A8180K5R [AITSEMI]
HIGH BRIGHTNESS LED DRIVER WITH INTERNAL SWITCH;
| 型号： | A8180K5R |
| 厂家： | 
AiT Semiconductor |
| 描述： | HIGH BRIGHTNESS LED DRIVER WITH INTERNAL SWITCH 驱动 |
| 文件： | 总19页 (文件大小：694K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
A8180
AiT Semiconductor Inc.
www.ait-ic.com
LED LIGHTING DRIVER
HIGH BRIGHTNESS LED DRIVER WITH INTERNAL SWITCH
DESCRIPTION
FEATURES
Simple low parts count
Internal 32V NDMOS switch
Up to 1.4A 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 32V
Output shutdown
Up to 1MHz switching frequency
Inherent open-circuit LED protection
Typical 4% output current accuracy
High-side current sense
Hysteretic control: no compensation
Adjustable constant LED current
Over temperature protection
Available in SOT89-5 package
The A8180 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 32V and provides an externally
output current up to 1.4A. Depending upon supply
voltage and external components, this can provides up
to 24 watts of output power.
The A8180 includes the output switch and a high-side
output current sensing circuit, which uses an external
resistor to set the nominal average output current.
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
The A8180 is available in SOT89-5 Package.
TYPICAL APPLICATION
ORDERING INFORMATION
Package Type
Part Number
A8180K5R
A8180K5VR
SOT89-5
SPQ: 1,000pcs/Reel
K5
V: Halogen free Package
R: Tape & Reel
Note
AiT provides all RoHS products
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LED LIGHTING DRIVER
HIGH BRIGHTNESS LED DRIVER WITH INTERNAL SWITCH
PIN DESCRIPTION
Top View
Pin #
Symbol
LX
Function
1
2
Drain of NDMOS switch
Ground (0V)
GND
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
3
ADJ
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
4
5
ISENSE
Input voltage (6V to 32V). Decouple to ground with 4.7uF or higher X7R
ceramic capacitor close to device
VIN
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LED LIGHTING DRIVER
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ABSOLUTE MAXIMUM RATINGS
VIN, Input Supply Voltage
-0.3V ~ +40V
+0.3V ~ -5V(NOTE1)
-0.3V ~ +40V
-0.3V ~+6V
1.7A
VISENSE, ISENSE Voltage
VLX, LX Output Voltage
VADJ, Adjust Pin Input Voltage
ILX, Switch Output Current
Maximum Junction Temperature
Operating Temperature Range NOTE2
Storage Temperature Range
Lead Temperature (Soldering, 10s)
150°C
-40°C ~ 125°C
-55°C ~ 150°C
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 A8180 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
Package
SOT89-5
θJA
θJC
160°C/W
45°C/W
NOTE: Thermal Resistance is specified with approximately 1 square of 1 oz copper.
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ELECTRICAL CHARACTERISTICS
Test conditions: VIN =12V, TA = 25°C, unless otherwise noted
Parameter
Symbol
VIN
VUVLO
VUVLO(HYS)
IQ(OFF)
Conditions
Min
6
Typ.
Max
32
Units
V
V
V
μA
Input voltage
Under voltage lock out
UVLO hysteresis
Quiescent supply current with output off
Quiescent supply current with output
switching
VIN rising
VIN falling
ADJ Pin grounded
ADJ Pin floating
f=250kHz
5.07
4.87
120
IQ(ON)
1.8
50
mA
mV
Measure on ISENSE pin
Mean current sense threshold voltage
VISENSE
96
100
104
with respect to VIN
Sense threshold hysteresis
ISENSE pin input current
ADJ pin floating voltage
VSENSE(HYS)
ISENSE
VADJ
±15
1.2
4
%
μA
V
VISENSE=VIN-0.1
ADJ pin floating
ADJ pin grounded
10
ADJ pin leakage current
IADJ
5
μA
ADJ pin pull up resistor to internal
supply voltage
RADJ
1
MΩ
DC voltage on ADJ pin to switch device
from active (on) state to quiescent (off) state
DC voltage on ADJ pin to switch device
from quiescent (off) state to active (on) state
Digital dimming ADJ pin input voltage high
Digital dimming ADJ pin input voltage low
DC brightness control
Recommended Digital dimming frequency
Duty cycle range of PWM signal applied to
ADJ pin during low frequency PWM
dimming mode
VADJ(OFF)
VADJ(ON)
VADJ falling
VADJ rising
0.15
0.2
0.25
0.3
V
0.2
1.5
0.25
V
VADJ(H)
VADJ(L)
VADJ(DC)
fADJ
V
V
V
0.2
1.2
20
0.3
0.1
kHz
fADJ=100Hz
fADJ =10kHz
0.1
100
％
％
DPWM(LF)
Brightness control range
1000:1
Duty cycle range of PWM signal applied to
ADJ pin during high frequency PWM
dimming mode
5
100
DPWM(HF)
Brightness control range
LX switch on resistance
LX switch leakage
20:1
0.35
0.1
RLX
ILX(LEAK)
0.7
5
1.4
Ω
μΑ
A
Continuous LX switch current
ILX(MEAN)
Delay time between
ADJ pin rising edge
and LX pin falling edge
Delay time between
ADJ pin falling edge
and LX pin rising edge
Chip enable delay time
Chip disable delay time
tEN,DELAY
480
25
ns
ns
tENB,DELAY
Recommended maximum operating frequency
Over temperature protection threshold
Over temperature protection hysteresis
fLX(MAX)
TOTP
TSD(HYS)
1
MHz
℃
Temperature rising
Temperature falling
160
20
℃
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LED LIGHTING DRIVER
HIGH BRIGHTNESS LED DRIVER WITH INTERNAL SWITCH
TYPICAL PERFORMANCE CHARACTERISTICS
Test conditions: VIN =12V, RS=0.1Ω, TA = 25°C, unless otherwise noted.
