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AAT3175
High Efficiency 1X/1.5X/2X Charge Pump For White LED Flash Applications General Description
The AAT3175 is a low noise, constant frequency charge pump DC/DC converter that uses a tri-mode load switch (1X), fractional (1.5X), and doubling (2X) conversion to maximize efficiency for white LED flash applications. The AAT3175 is capable of driving up to three flash LEDs at 300mA total current from a 2.7V to 5.5V input. A low external parts count (two 1F flying capacitors and two small 1F capacitors at VIN and VOUT) make this part ideally suited for small battery-powered applications. AnalogicTech's S2CwireTM (Simple Serial ControlTM) serial digital input is used to enable, disable, and set current for all LEDs with 16 level settings down to 0. The AAT3175 is equipped with built-in protection for VOUT short-circuit condition and auto-disable for load short-circuit condition on any one of the channels. Built-in soft-start circuitry prevents excessive inrush current during start-up. A low-current shutdown feature disconnects the load from VIN and reduces quiescent current to less than 1A. The AAT3175 is available in a Pb-free, space-saving, thermally-enhanced 12-pin 3x3mm TDFN package.
Features
* * * * * * * * * * * *
ChargePumpTM
VIN Range: 2.7V to 5.5V Up to 300mA Total Flash Current Fully Programmable Current with Single Wire -- 16 Logarithmic Current Levels Tri-Mode 1X, 1.5X, and 2X Charge Pump for Maximum Efficiency and VF Coverage Drives 3-in-1 or 2-in-1 Flash LEDs -- 0.5% Current Matching No Inductors, Low Noise Operation 1MHz Constant Switching Frequency Small Application Circuit Built-In Thermal Protection Automatic Soft-Start IQ <1A in Shutdown TDFN33-12 Package
Applications
* * * Programmable Current Sinks White LED Backlighting White Photo Flash for Mobile Phones
Typical Application
C1+
C1 1F
C2+
C12.7V to 5.5V
CIN 1F
C2VOUT
VIN
AAT3175
GND D1 D2
D1
D2
D3
COUT 1F
EN/SET
EN/SET
D3 D4
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AAT3175
High Efficiency 1X/1.5X/2X Charge Pump For White LED Flash Applications Pin Descriptions
Pin #
1 2 3 4 5 6 7 8 9 10 11 12 EP
Symbol
D4 EN/SET C1+ C1VOUT C2+ C2VIN GND D1 D2 D3
Function
Current sink input #4; 100mA max. S2Cwire serial interface control pin. Flying capacitor 1 positive terminal. Connect a 1F capacitor between C1+ and C1-. Flying capacitor 1 negative terminal. Charge pump output to drive load circuit. Requires 1F capacitor connected between this pin and ground. Flying capacitor 2 positive terminal. Connect a 1F capacitor between C2+ and C2-. Flying capacitor 2 negative terminal. Input power supply. Requires 1F capacitor connected between this pin and ground. Ground. Current sink input #1; 100mA max. Current sink input #2; 50mA max. Current sink input #3; 50mA max. Exposed paddle (bottom). Connect to GND directly beneath package.
