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PDF AAT1239-1 Data sheet ( Hoja de datos )
| Número de pieza | AAT1239-1 | |
| Descripción | 40V Step-Up Converter | |
| Fabricantes | Advanced Analogic Technologies | |
| Logotipo |  |
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SwitchRegTM
PRODUCT DATASHEET
AAT1239-1
40V Step-Up Converter for 4 to 10 White LEDs
General Description
The AAT1239-1 is a high frequency, high efficiency con-
stant current boost converter capable of driving up to
ten (10) series-connected white LEDs or 40V. It is an
ideal power solutions for backlight applications with up
to ten white LEDs in series. The input voltage is 2.7V to
5.5V for single-cell lithium-ion/polymer (Li-ion) based
portable devices.
The LED current is digitally controlled across a 6x oper-
www.DataaSthienegt4rUa.cnogme using AnalogicTech’s Simple Serial Control™
(S2Cwire™) interface. Programmability across 26 dis-
crete current steps provides high resolution, low noise,
flicker-free, constant LED outputs. In programming
AAT1239 operation, LED brightness increases based on
the data applied at the EN/SET pin. The SEL logic pin
changes the feedback voltage between two program-
mable ranges.
The AAT1239-1 features a high current limit and fast,
stable transitions for stepped or pulsed current applica-
tions. The high switching frequency (up to 2MHz) pro-
vides fast response and allows the use of ultra-small
external components, including chip inductors and
capacitors. Fully integrated control circuitry simplifies
design and reduces total solution size. The AAT1239-1
offers a true load disconnect feature which isolates the
load from the power source while in the OFF or disabled
state. This eliminates leakage current, making the devic-
es ideally suited for battery-powered applications.
The AAT1239-1 is available in the Pb-free, thermally-
enhanced 12-pin TSOPJW package.
Typical Application
Features
• Input Voltage Range: 2.7V to 5.5V
• Maximum Continuous Output 40V @ 30mA
• Drives up to 10 LEDs in Series
▪ Constant LED Current with 3.5% Accuracy Over
Temperature and Input Voltage Range
• Digital Control with S2Cwire Single Wire Interface
▪ 26 Discrete Steps
▪ No PWM Control Required
▪ No Additional Circuitry
• Up to 82% Efficiency
• Up to 2MHz Switching Frequency Allows Small External
Chip Inductor and Capacitors
• Hysteretic Control
▪ No External Compensation Components
▪ Excellent Load Transient Response
▪ High Efficiency at Light Loads
• Integrated Soft Start with No External Capacitor
• True Load Disconnect Guarantees <1.0μA Shutdown
Current
• Selectable Feedback Voltage Ranges for High Resolution
Control of Load Current
• Short-Circuit, Over-Voltage, and Over-Temperature
Protection
• 12-Pin TSOPJW Package
• -40°C to +85°C Temperature Range
Applications
• Color Display Backlight
• Digital Still Cameras (DSCs)
• Digital Photo Frames
• PDAs and Notebook PCs
• White LED Drivers
Li-Ion:
VIN = 2.7V to 4.2V
C1
2.2μF
Enable/Set
Feedback Voltage
Select
PVIN
VIN
LIN
SW
AAT1239-1
OVP
EN/SET
SEL
FB
PGND AGND
L1
2.2μH
DS1
SS16L or equivalent
R2
374k
R3
12k
ILED
20mA
R1 (RBALLAST)
30.1
C2
2.2μF
M673
White LEDs
OSRAM LW M678
or equivalent
1239-1.2007.10.1.0
www.analogictech.com
1
1 page  
SwitchRegTM
Typical Characteristics
Efficiency vs. LED Current
(10 White LEDs; RBALLAST = 30.1Ω)
80
78
76 VIN = 5V
74
72
www.DataSheet4U.com
70
68 VIN = 4.2V
VIN = 3.6V
66
2 4 6 8 10 12 14 16 18
ILED (mA)
20
PRODUCT DATASHEET
AAT1239-1
40V Step-Up Converter for 4 to 10 White LEDs
Efficiency vs. LED Current
(9 White LEDs; RBALLAST = 30.1Ω)
78
