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PDF AAT1231 Data sheet ( Hoja de datos )
| Número de pieza | AAT1231 | |
| Descripción | Step-Up DC/DC Converter | |
| Fabricantes | AAT | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de AAT1231 (archivo pdf) en la parte inferior de esta página. Total 27 Páginas | ||
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AAT1231/1231-1
Step-Up DC/DC Converters for
White LED Backlight Applications
General Description
Features
SwitchReg™
The AAT1231/1231-1 are high frequency, high effi-
• Input Voltage Range: 2.7V to 5.5V
ciency constant current boost converters capable of
• Maximum Continuous Output 24V @ 50mA
24V maximum output voltage. Both devices are
• Drives 6 LEDs in Series, 12 LEDs in Parallel/
ideal power solutions for backlight applications with
Series Configuration
up to six white LEDs in series or up to twelve white
— Constant LED Current with 6% Accuracy
LEDs in a parallel/series configuration. The input
• Digital Control with S2Cwire Single Wire Interface
voltage is 2.7V to 5.5V for single-cell lithium-
— 26 Discrete Steps
ion/polymer (Li-ion) based portable devices.
— No PWM Control Required
The LED current is digitally controlled across a 6x
operating range using AnalogicTech’s Simple Serial
Control™ (S2Cwire™) interface. Programmability
across 26 discrete current steps provides high reso-
lution, low noise, flicker-free, constant LED outputs.
In programming AAT1231 operation, LED brightness
increases based on the data received at the EN/SET
pin. In programming AAT1231-1 operation, LED
brightness decreases based on the data received at
the EN/SET pin. The SEL logic pin changes the feed-
back voltage between two programmable ranges.
— 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
The AAT1231 and the AAT1231-1 feature high current
High Resolution Control of Load Current
limit and fast, stable transitions for stepped or pulsed
• Short-Circuit, Over-Voltage, and Over-
www.DataSheet4U.com
current applications. The high switching frequency (up
Temperature Protection
to 2MHz) provides fast response and allows the use
• 12-Pin TSOPJW Package
of ultra-small external components, including chip
• -40°C to +85°C Temperature Range
inductors and capacitors. Fully integrated control cir-
cuitry simplifies design and reduces total solution size.
The AAT1231 and the AAT1231-1 offer a true load
Applications
disconnect feature which isolates the load from the
power source while in the OFF or disabled state. This
• Digital Still Cameras (DSCs)
eliminates leakage current, making the devices ideal-
• Mobile Handsets
ly suited for battery-powered applications.
• MP3 Players
The AAT1231 and the AAT1231-1 are available in Pb-
free, thermally-enhanced 12-pin TSOPJW packages.
• PDAs and Notebook PCs
• White LED Drivers
Typical Application
Li-Ion:
VIN = 2.7V to 4.2V
C1
2.2µF
Enable/Set
Select
PVIN
VIN
LIN
SW
PGND
OVP
AAT1231/
1231-1
EN/SET
SEL AGND FB
L = 2.2µH
DS1
R2
226kΩ
R3
12kΩ
R1 (RBALLAST)
30.1Ω
Up to 24V/
50mA max
C2
2.2µF
OSRAM
LW M678
Capable of Driving
Six LEDs in Series
(see Applications Section)
1231.2007.01.1.2
1
1 page  
Typical Characteristics
Efficiency vs. LED Current
(4 White LEDs; RBALLAST = 30.1Ω)
85
84 VIN = 5V
83
82
81
80
79 VIN = 3.6V VIN = 4.2V
78
77
2 4 6 8 10 12 14 16 18 20
LED Current (mA)
AAT1231/1231-1
Step-Up DC/DC Converters for
White LED Backlight Applications
Efficiency vs. LED Current