Pin Configuration
TDFN33-12 (Top View)
D4 EN/SET C1+ C1VOUT C2+
1 2 3 4 5 6
12 11 10 9 8 7
D3 D2 D1 GND VIN C2-
2
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AAT3175
High Efficiency 1X/1.5X/2X Charge Pump For White LED Flash Applications Absolute Maximum Ratings1
Symbol
VIN VEN/SET IOUT2 TJ TLEAD
Description
Input Voltage EN/SET to GND Voltage Maximum DC Output Current Operating Junction Temperature Range Maximum Soldering Temperature (at leads, 10 sec)
Value
-0.3 to 6 -0.3 to VIN + 0.3 300 -40 to 150 300
Units
V V mA C C
Thermal Information3
Symbol
PD JA
Description
Maximum Power Dissipation Maximum Thermal Resistance
4
Value
2.0 50
Units
W C/W
1. Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at conditions other than the operating conditions specified is not implied. Only one Absolute Maximum Rating should be applied at any one time. 2. Based on long-term current density limitation. 3. Mounted on an FR4 board. 4. Derate 20mW/C above 25C. 3175.2006.01.1.2
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AAT3175
High Efficiency 1X/1.5X/2X Charge Pump For White LED Flash Applications Electrical Characteristics1
CIN = COUT = C1 = C2 = 1.0F; TA = -40C to +85C, unless otherwise noted. Typical values are TA = 25C, VIN = 3.5V. Symbol Description Conditions Min
2.7 1X Mode, 3.0 VIN 5.5, Active, No Load Current 1.5X Mode, 3.0 VIN 5.5, Active, No Load Current 2X Mode, 3.0 VIN 5.5, Active, No Load Current EN/SET = 0 D1, D4 Max Setting D2, D3 Max Setting VF:D1:D4 = 3.6V, D2 and D3 in Parallel 0.3 1.0 2.0
Typ
Max
5.5 1.0 3.0 3.7 1.0 110 55 5.0
Units
V
Input Power Supply VIN Operation Range
ICC
Operating Current
mA
ISHDN IDX I(D-Match) VTH
Shutdown Current ISINK Average Current Accuracy Current Matching2
A mA % mV
90 45
100 50 0.5 250
1X to 1.5X or 1.5X to 2X Transition Threshold at Any ISINK Pin Charge Pump Section TSS Soft-Start Time FCLK Clock Frequency EN/SET VEN(L) Enable Threshold Low VEN(H) Enable Threshold High TEN/SET LO EN/SET Low Time TEN/SET HI MIN Minimum EN/SET High Time TEN/SET HI MAX Maximum EN/SET High Time TOFF EN/SET Off Timeout TLAT EN/SET Latch Timeout IEN/SET EN/SET Input Leakage
100 1000 VIN = 2.7V VIN = 5.5V 0.4 1.4 0.3 50 75 500 500 1 75
s kHz V V s ns s s s A
-1
1. The AAT3175 is guaranteed to meet performance specifications over the -40C to +85C operating temperature range and is assured by design, characterization, and correlation with statistical process controls. 2. Current matching is defined as the deviation of any sink current from the average of all active channels.
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AAT3175
High Efficiency 1X/1.5X/2X Charge Pump For White LED Flash Applications Typical Characteristics
CIN = COUT = C1 = C2 = 1F, TA = 25C, VIN = 3.5V, unless otherwise noted. Efficiency vs. Supply Voltage
100 90
300mA LED Pulse
(VIN = 3.8V)
Efficiency (%)
80 70 60 50 40 30
60mA VF = 3.0V 150mA VF = 3.2V
VOUT (2V/div)
IOUT (200mA/div)
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)
Time (100ms/div)
Turn-On to 1X Mode
(VIN = 4.2V; 300mA Load)
Turn-On to 1.5X Mode
(VIN = 4.0V; 300mA Load)
EN (2V/div) VOUT (2V/div) VSINK (1V/div) IIN (400mA/div) Time (200s/div)
EN (2V/div) VOUT (2V/div) VSINK (1V/div) IIN (400mA/div) Time (200s/div)
Turn-On to 2X Mode
(VIN = 3.8V; 300mA Load) EN (2V/div) VF (1V/div)
Turn-Off from 1.5X Mode
(VIN = 4.0V; 300mA Load)
EN (2V/div) VOUT (2V/div) VSINK (1V/div) IIN (400mA/div) Time (200s/div)
IIN (200mA/div)
Time (200s/div)
