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High Current, High Efficiency Charge Pump General Description
The AAT3174 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 AAT3174 is capable of driving a regulated output current up to 800mA. Output current levels can be easily programmed in 16 steps through AnalogicTech's Simple Serial ControlTM (S2CwireTM) 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 throughout the output current range for both flash and movie modes. Combined with a low external parts count (two 1F flying capacitors and two small bypass capacitors at VIN and OUT), the AAT3174 is ideally suited for small battery-powered applications. The AAT3174 has a thermal management system to protect 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 quiescent current to less than 1A. The AAT3174 is available in a Pb-free, thermallyenhanced 12-pin 3x3mm TDFN package and is specified over the -40C to +85C temperature range.
AAT3174
Features
* * * * * * * * * *
ChargePumpTM
Up to 800mA Output Current Tri-Mode 1X/1.5X/2X in Current Mode 16 Current Steps Set by S2Cwire External RSET to Set Maximum Current <1A of Shutdown Small Application Circuit No Inductors Automatic Soft Start 12-Pin TDFN 3x3mm Package -40C to +85C Temperature Range
Applications
* * * * * Camcorders Camera Phones Digital Still Cameras PDAs and Notebook PCs Smart Phones
Typical Application
C1 1F C2 1F
C1+ VIN (2.7V to 5.5V) VIN
C IN 4.7F
C1- C2+
C2OUT
COUT 2.2F Flash LED
AAT3174
Enable or S2Cwire
EN/SET RSET GND
FL
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High Current, High Efficiency Charge Pump Pin Descriptions
Pin #
1 2 3 4 5 6 7
AAT3174
Symbol
VIN C1+ C1GND FL RSET EN/SET
Function
Input power supply pin. Requires 4.7F bypass capacitor to ground. Flying capacitor C1 positive terminal. Connect a 1F capacitor between C1+ and C1-. Flying capacitor C1 negative terminal. Ground connection. Controlled current sink. Connect the flash LED cathode to this pin. Connect resistor here to set maximum output current. Charge pump enable / set input control pin. When in the low state, the AAT3174 is powered down and consumes less than 1A. When connected to logic high level, the AAT3174 charge pump is active. This pin should not be left floating. Not connected. Flying capacitor C2 negative terminal. Flying capacitor C2 positive terminal. Connect a 1F capacitor between C2+ and C2-. Charge pump output. Requires 2.2F bypass capacitor to ground. Connect to flash LED anode to drive the LED. Input power supply pin. Requires 4.7F bypass capacitor to ground. Exposed paddle (bottom). Connect to GND directly beneath package.
8 9 10 11 12 EP
N/C C2C2+ OUT VIN
Pin Configuration
TDFN33-12 (Top View)
VIN C1+ C1GND FL RSET
1 2 3 4 5 6
12 11 10 9 8 7
VIN OUT C2+ C2N/C EN/SET
2
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High Current, High Efficiency Charge Pump Absolute Maximum Ratings1
TA = 25C, unless otherwise noted. Symbol
VIN VEN VEN(MAX) IOUT TJ TS TLEAD
AAT3174
Description
Input Voltage EN to GND Voltage Maximum EN to Input Voltage Maximum Output Current Operating Temperature Range Storage Temperature Range Maximum Soldering Temperature (at leads, 10 sec)
Value
-0.3 to 6.0 -0.3 to 6.0 VIN + 0.3 1000 -40 to 150 -65 to 150 300
Units
V V V mA C C C
Thermal Information2
Symbol
JA PD
Description
Thermal Resistance Maximum Power Dissipation
Value
50 2.0
Units
C/W mW
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. Mounted on an FR4 board. 3174.2006.05.1.2
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High Current, High Efficiency Charge Pump Electrical Characteristics1
CIN = 4.7F, COUT = 2.2F, C1 = C2 = 1.0F; TA = -40C to +85C, unless otherwise noted. Typical values are TA = 25C, VIN = 3.6V. Symbol
Power Supply VIN
AAT3174
Description
Input Voltage Range
Conditions
Min
2.7
Typ
Max
5.5
Units
V A mA
ICC
Operating Current
ISHDN(MAX) IOUT(MAX)2 IDX TSS VRSET EN/SET VEN(L) VEN(H) TEN/SET LO TEN/SET HI TEN/SET HI MAX TOFF TLAT Input Current
VIN Pin Shutdown Current Maximum Output Current Output Current Accuracy Soft-Start Time RSET Pin Voltage Enable Threshold Low Enable Threshold High EN/SET Low Time Minimum EN/SET High Time Maximum EN/SET High Time EN/SET Off Timeout EN/SET Latch Timeout EN/SET Input Leakage
1X, No Load Current 3.0 VIN 5.5, 1.5X Mode, No Load Current 3.0 VIN 5.5, 2X Mode, No Load Current EN = 0 VF = 3.6V Programmed for 600mA; RSET = 187k
300 2.0 3.0 800 540 200 0.7 660 4.0 6.0 1.0
A mA mA s V
VIN = 2.7V VIN = 5.5V
0.4 1.4 0.3 50 60 500 500 1 60
-1
V V s ns s s s A
1. The AAT3174 is guaranteed to meet performance specifications from 0C to 70C. Specification over the -40C to +85C operating temperature range is assured by design, characterization, and correlation with statistical process controls. 2. Mounted on an FR4 board.
