ACTIVE-SEMI ACT111A

ACT111A
Rev 0, 14-Feb-11
4.8V to 30V Input, 1.5A LED Driver with Dimming Control
FEATURES
GENERAL DESCRIPTION
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•
•
•
•
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The ACT111A is a high efficient LED driver
employing current-mode buck converter topology
that supplies up to 1.5A from wide input voltage
range from 4.8V up to 30V. The ACT111A is
designed to operate as a constant source with
1.4MHz fixed frequency. ACT111A consists of a
PWM control circuit, a high precision band-gap
voltage reference, an oscillator, an error amplifier
with internal compensation network and the N
channel power MOSFET. An external sense
resistor in series with the LED monitors output
current allowing accurate current regulation, ideal
for driving high current LEDs. The built-in fault
condition protection circuits including current
limiting, UVLO and thermal shutdown prevent itself
from potentially faulty operation and burn-out.
Up to 92% Efficiency
Wide 4.8V to 30V Input Voltage Range
100mV Low Feedback Voltage
1.5A High Output Capacity
PWM Dimming
10kHz Maximum Dimming Frequency
Thermal Shutdown
SOT23-6 Package
APPLICATIONS
•
•
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High Brightness LED Driver
Architecture Detail Lighting
The ACT111A is ideal for single 1W to 5W LED
drivers. With its ultra low feedback voltage, a low
current ripple, high efficiency of up to 92% stepdown power LED driver can be easily composed of
with additional several external components such
as an inductor, a Schottky diode, a few resistors
and capacitors.
Constant Current Source
Hand-held Lighting
Automotive RCL, DRL, and Fog Lights
Indicators and Emergency Lighting
MR16 and other LED Bulb
TYPICAL APPLICATION CIRCUIT
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ACT111A
Rev 0, 14-Feb-11
ORDERING INFORMATION
PART NUMBER
TEMPERATURE RANGE
PACKAGE
PINS
PACKING
TOP MARK
ACT111AUS-T
-40°C to 85°C
SOT23-6
6
TAPE & REEL
FRWE
PIN CONFIGURATION
1
G
2
BST
3
FRWE
FB
6
DIM
5
IN
4
SW
SOT23-6
ACT111AUS-T
PIN DESCRIPTIONS
PIN NUMBER
PIN NAME
1
FB
Feedback Input for regulating LED current. The voltage at this pin is regulated to
0.1V. An external resistor is connected from this pin to ground to sense the LED
current.
2
G
Ground.
3
BST
Bootstrap pin. This provides power to the internal high-side N channel MOSFET
gate driver. Connect a 2.2nF capacitor from the pin to SW pin.
4
SW
Internal N channel power MOSFET source output pin. Connect it to one end of
power inductor.
5
IN
Power supply input. Bypass this pin with a 10µF ceramic capacitor to GND, placed
as close to the IC as possible.
6
DIM
PWM signal input for dimming control. Apply PWM signal with amplitude greater
than 2V to this pin. The device is enabled as DIM pin open and disabled when it is
connected to G.
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PIN DESCRIPTION
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ACT111A
Rev 0, 14-Feb-11
ABSOLUTE MAXIMUM RATINGSc
PARAMETER
VALUE
UNIT
-0.3 to 34
V
SW to G
-1 to VIN + 1
V
BST to G
VSW - 0.3 to VSW + 7
V
FB to G
-0.3 to +6
V
DIM to G
-0.3 to +3
V
Internally Limited
A
Junction to Ambient Thermal Resistance (θJA)
220
°C/W
Maximum Power Dissipation
0.5
W
Operating Junction Temperature
-40 to 150
°C
Storage Temperature
-55 to 150
°C
300
°C
IN to G
Continuous SW Current
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.
ELECTRICAL CHARACTERISTICS
(VIN = 12V, TA = 25°C, unless otherwise specified.)
PARAMETER
Input Voltage
VIN Turn-On Voltage
SYMBOL
TEST CONDITIONS
VIN
MIN
4.8
Input Voltage Rising
4.0
VIN UVLO Hysteresis
Supply Operation Current
VFB = 0.2V
30
V
4.7
V
VFB = 0.08V
mV
2
mA
1.15
1.4
1.65
MHz
90
92
95
%
75
5V ≤ VIN ≤ 20V
97
102
FB Leakage Current
CC Current Limit
UNIT
1
Minimum On-Time
Effective FB Voltage
4.4
MAX
250
Switching Frequency
Maximum Duty Cycle
TYP
Duty Cycle = 5%
1.8
2.4
PWM DIM Frequency
ns
107
mV
100
nA
3.0
A
10
kHz
DIM Threshold Voltage
DIM rising
1.66
V
DIM Hysteresis
DIM rising
100
mV
DIM Input Leakage
1
µA
High-Side Switch On-Resistance
0.3
Ω
Low-Side Switch On-Resistance
15
Ω
Thermal Shutdown Temperature
160
°C
Thermal Hysteresis
10
°C
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ACT111A
Rev 0, 14-Feb-11
TYPICAL PERFORMANCE CHARACTERISTICS
(TA = 25°C, unless otherwise specified.)