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AAT3175
High Efficiency 1X/1.5X/2X Charge Pump For White LED Flash Applications Typical Characteristics
CIN = COUT = C1 = C2 = 1F, TA = 25C, VIN = 3.5V, unless otherwise noted. Line Response
(1.5X Mode; 150mA Load) 4.2V 3.7V 3.6V
Load Characteristics
(VIN = 3.5V; 1.5X Mode; 150mA Load)
VIN (500mV/div) VOUT (500mV/div) VSINK (500mV/div) ILED (10mA/div) Time (1ms/div)
VIN (100mV/div) VOUT (100mV/div) VSINK (100mV/div)
Time (500ns/div)
Load Characteristics
(VIN = 3.0V; 2X Mode; 150mA Load)
30
Input Ripple vs. Input Voltage
(150mA Load)
Input Ripple (mV)
VIN (100mV/div) VOUT (100mV/div)
25 20 15 10 5 0
VSINK (100mV/div)
2.5
2.8
3.0
3.3
3.5
3.8
4.0
4.3
4.5
Time (500ns/div)
Input Voltage (V)
EN/SET Latch Timeout vs. Input Voltage
EN/SET Latch Timeout (s)
350 400
EN/SET Off Timeout vs. Input Voltage
EN/SET Off Timeout (s)
300 250 200 150 100 50 0 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5
350 300 250 200 150 100 50 0 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5
-40C
-40C
25C
85C
25C
85C
Input Voltage (V)
Input Voltage (V)
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AAT3175
High Efficiency 1X/1.5X/2X Charge Pump For White LED Flash Applications Typical Characteristics
CIN = COUT = C1 = C2 = 1F, TA = 25C, VIN = 3.5V, unless otherwise noted. Enable Threshold High vs. Input Voltage
Enable Threshold Low (V) Enable Threshold High (V)
1.2 1.1 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5 1.2 1.1 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5
Enable Threshold Low vs. Input Voltage
-40C
-40C
25C
85C
25C
85C
Input Voltage (V)
Input Voltage (V)
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AAT3175
High Efficiency 1X/1.5X/2X Charge Pump For White LED Flash Applications Functional Block Diagram
C1+ C1- C2+ C2-
VIN
1X, 1.5X, 2X Charge Pump
VOUT
Soft Start Control 1MHz Oscillator Voltage Reference D/A D/A 6 x 16 bit ROM D/A D/A D/A
D1 D2 D3 D4
EN/SET
S2Cwire Interface
D/A
GND
Functional Description
The AAT3175 is a tri-mode load switch (1X) and high efficiency (1.5X or 2X) charge pump device intended for white LED flash applications. To maximize power conversion efficiency, an internal sensing circuit monitors the voltage required on each constant current sink input and sets the load switch and charge pump modes based on the input battery voltage and the current sink input voltage. As the battery discharges over time, the AAT3175 charge pump is enabled when any of the four current sink inputs nears dropout. The charge pump initially starts in 1.5X mode. If the charge pump output droops enough for any current source output to become close to dropout, the charge pump will automatically transition to 2X mode. The AAT3175 requires only four external components: two 1F ceramic capacitors for the charge pump flying capacitors (C1 and C2), one 1F ceramic input capacitor (CIN), and one 0.33F to 1F ceramic charge pump output capacitor (COUT). The four constant current sink inputs (D1 to D4) can drive four individual LEDs with a maximum current
of 50mA each for D2 and D3. D1 and D4 are driven by two parallel current sources, resulting in a maximum of 100mA each. Unused sink inputs are connected to VOUT; otherwise, the part will operate only in 2X charge pump mode. The S2Cwire serial interface enables the AAT3175 and sets the current sink magnitudes. The D1~D4 current configuration is optimized to drive either 2-in-1 LEDs by combining D1/D2, D3/D4, or 3-in-1 LEDs by combining D2/D3.
