AS3145
320KHz, 2.0A Asynchronous
Step-Down LED Driver
DESCRIPTION
FEATURES
The AS3145 is a PWM buck converter designed to

Supply Voltage Range: 3.6V to 28V
provide a simple, high efficiency solution for driving

Feedback Reference Voltage: 0.25V(2%)
high power LEDs. With a 0.25V reference voltage

Low Current Consumption: 4mA
feedback control to minimize power dissipation, The

Internal Fixed Oscillator Frequency: 320KHz
AS3145 includes a high current P-MOSFET, high

Internal Soft-Start Function(SS)
efficiency and excellent transient characteristics. The

Built-in P-MOSFET for 2A Loading Capability
PWM control circuit is able to the duty ratio from o to

Over Current Protection
100%. The features include user accessible EN/DIM

Standard Package: SOP-8L
pin for enabling and PWM dimming of LEDs, thermal
shutdown, cycle-by-cycle current limit and over
APPLICATIONS
current protection.

High Power LED Driver
ORDER INFORMATION

MR16 & GU10 Solution
Part Number
Output Current

Constant Current Source
AS3145KBT
2.0A max.

General Lighting Solutions
EVALUATION BOARD
Board Number
Dimensions
EV3145-00A
50mmX x 50mmY x 1.4mmZ
“ANI” and “ANISEM” is Trademarks of ANISEM Semiconductor, Inc.
TYPICAL APPLICATION
AS3145 Rev.1.2
09/05/2010
www.anisem.com
ANISEM Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2008 ANISEM All Rights Reserved.
1
AS3145 – 320KHz, 2.0A ASYNCHRONOUS STEP-DOWN LED DRIVER
PACKAGE REFERENCE
ABSOLUTE MAXIMUM RATINGS(1)
TOP VIEW
FB
1
1
EN/DIM
2
2
COMP
3
3
SW
IN
4
4
SW
GND
GND
Part Number*
Package
Operating Temp
AS3145KBT
SOP-8L
-40°C to 125°C
Supply Voltage……..……………….….…....+28V
Output Current…..………………….….......+2.0V
FB Pin Voltage …………………….-0.3V to +1.2V
Allowable dissipation(SOP8)…………….650mW
Junction Temperature……………………….150ºC
Lead Temperature (Soldering, 10sec.) ……260°C
Storage Temperature Range ….... -55℃ to 125°C
Recommended Operating Conditions(2)
Input Voltage Range………….………3.6V to 25V
Operating Temperature ………… -40°C to 125°C
ƟJA
ƟJC
Thermal Resistance
SOT-8L………………….…..175……….45…...°C/W
NOTEs:
1)
Exceeding these ratings may damage the device.
2)
The device is not guaranteed to function outside of its operating conditions.
*Only for output voltage adjustable.
ELECTRICAL CHARACTERISTICS
VIN = VEN =12V, TA = 25°C Unless otherwise noted.
PARAMETER
CONDITIONS
Input Voltage Range
Feedback Voltage
ILOAD=0.2A
VREF change with Temp.
VIN=3.6~25V
Oscillation Frequency
VIN=3.6~25V, ILOAD=0.2~2A
Duty Cycle
MOSFET RDS(ON)
MIN
TYP
MAX
UNITS
3.6
-
25
V
0.245
0.25
0.255
V
12.5
mV
-
KHz
-
VFB=0.2V force driver ON
100
VFB=0.5V force driver OFF
0
VIN=5V, VFB=0V
70
150
VIN=12V, VFB=0V
42
90
Over Current Protection
Quiescent Current
320
%
3
VIN=3.6~25V
6
mA
-
1.12
V
1
20
uA
-1.0
-0.2
1.0
uA
0.8
EN Bias Current
FB Bias Current
A
4
VFB=0.5V force drive OFF
EN Threshold Voltage
mΩ
Linear Regulation
VIN=3.6~25V, ILOAD=0.2A
-
2
-
%
Load Regulation
ILOAD=0.2A~2A
-
0.1
-
%
Over Temp. Shutdown
150
ºC
Over Temp.Hysteresis
40
ºC
Note: 100% production test at +25℃; Specification over the temperature range are guaranteed by design.
AS3145 Rev.1.2
09/05/2010
www.anisem.com
ANISEM Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2008 ANISEM All Rights Reserved.
2
AS3145 – 320KHz, 2.0A ASYNCHRONOUS STEP-DOWN LED DRIVER
PIN FUNCTIONS
PIN NUMBER
PIN NAME
FUNCTION
1
FB
Error Amplifier Inverting Input.
2
EN
Enable Control.
3
COMP
Error Amplifier compensation Outuput.
4
IN
Power Supply (PMOS source)
5, 6
SW
PMOS high Current Output
7, 8
GND
Ground.
FUNCTION BLOCK DIAGRAM
EN
IN
2
4
ENABLE
CONTROL
REFERENCE
REGULATOR
320KHz
OSCILLATOR
OVER CURRENT
PROTECTION
2.50V
FB
1
ERROR
AMP
+
-
36K
PWM
CMP
500Ω
+
OUTPUT DRIVE
CONTROL
0.25
COMP
THERMAL
SHUTDOWN
3
INTERNAL
SOFT-START
AS3145 Rev.1.2
09/05/2010
7
8
5
6
GND
GND
SW
SW
www.anisem.com
