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High Efficiency 1.5X Fractional Charge Pump For White LED Applications General Description
The AAT3194 is a low noise, constant frequency charge pump DC/DC converters that use fractional (1.5X) conversion to increase efficiency in white LED applications. The devices can be used to produce current levels up to 20mA for each output from a 2.7V to 5.5V input. A low external parts count (two 1F flying capacitors and two small bypass capacitors at IN and OUT) makes these devices ideally suited for small, battery-powered applications. AnalogicTech's Simple Serial ControlTM (S2CwireTM) interface is used to enable, disable, and set the LED drive current for 32-level logarithmic scale LED brightness control. The AAT3194 has a thermal management system for protection in the event of a short-circuit condition on any of the output pins. Built-in soft-start circuitry prevents excessive inrush current during start-up. A high switching frequency enables the use of small external capacitors. A lowcurrent shutdown feature disconnects the load from VIN and reduces quiescent current to less than 1A. The AAT3194 is available in a Pb-free 12-pin TSOPJW package.
AAT3194
Features
* * * * * * * * * * * * * *
ChargePumpTM
VIN Range: 2.7V to 5.5V 20mA Full-Scale Current Simple Serial Control (S2Cwire) Interface -- 32-Position Logarithmic Scale with Digital Control Low Noise Constant Frequency Operation 33% Less Input Current Than Doubler Charge Pump High Accuracy Brightness Matching Small Application Circuit Regulated Output Current Automatic Soft Start No Inductors 600kHz Switching Frequency IQ <1A in Shutdown Temperature Range: -40C to 85C 12-Pin TSOPJW Package
Applications
* * Programmable Current Source White LED Backlighting
Typical Application
IN C1+ C1 1F OUT VBATTERY CIN 1F COUT 1F C1C2+ C2 1F
AAT3194
C2D1 D2 D3
EN/SET
EN/SET GND
D4 D4 D3 D2 D1
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High Efficiency 1.5X Fractional Charge Pump For White LED Applications Pin Descriptions
Pin #
1 2 3 4 5 6 7 8 9 10 11 12
AAT3194
Symbol
C2+ OUT C1C1+ D4 D3 D2 D1 EN/SET IN GND C2-
Function
Flying capacitor 2 positive terminal. Connect a 1F ceramic capacitor between C2+ and C2-. Charge pump output. Requires 1F bypass capacitor to ground. Flying capacitor 1 negative terminal. Flying capacitor 1 positive terminal. Connect a 1F ceramic capacitor between C1+ and C1-. Current source output 4. Current source output 3. Current source output 2. Current source output 1. Required reference current source. Do not leave pin floating. Control pin using S2Cwire serial interface. Input power supply. Requires 1F or larger ceramic capacitor to ground. Ground. Flying capacitor 2 negative terminal.
Pin Configuration
TSOPJW-12 (Top View)
C2+ OUT C1C1+ D4 D3
1 2 3 4 5 6
12 11 10 9 8 7
C2GND IN EN/SET D1 D2
2
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High Efficiency 1.5X Fractional Charge Pump For White LED Applications Absolute Maximum Ratings
TA = 25C, unless otherwise noted. Symbol
VIN VOUT VEN/SET VEN/SET(MAX) IOUT TJ
AAT3194
Description
Input Voltage Charge Pump Output EN/SET to GND Voltage Maximum EN/SET to Input Voltage Maximum DC Output Current (sum of IOUT and D currents) Operating Junction Temperature Range
Value
-0.3 to 6 -0.3 to 6 -0.3 to 6 0.3 120 -40 to 150
Units
V V V V mA C
Thermal Information1
Symbol
JA PD
Description
Thermal Resistance Maximum Power Dissipation2
Value
160 625
Units
C/W mW
1. Mounted on an FR4 board. 2. Derate 6.25mW/C above 25C 3194.2006.09.1.0
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High Efficiency 1.5X Fractional Charge Pump For White LED Applications Electrical Characteristics
VIN = 3.5V, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = 25C. Symbol Description Conditions Min Typ Max Units
2.7 Active, No Load Current EN = 0V 3.0V VIN 5.5V, TA = 25C, All Outputs Max Current 3.0V VIN 5.5V VD1:Dn = 3.6V, VIN = 3.3V VIN = 3.5V, IOUT(total) = 40mA 3 1 24 3 0.3 93 400 300 VIN = 2.7V to 5.5V VIN = 2.7V to 5.5V 0.5 1.4 0.3 50 500 VIN = 5.5V -1 1 75 V mA A mA %/V % % s kHz V V s ns s A
AAT3194
Input Power Supply VIN Operation Range ICC Operating Current ISHDN Shutdown Current IDX Output Current Output Current Line ID/VIN Regulation Current Matching Between Any I(D-Match) Two Outputs Efficiency Charge Pump tSS Soft-Start Time FCLK Clock Frequency EN/SET VEN(L) Enable Threshold Low VEN(H) Enable Threshold High tLO EN/SET Low Time Minimum EN/SET tHI High Time tOFF EN/SET Off Timeout Input EN/SET Input Leakage Current
16 -3
20
4
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High Efficiency 1.5X Fractional Charge Pump For White LED Applications Typical Characteristics
VIN = 3.5V, CIN = COUT = C1 = C2 = 1F; TA = 25C, unless otherwise noted.
