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AiT Semiconductor Inc.
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A8160A
DESCRIPTION
FEATURES
current through an external current sense
Other features include current limit protection,
ORDERING INFORMATION
Package Type
Part Number
APPLICATION
TYPICAL APPLICATION
LED BACKLIGHT DRIVER
ASYNCHRONIES BOOST FOR 10WLED DRIVER
The A8160A is a step-up DC-DC converter
specifically designed for driving white LEDs with a
constant current.
The internal MOSFET can support up to 10 White
LEDs for backlighting and OLED power application,
and the internal soft start function can reduce the
inrush current.
The A8160A uses current mode, fixed frequency of
approximately 1.0MHz architecture to regulate the
LED
resistor. The low feedback voltage of 300mV can
minimize power dissipation.
thermal shutdown protection, under-voltage lockout
(UVLO), and over-voltage function.
The A8160A is available in SOT-26 package.
V
Operating Range : 2.5V to 5.5V
IN
Internal Power N-MOSFET Switch
Wide Range for PWM Dimming
(100Hz to 200kHz)
1.0MHz Switch Frequency
300mV Feedback Voltage
1.2A SW Current Limit
Minimize the External Component Counts
Internal Compensation
Over Voltage Protection
Available in SOT-26 Package
Cellular Phones and Digital Cameras
PDAs and Smart Phones and MP3 and OLED
Portable Instruments
LCD Display Power
A8160AE6R-XXX
SOT-26 E6
A8160AE6VR-XXX
XXX: Feedback Voltage
Note
030 = 300mV
R: Tape & Reel
V: Halogen free Package
AiT provides all RoHS products
Suffix “ V “ means Halogen free Package
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High-light LED Flash
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A8160A
Pin #
Symbol
Function
PIN DESCRIPTION
1 SW Switching Pin.
LED BACKLIGHT DRIVER
ASYNCHRONIES BOOST FOR 10WLED DRIVER
Top View
2 GND
Ground Pin. The exposed pad must be soldered to a large PCB and
connected to GND for maximum power dissipation.
3 FB Feedback Pin. Feedback voltage is 0.3V.
4 EN Chip Enable (Active High).
5 V
Output Voltage Pin.
OUT
6 VIN Input Supply.
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AiT Semiconductor Inc.
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A8160A
Parameter
Min
Max.
Unit
ASYNCHRONIES BOOST FOR 10WLED DRIVER
LED BACKLIGHT DRIVER
ABSOLUTE MAXIMUM RATINGS
VIN, Supply Input Voltage −0.3V to 6V
SW, Switching Pin −0.3V to 40V
V
−0.3V to 40V
OUT
Other Pins −0.3V to 6V
PD, Power Dissipation, @ TA = 25°C SOT-26 0.392W
θJA ,Package Thermal Resistance
Lead Temperature (Soldering, 10 sec.) 260°C
Junction Temperature 150°C
Storage Temperature Range −65°C to150°C
Stress beyond above listed “Absolute Maximum Ratings” may lead permanent damage to the device. These are stress ratings only and
operations of the device at these or any other conditions beyond those indicated in the operational sections of the specifications are not
implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
NOTE1: θ
51-3 thermal measurement standard.
is measured in the natural convection at TA = 25°C on a low effective single layer thermal conductivity test board of JEDEC
JA
NOTE1
SOT-26 255°C/W
RECOMMENDED OPERATING CONDITIONS
NOTE2
Junction Temperature Range −40 125 °C
Ambient Temperature Range −40 85 °C
NOTE2: The device is not guaranteed to function outside its operating conditions.
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A8160A
Parameter
Symbol
Conditions
Min.
Typ.
Max.
Unit
ASYNCHRONIES BOOST FOR 10WLED DRIVER
LED BACKLIGHT DRIVER
ELECTRICAL CHARACTERISTICS
=3.7V, CIN=2.2uF, C
V
IN
Input Voltage VIN 2.5 5.5 V
OUT
=1uF, I
=20mA, L=22uH, TA = 25°C, unless otherwise specified
OUT
Under Voltage Lock Out V
2 2.2 2.45 V
UVLO
UVLO Hystersis 0.1 V
Quiescent Current IQ FB=1.5V, No Switching 400 600 uA
Supply Current IIN FB=0V, Switching 1 2 mA
Shutdown Current I
SHDN
V
< 0.4V 1 4 uA
EN
Line Regulation VIN=3 to 4.3V 1 %
Load Regulation 1mA to 20mA 1 %
Operation Frequency f
0.75 1 1.25 MHz
OSC
Maximum Duty Cycle 90 92 %
Clock Rate 0.1 200 kHz
Feedback Reference Voltage 285 300 315 mV
On Resistance R
Logic-High Voltage V
0.7 1.2 Ω
DS(ON)
1.4 V
IH
EN Threshold
Logic-Low Voltage VIL 0.5 V
EN Sink Current VIH 1 uA
EN Hystersis 0.1 V
Over-Voltage Threshold V
Over-Current Threshold I
OTP T
OTP Hystersis 30 °C
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OCP
34 36 38 V
OVP
1.2 A
160 °C
OTP
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AiT Semiconductor Inc.