Constant Current Output Level Settings
The constant current sink levels for D1 to D4 are set via the serial interface according to a logarithmic scale where each code is 1dB lower than the previous code. In this manner, LED brightness appears linear with each increasing code count. Because the inputs D1 to D4 are true independent constant current sinks, the voltage observed on any single given input will be determined by the actual forward voltage (VF) for the LED being driven. Since the input current sinks of the AAT3175 are programmable, no PWM (pulse width modulation) or additional control circuitry is needed to control LED brightness. This feature greatly reduces the burden
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AAT3175
High Efficiency 1X/1.5X/2X Charge Pump For White LED Flash Applications
on a microcontroller or system IC to manage LED or display brightness, allowing the user to "set it and forget it." With its high-speed serial interface (1MHz data rate), the input sink current of the AAT3175 can be changed successively to brighten or dim LEDs in smooth transitions (e.g., to fade-out) or in abrupt steps, giving the user complete programmability and real-time control of LED brightness. The S2Cwire serial interface has flexible timing. Data can be clocked-in at speeds greater than 1MHz, or much slower, such as 15kHz. After data is submitted, EN/SET is held high to latch the data. Once EN/SET has been held in the logic high state for time TLAT, the programmed current becomes active and the internal data register is reset to zero. For subsequent current level programming, the number of rising edges corresponding 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 AAT3175 enters into shutdown mode and draws less than 1A from VIN. The internal data register is reset to zero during shutdown.
S2Cwire Serial Interface
The current level magnitude is controlled by AnalogicTech's S2Cwire serial interface. The interface records rising edges of the EN/SET pin and decodes them into 16 different states. The 16 current level settings available are indicated in Table 1. D2, D3 IOUT (mA)
50 44 40 36 32 28 25 22 20 17 16 14 13 11 10 0
Auto-Disable Feature
Data
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
D1, D4 IOUT (mA)
100 88 80 72 64 56 50 44 40 34 32 28 26 22 20 0
The AAT3175 is equipped with an auto-disable feature for each LED channel. After the IC is enabled and started up, a test current of 150A (typical) is forced through each sink channel. The channel will be disabled if the voltage of that particular DX pin does not fall below a certain threshold. This feature is very convenient for disabling an unused channel or during an LED fail-short event.
Thermal Protection
The AAT3175 has a built-in thermal protection circuit that will shut down the charge pump if the die temperature rises above the thermal limit, as is generally the case during a short-circuit of the VOUT pin.
Table 1: Current Level Settings.
S2Cwire Serial Interface Timing
THI TLO T LAT TOFF
EN/SET
1 2 n-1 n 16
Data Reg
0
n-1
0
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AAT3175
High Efficiency 1X/1.5X/2X Charge Pump For White LED Flash Applications Applications Information
LED Selection
Although the AAT3175 is specifically intended for driving white LEDs, the device can also be used to drive most types of LEDs with forward voltage specifications ranging from 2.0V to 4.1V. LED applications may include display backlighting, camera photo-flash applications, color (RGB) LEDs, infrared (IR) diodes for remotes, and other loads benefiting from a controlled output current generated from a varying input voltage. Since the D1 to D4 input current sinks 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 necessary to drive high-VF type LEDs. The low dropout current sinks in the AAT3175 make it capable of driving LEDs with forward voltages as high as 4.1V at full current from an input supply as low as 3.5V. Outputs can be paralleled to drive high-current LEDs without complication. when choosing capacitors. If the LED current sources are only programmed for light current levels, then the capacitor size may be decreased.
Capacitor Characteristics
Ceramic composition capacitors are highly recommended over all other types of capacitors for use with the AAT3175. Ceramic capacitors offer many advantages over their tantalum and aluminum electrolytic counterparts. A ceramic capacitor typically has very low ESR, is lowest cost, has a smaller PCB footprint, and is non-polarized. Low-ESR ceramic capacitors help maximize charge pump transient response. Since ceramic capacitors are non-polarized, they are not prone to incorrect connection damage.
Equivalent Series Resistance
ESR is an important characteristic to consider when selecting a capacitor. ESR is a resistance internal to a capacitor that is caused by the leads, internal connections, size or area, material composition, and ambient temperature. Capacitor ESR is typically measured in milliohms for ceramic capacitors and can range to more than several ohms for tantalum or aluminum electrolytic capacitors.
