ACT6357 ACTIVE-SEMI | Alldatasheet
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Innovative Products. Active Solutions. - 1 - www.active-semi.com Copyright © 2007 Active-Semi, Inc. SIMPLIFIED APPLICATION CIRCUIT ACT6357/ACT6358 High-Efficiency, 40V Step-Up WLED Bias Supplies ACT6357 ACT6358 IN EN SW OV FB G BC SS VOUT Brightness Control Enable VIN 2.6V to 5.5V Up to
10 WLEDs
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 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 GENERAL DESCRIPTION The ACT6357 and ACT6358 step -up DC/DC con- verters drive white LEDs with an externally pro- grammable 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, cycle - by-cycle current limiting, and thermal shutdown pro- tection circuitry. The ACT6357 has 500mA current limit, while the ACT6358 has 1A current limit. Both parts are avail- able in a small 3mm x 3mm 8-pin TDFN33-8. Rev PrB, 30-Aug-07 Advanced Product Information – All Information Subject to Change
Rev PrB, 30-Aug-07 Innovative Products. Active Solutions. - 2 - www.active-semi.com Copyright © 2007 Active-Semi, Inc. PART NUMBER CURRENT LIMIT TEMPERATURE RANGE PACKAGE PACKAGING ACT6357NH-T 0.5A -40°C to 85°C TDFN33-8 TAPE & REEL ACT6358NH-T 1A -40°C to 85°C TDFN33-8 TAPE & REEL PINS PIN NAME DESCRIPTION
2 IN Supply Input
3 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. 4 BC Brightness Control. Accepts either a PWM or analog control signal to perform LED brightness control. For best results, PWM frequency must be between 100Hz and 10kHz, with high level above 1.7V. Analog control signal must be in the 0 to 1.5V range, providing a LED brightness dynamic range of 10 to 1. 5 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. 6 SS 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. 7 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. Ground G 8 SW Switch Output. Connect this pin to the inductor and the Schottky diode. EP EP Exposed Pad. Connect to ground. PIN CONFIGURATION PIN DESCRIPTIONS
ORDERING INFORMATION
G IN BC EN SW SS FB OV TDFN33-8
Rev PrB, 30-Aug-07 Innovative Products. Active Solutions. - 3 - www.active-semi.com Copyright © 2007 Active-Semi, Inc. ABSOLUTE MAXIMUM RATINGS PARAMETER VALUE UNIT SW to G -0.3 to 42 V IN, EN to G -0.3 to 6 V FB, OV, BC, SS to G -0.3 to VIN + 0.3 V Continuous SW Current Internally Limited Junction to Ambient Thermal Resistance (θJA) 42.5 °C/W 1.9 W Operating Junction Temperature -40 to 150 °C Storage Temperature -55 to 150 °C Lead Temperature (Soldering, 10 sec) 300 °C Maximum Power Dissipation : Do not exceed these limits to prevent damage to the device. Exposure to absolute maximum rating conditions for long periods may affect device reliability.
Rev PrB, 30-Aug-07 Innovative Products. Active Solutions. - 4 - www.active-semi.com Copyright © 2007 Active-Semi, Inc. (VIN = VEN = 3.3V, TA = 25°C, unless otherwise specified.)
ELECTRICAL CHARACTERISTICS
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT Power Switch Voltage Rating 40 V Input Voltage 2.6 5.5 V Under Voltage Lockout Threshold VIN Rising 2.1 2.25 2.45 V Under Voltage Lockout Hysteresis 80 mV Supply Current Not Switching 0.1 0.25 mA Switching 0.25 0.5 Supply Current in Shutdown EN = G 0.1 10 µA Maximum On Time VIN = 3.3V 2.6 4.0 5.8 µs Maximum On Time Constant (K) K = tMAXON × VIN 13.2 µs × V Minimum Off Time 220 320 450 ns FB Feedback Voltage VBC = 3.3V 275 290 305 mV VBC = 1.25V 197 207 217 VBC = 0.625V 98 106 114 ∆VFB/∆VBC Ratio 0.16 V/V FB Input Current VFB = 1V 0 200 nA BC Input Impedance VBC = 0 to 1.25V 400 kΩ Switch Current Limit ACT6357 320 500 750 mA ACT6358 620 1000 1500 Switch On Resistance VIN = 3.3V 0.55 0.9 Ω Switch Leakage Current VSW = 38V, EN = G 10 µA Over Voltage Protection Threshold VOV Rising 1.11 1.21 1.31 V OV Input Current VOV = 1.5V 0 200 nA EN Logic High Threshold 1.4 V EN Logic Low Threshold 0.4 V EN Input Current VEN = 0V or 5V 0 1 µA Thermal Shutdown Temperature 160 °C Thermal Shutdown Hysteresis 20 °C
