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PDF AAT3177 Data sheet ( Hoja de datos )
| Número de pieza | AAT3177 | |
| Descripción | High Efficiency Charge Pump | |
| Fabricantes | Advanced Analogic Technologies | |
| Logotipo |  |
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ChargePumpTM
PRODUCT DATASHEET
AAT3177
High Current, High Efficiency Charge Pump with Auto-Timer
General Description
The AAT3177 is a high output current, high efficiency,
low noise, low profile charge pump DC/DC converter.
The device is ideal for multi-functional LED photo-flash
applications where solution cost, size, and efficiency are
critical.
The AAT3177 is capable of driving a regulated output
current up to 800mA. Output current levels can be eas-
ily programmed in 16 steps through AnalogicTech’s
Simple Serial Control™ (S2Cwire™) interface controlled
by a single microcontroller GPIO line. This allows smooth
transitions and flexible adjustment of brightness in flash
or other lighting modes. The maximum output current
can also be set with an external RSET resistor.
The tri-mode (1X/1.5X/2X) operation of the internal
charge pump offers excellent power efficiency through-
out the output current range for both flash and movie
modes. Combined with a low external parts count (two
1μF flying capacitors and two small bypass capacitors at
VIN and OUT), the AAT3177 is ideally suited for small
battery-powered applications.
The AAT3177 has a thermal management system to pro-
tect the device in the event of a short-circuit condition at
the output pin. Built-in soft-start circuitry prevents
excessive inrush current during start-up. The shutdown
feature disconnects the load from VIN and reduces quies-
cent current to less than 1μA.
The AAT3177 is available in a Pb-free, thermally-
enhanced 12-pin 3x3mm TDFN package and is specified
over the -40°C to +85°C temperature range.
Features
• Up to 800mA Output Current
• Tri-Mode 1X/1.5X/2X in Current Mode
• 16 Current Level Steps Set by S2Cwire
• Flash Auto-Timer (Active for High Current Levels
Only)
• External RSET to Set Maximum Current
• <1μA of Shutdown
• Small Application Circuit
• No Inductors
• Automatic Soft Start
• 12-Pin TDFN 3x3mm Package
• -40°C to +85°C Temperature Range
Applications
• Camcorders
• Camera Phones
• Digital Still Cameras
• PDAs and Notebook PCs
• Smart Phones
Typical Application
1μF 1μF
2.7V
to 5.5V
C1+ C1- C2+ C2+
VIN
CIN
4.7μF
AAT3177
OUT
EN
0.1μF
EN/SET
CT
GND
FL
RSET
COUT
2.2μF
Flash
LED
187K
3177.2008.06.1.0
www.analogictech.com
1
1 page  
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ChargePumpTM
PRODUCT DATASHEET
AAT3177
High Current, High Efficiency Charge Pump with Auto-Timer
Typical Characteristics
VIN = 3.6V, CIN = 4.7μF, COUT = 2.2μF, C1 = C2 = 1μF, TA = 25°C, unless otherwise noted.
Efficiency vs. Supply Voltage
100
90
80
70
60 ILED = 300mA
50 ILED = 150mA
40
30
20
10
0
2.7 2.8 2.9 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4.0 4.1 4.2
Supply Voltage (V)
EN
(2V/div)
VOUT
(2V/div)
VSINK
(1V/div)
IIN
(200mA/div)
Turn-On to 1X Mode
(VIN = 4.2V; ILED = 150mA)
Time (200µs/div)
EN
(2V/div)
VOUT
(2V/div)
VSINK
(1V/div)
IIN
(200mA/div)
Turn-On to 1.5X Mode
(VIN = 3.2V; ILED = 150mA)
Time (200µs/div)
EN
(2V/div)
VOUT
(2V/div)
VSINK
(1V/div)
IIN
(500mA/div)
Turn-On to 1X Mode
(VIN = 4.2V; ILED = 600mA)
Time (200µs/div)
EN
(2V/div)
VOUT
(2V/div)
VSINK
(1V/div)
IIN
(500mA/div)
Turn-On to 2X Mode
(VIN = 3.2V; ILED = 600mA)
Time (200µs/div)
EN
(2V/div)
VF
(1V/div)
IIN
(200mA/div)
Turn-Off from 1.5X Mode
(VIN = 3.2V; ILED = 150mA)
Time (200µs/div)
3177.2008.06.1.0
www.analogictech.com
5
5 Page 
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ChargePumpTM
PRODUCT DATASHEET
AAT3177
High Current, High Efficiency Charge Pump with Auto-Timer
Next, choose R2 based on the desired flash level LED
current:
R2
=
R1
·
R1 · 600mA · 187kΩ
ILED (flash) - 600mA · 187kΩ
The current and resistance values used in the equations
come from the conditions placed on the IDX parameter of
the Electrical Characteristics table.
