AIMTRON AT1312AX-GRE

AT1312A/B/C
Preliminary Product Information
High Efficiency, Constant Current
White-LEDs Driver
Feature
Description
The AT1312A/B/C step-up converter drives white
•Operating Voltage:2.5V to 6.0V.
LEDs with a constant current to provide backlight in
•High Operating Frequency: 1MHz
cell phones, PDAs, and other hand-held devices. It
•High Output Voltage: Up to 16V/23V/28V
features allowing series connection of the white
LEDs so that the LED currents are identical for
•Shutdown Current <1µA
uniform brightness. An enable input can be pulsed
•16V/23V/28V Output Over-Voltage Protection repeatedly to adjust LED’s brightness. The fast 1.0
•Digital Dimming Control.
MHz current-mode PWM control allows for smaller
capacitor and inductor. Fault condition protection
•Built-in Cycle-by Cycle Current-Limiting.
uses cycle-by-cycle current limiting to sense
•Built-in Soft-Start Function.
maximum inductor current, thermal protection and
•0.2V Low Reference Voltage
over-voltage protection. Also included soft-start
eliminates inrush current during start-up. The 0.2V
•Tiny SOT-26 Package
low reference voltage minimized the power loss
across the current-setting resistor.
Application
• LED Module
• Compact Back Light Module
• Constant Current Source
The AT1312A/B/C is available in 6-pin SOT-26
packages.
Block Diagram
Aimtron reserves the right without notice to change this circuitry and specifications.
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Tel: 886-3-563-0878
Fax: 886-3-563-0879
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1
AT1312A/B/C
Preliminary Product Information
High Efficiency, Constant Current
White-LEDs Driver
Pin Configuration
SOT-25
(TOP VIEW)
VIN OVP EN
5
6
4
312
1
LX
A:1312AX
B:1312BX
C:1312CX
2
3
GND FB
Ordering Information
Part number
Package
Current
Limit
AT1312AX
SOT-26
400mA
AT1312AX_GRE SOT-26, Green 400mA
OVP
Protection
28V
28V
AT1312BX
SOT-26
AT1312BX_GRE SOT-26, Green
300mA
300mA
23V
23V
AT1312CX
SOT-26
AT1312CX_GRE SOT-26, Green
200mA
200mA
16V
16V
Marking
Date Code
,Date Code with one bottom
line
Date Code
,Date Code with one bottom
line
Date Code
,Date Code with one bottom
line
: Date Code
*For more marking information, contact our sales representative directly
Pin Description
Pin N0.
Symbol
I/O
Description
1
LX
I
Step-up Regulator N-MOS Drain. Place output diode and inductor.
2
GND
P
Ground
3
FB
I
4
EN
I
5
6
OVP
VIN
I
P
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.
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Tel: 886-3-563-0878
Fax: 886-3-563-0879
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2
AT1312A/B/C
Preliminary Product Information
High Efficiency, Constant Current
White-LEDs Driver
Absolute Maximum Ratings*1
Parameter
Rated Value
Unit
VIN voltage
-0.3 to +6.5
V
LX , OVP voltage
-0.3 to +28
V
EN , FB to GND
-0.3 to +6.5
V
0.6
A
Continuous power dissipation (SOT-26 Ta=+25 C)
0.35
W
Operating Junction Temperature Range
-30 to 85
℃
Lead Temperature (Soldering 5 sec)
260
℃
Storage Temperature
-65 to 125
℃
Package Thermal Resistance (ΘJA)
250
Switch Current (ILX)
O
ESD Susceptibility*2
HBM
2
MM
200
℃/W
KV
V
1. Stresses beyond those listed under “Absolute Maximum Ratings” 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 operational sections of the specifications is not implied. Exposure
to absolute maximum rating conditions for extended periods may affect device reliability.
2. Device are ESD sensitive. Handling precaution recommended. The Human Body model is a 100pF
capacitor discharged through a 1.5KΩ resistor into each pin.
Recommended Operation Conditions
Parameter
Symbol
Power supply voltage
VIN
Operating temperature
Top
Min.
Values
Typ.
Max.
2.5
―
6.0
V
-20
+25
+85
℃
Unit
7F, No.9,PARK AVENUE. II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C.
Tel: 886-3-563-0878
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3
AT1312A/B/C
Preliminary Product Information
High Efficiency, Constant Current
White-LEDs Driver
Electrical Characteristics
(VIN=2.5V, Ta=+25℃, unless otherwise noted)
Parameter
Symbol
Test Condition
Min.
