AIMTRON AT1313X-GRE

AT1313
High Efficiency, Constant Current
White-LED Driver
Feature
Description
•Operating Voltage:2.5V~5.5V
The AT1313 step-up converter drives white LEDs
with a constant current to provide backlight in cell
phones, PDAs, and other hand-held devices. It
features allowing series connection of the white
LEDs so that the LED currents are identical for
uniform brightness. An enable input can be pulsed
repeatedly to adjust LED’s brightness. The fast 1.4
MHz current-mode PWM control allows for smaller
capacitor and inductor. Fault condition protection
uses cycle-by-cycle current limiting to sense
maximum inductor current, thermal protection and
over-voltage protection. Also included soft-start
eliminates inrush current during start-up. The 0.2V
low reference voltage minimized the power loss
across the current-setting resistor.
•High Operating Frequency: 1.4MHz
•High Output Voltage: Up to 18V
•Shutdown Current <1µA
•18V Output Over-voltage protection
•Digital Dimming Control.
•Built-in Cycle-by Cycle Current-limiting.
•Built-in Soft-Start Function.
•0.2V Low Reference Voltage
•Tiny SOT-26 Package
Application
• LED Module
• Compact Back Light Module
• Constant Current Source
The AT1313 is available in 6-pin SOT-26 packages.
Block Diagram
VIN
LX
ON/OFF
Control
Logic / PWM
Dimming
Control
EN
VREF
0.2V
Soft-Start
VBG
1.23V
CTL
VREF
N
+
Control Logic
FB
OVP
18V
Current Limit
1.2A
VBG
+
Overvoltage
Protection
+
-
-
CTL
GND
Aimtron reserves the right without notice to change this circuitry and specifications.
7F, No.9, PARK AVENUE II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C.
Tel: 886-3-563-0878
Fax: 886-3-563-0879
WWW: http://www.aimtron.com.tw
10/31/2006 REV:2.0
Email:service@aimtron.com.tw
1
AT1313
High Efficiency, Constant Current
White-LED Driver
Pin Configuration
Ordering Information
Part number
AT1313X_GRE
▲▲▲▲▲
Package
SOT-26, Green
Marking
313, Date Code with one bottom line
: Date Code
*For more marking information, contact our sales representative directly
Pin Description
Pin N0.
1
2
Symbol
LX
GND
I/O
I
P
3
FB
I
4
EN
I
5
6
OVP
VIN
I
P
Description
Step-up Regulator N-MOS Drain. Place output diode and inductor.
Ground
Step-Up Regulator Feedback Input. Connect a sense resistor from FB to
ground.
Enable and Dimming Control Input. LED brightness and IC shutdown are
controlled by the voltage on EN. Driving low for longer than 4ms to
shutdown the IC.
Over-voltage protection input. Connect to the output.
Power supply.
Absolute Maximum Ratings[note1]
Parameter
VIN voltage
LX , OVP voltage
EN , FB to GND
Switch Current (ILX)
Continuous power dissipation (SOT-26 Ta=+25OC)
Operating Junction Temperature Range
Lead Temperature (Soldering 5 sec)
Storage Temperature
Package Thermal Resistance (ΘJA)
ESD Susceptibility (HBM)
ESD Susceptibility (MM)
Rated Value
-0.3 to +6.0
-0.3 to +18
-0.3 to +6.0
1.2
0.35
-35 to 85
260
-65 to 125
250
2
200
Unit
V
V
V
A
W
℃
℃
℃
℃/W
KV
V
Note1:Permanent device damage may occur if Absolute Maximum Ratings are exceeded. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability
7F, No.9, PARK AVENUE II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C.
Tel: 886-3-563-0878
Fax: 886-3-563-0879
WWW: http://www.aimtron.com.tw
10/31/2006 REV:2.0
Email:service@aimtron.com.tw
2
AT1313
High Efficiency, Constant Current
White-LED Driver
Recommended Operation Conditions
Parameter
Power supply voltage
Operating temperature
Symbol
Values
Typ.