(5 White LEDs; RBALLAST = 30.1Ω)
83
82 VIN = 5V
81
80 VIN = 4.2V
79 VIN = 3.6V
78
77
76
75
2 4 6 8 10 12 14 16 18 20
LED Current (mA)
Efficiency vs. LED Current
(6 White LEDs; RBALLAST = 30.1Ω)
81
80
VIN = 5V
79
78
77 VIN = 4.2V
76
75 VIN = 3.6V
74
73
2 4 6 8 10 12 14 16 18 20
LED Current (mA)
Efficiency vs. LED Current
(12 White LEDs; RBALLAST = 30.1Ω)
84
83
82 VIN = 5V
81
80
79 VIN = 4.2V
78
77
76 VIN = 3.6V
75
74
2 468
10 12 14 16 18 20
LED Current (mA)
Shutdown Current vs. Input Voltage
(EN = GND)
1.0
0.8
0.6
0.4
0.2
0.0
2.7
85°C
-40°C
25°C
3.1 3.5 3.9 4.3 4.7 5.1
Input Voltage (V)
5.5
Feedback Voltage vs. Temperature
(RBALLAST = 30.1Ω)
700
600
500
400
300
200
100
0
-40 -15 10 35 60
Temperature (°C)
85
1231.2007.01.1.2
5
5 Page 
AAT1231-1 have been designed to offer the sys-
tem designer two choices for the default FB voltage
based on the state of the SEL pin. Changing the
LED current from its initial default setting is easy by
using the S2Cwire single wire serial interface; the
FB voltage can be increased (as in the AAT1231;
see Table 2) or decreased (as in the AAT1231-1;
see Table 3) relative to the default FB voltage.
Current Limit and Over-Temperature
Protection
The switching of the N-channel MOSFET termi-
nates when a current limit of 2.5A (typical) is
exceeded. This minimizes power dissipation and
component stresses under overload and short-cir-
cuit conditions. Switching resumes when the cur-
rent decays below the current limit.
Thermal protection disables the AAT1231/1231-1
when internal dissipation becomes excessive.
Thermal protection disables both MOSFETs. The
junction over-temperature threshold is 140°C with
15°C of temperature hysteresis. The output voltage
automatically recovers when the over-temperature
fault condition is removed.
Over-Voltage Protection
Over-voltage protection prevents damage to the
AAT1231/1231-1 during open-circuit or high output
voltage conditions. An over-voltage event is
defined as a condition where the voltage on the
OVP pin exceeds the Over-Voltage Threshold Limit
(VOVP = 1.2V typical). When the voltage on the
OVP pin has reached the threshold limit, the con-
verter stops switching and the output voltage
decays. Switching resumes when the voltage on
the OVP pin drops below the lower hysteresis limit,
maintaining an average output voltage between the
upper and lower OVP thresholds multiplied by the
resistor divider scaling factor.
Under-Voltage Lockout
Internal bias of all circuits is controlled via the VIN
input. Under-voltage lockout (UVLO) guarantees
sufficient VIN bias and proper operation of all inter-
nal circuitry prior to soft start.
AAT1231/1231-1
Step-Up DC/DC Converters for
White LED Backlight Applications
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 cir-
cuit failure, the resistor divider can be selected
such that the over-voltage threshold occurs prior to
the output reaching 24V (VOUT(MAX)). The value of
R3 should be selected from 10kΩ to 20kΩ to mini-
mize losses without degrading noise immunity.
R2
=
R3
·
⎛
⎝
VOUT(MAX)
VOVP
-
1⎞⎠
AAT1231/1231-1
OVP
GND
VOUT
R2
R3
COUT
Figure 1: Over-Voltage Protection Circuit.
1.224V
1.168V
2
1
0
Time (5ms/div)
26
24
22
Figure 2: Over-Voltage Protection
Open Circuit Response (No LED).
1231.2007.01.1.2
11
11 Page | ||
| Páginas | Total 27 Páginas | |
| PDF Descargar | [ Datasheet AAT1231.PDF ] | |
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