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AAT1239-1 Schematic ( PDF Datasheet ) - Advanced Analogic Technologies

Teilenummer AAT1239-1
Beschreibung 40V Step-Up Converter
Hersteller Advanced Analogic Technologies
Logo Advanced Analogic Technologies Logo 




Gesamt 21 Seiten
AAT1239-1 Datasheet, Funktion
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






AAT1239-1 Datasheet, Funktion
SwitchRegTM
Typical Characteristics
Soft Start
(10 White LEDs; VFB = 0.6V)
0.6 3.3V
0.4 0V
0.2
0
www.DataSheet4U.com
2
1
0
Time (200µs/div)
PRODUCT DATASHEET
AAT1239-1
40V Step-Up Converter for 4 to 10 White LEDs
Soft Start
(10 White LEDs; VFB = 0.3V)
0V 0V
0.4
0.2
0
3.3V
2
1
0
Time (200µs/div)
Shutdown
(10 White LEDs; VFB = 0.6V)
3.3V
0V
0.6
0.4
0.2
0
0.5
0.0
Time (100µs/div)
Shutdown
(10 LEDs; VFB = 0.3V)
3.3V
0V
0.4
0.2
0
Time (50µs/div)
0.5
0
Output Ripple
(10 White LEDs; VIN = 3.6V; COUT = 2.2µF; ILED = 13mA)
VOUT
(AC Coupled)
(20mV/div)
VSW
(20V/div)
IL
(500mA/div)
Time (200ns/div)
Output Ripple
(10 White LEDs; VIN = 3.6V; COUT = 2.2µF; ILED = 20mA)
VOUT
(AC Coupled)
(20mV/div)
VSW
(20V/div)
IL
(500mA/div)
Time (200ns/div)
6
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1239-1.2007.10.1.0

6 Page









AAT1239-1 pdf, datenblatt
SwitchRegTM
PRODUCT DATASHEET
AAT1239-1
40V Step-Up Converter for 4 to 10 White LEDs
VOUT
(5V/div)
Over-Voltage Protection
Cold Temperature Apply Self-Recovery
ILED
(200mA/div)
where:
VFB(MAX) = 0.4V when SEL = Low
VFB(MAX) = 0.6V when SEL = High
i.e., for a maximum LED current of 20mA (SEL = High):
RBALLAST =
VFB
ILED(MAX)
=
0.6
0.020
= 30Ω 30.1Ω
www.DataSheet4U.coFmigure 3: Over-Voltage Protection
Constant Voltage Operation
(10 White LEDs; ILED = 20mA;
R2 = 12kΩ; R3 = 374kΩ).
While OVP is active, the maximum LED current program-
ming error (ΔILED) is proportional to voltage error across
an individual LED (ΔVFLED).
ΔVFLED =
(N · VFLED(TYP) - VOUT(OVP_MIN) - VFB)
N
To minimize the ΔILED error, the minimum OVP voltage
(VOUT(OVP_MIN)) may be increased, yielding a corresponding
increase in the maximum OVP voltage (VOUT(OVP_MAX)).
Measurements should confirm that the maximum switch-
ing node voltage (VSW(MAX)) is less than 45V under worst-
case operating conditions.
VSW(MAX) =
VOVP(MAX) ·
R3
R2
+ 1⎞⎠ + VF + VRING
VF = -Schottky Diode DS1 forward voltage at turn-OFF
VRING = Voltage ring occurring at turn-OFF
LED Selection and Current Setting
The AAT1239-1 is well suited for driving white LEDs with
constant current. Applications include main and sub-LCD
display backlighting, and color LEDs.
The LED current is controlled by the FB voltage and the
ballast resistor. For maximum accuracy, a 1% tolerance
resistor is recommended.
The ballast resistor (RBALLAST) value can be calculated as
follows:
R = VIBALLAST
FB(MAX)
LED(MAX)
Maximum ILED
Current (mA)
30
25
20
15
10
5
RBALLAST (Ω)
SEL = High SEL = Low
20.0
24.3
30.1
40.2
60.4
121.0
13.3
16.2
20.0
26.7
40.2
80.6
Table 1: Maximum LED Current and RBALLAST
Resistor Values (1% Resistor Tolerance).
Typical white LEDs are driven at maximum continuous
currents of 15mA to 20mA. The maximum number of
series connected LEDs is determined by the minimum
OVP voltage of the boost converter (VOUT(OVP_MIN)), minus
the maximum feedback voltage (VFB(MAX)) divided by the
maximum LED forward voltage (VFLED(MAX)). VFLED(MAX) can
be estimated from the manufacturers’ datasheet at the
maximum LED operating current.
V = VOUT(OVP_MIN)
·OVP(TYP)
R2
R3
+ 1⎞⎠
N=
(VOUT(OVP_MIN) - VFB(MAX))
VFLED(MAX)
Figure 4 shows the schematic of using ten LEDs in series.
Assume VFLED @ 20mA = 3.5V (typical) from LW M673
(OSRAM) datasheet.
VOUT(OVP_MIN) = 1.2V ·
374kΩ
10.4kΩ
+
1⎞⎠
= 38.6V
N
=
38.6V - 0.6V
3.5V
10.9
Therefore, under these typical operating conditions, ten
LEDs can be used in series.
12
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1239-1.2007.10.1.0

12 Page





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