─
+25
Min.
2.5
-30
VIN
Top
Unit
Max.
5.5
+85
V
℃
Electrical Characteristics
(VIN=2.5V, Ta=+25℃, unless otherwise noted)
Parameter
Operating V IN Range
Symbol
Test Condition
VIN input Voltage
VIN
Min.
2.5
-
5.5
V
Under Voltage Thershold
Switch- Off Input Current
Shutdown Current
Feedback Reference
FB Input Bias Current
Over-voltage Threshold
Over-voltage Hysteresis
OVP Leakage Current
UVLO
IIN1
IIN3
VFB
IFB
VOVP
VIN falling, 100mV hysteresis
No Switching , FB>0.2V
EN=0V
2.1
0.190
16
2.3
120
1
0.210
1
20
IOVP
EN=0V
2.5V< VIN <6.0V
-
2.2
100
0.2
18
2
-
1
V
uA
uA
V
uA
V
V
uA
-
0.1
-
%
1.4
90
0.5
1.2
0.4
4
1.6
-
MHz
%
ms
A
Ω
uA
uA
V
V
ms
ms
ms
Output Voltage Line Regulation
Switching Frequency
Maximum Duty
Soft-Start charging time
Switching Current Limit
LX ON Resistance
LX Leakage Current
EN Input Current
EN Input Level
EN low Shutdown Delay
EN Low Cycle Time
EN High Cycle Time
fOSC
DMAX
tSS
ILX
RLX
ILeakage
IEN
VIH
VIL
tCYCL
tCYCH
VFB =0.2V
VOUT Rising
VIN=3.0V,duty cycle=80% ,
VIN =2.5V, ILX =800mA
VLX =16V, EN=0V
EN=5V
Note(1)
Note(1)
1.2
0.05
2.0
0.05
0.05
Typ. Max. Units
1
1
0.5
5
5
Note(1): tCYCL and tCYCH are included rising time and falling time of PWM signal.
7F, No.9, PARK AVENUE II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C.
Tel: 886-3-563-0878
Fax: 886-3-563-0879
WWW: http://www.aimtron.com.tw
10/31/2006 REV:2.0
Email:service@aimtron.com.tw
3
AT1313
High Efficiency, Constant Current
White-LED Driver
Typical Characteristics
Efficiency vs. Vin (3 LED)
L:SR0302 D:RB501-40
Efficiency vs. Vin (4 LED)
L:SR0302 D:RB501-40
94
94
92
92
90
90
Efficiency (%)
Efficiency (%)
88
86
84
88
86
82
84
80
Io=100mA, L=22uH
78
Io=100mA, L=10uH
Io=100mA, L=22uH
82
Io=100mA, L=10uH
Io=100mA,L=6.8uH
Io=100mA,L=6.8uH
76
2
3
4
5
80
6
2
Vin (V)
3
4
5
6
Vin (V)
CH1:LX CH3:VOUT Ripple CH4:ILX
Conversion Efficiency
L:SR0302 D:RB501-40
100
Efficiency (%)
95
90
85
80
4LEDs, L=22uH,Vin=3V
75
3LEDs,L=22uH,Vin=3V
70
50
60
70
80
90
100
LED CURRENT(mA)
CH1:EN
CH3:FB
PWM Dimming Control Using the EN Pin
Switching Transient Waveform
CH1:EN CH3:FB CH4:IIN
Start-Up Waveform
7F, No.9, PARK AVENUE II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C.
Tel: 886-3-563-0878
Fax: 886-3-563-0879
WWW: http://www.aimtron.com.tw
10/31/2006 REV:2.0
Email:service@aimtron.com.tw
4
AT1313
High Efficiency, Constant Current
White-LED Driver
Application Circuit
10uH
MBR140WS
VIN
3.6V to 4.2V
4.7uF
4.7uF
VIN
LX
OVP
AT1313
ON
OFF
PWM
Signal
FB
EN
GND
2
Figure 1a. AT1313 Typical Application Circuit with 100mA Output .
