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AAT3156 Schematic ( PDF Datasheet ) - Advanced Analogic Technologies

Teilenummer AAT3156
Beschreibung High Efficiency 1X/1.5X/2X Charge Pump For White LED Applications
Hersteller Advanced Analogic Technologies
Logo Advanced Analogic Technologies Logo 




Gesamt 14 Seiten
AAT3156 Datasheet, Funktion
www.DataSheet4U.com
AAT3156
High Efficiency 1X/1.5X/2X Charge Pump
For White LED Applications
General Description
Features
ChargePump
The AAT3156 is a low noise, constant frequency
charge pump DC/DC converter that uses a tri-
mode load switch (1X), fractional (1.5X), and dou-
bling (2X) conversion to maximize efficiency for
white LED applications. The AAT3156 is capable of
driving six-channel LEDs at a total of 180mA from
a 2.7V to 5.5V input. The current sinks may be
operated individually or in parallel for driving high-
er-current LEDs. A low external parts count (two
1µF flying capacitors and two small 1µF capacitors
at VIN and VOUT) make this part ideally suited for
small battery-powered applications.
AnalogicTech's AS2Cwire™ (Advanced Simple
Serial Control™) serial digital input is used to
enable, disable, and set current for each LED with
a 16-level logarithmic scale plus four low-current
settings down to 50µA for optimized efficiency, with
a low housekeeping current of only 50µA.
• VIN Range: 2.7V to 5.5V
• Fully Programmable Current with Single Wire
— 16-Step Logarithmic Scale
— 15/20/30mA Max Current
— Four Low Current Settings Down to 50µA
— Low IQ (50µA) for Low Current Mode
• Tri-Mode 1X, 1.5X, and 2X Charge Pump for
Maximum Efficiency and VF Coverage
• Drives Six Channels of LEDs
• Individual Main/Sub-Group Control
• No Inductors, Low Noise Operation
• 1MHz Constant Switching Frequency
• Small Application Circuit
• Built-In Thermal Protection
• Built-In Auto-Disable For Open Circuit
• Automatic Soft-Start
• IQ <1µA in Shutdown
• Thermally-Enhanced QFN44-16 Package
Each output of the AAT3156 is equipped with built-
in protection for VOUT short circuit and auto disable
for LED failure condition. Built-in soft-start circuitry
www.DataSheet4U.comprevents excessive inrush current during start-up.
Applications
A low current shutdown feature disconnects the
• Color (RGB) Lighting
load from VIN and reduces quiescent current to less
than 1µA.
• Programmable Current Sinks
• White LED Backlighting
The AAT3156 is available in a space-saving, ther-
• White Photo Flash for DSCs
mally-enhanced 16-pin 4x4mm QFN package.
Typical Application
2.7V to 5.5V
VIN C1+
CIN C1-
1µF
C2+
AAT3156
C2-
VOUT
EN/SET
EN/SET
GND
D1
D2
D3
D4
D5
D6
C1
1µF
C2
1µF
D1 D2 D3 D4 D5 D6
COUT
1µF
3156.2005.06.1.1
1
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AAT3156 Datasheet, Funktion
www.DataSheet4U.com
AAT3156
High Efficiency 1X/1.5X/2X Charge Pump
For White LED Applications
Typical Characteristics
Load Characteristics
(VIN = 3.8V; 1.5X Mode; 15mA Load)
VIN
(40mV/div)
CP
(40mV/div)
VSINK
(40mV/div)
500ns/div
VIN
(40mV/div)
CP
(40mV/div)
VSINK
(40mV/div)
Load Characteristics
(VIN = 2.9V; 2X Mode; 15mA Load)
500ns/div
VIN
(40mV/div)
CP
(40mV/div)
VSINK
(40mV/div)
Load Characteristics
(VIN = 4.0V; 1.5X Mode; 20mA Load)
Load Characteristics
(VIN = 3.1V; 2X Mode; 20mA Load)
VIN
(40mV/div)
www.DataSheeCP t4U.com
(40mV/div)
VSINK
(40mV/div)
500ns/div
500ns/div
VIN
(40mV/div)
CP
(40mV/div)
VSINK
(40mV/div)
Load Characteristics
(VIN = 4.3V; 1.5X Mode; 30mA Load)
500ns/div
VIN
(40mV/div)
CP
(40mV/div)
VSINK
(40mV/div)
Load Characteristics
(VIN = 3.6V; 2X Mode; 30mA Load)
500ns/div
6 3156.2005.06.1.1
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6 Page









AAT3156 pdf, datenblatt
www.DataSheet4U.com
AAT3156
High Efficiency 1X/1.5X/2X Charge Pump
For White LED Applications
Power Efficiency and Device Evaluation
The charge pump efficiency discussion in the fol-
η
=
POUT
PIN
lowing sections only account for the efficiency of the
charge pump section itself. Due to the unique circuit
The expression to define the ideal efficiency (η)
architecture and design of the AAT3156, it is very
can be rewritten as:
difficult to measure efficiency in terms of a percent
value comparing input power over output power.
Since the AAT3156 outputs are pure constant cur-
rent sinks and typically drive individual loads, it is dif-
η
=
POUT
PIN
=
VOUT × IOUT
VIN × IOUT
=
VOUT
VIN
ficult to measure the output voltage for a given out-
put (D1 to D4) to derive an overall output power
-or-
measurement. For any given application, white LED
forward voltage levels can differ, yet the output drive
current will be maintained as a constant.
This makes quantifying output power a difficult task
η(%)
=
100
VOUT
VIN
when taken in the context of comparing to other white
LED driver circuit topologies. A better way to quantify
Charge Pump Section Efficiency
total device efficiency is to observe the total input
The AAT3156 contains a fractional charge pump that
power to the device for a given LED current drive
will boost the input supply voltage in the event where
level. The best white LED driver for a given applica-
tion should be based on trade-offs of size, external
VIN is less than the voltage required on the constant
current source outputs. The efficiency (η) can be
component count, reliability, operating range and
www.DataSheet4U.comtotal energy usage...not just "% efficiency."
simply defined as a linear voltage regulator with an
effective output voltage that is equal to one and a half
The AAT3156 efficiency may be quantified under
or two times the input voltage. Efficiency (η) for an
very specific conditions and is dependent upon the
ideal 1.5X charge pump can typically be expressed
input voltage versus the output voltage seen across
as the output power divided by the input power.
the loads applied to outputs D1 through D4 for a
given constant current setting. Depending on the
combination of VIN and voltages sensed at the cur-
rent sinks, the device will operate in "Load Switch"
η
=
POUT
PIN
mode. When any one of the voltages sensed at the
current sinks nears dropout, the device will operate
In addition, with an ideal 1.5X charge pump, the
in 1.5X or 2X charge pump mode. Each of these
output current may be expressed as 2/3 of the
modes will yield different efficiency values. One
input current. The expression to define the ideal
should refer to the following two sections for expla-
efficiency (η) can be rewritten as:
nations for each operational mode.
Load Switch Mode Efficiency
η = POUT =
PIN
VOUT × IOUT
VIN × 1.5IOUT
=
VOUT
1.5VIN
The AAT3156 load switch mode is operational at all
times and functions alone to enhance device power
conversion efficiency when VIN is greater than the
voltage across the load. When in "Load Switch"
mode, the voltage conversion efficiency is defined
as output power divided by input power:
-or-
η(%)
=
100
VOUT
1.5VIN
12 3156.2005.06.1.1
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