Typ. Max. Units
Operating V IN Range
VIN
VIN input Voltage
2.5
-
6.0
V
Under Voltage Thershold
UVLO
VIN falling, 100mV hysteresis
2.1
2.2
2.3
V
Switch- Off Input Current
IIN1
No Switching
-
100
120
µA
Shutdown Current
IIN3
EN=0V
-
-
1
µA
Feedback Reference
VFB
0.190
0.2
0.210
V
FB Input Bias Current
IFB
Over-voltage Threshold
VOVP
-
28
23
16
1
25
18
µA
V
V
V
VFB =0.2V
VOUT Rising (AT1312A)
VOUT Rising (AT1312B)
VOUT Rising (AT1312C)
Over-voltage Hysteresis
OVP Leakage Current
2
IOVP
Output Voltage Line Regulation
EN=0V
2.5V< VIN <6.0V
V
-
-
1
µA
-
0.1
-
%
Switching Frequency
fOSC
-
1
-
MHz
Maximum Duty
DMAX
-
90
-
%
Soft-Start charging time
tSS
0.05
0.5
-
ms
-
400
-
mA
-
300
-
mA
LX ON Resistance
RLX
VIN=3.0V,duty cycle=80% ,
(AT1312A)
VIN=3.0V,duty cycle=80% ,
(AT1312B)
VIN=3.0V,duty cycle=80% ,
(AT1312C)
VIN =2.5V, ILX =200mA
LX Leakage Current
ILeakage
VLX =16V/23V/28V, EN=0V
-
-
5
µA
EN Input Current
IEN
EN=5V
-
-
1
µA
VIH
0.1V hysteresis
2.0
-
-
V
-
-
0.8
V
-
4
-
ms
Switching Current Limit
EN Input Level
ILX
VIL
EN low Shutdown Delay
-
200
-
mA
-
0.3
-
Ω
EN Low Cycle Time
tCYCL
*1
0.05
-
5
ms
EN High Cycle Time
tCYCH
*1
0.05
-
5
ms
-
120
-
℃
Thermal Shutdown
*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
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4
AT1312A/B/C
Preliminary Product Information
High Efficiency, Constant Current
White-LEDs Driver
Typical Characteristics
Conversion Efficiency
L:SR0302 D:RB501-40
Efficiency vs. Vin (3 LED)
L:SR0302 D:RB501-40
5
7
Efficiency (%)
0
8
V
3
=
n
i
V
,
H
u
2
2
=
L
,
s
D
E
L
6
H
u
2
2
=
L
,
A
m
0
2
=
o
I
Efficiency (%)
5
8
H
u
0
1
=
L
,
A
m
0
2
=
o
I
V
3
=
n
i
V
,
H
u
2
2
=
L
,
s
D
E
L
4
0
7
H
u
8
.
6
=
L
,
A
m
0
2
=
o
I
V
3
=
n
i
V
,
H
u
2
2
=
L
,
s
D
E
L
3
H
u
7
.
4
=
L
,
A
m
0
2
=
o
I
5
6
0 8
8 8
6 8
4 8
8 7
6 7
2 7
0
2 8
0 7
4 7
9
0
9
L=22uH
Io=20mA,
L=10uH
Efficiency (%)
Efficiency (%)
Io=20mA,
Io=20mA, L=6.8uH
Io=20mA,L=4.7u
3
4
Vin (V)
6
L:SR0302 D:RB501-40
2
5
Efficiency vs. Vin (6 LED)
L:SR0302 D:RB501-40
Efficiency vs. Vin (4 LED)
90
88
86
84
82
80
78
76
74
72
70
4
3
2
0
2
5
1
0
1
5
0
Vin (V)
LED CURRENT(mA)
H 5
6
90
88
86
84
82
80
78
76
74
72
70
Io=20mA, L=22uH
Io=20mA, L=10uH
Io=20mA,L=6.8uH
Io=20mA,L=4.7uH
2
3
4
Vin (V)
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5
5
6
AT1312A/B/C
Preliminary Product Information
High Efficiency, Constant Current
White-LEDs Driver
Efficiency vs. Vin (4 LED)
L:SR0302 D:RB501-40
90
88
88
86
86
84
84
82
82
Efficiency (%)
90
80
78
78
H
u
0
1
=
L
70
H
u
7
.
4
=
L
,
A
m
0
1
=
o
I
H
u
7
.
4
=
L
,
A
m
0
1
=
o
I
72
H
u
8
.
6
=
L
,
A
m
0
1
=
o
I
74
H
u
0
1
=
L
,
A
m
0
1
=
o
I
H
u
2
2
=
L
76
H
u
8
.
