AAT3122_05 ANALOGICTECH | Alldatasheet

Document overview

  • Manufacturer or author: Provided By ALLDATASHEET.COM(FREE DATASHEET DOWNLOAD SITE)
  • PDF pages: 12

Technical content

Features

  • V IN Range: 2.7V to 5.5V
  • <1µA of Shutdown Current
  • 1 MHz Switching Frequency
  • Dual Mode 1X and 1.5X Charge Pump for Maximum Efficiency
  • Only Four External Components
  • Simple Serial Control (S 2Cwire) Interface
  • Low Noise Constant Frequency Operation
  • 33% Less Input Current Than Doubler Charge Pumps
  • Small Application Circuit
  • Regulated Output Current
  • Automatic Soft Start
  • No Inductors
  • TSOPJW-12 Package
  • -40°C to +85°C Temperature Range

Applications

  • Programmable Current Source
  • White LED Backlighting Typical Application CIN 1µF VBATTERY COUT 1µF EN/SET 1µF 1µF VIN VOUT C1+ C1- C2+ C2- DEN/SET GND AAT3122 D2 D3 D4 D5 D6

High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications 2 3122.2005.11.1.3 Pin Descriptions Pin Configuration TSOPJW-12 (Top View) C2+ OUT C1- C1+ D D C2- GND IN EN/SET D D Pin # Symbol Function 1 C2+ Flying capacitor 2 positive terminal. Connect a 1µF capacitor between C2+ and C2-. 2 OUT Charge pump output. Requires 1µF bypass capacitor to ground. 3 C1- Flying capacitor 1 negative terminal. 4 C1+ Flying capacitor 1 positive terminal. Connect a 1µF capacitor between C1+ and C1-. 5, 6, 7, 8 D Output current source with drive capability of up to 120mA. 9 EN/SET Input control pin. Serial data interface that controls the level of output current. See Application Information for more details. 10 IN Input power supply. Requires 1µF bypass capacitor to ground. 11 GND Ground. 12 C2- Flying capacitor 2 negative terminal.

Symbol Description Value Units ΘJA Thermal Resistance 160 °C/W PD Maximum Power Dissipation (TA = 25°C)4 625 mW Symbol Description Value Units VIN Input Voltage -0.3 to 6.0 V VOUT Charge Pump Output -0.3 to 6.0 V VEN/SET EN/SET to GND Voltage -0.3 to 6.0 V VEN/SET(MAX) Maximum EN/SET to Input Voltage 0.3 V IOUT

2 Maximum DC Output Current 150 mA

TJ Operating Junction Temperature Range -40 to 150 °C AAT3122 High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications 3122.2005.11.1.3 3 1. Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at condi- tions 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 6.25mW/°C above 25°C.

High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications 4 3122.2005.11.1.3 Electrical Characteristics1 VIN = 3.5V; CIN = COUT = C1 = C2 = 1.0µF; TA = -40°C to +85°C. Unless otherwise noted, typical values are TA = 25°C. Symbol Description Conditions Min Typ Max Units Input Power Supply VIN Operation Range 2.7 5.5 V Icc Operating Current 3.0 ≤ VIN ≤ 5.5, Active, 1.8 3.5 mANo Load Current ISHDN Shutdown Current EN = 0 1.0 µA ID Maximum Output Current V IN = 3.5V; Code = 32 108 120 132 mA Charge Pump TSS Soft-Start Time 200 µs FCLK Clock Frequency 1000 kHz ηCP Charge Pump Efficiency VIN = 3.6V, IOUT(T otal)= 120mA; 93 %Measured from IN to OUT EN/SET VEN(L) Enable Threshold Low V IN = 2.7V to 5.5V 0.5 V VEN(H) Enable Threshold High V IN = 2.7V to 5.5V 1.4 V TLO EN/SET Low Time 0.3 75 µs THI Minimum EN/SET High Time 50 ns TOFF EN/SET Off Timeout 500 µs Input Current EN/SET Input Leakage -1.0 1.0 µA 1. The AAT3122 is guaranteed to meet performance specifications over the -40°C to +85°C operating temperature range and is assu red by design, characterization, and correlation with statistical process controls.

High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications 3122.2005.11.1.3 5 Typical Characteristics Unless otherwise noted, VIN = 3.6V, CIN = COUT = C1 = C2 = 1µF, TA = 25°C. VIH and VIL vs. VIN 0.600 0.625 0.650 0.675 0.700 0.725 0.750 0.775 0.800 0.825 0.850 VIN (V) VIH VIL Quiescent Current vs. VIN 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 VIN (V) Quiescent Current (mA) VDIODE = 3.3V VDIODE = 3.4V VDIODE = 3.5V VDIODE = 3.6V IDIODE vs. VIN VIN (V) IDIODE (mA) VDIODE = 3.3V VDIODE = 3.4V VDIODE = 3.5V VDIODE = 3.6V Efficiency vs. VIN (ID = 80mA) 100 VIN (V) Efficiency (%) VDIODE = 3.3V VDIODE = 3.4V VDIODE = 3.5V VDIODE = 3.6V