1. Efficiency vs. Supply Voltage
L=33uH
2. Output Current Variation vs. Supply Voltage
L=33uH
3. Operating Frequency vs. Input Voltage
L=33uH
4. Duty Cycle vs. Input Voltage
L=33uH
5. Output Current vs. Supply Voltage
L=33uH
6. Output Current Variation vs. Supply Voltage
L=47uH
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LED LIGHTING DRIVER
HIGH BRIGHTNESS LED DRIVER WITH INTERNAL SWITCH
7. Operating Frequency vs. Supply Voltage
L=47uH
8. Duty Cycle vs. Supply Voltage
L=47uH
9. Output Current vs. Supply Voltage
L=47uH
10. Output Current variation vs. Supply Voltage
L=100uH
11. Operating Frequency vs. Supply Voltage
L=100uH
12. Duty Cycle vs. Supply Voltage
L=100uH
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13. Output Current vs. Supply Voltage
14. VADJ vs. Supply Voltage
L=33uH
L=100uH
15. Supply Current vs. Supply Voltage
L=33uH
16. Shutdown Current vs. Supply Voltage
17. LED Current vs. VADJ
18. LX Switch “on” Resistance vs. Temperature
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19. VADJ vs. Temperature
20. Voltage across RSENSE vs. Temperature
L=47uH
L=47uH
21. Output Current Change vs. Temperature
L=47uH
22. Output Current Change vs. Temperature
L=47uH
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BLOCK DIAGRAM
SOT89-5
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DETAILED INFORMATION
The device, 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 (VIN- VISENSE
)
< 85mV, the switch turns on again and the mean current on the LED is determined by
85 +115
(
)mV / RS = 100mV / RS
2
The high-side current-sensing scheme and on-board current-setting circuitry minimize the number of external
components while delivering LED current with ±4% accuracy, using a 1% sense resistor.
The A8180 allows dimming with a PWM signal at the ADJ input. A logic level below 0.2V at ADJ forces A8180
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
nominal average 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 1.0 MΩ) 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 1.0 MΩ 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
A8180 is built with a thermal shutdown (TSD) protection and a thermal pad. The TSD protests the IC from
over temperature (160℃). Also the thermal pad enhances power dissipation. As a result, the A8180 can
handle a large amount of current safely.
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HIGH BRIGHTNESS LED DRIVER WITH INTERNAL SWITCH
Setting Nominal Average Output Current with External Resistor RS
The nominal average output current in the LED(s) is determined by the value of the external current sense
resistor (RS) connected between VIN and ISENSE and is given by:
0.1
IOUT
=
RS
This equation is valid when ADJ pin is float or applied with a voltage higher than 1.2V (must be less than or
equal to 5V). Actually, RS sets the maximum average current which can be adjusted to a less one by dimming.
The table below gives values of nominal average output current for several preferred values of current setting
resistor (RS) in the typical application circuit shown on page 1.
Nominal Average Output Current (mA)
RS(Ω)
0.1
1000
760
667
333
0.13
0.15
0.3
Output Current Adjustment by External DC Control
The ADJ pin can be driven by an external dc voltage (VADJ), as shown, to adjust the output current to a value
below the nominal average value defined by RS.