6
=
L
,
A
m
0
1
=
o
I
72
,
A
m
0
1
=
o
I
74
,
A
m
0
1
=
o
I
76
80
H
u
2
2
=
L
,
A
m
0
1
=
o
I
Efficiency (%)
Efficiency vs. Vin (6 LED)
L:SR0302 D:RB501-40
70
2
3
4
5
6
2
3
4
5
Vin (V)
Vin (V)
Ch1:LX
Ch2:ILX
Ch3:Vo
Ch1:LX :10V/div , Ch2:ILX: 200mA/div, Ch3: Vo :100mV/div ,0.2uS/div
Switching Transient Waveform
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6
6
AT1312A/B/C
Preliminary Product Information
High Efficiency, Constant Current
White-LEDs Driver
Ch1:FB
Ch2:EN
Ch1:FB : 200mV/div , Ch2:ENABLE: 2V/div ,0.2mS/div
PWM Dimming Control Using the EN Pin
Ch1:IIN
Ch2:FB
Ch3:EN
Ch1:IIN : 200mA/div , Ch2:FB: 100mV/div , Ch3:ENABLE:2V/div ,0.5mS/div
Start-Up Waveform
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7
AT1312A/B/C
Preliminary Product Information
High Efficiency, Constant Current
White-LEDs Driver
Application Circuit
※ Use the tantalum capacitor to eliminate inductor noise on output terminal when you want to control dimming
function.
7F, No.9,PARK AVENUE. II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C.
Tel: 886-3-563-0878
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8
AT1312A/B/C
Preliminary Product Information
High Efficiency, Constant Current
White-LEDs Driver
Prevent Emission Caused by White LEDs Leakage
7F, No.9,PARK AVENUE. II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C.
Tel: 886-3-563-0878
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9
AT1312A/B/C
Preliminary Product Information
High Efficiency, Constant Current
White-LEDs Driver
Function Description
The AT1312 series are 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/23V/28V 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. AT1312 series
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 proportional to 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 1.0
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 components, 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 0.7V 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
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10
AT1312A/B/C
Preliminary Product Information
High Efficiency, Constant Current
White-LEDs Driver
high to enable the device , or drive EN low for shutdown.
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 AT1312 series 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/23V/28V( for AT1312A/B/C) 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 OVP protection circuitry stops the
internal N-MOS. When VOUT falls below 14V/21V/26V, IC will automatically recover
normal operation.
Thermal-Overload Protection
Thermal-overload protection limits total power dissipation in the AT1312 series.
When the junction temperature exceeds Tj=130 ℃, a thermal sensor activates the
thermal protection, which shuts down the IC, allowing the IC to cool. Once the device
cools down by 10 ℃, IC will automatically recover normal operation. For continuous
operation , do not exceed the absolute maximum junction-temperature rating of
Tj=120 ℃.
Power dissipation consideration
The AT1312 series 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. In continuous condition, the
step-up converter power dissipated internally across the internal N-MOS can be
approximated by :
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AT1312A/B/C
Preliminary Product Information
High Efficiency, Constant Current
White-LEDs Driver
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.
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AT1312A/B/C
Preliminary Product Information
High Efficiency, Constant Current
White-LEDs Driver
Application Information
External components of boost converter can be designed by performing simple
calculations.
Boost inductor
Inductor selection depends on input voltage, output voltage, maximum output 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:
V
D
∆I L = in ×
L
f OSC
D is the MOSFET turn on ratio and is decided by:
V −V in
D= O
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 AT1312 series are 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:
V − Vin
IO
V RIPPLE = I LPEAK × ESR + O
×
VO
C OUT × f OSC
For low ESR ceramic capacitors, the output ripple is dominated by the charging or
discharging of the output capacitor.
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13
AT1312A/B/C
Preliminary Product Information
High Efficiency, Constant Current
White-LEDs Driver
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 resistors 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
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14
AT1312A/B/C
Preliminary Product Information
High Efficiency, Constant Current
White-LEDs 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
00
MAX
0.057
0.006
0.051
0.020
0.008
0.122
0.118
0.069
0.022
0.037ref
0.075ref
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
-
-
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Tel: 886-3-563-0878
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15
AT1312A/B/C
Preliminary Product Information
High Efficiency, Constant Current
White-LEDs Driver
Reflow Profiles
Profile Feature
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
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
3°C/second max.
Pb-Free Assembly
Large Body
Small Body
Pkg. thickness
Pkg. thickness
≥2.5mm or Pkg.
≥2.5mm or Pkg.
3
volume ≥350mm
volume ≥350mm3
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
3°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
2/23/2006 REV:1.1
Email: service@aimtron.com.tw
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