High-Efficiency, Step-Up WLED Bias Supplies FEATURES High-Efficie
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ACT6359
High-Efficiency, Step-Up WLED Bias Supplies FEATURES
High-Efficiency DC/DC WLED Bias Supply Internal 40V, 0.55 Power MOSFET WLEDs String 500mA Peak Current Supports Analog Dimming Integrated Over-Voltage Protection (OVP) Thermal Shutdown Cycle-by-Cycle Over Current Protection Tiny SOT23-6 Package
GENERAL DESCRIPTION
ACT6359 step-up DC/DC converter drives white LEDs with externally programmable constant current. This device features integrated, power MOSFET that capable driving white LEDs series, providing inherent current matching uniform brightness. WLED brightness adjustment easily achieved simple external circuitry, which accepts either analog dimming control signal. ACT6359 features variety protection circuits, including integrated over voltage protection (OVP), cycle-by-cycle current limiting, thermal shutdown protection circuitry. ACT6359 500mA current limit, available small 6-pin SOT23-6 package.
APPLICATIONS
Displays Smart Phones Portable Media Players GPS/Personal Navigation Devices
SIMPLIFIED APPLICATION CIRCUIT
WLEDs VOUT ROV2
ACT6359
ROV1
COUT
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ACT6359
ORDERING INFORMATION
PART NUMBER
ACT6359US-T
CURRENT LIMIT
0.5A
TEMPERATURE RANGE
-40°C 85°C
PACKAGE PINS PACKAGING
SOT23-6 TAPE REEL
MARK
WJFR
CONFIGURATION
ACT6359
SOT23-6
DESCRIPTIONS
NAME
Ground
DESCRIPTION
Switch Output. Connect this inductor Schottky diode.
Over Voltage Protection Input. automatically disabled when voltage this exceeds 1.21V. Connect center point resistive voltage divider connected across string. Feedback Input. Connect this cathode bottom LED, current feedback resistor between this bias current. Enable Control. Drive logic high enable device. Connect logic disable device. should left floating; connect when unused. Supply Input
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ACT6359
ABSOLUTE MAXIMUM RATINGS
PARAMETER
Continuous Current Junction Ambient Thermal Resistance (JA) Maximum Power Dissipation Operating Junction Temperature Storage Temperature Lead Temperature (Soldering, sec)
VALUE
-0.3 -0.3 -0.3 Internally Limited 0.727
UNIT
°C/W
exceed these limits prevent damage device. Exposure absolute maximum rating conditions long periods affect device reliability.
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ACT6359
ELECTRICAL CHARACTERISTICS
(VIN 3.3V, 25°C, unless otherwise specified.)
PARAMETER
Power Switch Voltage Rating Input Voltage Under Voltage Lockout Threshold Under Voltage Lockout Hysteresis Supply Current Supply Current Shutdown Maximum Time Maximum Time Constant Minimum Time Feedback Voltage Input Current Switch Current Limit Switch Resistance Switch Leakage Current Over Voltage Protection Threshold Input Current Logic High Threshold Logic Threshold Input Current Thermal Shutdown Temperature Thermal Shutdown Hysteresis 1.8V Rising
TEST CONDITIONS
UNIT
2.25
2.45
Switching Switching 3.3V tMAXON
0.25 13.2 0.55
0.25
1.31
38V, Rising 1.5V 1.11
1.21
3.3V
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ACT6359
FUNCTIONAL BLOCK DIAGRAM
ENABLE CIRCUIT UVLO DRIVER
THERMAL SHUTDOWN COMPARATOR 1.21V
CONTROL LOGIC
MAXIMUM TIME MINIMUM TIME
BANDGAP REFERENCE
ERROR COMPARATOR 0.29V
ACT6359
Control Scheme
ACT6359 uses minimum off-time, currentmode control scheme achieve excellent performance under high duty-cycle operating conditions. This control scheme initiates switching cycle only when needed maintain output voltage regulation, resulting very high efficiency operation. During each switching cycle, N-channel power MOSFET turns increasing inductor current. switching cycle terminates when either inductor current reaches current limit (500mA) when cycle lasts longer than maximum ontime 4µs. Once MOSFET turns off, remains least minimum off-time 320ns, then another switching begins when error comparator detects that output falling regulation again.