Efficiency vs. Load Current
Efficiency (%)
85
VIN = 18V
75
VIN = 24V
65
55
0.1
1
75
VIN = 18V
VIN = 24V
65
55
VOUT = 5V
50
VIN = 12V
85
Efficiency (%)
VIN = 12V
ACT111A-002
95
ACT111A-001
95
Efficiency vs. Load Current
VOUT = 3.3V
50
10
0.1
1
Load Current (A)
Load Current (A)
FB Voltage vs. Temperature
Oscillator Frequency vs. Temperature
Oscillator Frequency (MHz)
FB Voltage (mV)
101
100
99
ACT111A-004
1.60
ACT111A-003
102
98
-40
10
1.50
1.40
1.30
1.20
-20
0
20
40
60
80
100
-40
120
-20
0
20
40
60
80
100
120
Temperature (°C)
Temperature (°C)
Peak Current Limit vs. Duty Cycle
Peak Current Limit (A)
ACT111A-005
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0
20
60
40
80
100
Duty Cycle
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ACT111A
Rev 0, 14-Feb-11
FUNCTIONAL BLOCK DIAGRAM
IN
LOGIC
DIM
CSA
REGULATOR
& UVLO
BST
OSCILLATOR
CONTROL
PWM Comparator
ILIM Comparator
Q1
DRIVER
SW
REFERENCE
& THERMAL
SHUTDOWN
COMPENSATION
EA
FB
G
connecting a PWM signal (frequency rage from
0.1kHz to 10kHz) the DIM pin. If the DIM pin is
unconnected or pulled high, the ACT111A operates
normally.
FUNCTIONAL DESCRIPTION
The ACT111A is a current-mode step-down 1.5A
LED driver with no extra external compensation
components. It has wide 4.8V to 30V input voltage
range for a variety of power sources. The 100mV low
feedback voltage and an external current sense
resistor makes it deliver LED current programmable
from 20mA to 700mA with efficiency up to 96%. The
device contains an internal, low-resistance, highvoltage power MOSFET, and operates at a high
1.4MHz operating frequency to ensure a compact,
high-efficiency design with excellent AC and DC
performance. It is in a space saving SOT23-6
package.
Inductor Selection
The optimum inductor for a given application has to
be chosen with operation condition. The inductor
current waveform is a triangle with an average
value equal to the load current in continuous
conduction mode (CCM). The peak switch current is
equal to the output current plus half the peak-topeak inductor ripple current and is limited to around
1.8A to protect itself and power stage from overload
condition. Therefore, the maximum output current to
a load depends on the switch current limit, the
inductor value, and the input and output voltages.
The ACT111A is a current mode regulator. It
controls the inductor peak current by the feedback
loop during each switching cycle. Therefore, it
improves loop dynamics. In steady state operation,
a pulse from the oscillator starts a cycle to turn on
the internal top MOSFET switch. Current in the
switch and the external inductor ramps up. As the
current level reaches the voltage level defined by
the internal error amplifier output, the internal switch
is turned off. The current in the inductor flows
through the external Schottky diode. The inductor
current is continuously adjusted by the internal error
amplifier. In the ACT111A, the voltage to the FB pin
compares to the internal accurate 100mV reference
voltage to generate error signal. Therefore, as a
current sense resistor in series with LED is
connected to the FB pin, the LED current is well
regulated.
The peak-to-peak inductor ripple current is usually
controlled to 20%-30% of the output current and the
inductor value is selected accordingly by:
L =
(1)
where f is 1.4MHz switching frequency of the
ACT111A, VO is the output voltage, VF is the
Schottky diode forward voltage drop (~0.4V), and D
is switching duty cycle given by:
D =
VO + V F
V IN + V F
(2)
The inductor’s RMS current rating must be greater
than the maximum load current and its saturation
current should be at least 30% higher. For high
LED dimming can be performed by directly
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( 1 − D )( V O + V F )
ΔIL × f
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ACT111A
Rev 0, 14-Feb-11
efficiency and good thermal condition, the inductor
DC resistance (DCR) should be less than 0.25Ω.
The peak inductor and switch current is:
I L( PK ) = I SW ( PK ) = IO +
ΔI L
Rectifier Diode Selection
Use a Schottky diode as the rectifier to conduct
current when the ACT111A internal top MOSFET
switch is off. In steady state operation, average
forward current in the diode is:
(3)
2
VIN − VO
VIN
The peak current must be less than the current limit
to maintain output regulation.
