ACTIVE-SEMI ACT6360_08

ACT6360
Rev0, 23-May-08
High-Efficiency, 40V Step-Up WLED Bias Supplies
FEATURES
GENERAL DESCRIPTION
• High-Efficiency DC/DC WLED Bias Supply
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.
• Internal 40V, 0.55Ω Power MOSFET
• Up to 10 WLEDs per String
• 1000mA Peak Current
• Supports Analog and PWM LED Dimming
• Integrated Over-Voltage Protection (OVP)
• Thermal Shutdown
• Tiny SOT23-6 Package
The ACT6360 features a variety of protection circuits, including integrated over voltage protection
(OVP), cycle-by-cycle current limiting, and thermal
shutdown protection circuitry.
APPLICATIONS
The ACT6360 has a 1000mA current limit, and is
available in a small 6-pin SOT23-6 package.
• Cycle-by-Cycle Over Current Protection
• TFT LCD Displays
• Smart Phones
• Portable Media Players
• GPS/Personal Navigation Devices
SIMPLIFIED APPLICATION CIRCUIT
L1
D1
VIN
IN
Up to
10 WLEDs
SW
VOUT
ROV2
CIN
ACT6360
OV
ROV1
ON
OFF
Innovative PowerTM
EN
FB
G
-1-
RFB
COUT
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Copyright © 2008 Active-Semi, Inc.
ACT6360
Rev0, 23-May-08
ORDERING INFORMATION
PART NUMBER
CURRENT
LIMIT
TEMPERATURE
RANGE
PACKAGE
PINS
PACKAGING
TOP MARK
ACT6360US-T
1A
-40°C to 85°C
SOT23-6
6
TAPE & REEL
WJFS
PIN CONFIGURATION
SW
1
G
2
OV
3
ACT6360
6
IN
5
EN
4
FB
SOT23-6
PIN DESCRIPTIONS
PIN
NAME
1
SW
2
G
3
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.
4
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.
5
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.
6
IN
Supply Input
Innovative PowerTM
DESCRIPTION
Switch Output. Connect this pin to the inductor and the Schottky diode.
Ground
-2-
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Copyright © 2008 Active-Semi, Inc.
ACT6360
Rev0, 23-May-08
ABSOLUTE MAXIMUM RATINGSc
PARAMETER
VALUE
UNIT
SW to G
-0.3 to 42
V
IN, EN to G
-0.3 to 6
V
FB, OV to G
-0.3 to VIN + 0.3
V
Continuous SW Current
Internally Limited
Junction to Ambient Thermal Resistance (θJA)
200
°C/W
0.727
W
Operating Junction Temperature
-40 to 150
°C
Storage Temperature
-55 to 150
°C
300
°C
Maximum Power Dissipation
Lead Temperature (Soldering, 10 sec)
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 PowerTM
-3-
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Copyright © 2008 Active-Semi, Inc.
ACT6360
Rev0, 23-May-08
ELECTRICAL CHARACTERISTICS
(VIN = VEN = 3.3V, TA = 25°C, unless otherwise specified.)
PARAMETER
TEST CONDITIONS
MIN
TYP
Power Switch Voltage Rating
Input Voltage
Under Voltage Lockout Threshold
2.6
VIN Rising
2.1
Under Voltage Lockout Hysteresis
2.25
MAX
UNIT
40
V
5.5
V
2.45
V
80
mV
Not Switching
0.1
0.25
Switching
0.25
0.5
Supply Current in Shutdown
EN = G
0.1
10
µA
Maximum On Time
VIN = 3.3V
4.0
5.8
µs
Maximum On Time Constant (K)
K = tMAXON × VIN
Supply Current
2.6
13.2
Minimum Off Time
FB Feedback Voltage
VEN ≥ 1.8V
FB Input Current
VFB = 1V
Switch Current Limit
320
450
ns
275
290
305
mV
0
200
nA
1000
1400
mA
0.55
0.9
Ω
0
10
µA
1.21
1.31
V
0
200
nA
Switch On Resistance
VSW = 38V, EN = G
Over Voltage Protection Threshold
VOV Rising
OV Input Current
VOV = 1.5V
1.11
EN Logic High Threshold
1.4
V
EN Logic Low Threshold
EN Input Current
µs × V
220
510
Switch Leakage Current
VEN = 0V, 3.3V
mA
18
0.4
V
36
µA
Thermal Shutdown Temperature
160
°C
Thermal Shutdown Hysteresis
20
°C
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-4-
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Copyright © 2008 Active-Semi, Inc.