AAT3194
Quiescent Current vs. Temperature
100 1.00 0.98 0.96 95
Efficiency vs. Supply Voltage
30mA 20mA
Efficiency (%)
90 85 80 75 70 65 60
IQ (mA)
0.94 0.92 0.90 0.88 0.86 -40 -20 0 20 40 60 80 100
40mA 80mA 60mA
3.0
3.2
3.4
3.6
3.8
4.0
4.2
4.4
Temperature (C)
Supply Voltage (V)
Quiescent Current vs. Supply Voltage
1.2 1.1 1.0 96 94
Efficiency vs. Load Current
Efficiency (%)
92 90 88 86 84 82 80 0 20 40 60 80
IQ (mA)
0.9 0.8 0.7 0.6 3.0 3.5 4.0 4.5 5.0 5.5
Supply Voltage (V)
Load Current (mA)
Shutdown Current vs. Temperature
1.000 710 700 690 680
Oscillator Frequency vs. Temperature
Shutdown Current (A)
FOSC (kHz)
-20 0 20 40 60 80 100
0.100
670 660 650 640 630 620 610 -40 -20 0 20 40 60 80 100
0.010
0.001 -40
Temperature (C)
Temperature (C)
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High Efficiency 1.5X Fractional Charge Pump For White LED Applications Typical Characteristics
VIN = 3.5V, CIN = COUT = C1 = C2 = 1F; TA = 25C, unless otherwise noted.
AAT3194
Normalized I DIODE vs. Temperature
1.02 1.01 1.00
IDIODE Response
(-31dB to 0dB)
ENSET (2V/div) 0dB
IDIODE
0.99 0.98 0.97 0.96 0.95 -40 -20 0 20 40 60 80 100
IDIODE -31dB Temperature (C)
Time (10s/div)
IDIODE vs. VIN
100 80
IDIODE Response
(-9dB to -10dB)
IDIODE (mA)
ENSET (2V/div) 0dB -10dB IDIODE -9dB
3.0 3.5 4.0 4.5
60 40 20 0
-31dB
VIN (V)
Time (10s/div)
IDIODE vs. VDIODE
100 1.000
VIH and VIL vs. VIN
VIH and VIL (V)
80
0.975 0.950 0.925 0.900 0.875 0.850 0.825 0.800 0.775 0.750
IDIODE (mA)
60 40 20 0 3.0 3.2 3.4 3.6 3.8 4.0
VIH VIL
2.5
3.0
3.5
4.0
4.5
5.0
5.5
V DIODE (V)
VIN (V)
6
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High Efficiency 1.5X Fractional Charge Pump For White LED Applications Typical Characteristics
VIN = 3.5V, CIN = COUT = C1 = C2 = 1F; TA = 25C, unless otherwise noted.