Device Switching Noise Performance
The AAT3175 operates at a fixed frequency of approximately 1MHz to control noise and limit harmonics that can interfere with the RF operation of cellular telephone handsets or other communication devices. Back-injected noise appearing on the input pin of the charge pump is 20mV peak-topeak, typically ten times less than inductor-based DC/DC boost converter white LED backlight solutions. The AAT3175 soft-start feature prevents noise transient effects associated with inrush currents during start-up of the charge pump circuit.
Ceramic Capacitor Materials
Ceramic capacitors less than 0.1F are typically made from NPO or C0G materials. NPO and C0G materials generally have tight tolerance and are very stable over temperature. Larger capacitor values are usually composed of X7R, X5R, Z5U, or Y5V dielectric materials. Large ceramic capacitors (i.e., greater than 2.2F) are often available in lowcost Y5V and Z5U dielectrics, but capacitors greater than 1F are not typically required for AAT3175 applications. Capacitor area is another contributor to ESR. Capacitors that are physically large will have a lower ESR when compared to an smaller capacitor made of equivalent material. These larger devices can improve circuit transient response when compared to an equal value capacitor in a smaller package size.
Capacitor Selection
Careful selection of the four external capacitors CIN, C1, C2, and COUT is important because they will affect turn-on time, output ripple, and transient performance. Optimum performance will be obtained when low equivalent series resistance (ESR) ceramic capacitors are used; generally, low ESR may be defined as less than 100m. A value of 1F for all four capacitors is a good starting point
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AAT3175
High Efficiency 1X/1.5X/2X Charge Pump For White LED Flash Applications Ordering Information
Package
TDFN33-12
Marking1
QAXYY
Part Number (Tape and Reel)2
AAT3175IWP-T1
All AnalogicTech products are offered in Pb-free packaging. The term "Pb-free" means semiconductor products that are in compliance with current RoHS standards, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. For more information, please visit our website at http://www.analogictech.com/pbfree.
Package Information
TDFN33-12
Index Area (D/2 x E/2)
Detail "B"
3.00 0.05
2.40 0.05
0.3 0.10 0.16 0.375 0.125 0.075 0.075 0.1 REF
Detail "A"
Top View
Bottom View
Pin 1 Indicator (optional)
7.5 7.5
+ 0.05 0.8 -0.20
0.229 0.051
Detail "B"
Option A: C0.30 (4x) max Chamfered corner Option B: R0.30 (4x) max Round corner
0.05 0.05
Side View
All dimensions in millimeters.
Detail "A"
1. XYY = assembly and date code. 2. Sample stock is generally held on part numbers listed in BOLD. 3175.2006.01.1.2
0.23 0.05
0.45 0.05
3.00 0.05
1.70 0.05
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AAT3175
High Efficiency 1X/1.5X/2X Charge Pump For White LED Flash Applications
(c) Advanced Analogic Technologies, Inc. AnalogicTech cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an AnalogicTech product. No circuit patent licenses, copyrights, mask work rights, or other intellectual property rights are implied. AnalogicTech reserves the right to make changes to their products or specifications or to discontinue any product or service without notice. Customers are advised to obtain the latest version of relevant information to verify, before placing orders, that information being relied on is current and complete. All products are sold subject to the terms and conditions of sale supplied at the time of order acknowledgement, including those pertaining to warranty, patent infringement, and limitation of liability. AnalogicTech warrants performance of its semiconductor products to the specifications applicable at the time of sale in accordance with AnalogicTech's standard warranty. Testing and other quality control techniques are utilized to the extent AnalogicTech deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily performed.
Advanced Analogic Technologies, Inc.
830 E. Arques Avenue, Sunnyvale, CA 94085 Phone (408) 737-4600 Fax (408) 737-4611 12
3175.2006.01.1.2

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