Rev PrB, 30-Aug-07 Innovative Products. Active Solutions. - 5 - www.active-semi.com Copyright © 2007 Active-Semi, Inc. FUNCTIONAL BLOCK DIAGRAM Control Scheme The ACT6357 and ACT6358 use a minimum off - time, current -mode control scheme to achieve excellent performance under high duty -cycle oper- ating conditions. This control scheme initiates a switching cycle only when needed to maintain out- put voltage regulation, resulting in very high effi- ciency operation. During each switching cycle, the N -channel power MOSFET turns on, increasing the inductor current. The switching cycle terminates when either the in- ductor 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 an- other switching begins when the error comparator detects that the output is falling out of regulation again. Soft-Start The ACT6357 and ACT6358 include a programma- ble soft -start function, which can be used to opti- mize an application between start -up time and start-up inrush current. Soft start is achieved by connecting a capacitor C SS between the SS pin and G. The soft start duration can be calculated from the following equation: where t SS 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 volt- age drops to zero, and the control switches at maxi- mum 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 re- sistor divider from the output node to G, with center tap at OV, and select the two resistors with the fol- lowing equation: where V OV is the over voltage detection threshold, ROV1 is the resistor between OV and G, and R OV2 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. 1V21.1 VRR OV 1OV2OV s Fμ5tC SSSS
Rev PrB, 30-Aug-07 Innovative Products. Active Solutions. - 6 - www.active-semi.com Copyright © 2007 Active-Semi, Inc. Setting the LED Current The LED current is programmed by appropriate selection of the feedback resistor R FB connected between FB and G. To set the LED current, choose the resistor according to the equation: where V FB is the FB feedback voltage (typically 207mV at VBC = 1.25V) and ILED is the desired maxi- mum LED current. Once the LED current is selected via RCS, it may be adjusted via the BC pin to provide a simple means of LED dimming. The BC pin sup- ports both analog as well as PWM dimming control. Analog Dimming Control To implement analog dimming, apply a voltage be- tween 0.1V to 1.25V to BC. The resulting LED cur- rent as a function of VBC is given by: BC may be overdriven, but driving V BC higher than 1.7V produces a constant LED current given by: Direct PWM Dimming Control The ACT6357 and ACT6358 support direct PWM dimming control, allowing LED current to be ad- justed 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 cur- rent proportionally with the PWM duty cycle, with resulting LED current given by: For best results, use PWM frequencies in the 100Hz to 10kHz range. Inductor Selection The ACT6357 and ACT6358 were designed for op- eration with inductors in the 4.7µH to 47µH range, and achieve best results under most operating con- ditions when using 22µH to 33µH. Keep in mind that larger-valued inductors generally result in con- tinuous conduction mode operation (CCM) and yield higher efficiency due to lower peak currents, while smaller inductors typically yield a smaller foot- print but at the cost of lower efficiency, resulting from higher peak currents (and their associated I 2R losses). For best results, choose an inductor with a 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). 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 ca- pacitor 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 ap- plications. For best performance, use X5R and X7R type ceramic capacitors, which possess less degra- dation in capacitance over voltage and temperature. Diode Selection The ACT6357 and ACT6358 require a Schottky diode as the rectifier. Select a low forward voltage drop Schottky diode with forward current (I F) rating that exceeds the peak current limit (500mA for the ACT6357 and 1A for the ACT6358) and a peak re- petitive reverse voltage (V RRM) rating that exceeds the maximum output voltage, typically set by the OV threshold. Shutdown The ACT6357 and ACT6358 feature low -current shutdown modes. In shutdown mode, the control circuitry is disabled and the quiescent supply cur- rent 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. 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 in- ductor may be connected directly to the battery, while the IC power is supplied by the system sup- ply. FB BC LED R V16.0I FB LED R mV290I DUTYR VI CS FB LED LED FB CS I VR
