ACT6357

ACT6357/ACT6358 Rev0, 03-Feb-08 Advanced Product Information―All Information Subject to Change 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 • Two Peak Current Options: − ACT6357: 0.5A − ACT6358: 1A GENERAL DESCRIPTION The ACT6357 and ACT6358 step-up DC/DC converters drive white LEDs with an externally programmable constant current. These devices feature integrated, 40V power MOSFETs that are capable of driving up to ten white LEDs in series, providing inherent current matching for uniform brightness. WLED brightness adjustment is easily achieved via a dual-function pin, which accepts either a PWM or an analog dimming control signal. The ACT6357 and ACT6358 feature a variety of protection circuits, including integrated over voltage protection (OVP), programmable soft-start, cycleby-cycle current limiting, and thermal shutdown protection circuitry. The ACT6357 has 500mA current limit, while the ACT6358 has 1A current limit. Both parts are available in a small 3mm x 3mm 8-pin TDFN33-8. • Supports Analog and PWM LED Dimming • Integrated Over-Voltage Protection (OVP) • Programmable Soft-Start Function • Thermal Shutdown • Cycle-by-Cycle Over Current Protection • Tiny TDFN33-8 Package APPLICATIONS • TFT LCD Displays • Smart Phones • Portable Media Players • GPS/Personal Navigation Devices SIMPLIFIED APPLICATION CIRCUIT L1 Up to 10 WLEDs OUT ROV2 VIN 2.6V to 5.5V CIN D1 IN SW Enable Brightness Control EN BC SS ACT6357 ACT6358 OV ROV1 FB CSS G RFB COUT Innovative Products. Active Solutions. -1- www.active-semi.com Copyright © 2008 Active-Semi, Inc. ACT6357/ACT6358 Rev0, 03-Feb-08 ORDERING INFORMATION PART NUMBER ACT6357NH-T ACT6358NH-T CURRENT LIMIT 0.5A 1A TEMPERATURE RANGE -40°C to 85°C -40°C to 85°C PACKAGE TDFN33-8 TDFN33-8 PINS 8 8 PACKAGING TAPE & REEL TAPE & REEL PIN CONFIGURATION G IN EN BC 1 2 3 4 8 SW OV SS FB ACT6357 ACT6358 7 6 5 TDFN33-8 PIN DESCRIPTIONS PIN 1 2 3 NAME G IN EN Ground Supply Input DESCRIPTION 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. Brightness Control. Multifunction pin accepts either a PWM or analog control signal. When using a PWM control signal, the best results are achieved when the PWM frequency is in the 100Hz to 10kHz range and when the PWM high voltage is 1.8V or higher. When using an analog control signal, the best results are achieved when the control voltage is in the 0V to 1.8V range. 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. Soft Start Control Input. Connect a capacitor from this pin to G to program the soft start duration. SS is internally discharged when IC the is disabled. 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. Switch Output. Connect this pin to the inductor and the Schottky diode. Exposed Pad. Connect to ground. 4 BC 5 6 7 8 EP FB SS OV SW EP Innovative Products. Active Solutions. -2- www.active-semi.com Copyright © 2008 Active-Semi, Inc. ACT6357/ACT6358 Rev0, 03-Feb-08 ABSOLUTE MAXIMUM RATINGS PARAMETER SW to G IN, EN to G FB, OV, BC, SS 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 42.5 1.9 -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 Products. Active Solutions. -3- www.active-semi.com Copyright © 2008 Active-Semi, Inc. ACT6357/ACT6358 Rev0, 03-Feb-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 VBC = 3.3V FB Feedback Voltage 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 220 275 197 98 2.6 0.1 0.25 0.1 4.0 13.2 320 290 207 106 0.16 0.25 0.5 10 5.8 mA µA µs µs × V 450 305 217 114 ns VBC = 1.25V VBC = 0.625V mV ∆VFB/∆VBC Ratio FB Input Current BC Input Impedance 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 = 0V or 5V VFB = 1V VBC = 0 to 1.25V ACT6357 ACT6358 VIN = 3.3V VSW = 38V, EN = G VOV Rising VOV = 1.5V 1.4 1.11 320 620 V/V 200 nA kΩ 750 1500 0.9 10 mA Ω µA V nA V 0.4 V µA °C °C 0 400 