIN = 5V 90 Efficiency (%) Efficiency (%) 80 L = 22µH 80 VIN = 3.6V VIN = 3.2V 70 70 60 8 LEDs 50 0 5 10 15 20 25 30 60 8 LEDs 50 0 5 10 15 20 25 30 Load Current (mA) Load Current (mA) Innovative PowerTM -7- www.active-semi.com Copyright © 2008 Active-Semi, Inc. ACT6359 Rev0, 13-May-08 PACKAGE OUTLINE SOT23-6 PACKAGE OUTLINE AND DIMENSIONS D b L1 θ 0.2 SYMBOL A DIMENSION IN MILLIMETERS MIN 1.050 0.000 1.050 0.300 0.100 2.820 1.500 2.650 DIMENSION IN INCHES MIN 0.041 0.000 0.041 0.012 0.004 0.111 0.059 0.104 MAX 1.250 0.100 1.150 0.500 0.200 3.020 1.700 2.950 MAX 0.049 0.004 0.045 0.020 0.008 0.119 0.067 0.116 E1 E A1 A2 b L e e1 c c D E E1 A1 A2 e e1 L L1 θ 0.950 TYP 1.800 2.000 0.037 TYP 0.071 0.079 A 0.700 REF 0.300 0° 0.600 8° 0.028 REF 0.012 0° 0.024 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 lifesupport 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 sales@activesemi.com or visit http://www.active-semi.com. For other inquiries, please send to: 1270 Oakmead Parkway, Suite 310, Sunnyvale, California 94085-4044, USA Innovative PowerTM -8- www.active-semi.com Copyright © 2008 Active-Semi, Inc.