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LED LIGHTING DRIVER
HIGH BRIGHTNESS LED DRIVER WITH INTERNAL SWITCH
The average output current is given by:
ADJ (0.3V≤VADJ≤1.2V)
0.1xV
1.2xR
IOUT
=
S
Note that 100% brightness setting corresponds to: (1.3V≤VADJ≤5V)
Output Current Adjustment by PWM Control
A Pulse Width Modulated (PWM) signal with duty cycle PWM can be applied to the ADJ pin, as shown below,
to adjust the output current to a value below the nominal average value set by resistor RS:
0.1xD
IOUT
=
(0≤D≤100%, 1.2V≤VADJ≤5V)
RS
V
PULSEx0.1xD
IOUT
=
(0≤D≤100%, 0.3V≤VPULSE≤1.2V)
1.2xR
S
PWM dimming provides reduced brightness by modulating the LED’s forward current between 0% and
100%.The LED brightness is controlled by adjusting the relative ratios of the on time to the off time. A 25%
brightness level is achieved by turning the LED on at full current for 25% of one cycle. To ensure this
switching process between on and off state is invisible by human eyes, the switching frequency must be
greater than 100 Hz. Above 100 Hz, the human eyes average the on and off times, seeing only an effective
brightness that is proportional to the LED’s on-time duty cycle. The advantage of PWM dimming is that the
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forward current is always constant, therefore the LED color does not vary with brightness as it does with
analog dimming. Pulsing the current provides precise brightness control while preserving the color purity.
The dimming frequency of A8180 can be as high as 20 kHz.
Shutdown Mode
Taking the ADJ pin to a voltage below 0.2V will turn off the output and the supply current will fall to a low
standby level of 50μA nominal.
Soft-start
An external capacitor from the ADJ pin to ground will provide soft-start delay, by increasing the time taken for
the voltage on this pin to rise to the turn-on threshold. Adding capacitance increases this delay by
approximately 0.06ms/nF.
Inherent Open-Circuit LED Protection
If the connection to the LED(s) is open circuited, the coil is isolated from the LX pin of the chip, so the device
will not be damaged.
Capacitor Selection
A low ESR capacitor should be used for input decoupling, as the ESR of this capacitor appears in series with
the supply source impedance and lowers overall efficiency. This capacitor has to supply the relatively high
peak current to the coil and smooth the current ripple on the input supply. A minimum value of 4.7uF is
acceptable if the input source is close to the device, but higher values will improve performance at lower input
voltages, especially when the source impedance is high. The input capacitor should be placed as close as
possible to the IC.
For maximum stability over temperature and voltage, capacitors with X7R, X5R, or better dielectric are
recommended. Capacitors with Y5V dielectric are not suitable for decoupling in this application and should
not be used.
Inductor Selection
Recommended inductor values for the A8180 are in the range 27uH to 100uH. Higher values of inductance
are recommended at lower output current in order to minimize errors due to switching delays, which result in
increased ripple and lower efficiency. Higher values of inductance also result in a smaller change in output
current over the supply voltage range. The inductor should be mounted as close to the device as possible with
low resistance connections to the LX and VIN pins. The chosen coil should have a saturation current higher
than the peak output current and a continuous current rating above the required mean output current. Suitable
coils for use with the A8180 are listed in the table below:
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L (uH)
33
47
68
100
DCR (Ω)
ISAT (A)
2.3
2
1.6
0.093
0.128
0.213
0.304
1.3
The inductor value should be chosen to maintain operating duty cycle and switch 'on'/'off' times within the
specified limits over the supply voltage and load current range.
The following equations can be used as a guide.
LX Switch 'On' time
L x ΔI
IN - VLED -IAVG x (R
tON
=
V
S
+ R +RLX)
L
LX Switch 'Off' time
L x ΔI
+ IAVG x (R
tOFF
=
V
LED + V
D
S
+ R )
L
Where:
L is the coil inductance (H)
RL is the coil resistance (Ω)
RS is the current sense resistance (Ω)
I
AVG is the required LED current (A)
ΔI is the coil peak-peak ripple current (A)
(Internally set to 0.3 x IAVG
VIN is the supply voltage (V)
)
VLED is the total LED forward voltage (V)
R
LX is the switch resistance (Ω) (=0.35Ω nominal)
VD is the diode forward voltage at the required load current (V)
Diode Selection
For maximum efficiency and performance, the rectifier (D1) should be a fast low capacitance Schottky diode
with low reverse leakage at the maximum operating voltage and temperature. They also provide better
efficiency than silicon diodes, due to a combination of lower forward voltage and reduced recovery time. It is
important to select parts with a peak current rating above the peak coil current and a continuous current rating
higher than the maximum output load current. It is very important to consider the reverse leakage of the diode
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when operating above 85°C. Excess leakage will increase the power dissipation in the device and if close to
the load may create a thermal runaway condition. The higher forward voltage and overshoot due to reverse
recovery time in silicon diodes will increase the peak voltage on the LX output. If a silicon diode is used, care
should be taken to ensure that the total voltage appearing on the LX pin including supply ripple, does not
exceed the specified maximum value.