500 1000 0.55 1.21 0 1.31 200 0 160 20 1 Innovative Products. Active Solutions. -4- www.active-semi.com Copyright © 2008 Active-Semi, Inc. ACT6357/ACT6358 Rev0, 03-Feb-08 FUNCTIONAL BLOCK DIAGRAM - Control Scheme The ACT6357 and ACT6358 use a minimum offtime, current-mode 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 for the ACT6357, 1A for the ACT6358) or when the cycle lasts longer than the maximum on-time 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 tSS is the required soft start duration. In a typical application, use 0.1µF to generate 20ms soft start time. Over Voltage Protection Both the ACT6357 and ACT6358 include 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 MOSFET. The ACT6357 and ACT6358's over-voltage protection 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⎥ V ⎣⎝1.21 ⎠ ⎦ Soft-Start The ACT6357 and ACT6358 include a programmable soft-start function, which can be used to optimize an application between start-up time and start-up inrush current. Soft start is achieved by connecting a capacitor CSS between the SS pin and G. The soft start duration can be calculated from the following equation: CSS = t SS × 5 µF s 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. Innovative Products. Active Solutions. -5- www.active-semi.com Copyright © 2008 Active-Semi, Inc. ACT6357/ACT6358 Rev0, 03-Feb-08 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: low DC-Resistance (DCR) and be sure to choose an inductor with a saturation current that exceeds the current limit (500mA for the ACT6357 and 1A for the ACT6358). R FB V = FB I LED Capacitor Selection The ACT6357 and ACT6358 only require 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 result 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. where VFB is the FB feedback voltage (typically 207mV at VBC = 1.25V) and ILED is the desired maximum LED current. Once the LED current is selected via RFB, it may be adjusted via the BC pin to provide a simple means of LED dimming. The BC pin supports both analog as well as PWM dimming control. Analog Dimming Control To implement analog dimming, apply a voltage between 0.1V to 1.25V to BC. The resulting LED current as a function of VBC is given by: ⎛V I LED = 0.16 × ⎜ BC ⎜R ⎝ FB ⎞ ⎟ ⎟ ⎠ BC may be overdriven, but driving VBC higher than 1.8V produces a constant LED current given by: I LED = 290 mV R FB Diode Selection The ACT6357 and ACT6358 require 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 for the ACT6357 and 1A for the ACT6358) and a peak repetitive reverse voltage (VRRM) rating that exceeds the maximum output voltage, typically set by the OV threshold. Direct PWM Dimming Control The ACT6357 and ACT6358 support direct PWM dimming control, allowing LED current to be adjusted via a PWM signal without the need for an external RC network. For PWM dimming, drive BC with a logic-level PWM signal to scale the LED current proportionally with the PWM duty cycle, with resulting LED current given by: Shutdown The ACT6357 and ACT6358 feature low-current shutdown modes. In shutdown mode, the control circuitry is disabled and the quiescent supply current drops to less than 1µA. To disable the ACT6357 and ACT6358, simply drive EN to a logic low. To enable the ICs, drive EN to a logic high or connect it to the input supply. ⎛V ⎞ I LED = ⎜ FB ⎟ × DUTY ⎜R ⎟ ⎝ FB ⎠ For best results, use PWM frequencies in the 100Hz to 10kHz range. Inductor Selection The ACT6357 and ACT6358 were designed for operation with inductors in the 4.7µH to 47µH range, and achieve best results under most operating conditions when using 22µH to 33µH. Keep in mind that larger-valued inductors generally result in continuous conduction mode operation (CCM) and yield higher efficiency due to lower peak currents, while smaller inductors