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PDF A8181 Data sheet ( Hoja de datos )
| Número de pieza | A8181 | |
| Descripción | HIGH BRIGHTNESS LED DRIVER | |
| Fabricantes | AiT Semiconductor | |
| Logotipo |  |
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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-
1 page  
AiT Semiconductor Inc.
www.ait-ic.com
Brightness control range
A8181
36V, 1.2A LED STEP-DOWN
HIGH BRIGHTNESS LED DRIVER WITH INTERNAL SWITCH
- 1000:1 -
-
Duty cycle range of PWM signal
applied to ADJ pin during high
frequency PWM dimming mode
DPWM(HF)
fADJ =10KHz
5 - 100 %
Brightness control range
- 20:1 -
-
LX switch on resistance
RLX
- 0.35 0.7 Ω
LX switch leakage
ILX(LEAK)
- 0.1 5 μA
Continuous LX switch current
ILX(MEAN)
- - 1.2 A
The delay time between
Chip enable delay time
TEN, DELAY ADJ pin rising edge and
-
480
-
ns
LX pin falling edge
The delay time between
Chip disable delay time
TENB, DELAY ADJ pin falling edge and
-
25
- ns
LX pin rising edge
Recommended maximum
operating frequency
fLX(MAX)
- - 1 MHz
Over temperature protection
threshold
TOTP
Temperature rising
- 160 - °C
Over temperature protection
hysteresis
TSD(HYS) Temperature falling
- 20 - °C
NOTE:100% production test at +25°C. Specifications over the temperature range are guaranteed by design and characterization.
REV1.0
- APR 2011 RELEASED -
-5-
5 Page 
AiT Semiconductor Inc.
www.ait-ic.com
DETAILED INFORMATION
A8181
36V, 1.2A LED STEP-DOWN
HIGH BRIGHTNESS LED DRIVER WITH INTERNAL SWITCH
The A8181, in conjunction with the coil (L1) and current sense resistor (RS), forms a self oscillating
continuous-mode buck converter. When input voltage VIN is first applied, the initial current in L1 and RS is zero
and there is no output from the current sense circuit. Under this condition, the (-) input to the comparator is at
ground and its output is high. This turns on an internal switch and switches the LX pin low, causing current to
flow from VIN to ground, via RS, L1 and the LED(s). The current rises at a rate determined by VIN and L1 to
produce a voltage ramp (VISENSE) across RS. When (VIN-VISENSE) > 115mV, the output of comparator switches
low and the switch turns off. The current flowing on the RS decreases at another rate. When (VINVISENSE) <
85mV, the switch turns on again and the mean current on the LED is determined by
The high-side current-sensing scheme and on-board current-setting circuitry minimize the number of external
components while delivering LED current with ±3% accuracy, using a 1% sense resistor.
The A8181 allows dimming with a PWM signal at the ADJ input. A logic level below 0.2V at ADJ forces A8181
to turn off the LED and the logic level at ADJ must be at least 1.2V (1.5V recommended) to turn on the full
LED current. The frequency of PWM dimming ranges from 100Hz to more than 20 kHz.
The ADJ pin can be driven by an external DC voltage (VADJ) to adjust the output current to a value below the
nominalaverage value defined by RS. The DC voltage is valid from 0.3V to 1.2V. When the dc voltage is
higher than 1.2V, the output current keeps constant. The LED current also can be adjusted by a resistor
connected to the ADJ pin. An internal pull-up resistor (typical 1.0mΩ) is connected to a 5V internal regulator.
The voltage of ADJ pin is divided by the internal and external resistor. The ADJ pin is pulled up to the internal
regulator (5V) by a 1.0mΩ resistor. It can be floated at normal working. When a voltage applied to ADJ falls
below the threshold (0.2V nom.), the output switch is turned off. The internal regulator and voltage reference
remain powered during shutdown to provide the reference for the shutdown circuit. Quiescent supply current
during shutdown is nominally 50uA and switch leakage is below 5uA. Additionally, to ensure the reliability, the
A8181 is built with a thermal shutdown (TSD) protection. The TSD protests the IC from over temperature (160
℃).
REV1.0
- APR 2011 RELEASED -
- 11 -
11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet A8181.PDF ] | |
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