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A8160A
TYPICAL PERFORMANCE CHARACTERISTICS
LED BACKLIGHT DRIVER
ASYNCHRONIES BOOST FOR 10WLED DRIVER
1. η VS I
3. F
OSC
VS V
2. I
O
4. V
IN
VS VIN
Q
VS VIN
FB
5. V
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EN
VS V
6. I
IN
VS DUTY
LED
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AiT Semiconductor Inc.
A8160A
7. V
FB
VS I
www.ait-ic. com
ASYNCHRONIES BOOST FOR 10WLED DRIVER
8. Power on from EN
LED
LED BACKLIGHT DRIVER
9. LED Backlighting 10. LCD Display Power
11. High-light LED Flash
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AiT Semiconductor Inc.
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A8160A
BLOCK DIAGRAM
LED BACKLIGHT DRIVER
ASYNCHRONIES BOOST FOR 10WLED DRIVER
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A8160A
DETAILED INFORMATION
Applications Information
LED Current Setting
LED BACKLIGHT DRIVER
ASYNCHRONIES BOOST FOR 10WLED DRIVER
The loop of Boost structure will keep the FB pin voltage equal to the reference voltage V
R
connects FB pin and GND, the current flows from V
SET
the current on R
, which is equal to following equation.
SET
through LED and R
OUT
to GND will be decided by
SET
. Therefore, when
REF
Dimming Control
a. Using a PWM Signal to EN Pin
For the brightness dimming control of the A8160A, the IC provides typically 300mV feedback voltage when
the EN pin is pulled constantly high. However, EN pin allows a PWM signal to reduce this regulation voltage
by changing the PWM duty cycle to achieve LED brightness dimming control. The relationship between the
duty cycle and FB voltage can be calculated as following equation.
VFB = Duty x 300mV
Where
Duty = duty cycle of the PWM signal
As shown in Figure 1, the duty cycle of the PWM signal is used to cut the internal 300mV reference voltage.
An internal low pass filter is used to filter the pulse signal. And then the reference voltage can be made by
connecting the output of the filter to the error amplifier for the FB pin voltage regulation.
However, the internal low pass filter 3db frequency is 500Hz. When the dimming frequency is lower then
500Hz, V
is also a PWM signal and the LED current is controlled directly by this signal. When the frequency
A
is higher than 500Hz, PWM is filtered by the internal low pass filter and the V
LED current is a DC current which eliminate the audio noise.
But there is an offset in error amplifier which will cause the V
filtered reference voltage is low and the offset can cause bigger variation of the output current. For the
A8160A, the minimum duty vs frequency is listed in following table.
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300mV = internal reference voltage
variation. In low PWM duty signal situation, the
A
approach a DC signal. And the
A
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A8160A
ASYNCHRONIES BOOST FOR 10WLED DRIVER
LED BACKLIGHT DRIVER
Figure 1 Block Diagram of Programmable FB Voltage Using PWM Signal
Duty Minimum
Dimming frequency <500Hz 4%
Dimming frequency >500Hz 10%
b. Using a DC Voltage
Using a variable DC voltage to adjust the brightness is a popular method in some applications. The dimming
control using a DC voltage circuit is shown in Figure 2. As the DC voltage increases, the current flows through
R3 increasingly and the voltage drop on R3 increase, i.e. the LED current decreases. For example, if the V
range is from 0V to 2.8V and V
is equal to 0.3V, the selection of resistors in Figure 2 sets the LED current
REF
from 21mA to 0mA. The LED current can be calculated by the following equation.
DC
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Figure 2 Dimming Control Using a DC Voltage
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AiT Semiconductor Inc.
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A8160A
ASYNCHRONIES BOOST FOR 10WLED DRIVER
LED BACKLIGHT DRIVER
c. Using a Filtered PWM signal
Another common application is using a filtered PWM signal as an adjustable DC voltage for LED dimming
control. A filtered PWM signal acts as the DC voltage to regulate the output current. The recommended
application circuit is shown as Figure 3. In this circuit, the output ripple depends on the frequency of PWM
signal. For smaller output voltage ripple (<100mV), the recommended frequency of 2.8V PWM signal should
be above 2kHz. To fix the frequency of PWM signal and change the duty cycle of PWM signal can get
different output current. The LED current can be calculated by the following equation.
By the above equation and the application circuit shown in Figure 3. We can get the relationship between the
LED current and PWM duty cycle. For example, when the PWM duty is equal to 60%, the LED current will be
equal to 8.6mA. When the PWM duty is equal to 40%, the LED current will be equal to 12.7mA.
Power Sequence
In order to assure the normal soft start function for suppressing the inrush current the input voltage should be
ready before EN pulls high.
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Figure 3 Dimming Control Using a Filtered PWM Signal
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A8160A
ASYNCHRONIES BOOST FOR 10WLED DRIVER
LED BACKLIGHT DRIVER
Soft-Start
The function of soft-start is made for suppressing the inrush current to an acceptable value at the beginning of
power-on. The A8160A provides a built-in soft-start function by clamping the output voltage of error amplifier
so that the duty cycle of the PWM will be increased gradually in the soft-start period.