4
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High Current, High Efficiency Charge Pump Typical Characteristics
VIN = 3.6V, CIN = 4.7F, COUT = 2.2F, C1 = C2 = 1F, TA = 25C, unless otherwise noted.
Efficiency vs. Supply Voltage
100 90 80
AAT3174
Turn-On to 1X Mode
(VIN = 4.2V; ILED = 150mA)
Efficiency (%)
70 60 50 40 30 20 10 0 ILED = 150mA
EN (2V/div)
ILED = 300mA
VOUT (2V/div) VSINK (1V/div) IIN (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 (200s/div)
Turn-On to 1.5X Mode
(VIN = 3.2V; ILED = 150mA)
Turn-On to 1X Mode
(VIN = 4.2V; ILED = 600mA)
EN (2V/div) VOUT (2V/div) VSINK (1V/div) IIN (200mA/div)
EN (2V/div) VOUT (2V/div) VSINK (1V/div) IIN (500mA/div)
Time (200s/div)
Time (200s/div)
Turn-On to 2X Mode
(VIN = 3.2V; ILED = 600mA)
Turn-Off from 1.5X Mode
(VIN = 3.2V; ILED = 150mA)
EN (2V/div) VOUT (2V/div) VSINK (1V/div) IIN (500mA/div)
EN (2V/div) VF (1V/div)
IIN (200mA/div)
Time (200s/div)
Time (200s/div)
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High Current, High Efficiency Charge Pump Typical Characteristics
VIN = 3.6V, CIN = 4.7F, COUT = 2.2F, C1 = C2 = 1F, TA = 25C, unless otherwise noted.
Operating Characteristic
(VIN = 3.3V; 1.5X Mode; ILED = 300mA) VIN (100mV/div) VOUT (200mV/div) VSINK (200mV/div)
AAT3174
Operating Characteristic
(VIN = 2.9V; 2X Mode; ILED = 300mA)
VIN (100mV/div) VOUT (200mV/div) VSINK (200mV/div)
Time (2s/div)
Time (2s/div)
LED Current vs. RSET
(Data = 1)
1000 900 800 700
160 140 120
TLAT vs. VIN
-40C
25C
ILED (mA)
600 500 400 300 200 100 0 100 200 300 400 500 600 700 800 900 1000
TLAT (s)
100 80 60 40 20 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
85C
RSET (k)
Input Voltage (V)
TOFF vs. VIN
180 160 140 120 100 80 60 40 20 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
25C -40C 85C
TOFF (s)
Input Voltage (V)
6
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High Current, High Efficiency Charge Pump Typical Characteristics
VIN = 3.6V, CIN = 4.7F, COUT = 2.2F, C1 = C2 = 1F, TA = 25C, unless otherwise noted.
VIH vs. VIN Over Temperature
1.0 0.9 0.8 1.0
AAT3174
VIL vs. VIN Over Temperature
-40C
0.9 0.8
-40C
VIH (V)
0.7 0.6 0.5 0.4
25C
85C
VIL (V)
0.7 0.6 0.5 0.4
25C
85C
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
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
Input Voltage (V)
Input Voltage (V)
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High Current, High Efficiency Charge Pump Functional Block Diagram
C1+ C1C2+ C2-
AAT3174
VIN
Charge Pump Section 1 Charge Pump Section 2
1MHz Oscillator Soft-Start Control
OUT
FL
EN/SET
System Control; S2Cwire; Timing
RSET
GND
Functional Description
The AAT3174 is a high efficiency, low noise, dual stage tri-mode 1X/1.5X/2X charge pump device intended for photo-flash LED applications. The device requires only four external components: two ceramic capacitors for the charge pump flying capacitors, one ceramic capacitor for CIN, and one ceramic capacitor for COUT. The charge pump is designed to deliver regulated load currents up to 800mA. The dual stage charge pump section contains soft-start circuitry to prohibit excessive inrush current during start-up. System efficiency is maximized with a tri-mode, dual stage charge pump topology. The internal clock oscillator at 1MHz allows the use of small external components.