AAT3194
Turn-On
ENSET (2V/div) OUT (5V/div) VDIODE (2V/div) IIN (50mA/div) Time (100s/div) ENSET (2V/div) OUT (5V/div) VDIODE (5V/div) IIN (50mA/div)
Turn-Off
Time (200s/div)
40mA Load Characteristics
60mA Load Characteristics
IN
IN
10mV/div
OUT
OUT
VDIODE Time (1s/div)
VDIODE
20mV/div
Time (1s/div)
80mA Load Characteristics
IN
OUT
VDIODE
20mV/div
Time (1s/div)
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High Efficiency 1.5X Fractional Charge Pump For White LED Applications Functional Block Diagram
IN
AAT3194
Soft Start 600kHz Oscillator Voltage Reference 1.5X Charge Pump
C1+ C1C2+ C2OUT
EN/SET
S2Cwire Interface
5
32x8 bit ROM
8
Current Mode DAC
D1 D2 D3 D4
GND
Functional Description
The AAT3194 is a high efficiency 1.5X fractional charge pumps intended for white LED backlight applications. The fractional charge pump consists of a linear regulator followed by a 1.5X charge pump. The AAT3194 requires only four external components: two 1F ceramic capacitors for the charge pump flying capacitors (C1 and C2), one 1F ceramic capacitor for CIN, and one 0.33F to 1F ceramic capacitor for COUT. The charge pump output is converted into four constant current outputs (D1 to D4) to drive four individual LEDs with a maximum of 20mA each. The current source output magnitude is controlled by the EN/SET serial data S2Cwire interface. The interface records rising edges of the EN/SET pin and decodes them into 32
individual current level settings each 1dB apart (see Table 1, Current Level Settings). Code 32 is full scale, and Code 1 is full scale attenuated by 31dB. The modulo 32 interface wraps states back to state 1 after the 32nd clock. With each EN/SET pulse, the output current increases by 1dB. To decrease the output current by 1dB, 31 EN/SET clock pulses are required. The counter can be clocked at speeds up to 1MHz, so intermediate states are not visible. The first rising edge of EN/SET enables the IC and initially sets the output LED current to -31dB, the lowest setting equal to 525A. Once the final clock cycle is input for the desired brightness level, the EN/SET pin is held high to maintain the device output current at the programmed level. The device is disabled 500s after the EN/SET pin transitions to a logic low state.
8
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High Efficiency 1.5X Fractional Charge Pump For White LED Applications Applications Information
Current Level Settings
LED current level is set via the serial interface according to a logarithmic scale where each code is 1dB greater than the previous code. In this manner, the LED brightness appears linear with each increasing code.
AAT3194
Normalized Current Level Settings
1.0
Normalized Current to Full Scale
0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
Code
Code
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
20mA max
0.549 0.627 0.706 0.784 0.863 1.020 1.098 1.255 1.412 1.569 1.804 1.961 2.275 2.510 2.824 3.137
Code
17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
20mA max
3.529 4.000 4.471 5.020 5.647 6.353 7.059 7.922 8.941 10.039 11.216 12.627 14.118 15.843 17.804 20.000
Table 1: Current Level Settings.
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High Efficiency 1.5X Fractional Charge Pump For White LED Applications
EN/SET Serial Interface
The current source output magnitude is controlled by the EN/SET pin using AnalogicTech's Simple Serial Control (S2Cwire) interface. The interface records rising edges of the EN/SET pin and decodes them into 32 individual current level settings each 1dB apart. Code 32 is full scale, and Code 1 is full scale attenuated by 31dB. The modulo 32 interface wraps states back to state 1 after the 32nd clock, so 1dB of attenuation is achieved by clocking the EN/SET pin 31 times (see graph titled, "IDIODE Response -9dB to -10dB"). The counter can be clocked at speeds up to 1MHz, so intermediate states are not visible. The first rising edge of EN/SET enables the IC and initially sets the output LED current to -31dB, the lowest setting equal to 525A. Once the final clock cycle is input for the desired brightness level, the EN/SET pin is held
tHI
AAT3194
high to maintain the device output current at the programmed level. The device is disabled 500s after the EN/SET pin transitions to a logic low state. The EN/SET timing is designed to accommodate a wide range of data rates. After the first rising edge of EN/SET, the charge pump is enabled and reaches full capacity after the soft-start time (TSS). During the soft-start time, multiple clock pulses may be entered on the EN/SET pin to set the final output current level with a single burst of clocks. Alternatively, the EN/SET clock pulses may be entered one at a time to gradually increase the LED brightness over any desired time period. A constant current is sourced as long as EN/SET remains in a logic high state. The current source outputs are switched off after EN/SET has remained in a low state for at least the tOFF timeout period (see Figure 1).
tLO
tOFF
EN/SET Code
OFF
1
2
3
OFF
Figure 1: EN/SET Timing Diagram.
LED Selection
The AAT3194 is designed to drive white LEDs with forward voltages to 4.2V. Since the D1:D4 output current sources are matched with negligible voltage dependence, the LED brightness will be matched regardless of their forward voltage matching.