MOSFET. over-voltage protection circuit detects this condition switching ceases voltage reaches 1.21V. maximum output voltage, connect resistor divider from output node with center select resistors with following equation:
ROV1 1.21V
where over voltage detection threshold, ROV1 resistor between ROV2 resistor from output pin. first estimate, threshold often times number LEDs string.
Setting Current
current programmed appropriate selection feedback resistor connected between current, choose resistor according equation: where feedback voltage (typically 290mV 3.3V) ILED desired maximum current.
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Over Voltage Protection
ACT6359 includes internal over-voltage protection circuitry that monitors voltage. Over-voltage protection critical when LEDs string fails open circuit. When this happens feedback voltage drops zero, control switches maximum time causing output voltage keep rising until exceeds maximum voltage rating power
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ACT6359
Capacitor Selection
ACT6359 requires only tiny 0.47µF output capacitor most applications. circuits driving fewer LEDs, 4.7µF input capacitor generally suitable. circuits driving more than LEDs, 10µF input capacitor required. When choosing larger inductor which results operation, stability ripple improved adding small feed forward capacitor from About 3000pF good starting point most applications, although larger value used achieve best results applications with fewer LEDs. Ceramic capacitors recommended most applications. best performance, type ceramic capacitors, which possess less degradation capacitance over voltage temperature.
Diode Selection
ACT6359 requires Schottky diode rectifier. Select forward voltage drop Schottky diode with forward current (IF) rating that exceeds peak current limit (500mA) peak repetitive reverse voltage (VRRM) rating that exceeds maximum output voltage, typically threshold.
Shutdown
ACT6359 features low-current shutdown mode. shutdown mode, control circuitry disabled quiescent supply current drops less than 1µA. disable simply drive logic low. enable ICs, drive logic high connect input supply.
Input Voltage Applications
applications that have input voltage range, such those powered from cells, ACT6359 still used there suitable system supply (such 3.3V) available power controller. such application, inductor connected directly battery, while power supplied system supply.
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ACT6359
TYPICAL PERFORMANCE CHARACTERISTICS
(VVIN 3.6V, 25°C, unless otherwise specified.)
Efficiency Load Current
3.6V ACT6359-001 33µH
Efficiency Load Current
ACT6359-002 33µH
Efficiency
22µH
Efficiency
3.6V
3.2V
LEDs
LEDs
Load Current (mA)
Load Current (mA)
Efficiency Load Current
3.6V 33µH ACT6359-003
Efficiency Load Current
ACT6359-004 33µH
Efficiency
Efficiency
22µH
3.6V
3.2V
LEDs
LEDs
Load Current (mA)
Load Current (mA)
Efficiency Load Current
3.6V 33µH ACT6359-005
Efficiency Load Current
ACT6359-006 33µH
Efficiency
Efficiency
22µH
3.6V
3.2V
LEDs
LEDs
Load Current (mA)
Load Current (mA)
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ACT6359
PACKAGE OUTLINE
SOT23-6 PACKAGE OUTLINE DIMENSIONS
SYMBOL
DIMENSION MILLIMETERS
1.050 0.000 1.050 0.300 0.100 2.820 1.500 2.650
DIMENSION INCHES
0.041 0.000 0.041 0.012 0.004 0.111 0.059 0.104
1.250 0.100 1.150 0.500 0.200 3.020 1.700 2.950
0.049 0.004 0.045 0.020 0.008 0.119 0.067 0.116
0.950 1.800 2.000
0.037 0.071 0.079
0.700 0.300 0.600
0.028 0.012 0.024
Active-Semi, Inc. reserves right modify circuitry specifications without notice. Users should evaluate each product make sure that suitable their applications. Active-Semi products intended authorized critical components lifesupport devices systems. Active-Semi, Inc. does assume liability arising product circuit described this datasheet, does convey patent license. Active-Semi logo trademarks Active-Semi, Inc. more information this other products, contact sales@activesemi.com visit http://www.active-semi.com. other inquiries, please send 1270 Oakmead Parkway, Suite 310, Sunnyvale, California 94085-4044,
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