The tri-mode charge pump operation further optimizes power conversion efficiency. Depending upon the variance of load current (at different modes), input voltage, and nominal LED forward voltage, the charge pump will operate in a 1X, 1.5X, or 2X mode to generate the output voltage required to power the load for a given controlled constant current. This results in significant power savings over voltage doubling architectures, especially when the LEDs are also operated at lower current levels in movie, viewing, or flashlight modes.
S2Cwire Serial Interface
The AAT3174 utilizes Analogic Tech's single wire S2Cwire interface to enable/disable the charge pump and adjust the output current at 16 current levels. Each code defines the output current to be a percentage of the maximum current set by the resistor at the RSET pin (see Table 1).
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High Current, High Efficiency Charge Pump
Total Output (% of IMAX)
100.0 89.1 79.4 70.8 63.1 56.2 50.1 44.7 39.8 35.5 31.6 28.2 25.1 22.4 20.0 0.0
AAT3174
Data
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
The S2Cwire interface records rising edges of the EN/SET pin and decodes them into 16 individual current level settings with Code 1 reserved for maximum 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 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 AAT3174 enters into shutdown mode and draws less than 1A from VIN. Data and address registers are reset to 0 during shutdown.
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
0
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High Current, High Efficiency Charge Pump Application Information
Flash/Torch Control Using the RSET Pin
An alternative method can be used for flash/torch control that eliminates the need to use the S2Cwire single-wire interface. By using any typical digital I/O port, an additional enable can be created (see Figure 1). The I/O port output configuration can be any one of open-drain NMOS, open-drain PMOS, or push-pull type. The control will always act as an active-low flash enable or, equivalently, an active-high torch enable (see Table 2). EN
0 0 1 1
AAT3174
According to I/O port type, the following equations can be used to calculate appropriate resistor values. For an open-drain NMOS I/O port output configuration, the line is pulled low to GND or left floating, according to state. To calculate the appropriate R1 and R2 resistor values, first calculate the R1 resistor value needed for the desired torch level LED current:
R1 =
600mA * 187k ILED (torch)
ENFL
0 1 0 1
Mode
Off Off Flash Torch
Next, choose R2 based on the desired flash level LED current:
R1 * 600mA * 187k R1 * ILED (flash) - 600mA * 187k
R2 =
Table 2: Flash/Torch Control Modes.
The current and resistance values used in the equations come from the conditions placed on the IDX parameter of the Electrical Characteristics table.
C1 1F C2 1F
C1+ 2.7V to 5.5V
CIN 4.7F
C1- C2+
C2VOUT
VIN
AAT 3174
COUT 2.2F
Flash LED
EN
EN/SET GND
F1 RSET
R1 R2
ENFL
Figure 1: Flash/Torch Control Using the RSET Pin.
10
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High Current, High Efficiency Charge Pump
For examples of standard 1% values where the LED flash current level is targeted for 700mA, see Table 3. R1 (k)
920 732 649 562
AAT3174
Next, choose a reasonable value for R1. A value that is slightly larger than RSET, calculated from above, is appropriate. Calculate R2 and then calculate the torch mode current level that results:
RSET * R1 R1 - RSET VIO R 2 - R1 R1 * R2 0.7V * R2
R2 (k)
193 205 210 223
ILED Torch (mA)
122 153 173 200
ILED Flash (mA)
703 701 707 703
R2 =
ILED (torch) = 600mA * 187k *
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 example, the necessary values can then be calculated. As a reference, the equations applicable to the PMOS case are:
Once again, the current and resistance values used in the equations come from the conditions placed on the IDX parameter of the Electrical Characteristics table. 0.7V is the typical value for the VRSET parameter. The value to use for VIO must come from the I/O supply voltage used in the system. Example standard 1% values are provided in Table 4. R1 (k)
169 165 162 160
R1 =
600mA * 187k ILED (flash)
R2 (k)
1000 1000 1000 1000
ILED Torch (mA)
95 111 124 132
ILED Flash (mA)
776 792 805 813
VIO -1 0.7 R2 = ILED (torch) 1 R1 600mA * 187k
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. For a push-pull I/O port output configuration, first calculate the overall RSET value needed for the desired flash level LED current:
Table 4: Push-Pull I/O Example Resistor Values. In all of the approaches mentioned, the open-drain NMOS or PMOS type configurations offer the most flexibility for current level selection. When configured as an output, if the I/O port is only push-pull type, then the equivalent open-drain NMOS can also be realized. To realize this, activate the port as output only when driving the line low. Otherwise, to release the line, set the port to be tri-stated.