ID _ AVG = IO
Input Capacitor Selection
The Schottky diode must have current rating
higher than the maximum output current and the
reverse voltage rating higher than the maximum
input voltage.
A step-down regulator draws pulsing current from
input source. The input capacitor is required to
reduce the voltage ripple at the ACT111A input and
force the pulsing current into a local loop to
minimize EMI. The input capacitor must have low
impedance at the switching frequency to effectively
reduce the voltage ripple and EMI, and it must have
an adequate RMS ripple current rating. The RMS
current for the input capacitor is:
ICIN _ RMS = IO ×
VO (VIN − VO )
VIN
<
IO
2
(6)
PWM and Analog Dimming
There are two dimming schemes to control LED
average current during steady state operation. As
those applications requiring a PWM logic signal to
control dimming, the PWM signal could be directly
applied to the DIM pin of the ACT111A as shown in
Figure 1. The LEDs turn on with full load to
completely turn off. The average LED current
increase proportionally to the duty cycle of the
PWM signal. The turn-on threshold voltage is 1.66V
with 100mV hysteresis. The frequency of the PWM
signal is from 100 Hz up to 10 kHz.
(4)
For best performance choose a ceramic type
capacitor with X5R or X7R dielectrics due to their
low ESR and small temperature coefficients.
However, low ESR tantalum or electrolytic types
may also be used, provided that the RMS ripple
current rating is higher than 50% of the output
current. For most applications, a 10μF capacitor is
sufficient. The input capacitor should be placed
close to the IN and G pins of the ACT111A, with
shortest possible traces. In the case of tantalum or
electrolytic types, connect a small parallel 0.1μF
ceramic capacitor right next to the ACT111A.
If analog dimming scheme is preferred in an
application, a DC voltage to control the FB voltage,
as shown in Figure 2 is used. As the DC voltage
increases from 0 to certain level determined by the
application like 5V, current starts to flow down RDIM,
R1 and RS. As the control loop maintains the
feedback voltage VFB to be 100mV, the current
through the LEDs will linearly decrease to zero.
Output Capacitor Selection
Figure 1:
A ceramic capacitor with X5R or X7R dielectric
provides the best results over a wide range of
applications. The output capacitor also needs to
have low ESR to keep low output voltage ripple.
The output ripple voltage is:
PWM Dimming
VO _ RIPPLE = IO × K RIPPLE × ESR +
IO × K RIPPLE
8 × f × CO
ACT111A
PWM
RS
(5)
where IO is the output current, KRIPPLE is the ripple
factor (typically 20% to 30%), ESR is the equivalent
series resistor of the output capacitor, f is 1.4MHz
switching frequency, L is the inductor value, and CO
is the output capacitance. In the case of ceramic
output capacitors, ESR is very small and does not
contribute to the ripple. In the case of tantalum or
electrolytic type, the ripple is dominated by ESR
multiplied by the ripple current. In this case, the
output capacitor is chosen to have low ESR
capacitor with ESR typically less than 50mΩ.
Innovative PowerTM
R1
FB
DIM
Figure 2:
Analog Dimming
VDIM
ACT111A
DIM
RDIM
FB
R1
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ACT111A
Rev 0, 14-Feb-11
The following equation determines resistor values:
R DIM = R1
VDIM (MAX ) − VFB
(7)
VFB
According to the equation, Table 1 shows the
respective resister values with different DC dimming
voltage. VTB is 100mV, R1 is chosen to be 30kΩ.
Table 1:
Open LED Protection
VDIM(MAX) (V)
R1 (kΩ)
RDIM (kΩ)
5
30
1470
3.3
30
976
2
30
576
In case of LED failure, the ACT111A will operate at
maximum duty cycle due to the feedback voltage
drops to zero. This will results in the output voltage
moving up. To prevent over voltage on the output, a
Zener and a series resistor are used as shown in
Figure 3 and Figure 6 (ZD1 and R4).
Thermal Shutdown
The ACT111A automatically turns off when the IC
junction temperature exceeds 160°C, and reenables
when the IC junction temperature drops by 10°C (typ).
PC Board Layout
To achieve good performance, it is extremely
important to have optimized component placement
and layout on PCB for a high switching frequency
and high efficiency regulator. Here are
recommendations for the layout: Place input
capacitor to IN pin, inductor and diode to SW pin as
close as possible to reduce the voltage ringing at
these pins. Place the current sense resistor close to
FB pin. Minimize ground noise by connecting high
current ground returns, the input capacitor ground
lead, and the output filter ground lead to a single
point (star ground configuration). There are two
power loops in normal operation, one is formed
when the SW is high and the high current flows
through input capacitor, internal MOSFET, inductor,
LEDs, RSENSE to ground. The other loop is through
inductor, LEDs, RSENSE, ground to diode. Make
these loop areas as small as possible to minimize
noise interaction. SW pad is a noisy node switching
from VIN to GND. It should be isolated away from
the rest of circuit for good EMI and low noise
operation.
