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AAT3142 Schematic ( PDF Datasheet ) - AAT

Teilenummer AAT3142
Beschreibung High Efficiency 1X/1.5X/2X Charge Pump
Hersteller AAT
Logo AAT Logo 




Gesamt 16 Seiten
AAT3142 Datasheet, Funktion
AAT3142
High Efficiency 1X/1.5X/2X Charge Pump
for White LED Applications
General Description
Features
ChargePump
The AAT3142 is a low noise, constant frequency
charge pump DC/DC converter that uses a tri-
• VIN Range: 2.7V to 5.5V
• Tri-Mode 1X, 1.5X, and 2X Charge Pump for
mode load switch (1X), fractional (1.5X), and dou-
bling (2X) conversion to maximize efficiency for
white LED applications. The device produces cur-
Maximum Efficiency and VF Coverage
• Drives Low-VF and High-VF Type LEDs
• Up to Three 30mA Outputs
rent levels up to 30mA on each of its three current
• 32-Position Logarithmic Scale with Digital
source outputs to drive various arrangements of
Control
LEDs from a 2.7V to 5.5V input. Outputs may be
• Low Noise Constant Frequency Operation
operated individually or in parallel for driving high-
• 1MHz Switching Frequency
er-current LEDs. A low external parts count (two
• Small Application Circuit
1µF flying capacitors and two small 1µF capacitors
• Regulated Output Current
at VIN and CP) make the AAT3142 ideally suited for
small battery-powered applications.
• Automatic Soft Start
• No Inductors
AnalogicTech's Simple Serial Control™ (S2Cwire™)
digital input is used to enable, disable, and set the
• IQ < 1µA in Shutdown
• 12-Pin TSOPJW Package
LED drive current with a 32-level logarithmic scale
LED brightness control. The AAT3142 has a thermal
management system to protect the device in the
event of a short-circuit condition at an output pin.
Applications
Built-in soft-start circuitry prevents excessive inrush
current during start-up. A high charge pump switch-
• Color (RGB) Lighting
ing frequency enables the use of very small external •www.DataSheet4U.com Programmable Current Sources
capacitors. In shutdown mode, the device discon-
• White LED Backlighting
nects the load from VIN and reduces quiescent cur-
rent to less than 1µA. The AAT3142 is available in
• White Photo Flash for Digital Still Cameras
the very small, Pb-free 12-pin TSOPJW package.
Typical Application
VBATTERY
CIN CCP
1μF 1μF
EN/SET
VIN C1+
CP C1-
C2+
AAT3142
C2-
D1
D2
D3
EN/SET
GND
C1
1μF
C2
1μF
D3 D2 D1
3142.2007.03.1.2
1






AAT3142 Datasheet, Funktion
AAT3142
High Efficiency 1X/1.5X/2X Charge Pump
for White LED Applications
Typical Characteristics
VIN = 3.5V, CIN = CCP = C1 = C2 = 1µF, TA = 25°C, unless otherwise noted.
Turn-On to 1X Mode
(3x19mA Load)
Turn-On to 1X Mode
(3x30mA Load)
EN/SET
(2V/div)
VCP
(4V/div)
VDIODE
(2V/div)
IIN
(100mA/div)
EN/SET
(2V/div)
VCP
(4V/div)
VDIODE
(2V/div)
IIN
(100mA/div)
Time (100µs/div)
Time (100µs/div)
EN/SET
(2V/div)
VCP
(4V/div)
VDIODE
(2V/div)
IIN
(100mA/div)
Turn-On to 1.5X Mode
(3x19mA Load)
Time (100µs/div)
EN/SET
(2V/div)
VCP
(4V/div)
VDIODE
(2V/div)
IIN
(100mA/div)
Turn-On to 1.5X Mode
(3x30mA Load)
Time (100µs/div)
Turn-Off from Full-Scale 2X Mode
EN/SET
(2V/div)
VDIODE
(2V/div)
IIN
(200mA/div)
Time (200µs/div)
6 3142.2007.03.1.2

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AAT3142 pdf, datenblatt
AAT3142
High Efficiency 1X/1.5X/2X Charge Pump
for White LED Applications
S2Cwire Serial Interface
The current source output magnitude is controlled
by the EN/SET pin, using AnalogicTech's S2Cwire
interface. The interface records rising edges of the
EN/SET pin and decodes them into 32 individual
current level settings with Code 1 reserved for no
current. Once EN/SET has been held in the logic
high state for time TLAT, the programmed current is
seen at the current source outputs, and the internal
data register is reset to 0. For subsequent current
level programming, the number of rising edges cor-
responding to the desired code must be entered on
the EN/SET pin.
When EN/SET is held low for an amount of time
greater than TOFF, the AAT3142 enters into shut-
down mode and draws less than 1µA from VIN. The
internal data register is reset to 0 during shutdown.
S2Cwire Serial Interface Timing
EN/SET
Data Reg
THI
TLO
TLAT
12
n-1 n <= 32
0
TOFF
n0
LED Selection
The AAT3142 is specifically intended for driving
white LEDs. However, the device design will allow
the AAT3142 to drive most types of LEDs with for-
ward voltage specifications ranging from 1.0V to
4.3V. LED applications may include main and sub-
LCD display backlighting, camera photo-flash appli-
cations, color (RGB) LEDs, infrared (IR) diodes for
remotes, and other loads benefiting from a controlled
output-current generated from a varying input-volt-
age. Since the D1 to D3 output current sources are
matched with negligible voltage dependence, the
LED brightness will be matched regardless of the
specific LED forward voltage (VF) levels.
In some instances (e.g., in high luminous output
applications such as photo flash), it may be neces-
sary to drive high-VF type LEDs. The low-dropout
current sources in the AAT3142 make it capable of
driving LEDs with forward voltages as high as 4.3V
at full current from an input supply as low as 3.0V.
Outputs can be paralleled to drive high-current
LEDs without complication.
Termination of Unused Current Source
Outputs
If any outputs (D1 to D3) are not used, they should
be terminated by connecting the respective unused
output directly to ground. This is required to assure
correct charge pump mode operation. If a given
unused output is not terminated to ground, it will
appear to the respective output’s feedback control
as an infinite impedance load and the unused con-
stant current source will be set for a maximum volt-
age. Although no current flows from the unused
current source, the voltage sensed at that node
could force the charge pump control to activate the
charge pump when it is not necessary. To prevent
this effect, simply connect the unused constant
current source outputs to ground.
Device Switching Noise Performance
The AAT3142 operates at a fixed frequency of
approximately 1MHz to control noise and limit har-
monics that can interfere with the RF operation of
cellular telephone handsets or other communication
12 3142.2007.03.1.2

12 Page





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