ACT6360
Rev0, 23-May-08
FUNCTIONAL BLOCK DIAGRAM
IN
SW
EN
ENABLE
CIRCUIT
UVLO
THERMAL
SHUTDOWN
DRIVER
CONTROL
LOGIC
OV COMPARATOR
+
OV
1.21V
G
MAXIMUM
ON TIME
-
MINIMUM
OFF TIME
BANDGAP
REFERENCE
FB
+
ERROR
COMPARATOR
0.29V
ACT6360
The over-voltage protection circuit detects this condition and switching ceases if the voltage at the OV
pin reaches 1.21V.
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.
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⎥
⎣⎝ 1.21V ⎠ ⎦
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 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 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.
Innovative PowerTM
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.
-5-
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Copyright © 2008 Active-Semi, Inc.
ACT6360
Rev0, 23-May-08
Capacitor Selection
The ACT6360 requires only 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 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 1µA. 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.
Innovative PowerTM
-6-
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Copyright © 2008 Active-Semi, Inc.
ACT6360
Rev0, 23-May-08
TYPICAL PERFORMANCE CHARACTERISTICS
(VVIN = 3.6V, TA = 25°C, unless otherwise specified.)
Efficiency vs. Load Current
Efficiency (%)
90
L = 22µH
L = 33µH
VIN = 5V
90
Efficiency (%)
L = 33µH
ACT6360-002
VIN = 3.6V
Efficiency vs. Load Current
100
ACT6360-001
100
80
70
60
VIN = 3.6V
VIN = 3.2V
80
70
60
4 LEDs
4 LEDs
50
50
0
5
10
15
20
25
30
0
5
Load Current (mA)
25
L = 33µH
VIN = 5V
90
Efficiency (%)
90
L = 22µH
70
VIN = 3.6V
VIN = 3.2V
80
70
60
60
6 LEDs
6 LEDs
50
50
0
5
10
15
20
25
30
0
5
Load Current (mA)
15
20
25
30
Efficiency vs. Load Current
90
L = 33µH
VIN = 5V
90
Efficiency (%)
L = 33µH
ACT6360-006
100
ACT6360-005
VIN = 3.6V
L = 22µH
80
10
Load Current (mA)
Efficiency vs. Load Current
100
Efficiency (%)
30
ACT6360-004
100
ACT6360-003
L = 33µH
Efficiency (%)
20
Efficiency vs. Load Current
VIN = 3.6V
80
15
Load Current (mA)
Efficiency vs. Load Current
100
10
70
60
VIN = 3.6V
80
VIN = 3.2V
70
60
8 LEDs
8 LEDs
50
50
0
5
10
15
20
25
30
0
Load Current (mA)
Innovative PowerTM
5
10
15
20
25
30
Load Current (mA)
-7-
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Copyright © 2008 Active-Semi, Inc.
ACT6360
Rev0, 23-May-08
TYPICAL PERFORMANCE CHARACTERISTICS
(VVIN = 3.6V, TA = 25°C, unless otherwise specified.)
ACT6360 Efficiency vs. Load Current
VIN = 3.6V
L = 33µH
90
Efficiency (%)
ACT6360-007
100
80
L = 22µH
70
60
10 LEDs
50
0
5
10
15
20
25
30
Load Current (mA)
ACT6360 Efficiency vs. Load Current
ACT6360-008
100
L = 33µH
VIN = 5V
Efficiency (%)
90
VIN = 3.6V
80
VIN = 3.2V
70
60
10 LEDs
50
0
5
10
15
20
25
30
Load Current (mA)
Innovative PowerTM
-8-
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Copyright © 2008 Active-Semi, Inc.
ACT6360
Rev0, 23-May-08
PACKAGE OUTLINE
SOT23-6 PACKAGE OUTLINE AND DIMENSIONS
D
θ
b
SYMBOL
L
E
E1
c
e
MAX
MIN
MAX
A
1.050
1.250
0.041
0.049
A1
0.000
0.100
0.000
0.004
A2
1.050
1.150
0.041
0.045
b
0.300
0.500
0.012
0.020
c
0.100
0.200
0.004
0.008
D
2.820
3.020
0.111
0.119
E
1.500
1.700
0.059
0.067
E1
2.650
2.950
0.104
0.116
e
A
A2
A1
e1
DIMENSION IN
INCHES
MIN
L1
0.2
DIMENSION IN
MILLIMETERS
e1
L
0.950 TYP
1.800
2.000
0.700 REF
0.037 TYP
0.071
0.079
0.028 REF
L1
0.300
0.600
0.012
0.024
θ
0°
8°
0°
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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