Document
AiT Semiconductor Inc.
www.ait-ic.com
A8181
36V, 1.2A LED STEP-DOWN HIGH BRIGHTNESS LED DRIVER WITH INTERNAL SWITCH
DESCRIPTION
The A8181 is a continuous mode inductive step-down converter, designed for driving single or multiple series connected LEDs efficiently from a voltage source higher than the LED voltage. The device operates from an input supply between 6V and 36V and provides an externally output current up to 1.2A. Depending upon supply voltage and external components, this can provides up to 24 watts of output power.
The A8181 includes the output switch and a high-side output current sensing circuit, which uses an external resistor to set the nominal average output current.
FEATURES
Simple low parts count Internal 36V NDMOS switch Up to 1.2A output current Single pin on/off and brightness control using
DC voltage or PWM Soft Start High efficiency (up to 97%) Wide input voltage range: 6V to 36V Output shutdown Up to 1MHz switching frequency Inherent open-circuit LED protection Typical 3% output current accuracy High-side current sense Hysteretic control: no compensation Adjustable constant LED current Over temperature protection Available in SOT-25 package
Output current can be adjusted by applying an external control signal to the 'ADJ' pin. The ADJ pin will accept either a DC voltage or a PWM waveform. During DC dimming, this will provide a continuous output current that is proportional to the external applied DC voltage. During the PWM dimming, this will provide a gated output current and the average current is proportional to the duty cycle. Applying a voltage of 0.2V or lower to the ADJ pin turns the output off and switches the device into a low current standby state.
APPLICATIONS
Low voltage halogen replacement LEDs Automotive lighting Low voltage industrial lighting LED back-up lighting Illuminated signs LCD TV backlighting
TYPICAL APPLICATION
The A8181 is available in SOT-25 Packages.
ORDERING INFORMATION
Package Type
Part Number
SOT-25 Note
E5
A8181E5R A8181E5VR
V: Green Package
R : Tape & Reel
AiT provides all Pb free products Suffix “ V “ means Green Package
REV1.0
- APR 2011 RELEASED -
-1-
AiT Semiconductor Inc.
www.ait-ic.com
PIN DESCRIPTION
A8181
36V, 1.2A LED STEP-DOWN HIGH BRIGHTNESS LED DRIVER WITH INTERNAL SWITCH
Pin # 1 2
3
4 5
TOP VIEW
Symbol
Function
LX GND
ADJ
ISENSE VIN
Drain of NDMOS switch Ground(0V) Multi-function On/Off and brightness control pin: Leave floating for normal operation. Drive to voltage below 0.2V to turn off output current Drive with DC voltage (0.3V < VADJ < 1.2V) to adjust output current from
25% to 100% of IOUTnom. If the ADJ voltage is larger than 1.2V, the output current is IOUTnom. Drive with PWM signal from open-collector or open-drain transistor, to adjust output current. Connect a capacitor from this pin to ground to activate soft-start. (soft-start time is approx.0.06ms/nF) Connect resistor RS from this pin to VIN to define nominal average output current IOUTnom = 0.1/RS Input voltage (6V to 36V). Decouple to ground with 4.7uF or higher X7R ceramic capacitor close to device
REV1.0
- APR 2011 RELEASED -
-2-
AiT Semiconductor Inc.
www.ait-ic.com
ABSOLUTE MAXIMUM RATINGS
A8181
36V, 1.2A LED STEP-DOWN HIGH BRIGHTNESS LED DRIVER WITH INTERNAL SWITCH
VIN, Input Supply Voltage
-0.3V to +40V
VISENSE, ISENSE Voltage
+0.3V to -5V NOTE1
VLX, LX Output Voltage
-0.3V to +40V
VADJ, Adjust Pin Input Voltage
-0.3V to +6V
ILX, Switch Output Current
1.5A
Maximum Junction Temperature
150°C
Operating Temperature Range NOTE2
-40°C to 125°C
Storage Temperature Range
-55°C to 150°C
Lead Temperature (Soldering, 10s)
300°C
Stresses above may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at
these or any other conditions beyond those indicated in the Electrical Characteristics is not implied. Exposure to absolute maximum
rating conditions for extended periods may affect device reliability.
NOTE1: VISENSE measured respect to VIN. NOTE2: The A8181 is guaranteed to meet performance specifications from 0°C to 70°C. Specifications over the -40°C to 125°C
operating temperature range are assured by design, characterization and correlation with statistical process controls.
THERMAL RESISTANCE NOTE3
Package
θJA
SOT-25
250°C/W
NOTE3: Thermal Resistance is specified with approximately 1 square of 1 oz copper.
θJC 130°C/W
REV1.0
- APR 2011 RELEASED -
-3-
AiT Semiconductor Inc.
www.ait-ic.com
ELECTRICAL CHARACTERISTICS
A8181
36V, 1.2A LED STEP-DOWN HIGH BRIGHTNESS LED DRIVER WITH INTERNAL SWITCH
Test conditions: VIN =12V, TA = 25°C, unless otherwise noted.
Parameter
Symbol
Conditions
Input voltage
VIN
Under voltage lock out
VUVLO
VIN Rising
UVLO hysteresis
VUVLO(HYS) VIN falling
Quiescent supply current with output off
IQ(OFF)
ADJ Pin grounded
Quiescent supply current with out.