typically yield a smaller footprint but at the cost of lower efficiency, resulting from higher peak currents (and their associated I2R losses). For best results, choose an inductor with a Innovative Products. Active Solutions. Low Input Voltage Applications In applications that have low input voltage range, such as those powered from 2-3 AA cells, the ACT6357 and ACT6358 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. -6www.active-semi.com Copyright © 2008 Active-Semi, Inc. ACT6357/ACT6358 Rev0, 03-Feb-08 TYPICAL PERFORMANCE CHARACTERISTICS (VVIN = 3.6V, TA = 25°C, unless otherwise specified.) ACT6357 Efficiency vs. Load Current 100 VIN = 3.6V 100 ACT6357/ACT6358-001 L = 33µH ACT6357 Efficiency vs. Load Current ACT6357/ACT6358-002 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) ACT6357 Efficiency vs. Load Current 100 VIN = 3.6V L = 33µH 90 100 ACT6357/ACT6358-003 ACT6357 Efficiency vs. Load Current ACT6357/ACT6358-004 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) ACT6357 Efficiency vs. Load Current 100 VIN = 3.6V L = 33µH 90 100 ACT6357/ACT6358-005 ACT6357 Efficiency vs. Load Current ACT6357/ACT6358-06 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 Products. Active Solutions. -7- www.active-semi.com Copyright © 2008 Active-Semi, Inc. ACT6357/ACT6358 Rev0, 03-Feb-08 TYPICAL PERFORMANCE CHARACTERISTICS (VVIN = 3.6V, TA = 25°C, unless otherwise specified.) ACT6358 Efficiency vs. Load Current 100 VIN = 3.6V L = 33µH 90 100 ACT6357/ACT6358-007 ACT6358 Efficiency vs. Load Current ACT6357/ACT6358-008 L = 33µH VIN = 5V 90 Efficiency (%) Efficiency (%) 80 80 VIN = 3.6V VIN = 3.2V L = 22µH 70 70 60 6 LEDs 0 5 10 15 20 25 30 60 6 LEDs 0 5 10 15 20 25 30 50 50 Load Current (mA) Load Current (mA) ACT6358 Efficiency vs. Load Current 100 VIN = 3.6V L = 33µH 90 100 ACT6357/ACT6358-009 ACT6358 Efficiency vs. Load Current ACT6357/ACT6358-010 L = 33µH VIN = 5V 90 Efficiency (%) Efficiency (%) 80 80 VIN = 3.6V VIN = 3.2V L = 22µH 70 70 60 8 LEDs 0 5 10 15 20 25 30 60 50 0 5 10 15 20 25 8 LEDs 30 50 Load Current (mA) Load Current (mA) ACT6358 Efficiency vs. Load Current 100 VIN = 3.6V L = 33µH 100 ACT6357/ACT6358-011 ACT6358 Efficiency vs. Load Current ACT6357/ACT6358-012 L = 33µH VIN = 5V 90 90 Efficiency (%) Efficiency (%) 80 L = 22µH 80 VIN = 3.6V VIN = 3.2V 70 70 60 10 LEDs 50 0 5 10 15 20 25 30 60 10 LEDs 50 0 5 10 15 20 25 30 Load Current (mA) Load Current (mA) Innovative Products. Active Solutions. -8- www.active-semi.com Copyright © 2008 Active-Semi, Inc. ACT6357/ACT6358 Rev0, 03-Feb-08 TYPICAL PERFORMANCE CHARACTERISTICS (VVIN = 3.6V, TA = 25°C, unless otherwise specified.) LED Current vs. BC Duty Cycle 30 28 24 20 10kHz 30 25 ACT6357/ACT6358-013 LED Current vs. BC Voltage ACT6357/ACT6358-014 LED Current (mA) 20 15 10 5 0 ILED (mA) 16 12 8 4 0 0 20 1kHz 100Hz 40 60 80 100 0 1 2 3 4 5 5.5 Duty Cycle (%) BC Voltage (V) Soft-Start Time vs. Capacitance 600 500 400 10 LEDs 300 200 100 0 0 0.5 1 1.5 2 2.5 6 LEDs 4 LEDs ACT6357/ACT6358-015 Soft-Start Time (ms) Capacitance (µF) Innovative Products. Active Solutions. -9- www.active-semi.com Copyright © 2008 Active-Semi, Inc. ACT6357/ACT6358 Rev0, 03-Feb-08 PACKAGE OUTLINE TDFN33-8 PACKAGE OUTLINE AND DIMENSIONS D SYMBOL A A1 E DIMENSION IN MILLIMETERS MIN 0.700 0.000 DIMENSION IN INCHES MIN 0.028 0.000 MAX 0.800 0.050 MAX 0.031 0.002 A3 D E D2 0.200 REF 2.850 2.850 2.100 1.350 0.250 3.150 3.150 2.500 1.750 0.350 0.008 REF 0.112 0.112 0.083 0.053 0.010 0.124 0.124 0.098 0.069 0.014 PIN #1 INDEX AREA D/2 x E/2 E2 b e L K D2 0.650 TYP 0.300 0.200 0.500 --- 0.026 TYP 0.012 0.008 0.020 --- PIN #1 INDEX AREA D/2 x E/2 E2 K L e b 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 Products. Active Solutions. - 10 - www.active-semi.com Copyright © 2008 Active-Semi, Inc.