Rev0, 03-Feb-08 Advanced Product InformationAll Information Subject Ch
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ACT6357/ACT6358
Rev0, 03-Feb-08 Advanced Product InformationAll Information Subject Change
High-Efficiency, Step-Up WLED Bias Supplies FEATURES
High-Efficiency DC/DC WLED Bias Supply Internal 40V, 0.55 Power MOSFET WLEDs String Peak Current Options:
ACT6357: 0.5A ACT6358:
GENERAL DESCRIPTION
ACT6357 ACT6358 step-up DC/DC converters drive white LEDs with externally programmable constant current. These devices feature integrated, power MOSFETs that capable driving white LEDs series, providing inherent current matching uniform brightness. WLED brightness adjustment easily achieved dual-function pin, which accepts either analog dimming control signal. ACT6357 ACT6358 feature variety protection circuits, including integrated over voltage protection (OVP), programmable soft-start, cycleby-cycle current limiting, thermal shutdown protection circuitry. ACT6357 500mA current limit, while ACT6358 current limit. Both parts available small 8-pin TDFN33-8.
Supports Analog Dimming Integrated Over-Voltage Protection (OVP) Programmable Soft-Start Function Thermal Shutdown Cycle-by-Cycle Over Current Protection Tiny TDFN33-8 Package
APPLICATIONS
Displays Smart Phones Portable Media Players GPS/Personal Navigation Devices
SIMPLIFIED APPLICATION CIRCUIT
WLEDs ROV2
2.6V 5.5V
Enable Brightness Control
ACT6357 ACT6358
ROV1
COUT
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ACT6357/ACT6358
Rev0, 03-Feb-08
ORDERING INFORMATION
PART NUMBER
ACT6357NH-T ACT6358NH-T
CURRENT LIMIT
0.5A
TEMPERATURE RANGE
-40°C 85°C -40°C 85°C
PACKAGE
TDFN33-8 TDFN33-8
PINS
PACKAGING
TAPE REEL TAPE REEL
CONFIGURATION
ACT6357 ACT6358
TDFN33-8
DESCRIPTIONS
NAME
Ground Supply Input
DESCRIPTION
Enable Control. Drive logic high enable device. Connect logic disable device. should left floating; connect when unused. Brightness Control. Multifunction accepts either analog control signal. When using control signal, best results achieved when frequency 100Hz 10kHz range when high voltage 1.8V higher. When using analog control signal, best results achieved when control voltage 1.8V range. Feedback Input. Connect this cathode bottom LED, current feedback resistor between this bias current. Soft Start Control Input. Connect capacitor from this program soft start duration. internally discharged when disabled. Over Voltage Protection Input. automatically disabled when voltage this exceeds 1.21V. Connect center point resistive voltage divider connected across string. Switch Output. Connect this inductor Schottky diode. Exposed Pad. Connect ground.
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ACT6357/ACT6358
Rev0, 03-Feb-08
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 42.5
UNIT
°C/W
exceed these limits prevent damage device. Exposure absolute maximum rating conditions long periods affect device reliability.
Innovative Products. Active Solutions.
www.active-semi.com Copyright 2008 Active-Semi, Inc.
ACT6357/ACT6358
Rev0, 03-Feb-08
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 3.3V Feedback Voltage Rising
TEST CONDITIONS
UNIT
2.25
2.45
Switching Switching 3.3V tMAXON
0.25 13.2 0.16
0.25
1.25V 0.625V
VFB/VBC Ratio Input Current Input Impedance 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 1.25V ACT6357 ACT6358 3.3V 38V, Rising 1.5V 1.11
1500
1000 0.55
1.21
1.31
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ACT6357/ACT6358
Rev0, 03-Feb-08
FUNCTIONAL BLOCK DIAGRAM
Control Scheme
ACT6357 ACT6358 minimum offtime, current-mode 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 ACT6357, ACT6358) when cycle lasts longer than maximum on-time 4µs. Once MOSFET turns off, remains least minimum off-time 320ns, then another switching begins when error comparator detects that output falling regulation again.
where required soft start duration. typical application, 0.1µF generate 20ms soft start time.
Over Voltage Protection
Both ACT6357 ACT6358 include 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 MOSFET. ACT6357 ACT6358's over-voltage protection 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 1.21
Soft-Start
ACT6357 ACT6358 include programmable soft-start function, which used optimize application between start-up time start-up inrush current. Soft start achieved connecting capacitor between soft start duration calculated from following equation:
where over voltage detection threshold, ROV1 resistor between ROV2 resistor from output pin. first estimate, threshold often times number LEDs string.
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ACT6357/ACT6358
Rev0, 03-Feb-08
Setting Current
current programmed appropriate selection feedback resistor connected between current, choose resistor according equation:
DC-Resistance (DCR) sure choose inductor with saturation current that exceeds current limit (500mA ACT6357 ACT6358).
Capacitor Selection
ACT6357 ACT6358 only require 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 result applications with fewer LEDs Ceramic capacitors recommended most applications. best performance, type ceramic capacitors, which possess less degradation capacitance over voltage temperature.
where feedback voltage (typically 207mV 1.25V) ILED desired maximum current. Once current selected RFB, adjusted provide simple means dimming. supports both analog well dimming control.