RSET =
600mA * 187k ILED (flash)
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High Current, High Efficiency Charge Pump
Device Power Efficiency
The AAT3174 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. current. For ideal conversion, the 2X mode efficiency is given by:
VF VF * ILED = VIN * 2IIN 2 * VIN
AAT3174
=
=
POUT PIN
LED Selection
The AAT3174 is designed to drive high-intensity white LEDs. It is particularly suitable for LEDs with an operating 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 AAT3174 provides a high-current, programmable ideal constant current source.
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,
V V *I = F LED F VIN * IIN VIN
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. In general, low ESR may be defined as less than 100m. A value of 1F for the flying capacitors is a good starting point when choosing capacitors. If the LED current sinks are only programmed for light current levels, then the capacitor size may be decreased. Ceramic composition capacitors are highly recommended over all other types of capacitors for use with the AAT3174. 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.
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 introduces negligible voltage drop from input to output. The AAT3174 further maintains optimized performance and efficiency by detecting when the input voltage is not sufficient to sustain LED current. The device automatically 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:
VF VF * ILED = VIN * 1.5IIN 1.5 * VIN
=
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 capac3174.2006.05.1.2
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 output voltage can be boosted to twice the input voltage. The doubling conversion ratio introduces a corresponding doubling of the input 12
High Current, High Efficiency Charge Pump
itors and can range to more than several ohms for tantalum or aluminum electrolytic capacitors. The junction-to-ambient thermal resistance (JA) for the package can be significantly reduced by following a couple of important PCB design guidelines. The PCB area directly underneath the package should be plated so that the exposed paddle can be mated to the top layer PCB copper during the re-flow process. This area should also be connected to the top layer ground pour when available. Further, multiple copper plated thru-holes should be used to electrically and thermally connect the top surface paddle area to additional ground plane(s) and/or the bottom layer ground pour. The chip ground is internally connected to both the paddle and the GND pin. The GND pin conducts large currents and it is important to minimize any differences in potential that can result between the GND pin and exposed paddle. It is good practice to connect the GND pin to the exposed paddle area using a trace as shown in Figure 2.
AAT3174
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 are often available in lower-cost dielectrics, but capacitors greater than 4.7F are not typically required for AAT3174 applications. Capacitor area is another contributor to ESR. Capacitors that are physically large will have a lower ESR when compared to an equivalent material smaller capacitor. These larger devices can improve circuit transient response when compared to an equal value capacitor in a smaller package size.
Thermal Protection
The AAT3174 has a thermal protection circuit that will shut down the charge pump if the die temperature rises above the thermal limit, as is the case during a short-circuit of the OUT pin.
PCB Layout
To achieve adequate electrical and thermal performance, careful attention must be given to the PCB layout. In the worst-case operating condition, the chip must dissipate considerable power at full load. Adequate heat-sinking must be achieved to ensure intended operation. Figure 2 illustrates an example of an adequate PCB layout. The bottom of the package features an exposed metal paddle. The exposed paddle acts, thermally, to transfer heat from the chip and, electrically, as a ground connection. Figure 2: Example PCB Layout. The flying capacitors C1 and C2 should be connected close to the chip. Trace length should be kept short to minimize path resistance and potential coupling. The input and output capacitors should also be placed as close to the chip as possible.
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High Current, High Efficiency Charge Pump Ordering Information
Package
TDFN33-12
AAT3174
Marking1
RSXYY
Part Number (Tape and Reel)2
AAT3174IWP-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
Index Area (D/2 x E/2)
TDFN33-12
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
Top View
Bottom View
Pin 1 Indicator (optional)
7.5 7.5
+ 0.05 0.8 -0.20
0.229 0.051
0.05 0.05
Option A: C0.30 (4x) max Chamfered corner
Option B: R0.30 (4x) max Round corner
Detail "B"
Side View
All dimensions in millimeters. 1. XYY = assembly and date code. 2. Sample stock is generally held on part numbers listed in BOLD.
(c) Advanced Analogic Technologies, Inc.
Detail "A"
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. AnalogicTech and the AnalogicTech logo are trademarks of Advanced Analogic Technologies Incorporated. All other brand and product names appearing in this document are registered trademarks or trademarks of their respective holders.
Advanced Analogic Technologies, Inc.
830 E. Arques Avenue, Sunnyvale, CA 94085 Phone (408) 737-4600 Fax (408) 737-4611 14
3174.2006.05.1.2
0.23 0.05
0.45 0.05
Detail "A"
3.00 0.05
1.70 0.05

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