10uH
MBR140WS
VIN
4.7uF
4.7uF
VIN
LX
OVP
AT1313
ON
OFF
PWM
Signal
FB
EN
0.333
GND
From DSP
1
AO3400
Figure 1b. AT1313 Typical Application Circuit with 200mA Output .
7F, No.9, PARK AVENUE II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C.
Tel: 886-3-563-0878
Fax: 886-3-563-0879
WWW: http://www.aimtron.com.tw
10/31/2006 REV:2.0
Email:service@aimtron.com.tw
5
AT1313
High Efficiency, Constant Current
White-LED Driver
Application Circuit
10uH
MBR140WS
VIN
5.0V
4.7uF
10uF
VIN
LED1
……
LED12
10uF
LX
OVP
……
AT1313
ON
OFF
PWM
Signal
FB
EN
GND
Figure 1c. AT1313 for Innolux 8” Panel LED Back light unit
1.2
2.7
.
7F, No.9, PARK AVENUE II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C.
Tel: 886-3-563-0878
Fax: 886-3-563-0879
WWW: http://www.aimtron.com.tw
10/31/2006 REV:2.0
Email:service@aimtron.com.tw
6
AT1313
High Efficiency, Constant Current
White-LED Driver
Function Description
The AT1313 is a high efficiency and constant current DC-DC converter IC which is designed primarily
for use in LED module applications. The output voltage of the step-up converter can be set from Vin to
16V with external sense resistor. The device suits to drive series-connected LEDs and provides even
illumination by sourcing the same output current through each LED. AT1313 also consists of a logic
shutdown , cycle-by-cycle current-limited , soft-start functions.
Logic control input or PWM duty cycle control allows easy adjustment of LEDs brightness and on/off
control. The average LED current is proportionable the duty-cycle of the PWM signal. Typical PWM
frequency should be between 100Hz and 1kHz.
The boost converter operates in current-mode PWM and a constant frequency of 1.4 MHz. Depending
on duty cycle of each switching cycle can regulate output voltage. On the rising edge of the internal
clock , the control and driver logic block sets internal flip-flop when the output voltage is too low,
which turns on the N-MOS. The external inductor current ramps up linearly, storing energy in a
magnetic filed. Once peak current of inductor over trans-conductance output level , the N-MOS turns
off, the flip-flop resets, and external schottky diode turns on. This forces the current through the
inductor to ramp back down, transferring the energy stored in the magnetic field to the output capacitor
and LEDs. To reduce external component amount , the device will be built-in internal loop
compensation.
Enable Control
Digital logic of EN provides an electrical ON/OFF control of the power supply. Connecting this pin to
ground or to any voltage less than 0.5V and sustain the level over 4ms will completely turn off the
regulator. In this state, current drain from the input supply is less than 1uA, the internal reference, error
amplifier, comparators, and biasing circuitry turn off . If holding time of low level is less than 3ms on
this pin, then the device only shutdown driver logic block.
Dimming Control
Digital logic of EN also provides LEDs brightness control by applying a PWM signal on EN pin. With
this way, the LEDs operate with either zero or full current . The average LED current is proportional to
the duty-cycle of the PWM signal. Typical PWM frequency should be between 100Hz and 1kHz.
Output current is given by:
I LED =
200mV × TON − PWM
RSENSE × TS − PWM
Where:
TON-PWM : On time of PWM signal
TS-PWM : A cycle time of PWM signal
If dimming control is not required , EN works as a simple on/off control. Drive EN high to enable the
device , or drive EN low for shutdown.
7F, No.9, PARK AVENUE II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C.