Reducing Output Ripple
Peak to peak ripple current in the LED(s) can be reduced, if required, by shunting a capacitor CLED across the
LED(s) as shown below:
A value of 1uF will reduce the supply ripple current by a factor three (approx.). Proportionally lower ripple can
be achieved with higher capacitor values. Note that the capacitor will not affect operating frequency or
efficiency, but it will increase start-up delay and reduce the frequency of dimming, by reducing the rate of rise
of LED voltage. By adding this capacitor the current waveform through the LED(s) changes from a triangular
ramp to a more sinusoidal version without altering the mean current value.
Operation at Low Supply Voltage
The internal regulator disables the drive to the switch until the supply has risen above the startup threshold
(VUVLO). Above this threshold, the device will start to operate. However, with the supply voltage below the
specified minimum value, the switch duty cycle will be high and the device power dissipation will be at a
maximum. Care should be taken to avoid operating the device under such conditions in the application, in
order to minimize the risk of exceeding the maximum allowed die temperature. (See next section on thermal
considerations). The drive to the switch is turned off when the supply voltage falls below the under-voltage
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threshold (VUVLO-0.2V). This prevents the switch working with excessive 'on' resistance under conditions
where the duty cycle is high.
Thermal Considerations
When operating the device at high ambient temperatures, or when driving maximum load current, care must
be taken to avoid exceeding the package power dissipation limits. The graph below gives details for power
derating. This assumes the device to be mounted on a 25mm2 PCB with 1oz copper standing in still air.
Note that the device power dissipation will most often be a maximum at minimum supply voltage. It will
also increase if the efficiency of the circuit is low. This may result from the use of unsuitable coils, or
excessive parasitic output capacitance on the switch output.
Thermal Compensation of Output Current
High luminance LEDs often need to be supplied with a temperature compensated current in order to maintain
stable and reliable operation at all drive levels. The LEDs are usually mounted remotely from the device, so
internal circuits for the A8180 have been optimized to minimize the change in output current when no
compensation is employed. If output current compensation is required, it is possible to use an external
temperature sensing network - normally using Negative Temperature Coefficient (NTC) thermistors and/or
diodes, mounted very close to the LED(s). The output of the sensing network can be used to drive the ADJ pin
in order to reduce output current with increasing temperature.
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Thermal Shutdown Protection
To ensure the reliability, the A8180 is built with a thermal shutdown (TSD) protection function. The TSD
protests the IC from over temperature (160℃). When the chip temperature decreases (140℃), the IC
recovers again.
Layout Considerations
Careful PCB layout is critical to achieve low switching losses and stable operation. Use a multilayer board
whenever possible for better noise immunity. Minimize ground noise by connecting high-current ground
returns, the input bypass-capacitor ground lead, and the output-filter ground lead to a single point (star ground
configuration).
LX Pin
The LX pin of the device is a fast switching node, so PCB tracks should be kept as short as possible. To
minimize ground 'bounce', the ground pin of the device should be soldered directly to the ground plane.
Coil and Decoupling Capacitors and Current Sense Resistor
It is particularly important to mount the coil and the input decoupling capacitor as close to the device pins as
possible to minimize parasitic resistance and inductance, which will degrade efficiency. It is also important to
minimize any track resistance in series with current sense resistor RS. It’s best to connect VIN directly to one
end of RS and ISENSE directly to the opposite end of RS with no other currents flowing in these tracks. It is
important that the cathode current of the Schottky diode does not flow in a track between RS and VIN as this
may give an apparent higher measure of current than is actually because of track resistance.
ADJ Pin
The ADJ pin is a high impedance input, so when left floating, PCB traces to this pin should be as short as
possible to reduce noise pickup. ADJ pin can also be connected to a voltage between 1.2V~5V. In this case,
the internal circuit will clamp the output current at the value which is set by ADJ=1.2V.
High Voltage Traces
Avoid running any high voltage traces close to the ADJ pin, to reduce the risk of leakage due to board
contamination. Any such leakage may raise the ADJ pin voltage and cause excessive output current. A
ground ring placed around the ADJ pin will minimize changes in output current under these conditions.
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PACKAGE INFORMATION
Dimension in SOT89-5 (Unit: mm)
MILLIMETERS
INCHES
Symbol
Min
Max
Min
Max
A
b
1.397
0.356
0.406
2.388
3.397
0.787
4.394
1.397
1.600
0.508
0.533
2.591
4.242
1.194
4.597
1.702
0.055
0.014
0.016
0.094
0.155
0.031
0.173
0.055
0.063
0.020
0.021
0.102
0.167
0.047
0.181
0.067
b1
B
C
C1
D
D1
e
1.500 TYP
0.060 TYP
H
0.356
0.432
0.014
0.017
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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 server 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.
REV3.0
- APR 2010 RELEASED, JAN 2017 UPDATED -
- 19 -
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