Analog Dimming Control
implement analog dimming, apply voltage between 0.1V 1.25V resulting current function given
0.16
overdriven, driving higher than 1.8V produces constant current given
Diode Selection
ACT6357 ACT6358 require Schottky diode rectifier. Select forward voltage drop Schottky diode with forward current (IF) rating that exceeds peak current limit (500mA ACT6357 ACT6358) peak repetitive reverse voltage (VRRM) rating that exceeds maximum output voltage, typically threshold.
Direct Dimming Control
ACT6357 ACT6358 support direct dimming control, allowing current adjusted signal without need external network. dimming, drive with logic-level signal scale current proportionally with duty cycle, with resulting current given
Shutdown
ACT6357 ACT6358 feature low-current shutdown modes. shutdown mode, control circuitry disabled quiescent supply current drops less than 1µA. disable ACT6357 ACT6358, simply drive logic low. enable ICs, drive logic high connect input supply.
DUTY best results, frequencies 100Hz 10kHz range.
Inductor Selection
ACT6357 ACT6358 were designed operation with inductors 4.7µH 47µH range, achieve best results under most operating conditions when using 22µH 33µH. Keep mind that larger-valued inductors generally result continuous conduction mode operation (CCM) yield higher efficiency lower peak currents, while smaller inductors typically yield smaller footprint cost lower efficiency, resulting from higher peak currents (and their associated losses). best results, choose inductor with
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Input Voltage Applications
applications that have input voltage range, such those powered from cells, ACT6357 ACT6358 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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ACT6357/ACT6358
Rev0, 03-Feb-08
TYPICAL PERFORMANCE CHARACTERISTICS
(VVIN 3.6V, 25°C, unless otherwise specified.)
ACT6357 Efficiency Load Current
3.6V ACT6357/ACT6358-001 33µH
ACT6357 Efficiency Load Current
ACT6357/ACT6358-002 33µH
Efficiency
22µH
Efficiency
3.6V
3.2V
LEDs
LEDs
Load Current (mA)
Load Current (mA)
ACT6357 Efficiency Load Current
3.6V 33µH ACT6357/ACT6358-003
ACT6357 Efficiency Load Current
ACT6357/ACT6358-004 33µH
Efficiency
Efficiency
22µH
3.6V
3.2V
LEDs
LEDs
Load Current (mA)
Load Current (mA)
ACT6357 Efficiency Load Current
3.6V 33µH ACT6357/ACT6358-005
ACT6357 Efficiency Load Current
ACT6357/ACT6358-06 33µH
Efficiency
Efficiency
22µH
3.6V
3.2V
LEDs
LEDs
Load Current (mA)
Load Current (mA)
Innovative Products. Active Solutions.
www.active-semi.com Copyright 2008 Active-Semi, Inc.
ACT6357/ACT6358
Rev0, 03-Feb-08
TYPICAL PERFORMANCE CHARACTERISTICS
(VVIN 3.6V, 25°C, unless otherwise specified.)
ACT6358 Efficiency Load Current
3.6V 33µH ACT6357/ACT6358-007
ACT6358 Efficiency Load Current
ACT6357/ACT6358-008 33µH
Efficiency
Efficiency
3.6V
3.2V
22µH
LEDs
LEDs
Load Current (mA)
Load Current (mA)
ACT6358 Efficiency Load Current
3.6V 33µH ACT6357/ACT6358-009
ACT6358 Efficiency Load Current
ACT6357/ACT6358-010 33µH
Efficiency
Efficiency
3.6V
3.2V
22µH
LEDs
LEDs
Load Current (mA)
Load Current (mA)
ACT6358 Efficiency Load Current
3.6V 33µH ACT6357/ACT6358-011
ACT6358 Efficiency Load Current
ACT6357/ACT6358-012 33µH
Efficiency
Efficiency
22µH
3.6V
3.2V
LEDs
LEDs
Load Current (mA)
Load Current (mA)
Innovative Products. Active Solutions.
www.active-semi.com Copyright 2008 Active-Semi, Inc.
ACT6357/ACT6358
Rev0, 03-Feb-08
TYPICAL PERFORMANCE CHARACTERISTICS
(VVIN 3.6V, 25°C, unless otherwise specified.)
Current Duty Cycle
10kHz ACT6357/ACT6358-013
Current Voltage
ACT6357/ACT6358-014
Current (mA)
ILED (mA)
1kHz 100Hz
Duty Cycle
Voltage
Soft-Start Time Capacitance
LEDs LEDs LEDs ACT6357/ACT6358-015
Soft-Start Time (ms)
Capacitance (µF)
Innovative Products. Active Solutions.
www.active-semi.com Copyright 2008 Active-Semi, Inc.
ACT6357/ACT6358
Rev0, 03-Feb-08
PACKAGE OUTLINE
TDFN33-8 PACKAGE OUTLINE DIMENSIONS
SYMBOL
DIMENSION MILLIMETERS
0.700 0.000
DIMENSION INCHES
0.028 0.000
0.800 0.050
0.031 0.002
0.200 2.850 2.850 2.100 1.350 0.250 3.150 3.150 2.500 1.750 0.350
0.008 0.112 0.112 0.083 0.053 0.010 0.124 0.124 0.098 0.069 0.014
INDEX AREA
0.650 0.300 0.200 0.500
0.026 0.012 0.008 0.020
INDEX AREA
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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