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PDF AAT1236 Data sheet ( Hoja de datos )
| Número de pieza | AAT1236 | |
| Descripción | High Efficiency White LED Drivers | |
| Fabricantes | Advanced Analog Technology | |
| Logotipo |  |
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General Description
The AAT1236 is a highly integrated, high efficiency
power solution for white LED and keypad backlights
in mobile/portable devices. It is based on a switching
boost converter which steps up the single cell lithi-
um-ion/polymer battery voltage to drive 5 strings of
series-connected white LEDs with precision current
regulation. The AAT1236 is capable of driving a total
of four LEDs per channel.
The boost converter can produce an output drive of
up to 24V at 100mA. The high switching frequency
(up to 2MHz) provides fast response to load tran-
sients and allows the use of small external compo-
nents. A fully integrated control circuit simplifies the
design and reduces total solution size.
A two-wire I2C serial digital interface is used to indi-
vidually turn each output sink on/off and adjust the
LED current by group. Unlike conventional pulse
width modulation (PWM) control of LED brightness,
the AAT1236 drives the LEDs with constant, non-
pulsating current. The interface is fully compliant to
the Fast/Standard mode I2C specification, allowing a
transfer rate of up to 400kHz.
A similar device is also available with a proprietary
Advanced Simple Serial Control™ (AS2Cwire™) sin-
gle wire interface; please see the AAT1235 datasheet.
The AAT1236 is available in a Pb-free, thermally-
enhanced 16-pin 3x4mm TDFN package and is
specified for operation over the -40°C to +85°C tem-
perature range.
Typical Application
L=2.2µH
D1
AAT1236
High Efficiency White LED Drivers
for Backlight and Keypad
Features
SwitchReg™
• Input Supply Voltage Range: 2.7V to 5.5V
• Maximum Boost Output Drive: Up to 24V at 100mA
• Up to 85% Efficient Operation
• Up to 2MHz Switching Frequency with Small
Inductor
• User-Programmable Full-Scale LED Current,
Up to 30mA
• Two-Wire, I2C Compliant Serial Interface
— Two Addressable Registers
• Independent LED Current Control by Group
— Backlight Group B1-B2, 16 Settings
— Auxiliary Group A1-A3, 16 Settings
• Independent LED ON/OFF Control
— Fast, 400kHz Serial Transfer Rate
• Non-Pulsating, High-Performance LED Current
Drive for Uniform Illumination
— 10% Absolute Accuracy
— 2% Channel-to-Channel Matching
• Over-Voltage and Over-Temperature Protection
• Automatic Soft-Start Minimizes Large Inrush
Current at Startup
• Available in 3x4mm TDFN34-16 Package
Applications
• Digital Still Cameras (DSCs)
• Keypad Backlight
• Large Panel Displays
• Mobile Handsets
• PDAs and Notebook PCs
• Personal Media Players
• White LED Backlight
Up to 24V max
Keypad or
RGB LEDs
COUT
2.2µF
1236.2007.02.1.1
Input :
2.7V~5.5V
CIN
2.2µF
LIN
VIN
IN
Enable
I2C
Interface
SDA
SCL
Backlight
LEDs
SW B 1 B 2 A 1 A 2 A 3
AAT1236
OV
EN SDA SCL
RSET GND AGND
R1
22.6kΩ
R2
187kΩ
R3
12.1kΩ
1
1 page  
AAT1236
High Efficiency White LED Drivers
for Backlight and Keypad
Electrical Characteristics (continued)1
VIN = 3.6V; CIN = 2.2µF;TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = 25°C.
Symbol Description
Thermal Protection
TJ-TH
TJ-HYS
TJ Thermal Shutdown Threshold
TJ Thermal Shutdown Hysteresis
Conditions
Min Typ Max Units
140 °C
15 °C
I2C Interface Timing Details
SDA
SCL
TLOW
TSU_DAT
THD_STA
THD_DAT
THIGH
TSU_STA
THD_STA
TSU_STO
TBUF
1. The AAT1236 is guaranteed to meet performance specifications over the -40°C to +85°C operating temperature range and is assured
by design, characterization, and correlation with statistical process controls.
1236.2007.02.1.1
5
5 Page 
AAT1236
High Efficiency White LED Drivers
for Backlight and Keypad
vides direct feedback in order to maintain the
desired LED currents.
The switching cycle initiates when the N-channel
MOSFET is turned ON and current ramps up in the
inductor. The ON interval is terminated when the
inductor current reaches the programmed peak
current level. During the OFF interval, the input
current decays until the lower threshold, or zero
inductor current, is reached. The lower current is
equal to the peak current minus a preset hysteresis
threshold, which determines the inductor ripple cur-
rent. Peak current is adjusted by the controller until
the desired LED output current level is met.
The magnitude of the feedback error signal deter-
mines the average input current. Therefore, the
AAT1236 controller implements a programmed cur-
rent source connected to the output capacitor, par-
allel with the LED channels. There is no right-half
plane zero, and loop stability is achieved with no
additional compensation components. The con-
troller responds by increasing the peak inductor
current, resulting in higher average current in the
inductor and LED channels.
Under light load conditions, the inductor OFF inter-
val current goes below zero and the boost convert-
er enters discontinuous mode operation. Further
reduction in the load current results in a correspon-
ding reduction in the switching frequency. The
AAT1236 provides pulsed frequency operation
which reduces switching losses and maintains high
efficiency under light load conditions.
Operating frequency varies with changes in the
input voltage, output voltage, and inductor size.
Once the boost converter has reached continuous
mode, further increases in the LED current will not
significantly change the operating frequency. A
small 2.2µH (±20%) inductor is selected to main-
tain high frequency switching (up to 2MHz) and
high efficiency operation for outputs up to 24V.
Soft Start / Enable
The input disconnect switch is activated when a
valid supply voltage is present and the EN/SET pin
is strobed high. Slew rate control on the input dis-
connect switch ensures minimal inrush current as
the output voltage is charged to the input voltage,
prior to switching of the N-channel power MOSFET.
A monotonic turn-on is guaranteed by the built-in
soft-start circuitry, which eliminates output current
overshoot across the full input voltage range and
over all load conditions.
Current Limit and Over-Temperature
Protection
The switching of the N-channel MOSFET termi-
nates when a current limit of 1.5A (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 AAT1236 when inter-
nal power dissipation becomes excessive, as it dis-
ables both MOSFETs. The junction over-temperature
threshold is 140°C with 15°C of temperature hystere-
sis. The output voltage automatically recovers when
the over-temperature fault condition is removed.
Over-Voltage Protection
Over-voltage protection prevents damage to the
AAT1236 during open-circuit on any LED channel
causing high output voltage conditions. An over-
voltage event is defined as a condition where the
voltage on the OV pin exceeds the over-voltage
threshold limit (VOV = 1.2V typical). When the volt-
age on the OV pin has reached the threshold limit,
the converter stops switching and the output volt-
age decays. Switching resumes when the voltage
on the OV pin drops below the lower hysteresis
limit, maintaining an average output voltage
between the upper and lower OV thresholds multi-
plied 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.
1236.2007.02.1.1
11
11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet AAT1236.PDF ] | |
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