Tel: 886-3-563-0878
Fax: 886-3-563-0879
WWW: http://www.aimtron.com.tw
10/31/2006 REV:2.0
Email:service@aimtron.com.tw
7
AT1313
High Efficiency, Constant Current
White-LED Driver
Soft-Start
Soft-start allows a gradual increase of the internal current-limit level for the step-up converter during
power-up to reduce input surge currents. As the internal current source charges the internal soft-start
capacitor, the peak N-MOS current is limited by the voltage on the capacitor. In another story, when
toggle or a logic-level transition on EN pin from low to high, soft-start function must work to enable
constant current charging internal capacitor. When soft-start process has finished or appeared falling
edge of PWM signal on EN pin , soft-start capacitor must be discharged to ground level.
Cycle-by-Cycle Over-Current Protection
The AT1313 provides cycle-by-cycle over-current protection. Current limit is accomplished using a
separate dedicated comparator. The cycle-by-cycle current limit abbreviates the on-time of the N-MOS
in event that the current of flowing N-MOS is greater than the current limit value. The current-limit
feature protection against a hard short or over-current fault at the output.
Over-Voltage Protection
If VOUT is above 16V or LEDs are disconnected from the circuit, the FB pin is similar to pull down to
ground with a sense resistor. This will cause N-MOS to switch with a maximum duty cycle and come
out output over-voltage. This may cause the LX pin voltage to exceed its maximum voltage rating to
damage built-in N-MOS. In the state, the OVLO protection circuitry stops the internal N-MOS . When
VOUT falls below 16V, IC will automatically recover normal operation.
Power dissipation consideration
The AT1312 maximum power dissipation depends on the thermal resistance of the IC package and
circuit board, the temperature difference between the die junction and ambient air, and the rate of any
airflow. The power dissipation in the device depends on the operating conditions of the regulator.
The step-up converter dissipates power across the internal N-MOS as the controller ramps up the
inductor current. In continuous condition, the power dissipated internally can be approximated by :
Pboost = [(
I O × VO 2 1 Vin × D 2
) ] × RDS (ON ) × D
) + (
Vin
12 f OSC × L
where
IO : It is the load current.
fOSC : It is a switching frequency.
7F, No.9, PARK AVENUE II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C.
Tel: 886-3-563-0878
Fax: 886-3-563-0879
WWW: http://www.aimtron.com.tw
10/31/2006 REV:2.0
Email:service@aimtron.com.tw
8
AT1313
High Efficiency, Constant Current
White-LED Driver
Applications Information
External components of main boost converter can be designed by performing simple calculations. It
need to follow regulation by the output voltage and the maximum load current, as well as maximum
and minimum input voltages. Begin by selecting an inductor value. Once L is know, choose the diode
and capacitors.
Boost inductor
Inductor selection depends on input voltage, output voltage, maximum current , switching frequency
and availability of inductor values. The following boost circuit equations are useful in choosing the
inductor values based on the application. They allow the trading of peak current and inductor value
while allowing for consideration of component availability and cost.
The peak inductor current is given by:
I Lpeak = I LAVG +
I LAVG =
∆I L
2
IO
1− D
where:
△IL is the inductor peak-to-peak current ripple and is decided by:
∆I L =
Vin
D
×
L
f OSC
D is the MOSFET turn on ratio and is decided by:
D=
VO −V in
VO
fOSC is the switching frequency.
The inductor should be chosen to be able to handle this current and inductor saturation current rating
should be greater than IPEAK.
Diode selection
The output diode has average current of IO, and peak current the same as the inductor’s peak current
and a voltage rating at least 1.5 times the output voltage. Schottky diode is recommended and it should
be able to handle those current.
Output Capacitor
The AT1313 is specially compensated to be stable with capacitors which have a worst- case minimum
value of 1uF at the particular VOUT being set. Output ripple voltage requirements also determine the
minimum value and type of capacitors. Output ripple voltage consists of two components the voltage
drop caused by the switching current through the ESR of the output capacitor and the charging and
discharging of the output capacitor:
7F, No.9, PARK AVENUE II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C.