Rev PrB, 30-Aug-07 Innovative Products. Active Solutions. - 7 - www.active-semi.com Copyright © 2007 Active-Semi, Inc. TYPICAL PERFORMANCE CHARACTERISTICS (VVIN = 3.6V, TA = 25°C, unless otherwise specified.) ACT6357 Efficiency vs. Load Current Efficiency (%) Load Current (mA) ACT6357/ACT6358-001 5 0 ACT6357 Efficiency vs. Load Current Efficiency (%) ACT6357/ACT6358-002 100 10 15 20 25 100
4 LEDs
ACT6357 Efficiency vs. Load Current Efficiency (%) ACT6357/ACT6358-003 100
6 LEDs
Load Current (mA) 5 0 10 15 20 25 30 Load Current (mA) 5 0 10 15 20 25 30 VIN = 3.6V L = 33µH L = 22µH L = 33µH VIN = 3.2V VIN = 5V VIN = 3.6V VIN = 3.6V L = 33µH L = 22µH ACT6357 Efficiency vs. Load Current Efficiency (%) Load Current (mA) ACT6357/ACT6358-004 5 0 ACT6357 Efficiency vs. Load Current Efficiency (%) ACT6357/ACT6358-005 100 10 15 20 25 100
8 LEDs
ACT6357 Efficiency vs. Load Current Efficiency (%) ACT6357/ACT6358-06 100 Load Current (mA) 5 0 10 15 20 25 30 Load Current (mA) 5 0 10 15 20 25 30 VIN = 5V L = 33µH VIN = 3.6V L = 33µH VIN = 3.2V VIN = 3.6V L = 33µH L = 22µH VIN = 5V VIN = 3.2V VIN = 3.6V
Rev PrB, 30-Aug-07 Innovative Products. Active Solutions. - 8 - www.active-semi.com Copyright © 2007 Active-Semi, Inc. ACT6358 Efficiency vs. Load Current Efficiency (%) ACT6357/ACT6358-007 100 ACT6358 Efficiency vs. Load Current Efficiency (%) ACT6357/ACT6358-009 100 Load Current (mA) 5 0 10 15 20 25 30 Load Current (mA) 5 0 10 15 20 25 30 ACT6358 Efficiency vs. Load Current Efficiency (%) Load Current (mA) ACT6357/ACT6358-008 5 0 100 10 15 20 25 L = 33µH VIN = 3.2V VIN = 5V VIN = 3.6V VIN = 3.6V L = 33µH L = 22µH TYPICAL PERFORMANCE CHARACTERISTICS (VVIN = 3.6V, TA = 25°C, unless otherwise specified.) ACT6358 Efficiency vs. Load Current Efficiency (%) Load Current (mA) ACT6357/ACT6358-010 5 0 ACT6358 Efficiency vs. Load Current Efficiency (%) ACT6357/ACT6358-011 100 10 15 20 25 100
10 LEDs
ACT6358 Efficiency vs. Load Current Efficiency (%) ACT6357/ACT6358-012 100 Load Current (mA) 5 0 10 15 20 25 30 Load Current (mA) 5 0 10 15 20 25 30 VIN = 5V L = 33µH VIN = 3.6V L = 33µH L = 22µH L = 33µH VIN = 3.2V VIN = 5V VIN = 3.6V VIN = 3.6V L = 33µH L = 22µH VIN = 3.2V VIN = 3.6V
Rev PrB, 30-Aug-07 Innovative Products. Active Solutions. - 9 - www.active-semi.com Copyright © 2007 Active-Semi, Inc. LED Current vs. BC Voltage LED Current (mA) BC Voltage (V) ACT6357/ACT6358-014 LED Current vs. BC Duty Cycle ILED (mA) Duty Cycle (%) ACT6357/ACT6358-013 60 40 20 0 80 100 5.5 5 0 4 3 2 1 TYPICAL PERFORMANCE CHARACTERISTICS (VVIN = 3.6V, TA = 25°C, unless otherwise specified.) Soft-Start Time vs. Capacitance Soft-Start Time (ms) Capacitance (µF) ACT6357/ACT6358-015 0.5 0 100 200 300 400 600 1 1.5 2 2.5 500 10kHz 1kHz 100Hz
Rev PrB, 30-Aug-07 Innovative Products. Active Solutions. - 10 - www.active-semi.com Copyright © 2007 Active-Semi, Inc. Active-Semi, Inc. reserves the right to modify the circuitry or specifications without notice. Users should evaluate each produc t to make sure that it is suitable for their applications. Active -Semi products are not intended or authorized for use as critical compone nts in life- support devices or systems. Active-Semi, Inc. does not assume any liability arising out of the use of any product or circuit des cribed 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@active- semi.com or visit http://www.active-semi.com . For other inquiries, please send to:
1270 Oakmead Parkway, Suite 310, Sunnyvale, California 94085-4044, USA
TDFN33-8 PACKAGE OUTLINE AND DIMENSIONS D E e b L K PIN #1 INDEX AREA D/2 x E/2 PIN #1 INDEX AREA D/2 x E/2 SYMBOL DIMENSION IN MILLIMETERS DIMENSION IN INCHES MIN MAX MIN MAX A 0.700 0.800 0.028 0.031 A1 0.000 0.050 0.000 0.002 A3 0.200 REF D 2.850 3.150 0.112 0.124 E 2.850 3.150 0.112 0.124 D2 2.100 2.500 0.083 0.098 E2 1.350 1.750 0.053 0.069 b 0.250 0.350 0.010 0.014 e 0.650 TYP 0.026 TYP L 0.300 0.500 0.012 0.020