VIN = 5V
76
74
72
70 VIN = 4.2V
VIN = 3.6V
68
66
2 4 6 8 10 12 14 16 18
ILED (mA)
20
Shutdown Current vs. Input Voltage
(EN = GND)
1.0
0.8
0.6
85°C
0.4
25°C
0.2 -40°C
0.0
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
Input Voltage (V)
Line Transient
(10 White LEDs; RBALLAST = 30.1Ω)
33.2
33
32.8
3.6V
4.2V
0.62
0.6
0.58
Time (50µs/div)
2.0
1.5
1.0
0.5
0.0
-0.5
-1.0
-1.5
-2.0
2.7
Accuracy ILED vs. Input Voltage
(VFB = 0.6V; RBALLAST = 30.1Ω)
-40°C
25°C 85°C
3.2 3.7 4.2 4.7 5.2 5.7
Input Voltage (V)
1.5
1.0
0.5
0.0
-0.5
-1.0
-1.5
-40
Accuracy ILED vs. Temperature
(VFB = 0.6V; RBALLAST = 30.1Ω)
-15 10 35 60
Temperature (°C)
85
1239-1.2007.10.1.0
www.analogictech.com
5
5 Page 
SwitchRegTM
PRODUCT DATASHEET
AAT1239-1
40V Step-Up Converter for 4 to 10 White LEDs
Application Information
Over-Voltage Protection
OVP Protection with Open Circuit Failure
The OVP protection circuit consists of a resistor network
tied from the output voltage to the OVP pin (see Figure
1). To protect the device from open circuit failure, the
resistor divider can be selected such that the over-volt-
www.DataSahgeeet4thUr.ceosmhold occurs prior to the output reaching 40V
(VOUT(MAX)). The value of R3 should be selected from 10kΩ
to 20kΩ to minimize losses without degrading noise
immunity.
R2
=
R3
·
⎛
⎝
VOUT(MAX)
VOVP
-
1⎞⎠
AAT1239-1
OVP
GND
VOUT
R2
R3
COUT
Figure 1: Over-Voltage Protection Circuit.
1.238V
1.142V
40
30
4
2
0
Time (4ms/div)
Figure 2: Over-Voltage Protection
Open Circuit Response (No LED).
Assume R3 = 12kΩ and VOUT(MAX) = 40V. Selecting 1%
resistor for high accuracy, this results in R2 = 374kΩ
(rounded to the nearest standard value). The minimum
OVP threshold can be calculated:
V = VOUT(OVP_MIN)
·OVP(MIN)
⎛
⎝
R2
R3
+ 1⎞⎠
= 35.4V
To avoid OVP detection and subsequent reduction in the
programmed output current (see following section), the
maximum operating voltage should not exceed the
minimum OVP set point.
V < VOUT(MAX)
OUT(OVP_MIN)
In some cases, this may disallow configurations with
high LED forward voltage (VFLED) and/or greater than ten
series white LEDs. VFLED unit-to-unit tolerance can be as
high as +15% of nominal for white LED devices.
OVP Constant Voltage Operation
Under closed loop constant current conditions, the out-
put voltage is determined by the operating current, LED
forward voltage characteristics (VFLED), quantity of series
connected LEDs (N), and the feedback pin voltage (VFB).
VOUT = VFB + N · VFLED
When the rising OVP threshold is exceeded, switching is
stopped and the output voltage decays. Switching auto-
matically restarts when the output drops below the
lower OVP hysteresis voltage (100mV typical) and, as a
result, the output voltage increases. The cycle repeats,
maintaining an average DC output voltage proportional
to the average of the rising and falling OVP levels (mul-
tiplied by the resistor divider scaling factor). High oper-
ating frequency and small output voltage ripple ensure
DC current and negligible flicker in the LED string(s).
The waveform in Figure 3 shows the output voltage and
LED current at cold temperature with a ten series white
LED string and VOVP = 40V. As shown, the output voltage
rises as a result of the increased VFLED which triggers the
OVP constant voltage operation. Self heating of the
LEDs triggers a smooth transition back to constant cur-
rent control.
1239-1.2007.10.1.0
www.analogictech.com
11
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| Páginas | Total 21 Páginas | |
| PDF Descargar | [ Datasheet AAT1239-1.PDF ] | |
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