Tel: 886-3-563-0878
Fax: 886-3-563-0879
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10/31/2006 REV:2.0
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9
AT1313
High Efficiency, Constant Current
White-LED Driver
V RIPPLE = I LPEAK × ESR +
VO − Vin
IO
×
VO
C OUT × f OSC
For low ESR ceramic capacitors, the output ripple is dominated by the charging or discharging of the
output capacitor.
PCB layout guidelines
Careful printed circuit layout is extremely important to avoid causing parasitical capacitance and line
inductance. The following layout guidelines are recommended to achieve optimum performance.
‧ Please the boost converter diode and inductor close to the LX pin and no via. Keep traces short,
direct, and wide.
‧ Please ceramic bypass capacitors near the input/output pin.
‧ Locate all feedback sense resistor as close to the feedback pins as possible.
‧ The ground connections of VIN and VOUT should be as close together as possible.
7F, No.9, PARK AVENUE II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C.
Tel: 886-3-563-0878
Fax: 886-3-563-0879
WWW: http://www.aimtron.com.tw
10/31/2006 REV:2.0
Email:service@aimtron.com.tw
10
AT1313
High Efficiency, Constant Current
White-LED Driver
Small Outline SOT-26
b
e
E
C
e1
D
r
E1
L
A A2
A1
SYMBOL
A
A1
A2
b
C
D
E
E1
L
e
e1
r
INCHES
MIN
0.035
0.000
0.035
0.010
0.003
0.110
0.102
0.059
0.014
MAX
0.057
0.006
0.051
0.020
0.008
0.122
0.118
0.069
0.022
0.037ref
0.075ref
00
100
MILLIMETERS
MIN
MAX
0.90
1.45
0.00
0.15
0.90
1.30
0.25
0.50
0.08
0.20
2.80
3.10
2.60
3.00
1.50
1.75
0.35
0.55
0.95ref
1.90ref
00
100
NOTES
-
-
7F, No.9, PARK AVENUE II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C.
Tel: 886-3-563-0878
Fax: 886-3-563-0879
WWW: http://www.aimtron.com.tw
10/31/2006 REV:2.0
Email:service@aimtron.com.tw
11
AT1313
High Efficiency, Constant Current
White-LED Driver
Reflow Profiles
Profile Feature
Sn-Pb Eutectic Assembly
Large Body
Small Body
Pkg. thickness
Pkg. thickness
<2.5mm or Pkg.
≥2.5mm or Pkg.
3
volume ≥350mm3 volume <350mm
Pb-Free Assembly
Large Body
Small Body
Pkg. thickness
Pkg. thickness
<2.5mm or Pkg.
≥2.5mm or Pkg.
volume<350mm3
volume ≥350mm3
Average ramp-up rate
(TL to TP)
Preheat
-Temperature Min(Tsmin)
-Temperature Max (Tsmax)
-Time (min to max)(ts)
Tsmax to TL
-Ramp-up Rate
Time maintained above:
-Temperature (TL)
-Time (tL)
Peak Temperature(TP)
Time within 5°C of actual Peak
Temperature (tP)
Ramp-down Rate
Time
25°C
to
Peak
Temperature
3°C/second max.
3°C/second max.
100°C
150°C
60-120 seconds
150°C
200°C
60-180 seconds
3°C/second max.
183°C
60-150 seconds
217°C
60-150 seconds
225+0/-5°C
10-30 seconds
240+0/-5°C
10-30 seconds
6°C/second max.
6 minutes max.
245+0/-5°C
10-30 seconds
250+0/-5°C
20-40 seconds
6°C/second max.
8 minutes max.
*All temperatures refer to topside of the package, measured on the package body surface.
7F, No.9, PARK AVENUE II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C.
Tel: 886-3-563-0878
Fax: 886-3-563-0879
WWW: http://www.aimtron.com.tw
10/31/2006 REV:2.0
Email:service@aimtron.com.tw
12