For examples of standard 1% values where the LED flash
current level is targeted for 700mA, see Table 3.
R1 (kΩ)
920
732
649
562
R2 (kΩ)
193
205
210
223
ILED Torch
(mA)
122
153
173
200
ILED Flash
(mA)
703
701
707
703
Table 3: Open-Drain I/O Example Resistor Values.
If the I/O port must be configured as an open-drain PMOS
type output, the appropriate equations can be generated
from these same concepts. As done in the previous exam-
ple, the necessary values can then be calculated.
As a reference, the equations applicable to the PMOS
case are:
600mA · 187kΩ
R1 = ILED (flash)
VIO
0.7
-
1
R2
=
1
R1
-
ILED (torch)
600mA · 187kΩ
The value to use for VIO must come from the I/O supply
voltage used in the system. 0.7V is the typical value of
the VRSET parameter found in the Electrical Characteristics
section of this datasheet.
Device Power Efficiency
The AAT3177 power conversion efficiency depends on
the charge pump mode. By definition, device efficiency
is expressed as the output power delivered to the LED
divided by the total input power consumed.
η
=
POUT
PIN
When the input voltage is sufficiently greater than the
LED forward voltage, the device optimizes efficiency by
operating in 1X mode. In 1X mode, the device is working
as a bypass switch and passing the input supply directly
to the output. The power conversion efficiency can be
approximated by:
η
=
VF · ILED
VIN · IIN
≈
VF
VIN
Due to the very low 1X mode quiescent current, the
input current nearly equals the current delivered to the
LED. Further, the low-impedance bypass switch intro-
duces negligible voltage drop from input to output.
The AAT3177 further maintains optimized performance
and efficiency by detecting when the input voltage is not
sufficient to sustain LED current. The device automati-
cally switches to 1.5X mode when the input voltage
drops too low in relation to the LED forward voltage.
In 1.5X mode, the output voltage can be boosted to 3/2
the input voltage. The 3/2 conversion ratio introduces a
corresponding 1/2 increase in input current. For ideal
conversion, the 1.5X mode efficiency is given by:
η
=
VF · ILED
VIN · 1.5IIN
=
VF
1.5 · VIN
Similarly, when the input falls further, such that 1.5X
mode can no longer sustain LED current, the device will
automatically switch to 2X mode. In 2X mode, the out-
put voltage can be boosted to twice the input voltage.
The doubling conversion ratio introduces a correspond-
ing doubling of the input current. For ideal conversion,
the 2X mode efficiency is given by:
η=
VF · ILED
VIN · 2IIN
=
VF
2 · VIN
LED Selection
The AAT3177 is designed to drive high-intensity white
LEDs. It is particularly suitable for LEDs with an operat-
ing forward voltage in the range of 4.2V to 1.5V.
The charge pump device can also drive other loads that
have similar characteristics to white LEDs. For various
load types, the AAT3177 provides a high-current, pro-
grammable ideal constant current source.
3177.2008.06.1.0
www.analogictech.com
11
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| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet AAT3177.PDF ] | |
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