In addition, with an ideal 1.5X charge pump, the output current may be expressed as 2/3 of the input current. The expression to define the ideal efficiency () can be rewritten as:
VOUT * IOUT V POUT = = OUT PIN VIN * 1.5IOUT 1.5VIN
=
Charge Pump Efficiency
The AAT3194 uses a fractional charge pump. The efficiency () can be simply defined as a linear voltage regulator with an effective output voltage that is equal to one and one half times the input voltage. Efficiency () for an ideal 1.5X charge pump can typically be expressed as the output power divided by the input power: -or-
(%) = 100
VOUT 1.5VIN
=
POUT PIN
For a charge pump with an output of 5 volts and a nominal input of 3.5 volts, the theoretical efficiency is 95%. Due to internal switching losses and IC quiescent current consumption, the actual efficiency can be measured at 93%. These figures are in close agreement for output load conditions from 1mA to 100mA. Efficiency will decrease as load
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High Efficiency 1.5X Fractional Charge Pump For White LED Applications
current drops below 0.05mA or when the level of the power supply of IN approaches OUT. Refer to the Typical Characteristics section of this datasheet for measured plots of efficiency versus input voltage and output load current for the given charge pump output voltage options. formance. 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 all four capacitors is a good starting point when choosing capacitors. If the LED current sources are only programmed for minimal current levels, then the capacitor size may be decreased.
AAT3194
Power Efficiency and Device Evaluation
The charge pump efficiency discussion in the previous section only accounts for efficiency of the charge pump section itself. Due to the unique circuit architecture and design of the AAT3194, it is very difficult to measure efficiency in terms of a percent value comparing input power over output power. Since the device outputs are pure constant current sources, it is difficult to measure the output voltage for a given output (D1 to D4) to derive an output power 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 when taken in the context of comparing to other white LED driver circuit topologies. A better way to quantify total device efficiency is to observe the total input power to the device for a given LED current drive level. The best white LED driver for a given application should be based on trade-offs of size, external components count, reliability, operating range, and total energy usage...not just "% efficiency."
AAT3194 Input Power vs. LED Current
700 600
Capacitor Characteristics
Ceramic composition capacitors are highly recommended over all other types of capacitors for use with the AAT3194. 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. 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 low-cost Y5V and Z5U dielectrics, but capacitors greater than 1F are not typically required for AAT3194 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.
VIN = 3.6V
Input Power (mW)
500 400 300 200 100 0 0 20 40 60 80 100
Output (LED) Current (mA)
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 per3194.2006.09.1.0
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High Efficiency 1.5X Fractional Charge Pump For White LED Applications
Test Current/Channel Disable
Each channel of the output is equipped with a test current function. The AAT3194 uses a small (~2A) current source injected into each output pin to detect the presence of an LED. Unused channels that are tied to ground or LED load fail short will be automatically diasbled instead of wasting the programmed output current.
AAT3194
Thermal Protection
The AAT3194 has a thermal protection circuit that will shut down the charge pump and current outputs if the die temperature rises above the thermal limit.
Application Circuits
Typical AAT3194 Application Circuit:
IN
C1+ C1 1F
OUT VBATTERY CIN 1F COUT 1F
C1C2+ C2 1F
AAT3194
C2D1 D2 D3 D4
EN/SET
EN/SET GND
D4
D3
D2
D1
THI > 50ns
300ns < TLO < 75s
50ns minimum to enable
ON/1
2
3
4
5
6
n (n < =32)
OFF
Enable / Disable / LED Brightness Level Set Data Input
12
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High Efficiency 1.5X Fractional Charge Pump For White LED Applications Ordering Information
Package
TSOPJW-12
AAT3194
Marking1
UUXYY
Part Number (Tape and Reel)2
AAT3194ITP-20-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
+ 0.10 - 0.05
TSOPJW-12
0.20
2.40 0.10
0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC
2.85 0.20
7 NOM 3.00 0.10
0.9625 0.0375
0.04 REF
0.15 0.05
+ 0.10 1.00 - 0.065
0.055 0.045
4 4
0.010
0.45 0.15 2.75 0.25
All dimensions in millimeters.
1. XYY = assembly and date code. 2. Sample stock is generally held on part numbers listed in BOLD. 3194.2006.09.1.0
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High Efficiency 1.5X Fractional Charge Pump For White LED Applications
AAT3194
(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. 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
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