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ACT111A
Rev 0, 14-Feb-11
TYPICAL APPLICATIONS
Figure 3:
12VAC Input 3x0.35A LED Driver with PWM Dimming
Efficiency vs. Load Current
Output Current (mA)
Efficiency (%)
90
VIN =12VAC
80
70
60
300
ACT111A-007
VIN =12VDC
Output Current vs. Input Voltage
400
ACT111A-006
100
380
360
340
320
300
400
500
600
12
700
15
18
21
24
Input Voltage (V)
Load Current (mA)
Figure 4:
Figure 5:
PCB Top Layer
PCB Bottom Layer
18mm
11.8mm
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ACT111A
Rev 0, 14-Feb-11
Table 2:
Bill of Material
ITEM
REFERENCE
DESCRIPTION
MANUFACTURER
1
U1
IC, ACT111A
2
C1
Capacitor Tantalum, 47µF/25V, E Case
AVX
3
C2
Capacitor, Ceramic, 0.01µF/50V, 0603
POE
4
C3
Capacitor, Ceramic, 100pF/25V, 0603
POE
5
C4
Capacitor Tantalum, 47µF/16V, D Case
AVX
6
D1 - D4
7
D5
8
ZD1
9
Active-Semi
Diode Schottky, 40V/1A, SS14, SMA
PANJIT
Schottky Barrier Rectifier, SR24, 40V/2.0A, SMB
PANJIT
Diode Zener, GLZ13A, 13V, 0.5W, MINI-MELF
PANJIT
R1
Meter Film Resistor, 30kΩ, 0603, 5%
TY-OHM
10
R2
Meter Film Resistor, 0.28Ω, 1206, 1%
TY-OHM
11
R4
Meter Film Resistor, 510Ω, 1206, 5%
TY-OHM
12
L1
SMD Power Inductor, SR0604100ML, 10µH, ±20%
QianRu
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ACT111A
Rev 0, 14-Feb-11
Figure 6:
24VDC Input 5×0.7A LED Driver with PWM Dimming
Efficiency vs. Load Current
Output Current (mA)
90
80
70
750
700
650
600
60
300
ACT111A-009
Efficiency (%)
Output Current vs. Input Voltage
800
ACT111A-008
100
400
500
600
12
700
15
18
21
24
Input Voltage (V)
Load Current (mA)
Figure 7:
Figure 8:
PCB Top Layer
PCB Bottom Layer
30mm
18mm
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ACT111A
Rev 0, 14-Feb-11
Table 3:
Bill of Material
ITEM
REFERENCE
1
U1
IC, ACT111A
2
C1
Capacitor Tantalum, 47µF/35V, E Case
AVX
3
C3
Capacitor, Ceramic, 0.01µF/50V, 0603
POE
4
C4
Capacitor, Ceramic, 100pF/25V, 0603
POE
5
C5
Capacitor Tantalum, 10µF/25V, D Case
AVX
6
D1
Schottky Barrier Rectifier, SR24, 40V/2.0A, SMB
PANJIT
7
ZD1
Diode Zener, GLZ21A, 21V, 0.5W, MINI-MELF
PANJIT
8
R1
Meter Film Resistor, 30kΩ, 0603, 5%
TY-OHM
9
R2
Meter Film Resistor, 0.14Ω, 1206, 1%
TY-OHM
10
R4
Meter Film Resistor, 1kΩ, 1206, 5%
TY-OHM
11
L1
SMD Power Inductor, SR0604100ML, 10µH, ±20%
QianRu
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DESCRIPTION
MANUFACTURER
Active-Semi
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ACT111A
Rev 0, 14-Feb-11
PACKAGE OUTLINE
SOT23-6 PACKAGE OUTLINE AND DIMENSIONS
D
θ
SYMBOL
0.2
E
E1
c
e
A
A1
A2
e1
DIMENSION IN
INCHES
MIN
MAX
MIN
MAX
A
-
1.450
-
0.057
A1
0.000
0.150
0.000
0.006
A2
0.900
1.300
0.035
0.051
b
0.300
0.500
0.012
0.020
c
0.080
0.220
0.003
0.009
L
b
DIMENSION IN
MILLIMETERS
D
2.900 BSC
0.114 BSC
E
1.600 BSC
0.063 BSC
E1
2.800 BSC
0.110 BSC
e
0.950 BSC
0.037 BSC
e1
1.900 BSC
0.075 BSC
L
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 life-support 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
[email protected] or visit http://www.active-semi.com.
®
is a registered trademark of Active-Semi.
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