ANISEM Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2008 ANISEM All Rights Reserved.
3
AS3145 – 320KHz, 2.0A ASYNCHRONOUS STEP-DOWN LED DRIVER
OPERATION
VOLTAGE REFERENCE
A 2.5V reference regulator supplies AS3145 internal
circuits and uses the resistive dividers to provide a
0.25V precision reference voltage on the
non-inverting terminal of error amplifier.
SETTING THE LED CURRENT
AS3145 is a constant current buck regulator. the
LEDs are connected between Vo and FB pin as
show in the typical application circuit. The FB pin is
at 0.25V in regulation and therefore the LEDs current
IF is set by VFB and the resistor R2//R3 from FB to
ground by the following equation:
IF =
VFB
R2&R3
IF should not exceed the 2A current and R2//R3
minimum must be approximately 0.13Ω.
OSCILLATOR
The fixed frequency generates from an internal
oscillator, and the typical values are 320KHz.
THERMAL PROTECTION
The thermal protection is functional due to a heavy
loading drop and junction temperature achieve
150ºC, then AS3145 output turn off. when junction
temperature is lower than 150ºC, AS3145 starts
again and power switch turns on.
OVER CURRENT PROTECTION
The AS3145 uses cycle-by-cycle current limit to
protect the internal power switch. During each
switching cycle, a current limit comparator detects if
the power switch current exceeds the internal setting
current, and begins over current protection decrease
the oscillator frequency to prevent thermal issue.
OUTPUT VOLTAGE
The output voltage is primarily determined by the
number of LEDs(n) connected from Vo to FB pin and
therefore Vo can be written as:
VOUT =(ሺn×VF ሻ+VFB )
Where VF is the forward voltage of one LED at the
set LED current level.
AS3145 Rev.1.2
09/05/2010
www.anisem.com
ANISEM Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2008 ANISEM All Rights Reserved.
4
AS3145 – 320KHz, 2.0A ASYNCHRONOUS STEP-DOWN LED DRIVER
PACKAGE DESCRIPTION
Package
8-Lead Plastic SOP-8L
4.80min
5.00max
8
7
6
5
3.80min
4.00max
1
2
3
NOTE:
1. DIMENSIONS ARE IN MILLIMETERS
2. DRAWING NOT TO SCALE
3. DIMENSIONS ARE INCLUSIVE OF PLATING
4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
5. MOLD FLASH SHALL NOT EXCEED 0.254mm
6. JEDEC PACKAGE REFERENCE IS MO-193
5.80min
6.20max
4
1.27typ.
0.35min
0.49max
4.80min
5.00max
3.80min
4.00max
1.35min
1.75max
0.40min
0.90max
AS3145 Rev.1.2
09/05/2010
1.35min
1.75max
0.25typ.
0.10min
0.25max
8°max
www.anisem.com
ANISEM Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2008 ANISEM All Rights Reserved.
5
AS3145 – 320KHz, 2.0A ASYNCHRONOUS STEP-DOWN LED DRIVER
© ANISEM Semiconductor Co., Ltd
ANISEM assume responsibility for use of any circuitry other than circuitry entirely embodied in an ANISEM product. No circuit patent licenses, copyrights,
mask work rights, or other intellectual property rights are implied. ANISEM reserves the right to make changes to their products or specifications or to
discontinue any product or service without notice. Customers are advised to obtain the latest version of relevant information to verify, before placing orders,
that information being relied on is current and complete. All products are sold subject to the terms and conditions of sale supplied at the time of order
acknowledgement, including those pertaining to warranty, patent infringement, and limitation of liability. ANISEM warrants performance of its
semiconductor products to the specifications applicable at the time of sale in accordance with ANISEM’s standard warranty. Testing and other quality
control techniques are utilized to the extent ANISEM deems necessary to support this warranty. Specific testing of all parameters of each device is not
necessarily performed.
AS3145 Rev.1.2
09/05/2010
www.anisem.com
ANISEM Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2008 ANISEM All Rights Reserved.
6