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ACT6360
Rev0, 23-May-08
High-Efficiency, 40V Step-Up WLED Bias Supplies FEATURES
* High-Efficiency DC/DC WLED Bias Supply * Internal 40V, 0.55 Power MOSFET * Up to 10 WLEDs per String * 1000mA 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 ACT6360 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 ACT6360 features a variety of protection circuits, including integrated over voltage protection (OVP), cycle-by-cycle current limiting, and thermal shutdown protection circuitry. The ACT6360 has a 1000mA 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
ACT6360
ON OFF
OV ROV1
EN G
FB RFB COUT
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www.active-semi.com Copyright (c) 2008 Active-Semi, Inc.
ACT6360
Rev0, 23-May-08
ORDERING INFORMATION
PART NUMBER
ACT6360US-T
CURRENT LIMIT
1A
TEMPERATURE RANGE
-40C to 85C
PACKAGE
SOT23-6
PINS
6
PACKAGING
TAPE & REEL
TOP MARK
WJFS
PIN CONFIGURATION
SW 1 6 IN
G
2
ACT6360
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
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www.active-semi.com Copyright (c) 2008 Active-Semi, Inc.
ACT6360
Rev0, 23-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 (JA) 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.
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ACT6360
Rev0, 23-May-08
ELECTRICAL CHARACTERISTICS
(VIN = VEN = 3.3V, TA = 25C, 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 x VIN 220 275 2.6
0.1 0.25 0.1 4.0 13.2 320 290 0 510 1000 0.55
0.25 0.5 10 5.8
mA A s s x V
450 305 200 1400 0.9 10 1.31 200
ns mV nA mA A 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 A C C
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ACT6360
Rev0, 23-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
ACT6360
Control Scheme
The ACT6360 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 (1000mA) or when the cycle lasts longer than the maximum ontime of 4s. 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.
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 x 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:
Over Voltage Protection
The ACT6360 includes internal over-voltage protection circuitry that monitors the OV pin voltage. Overvoltage 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.
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R FB =
V FB I LED
where VFB is the FB feedback voltage (typically 290mV at VEN = 3.3V) and ILED is the desired maximum LED current.
www.active-semi.com Copyright (c) 2008 Active-Semi, Inc.
ACT6360
Rev0, 23-May-08
Capacitor Selection
The ACT6360 requires only a tiny 0.47F output capacitor for most applications. For circuits driving 6 or fewer LEDs, a 4.7F input capacitor is generally suitable. For circuits driving more than 6 LEDs, a 10F 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 ACT6360 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 1A and a peak repetitive reverse voltage (VRRM) rating that exceeds the maximum output voltage, typically set by the OV threshold.
Shutdown
The ACT6360 features a low-current shutdown mode. In shutdown mode, the control circuitry is disabled and the quiescent supply current drops to less than 1A. 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 ACT6360 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.
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ACT6360
Rev0, 23-May-08
TYPICAL PERFORMANCE CHARACTERISTICS
(VVIN = 3.6V, TA = 25C, unless otherwise specified.)
Efficiency vs. Load Current
100 VIN = 3.6V 100 ACT6360-001 L = 33H
Efficiency vs. Load Current
ACT6360-002 L = 33H VIN = 5V
90
90
Efficiency (%)
L = 22H 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 = 33H 90 100 ACT6360-003
Efficiency vs. Load Current
ACT6360-004 L = 33H VIN = 5V
90
Efficiency (%)
Efficiency (%)
80
L = 22H
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 = 33H 90 100 ACT6360-005
Efficiency vs. Load Current
ACT6360-006 L = 33H VIN = 5V 90
Efficiency (%)
Efficiency (%)
80
L = 22H
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)
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www.active-semi.com Copyright (c) 2008 Active-Semi, Inc.
ACT6360
Rev0, 23-May-08
TYPICAL PERFORMANCE CHARACTERISTICS
(VVIN = 3.6V, TA = 25C, unless otherwise specified.)
ACT6360 Efficiency vs. Load Current
100 ACT6360-007 VIN = 3.6V L = 33H
90
Efficiency (%)
80
L = 22H
70
60 10 LEDs 50 0 5 10 15 20 25 30
Load Current (mA)
ACT6360 Efficiency vs. Load Current
100 ACT6360-008 L = 33H VIN = 5V 90
Efficiency (%)
80
VIN = 3.6V
VIN = 3.2V
70
60 10 LEDs 50 0 5 10 15 20 25 30
Load Current (mA)
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ACT6360
Rev0, 23-May-08
PACKAGE OUTLINE
SOT23-6 PACKAGE OUTLINE AND DIMENSIONS
D b L1 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
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
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