Current Limiting
The current flow through inductor as charging period is detected by a current sensing circuit. As the value
comes across the current limiting threshold, the N-MOSFET will be turned off so that the inductor will be
forced to leave charging stage and enter discharging stage. Therefore, the inductor current will not increase
over the current limiting threshold.
OVP/UVLO/OTP
The Over Voltage Protection is detected by a junction breakdown detecting circuit. Once V
detecting voltage, SW pin stops switching and the power N-MOSFET will be turned off. Then, the V
clamped to be near V
. As the output voltage is higher than a specified value or input voltage is lower than a
OVP
goes over the
OUT
OUT
will be
specified value, the chip will enter protection mode to prevent abnormal function. As the die temperature is
higher than 160°C, the chip also will enter protection mode. The power MOSFET will be turned off during
protection mode to prevent abnormal operation.
Capacitor Selection
Input ceramic capacitor of 2.2uF and output ceramic capacitor of 1uF are recommended for the A8160A
applications for driving 10 series WLEDs. For better voltage filtering, ceramic capacitors with low ESR are
recommended. X5R and X7R types are suitable because of their wider voltage and temperature ranges.
Inductor Selection
The recommended value of inductor for 10 WLEDs applications is from 10uH to 47uH. Small size and better
efficiency are the major concerns for portable devices, such as the A8160A used for mobile phone. The
inductor should have low core loss at 1.0MHz and low DCR for better efficiency. The inductor saturation
current rating should be considered to cover the inductor peak current.
Thermal Considerations
For continuous operation, do not exceed absolute maximum operation junction temperature. The maximum
power dissipation depends on the thermal resistance of IC package, PCB layout, the rate of surroundings
airflow and temperature difference between junction to ambient. The maximum power dissipation can be
calculated by following formula:
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A8160A
LED BACKLIGHT DRIVER
ASYNCHRONIES BOOST FOR 10WLED DRIVER
Where T
P
is the maximum operation junction temperature, TA is the ambient temperature and the θJA is
J(MAX)
D(MAX)
=(T
J(MAX)−TA
) /θJA
the junction to ambient thermal resistance.
For the recommended operating conditions specification of A8160A, the maximum junction temperature of the
die is 125°C. The junction to ambient thermal resistance θ
is layout dependent. The junction to ambient
JA
thermal resistance for SOT-26 package is 255°C/W on the standard JEDEC 51-3 single layer thermal test
board. The maximum power dissipation at T
P
=(125°C−25°C)/(255°C/W)=0.392W
D(MAX)
The maximum power dissipation depends on operating ambient temperature for fixed T
resistance θ
. For A8160A packages, the Figure 4 of derating curves allows the designer to see the effect or
JA
=25°C can be calculated by following formula:
A
and thermal
J(MAX)
rising ambient temperature on the maximum power allowed.
Layout Consideration
For best performance of the A8160A, the following guidelines must be strictly followed.
Input and Output capacitors should be placed close to the IC and connected to ground plane to reduce
noise coupling.
The GND and Exposed Pad should be connected to a strong ground plane for heat sinking and noise
protection.
Keep the main current traces as possible as short and wide.
SW node of DC-DC converter is with high frequency voltage swing. It should be kept at a small area.
Place the feedback components as close as possible to the IC and keep away from the noisy devices.
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Figure 6 Derating Curves for A8160A Packages
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A8160A
SYMBOL
MIN
MAX
PACKAGE INFORMATION
Dimension in SOT-26 Package (Unit: mm)
LED BACKLIGHT DRIVER
ASYNCHRONIES BOOST FOR 10WLED DRIVER
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A 1.050 1.250
A1 0.000 0.100
A2 1.050 1.150
b 0.300 0.500
c 0.100 0.200
D 2.820 3.020
E 1.500 1.700
E1 2.650 2.950
e 0.950(BSC)
e1 1.800 2.000
L 0.300 0.600
θ 0° 8°
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A8160A
ASYNCHRONIES BOOST FOR 10WLED DRIVER
LED BACKLIGHT DRIVER
IMPORTANT NOTICE
AiT Semiconductor Inc. (AiT) reserves the right to make changes to any its product, specifications, to
discontinue any integrated circuit product or service without notice, and advises its customers to obtain the
latest version of relevant information to verify, before placing orders, that the information being relied on is
current.
AiT Semiconductor Inc.'s integrated circuit products are not designed, intended, authorized, or warranted to
be suitable for use in life support applications, devices or systems or other critical applications. Use of AiT
products in such applications is understood to be fully at the risk of the customer. As used herein may involve
potential risks of death, personal injury, or servere property, or environmental damage. In order to minimize
risks associated with the customer's applications, the customer should provide adequate design and
operating safeguards.
AiT Semiconductor Inc. assumes to no liability to customer product design or application support. AiT
warrants the performance of its products of the specifications applicable at the time of sale.
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