High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications 6 3122.2005.11.1.3 Typical Characteristics Unless otherwise noted, VIN = 3.6V, CIN = COUT = C1 = C2 = 1µF, TA = 25°C. 80mA Load Characteristics Time (1µs/div) 20mV/div VIN OUT VDIODE Turn-Off Time (200µs/div) ENSET (1V/div) VDIODE (2V/div) IIN (100mA/div) Load Switch to Charge Pump (80mA) Time (50µs/div) VIN (20mV/div) OUT (1V/div) VDIODE (1V/div) IIN (200mV/div) Charge Pump to Load Switch (80mA) Time (50µs/div) VIN (10mV/div) OUT (2V/div) VDIODE (2V/div) IIN (100mA/div) Turn-On to Full-Scale Load Switch Time (50µs/div) ENSET (1V/div) OUT (2V/div) VDIODE (2V/div) IIN (100mA/div) Turn-On to Full-Scale Charge Pump Time (50µs/div) ENSET (1V/div) OUT (2V/div) VDIODE (1V/div) IIN (200mA/div)

1.5X Charge Pump S2Cwire Interface 32x8 bit ROM Current Mode DAC VIN C1+ C1- C2+ C2- OUT D GND EN/SET AAT3122 High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications 3122.2005.11.1.3 7 Functional Description The AAT3122 is a dual mode load switch (1X) and high efficiency (1.5X) fractional charge pump device intended for white LED backlight applications. The fractional charge pump consists of a low dropout lin- ear voltage regulator followed by a 1.5X charge pump. To maximize power conversion efficiency, an internal feedback control sensing circuit monitors the voltage required on the constant current source output. This control circuit then sets the load switch and charge pump functions based upon the input voltage level versus the output voltage level needed. This function significantly enhances overall device efficiency when the input voltage level is greater than the voltage required at the constant current source output. Switchover between the 1.5X (charge pump) operating mode and the 1X (load switch) mode occurs automatically (as a function of input and output voltages) and does not require user intervention to maintain maximum efficiency. The AAT3122 requires only four external compo- nents: two 1µF ceramic capacitors for the charge pump flying capacitors (C 1 and C 2), one 1µF ceramic capacitor for C IN, and one 0.33µF to 1µF ceramic capacitor for COUT. The LDO/1.5X charge pump output is converted into a constant current output capable of driving up to six individual LEDs with a maximum of 20mA each. The current source output magnitude is controlled by the EN/SET seri- al data S 2Cwire interface. The interface records ris- ing edges of the EN/SET pin and decodes them into 32 individual current level settings each 1dB apart. This is summarized in Figure 1 and Table 1. 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.

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 man- ner, the LED brightness appears linear with each increasing code. Table 1 depicts the relationship between each rising edge of the EN/SET and the output current in mA. Table 1: Current Level Settings. EN/SET Serial Interface The current source output magnitude is controlled by the EN/SET serial interface. The interface records rising edges of the EN/SET pin and decodes them into 32 individual current level set- tings each 1dB apart. Code 32 is full scale, and Code 1 is full scale attenuated by 31dB. The mod- ulo 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. The counter can be clocked at speeds up to 1MHz, so interme- diate states are not visible. The first rising edge of EN/SET enables the IC and initially sets the output LED current to 3.3mA, the lowest setting. 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 500µs after the EN/SET pin tran- sitions 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 reach- es full capacity after the soft-start time (T SS). 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 T OFF timeout period. Code I OUT (mA) Code I OUT (mA) 1 3.3 17 21.2 2 3.8 18 24.0 3 4.2 19 26.8 4 4.7 20 30.1 5 5.2 21 33.9 6 6.1 22 38.1 7 6.6 23 42.4 8 7.5 24 47.5 9 8.5 25 53.6 10 9.4 26 60.2 11 10.8 27 67.3 12 11.8 28 75.8 13 13.6 29 84.7 14 15.1 30 95.1 15 16.9 31 106.8 16 18.8 32 120.0 AAT3122 High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications 8 3122.2005.11.1.3 Figure 1: Normalized Current Level Settings. 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1 2 3 4 5 6 7 8 91 01 11 21 31 41 51 61 71 81 92 02 12 22 32 42 52 62 72 82 93 03 13 2 Code Normalized Current to Full Scale

The AAT3122 is specifically intended for driving white LEDs. However, the device design will allow the AAT3122 to drive most types of LEDs with forward voltage specifications ranging from 2.0V to 4.3V. LED applications may include main and sub-LCD dis- play 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. Device Switching Noise Performance The AAT3122 operates at a fixed frequency of approximately 1MHz to control noise and limit har- monics that can interfere with the RF operation of cellular telephone handsets or other communica- tion devices. Back-injected noise appearing on the input pin of the charge pump is 20mV peak-to- peak, typically ten times less than inductor-based DC/DC boost converter white LED backlight solu- tions. The AAT3122 soft-start feature prevents noise transient effects associated with inrush cur- rents during start-up of the charge pump circuit. Power Efficiency and Device Evaluation Due to the unique charge pump circuit architecture and design of the AAT3122, it is very difficult to measure efficiency in terms of a percent value comparing input power over output power. Since the AAT3122 output is purely a constant cur- rent source, it is difficult to measure the output volt- age to derive an overall output power measure- ment. For any given application, white LED forward voltage levels can differ, yet the output drive cur- rent 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 applica- tion should be based on trade-offs of size, external component count, reliability, operating range, and total energy usage...not just % efficiency. Charge Pump Efficiency The AAT3122 is a fractional charge pump. The effi- ciency (η) can be simply defined as a linear voltage reg- ulator with an effective output voltage that is equal to one and a half times the input voltage. Efficiency (η) for an ideal 1.5X charge pump can typically be expressed as the output power divided by the input power. η = P OUT PIN 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 (η) can be rewritten as: η = P OUT = (VOUT x IOUT)/(VIN x 1.5IOUT) = VOUT PIN 1.5VIN η(%) = 100 ⎛ VOUT ⎞ ⎝1.5VIN⎠ For a charge pump with an output of 5 volts and a nom- inal input of 3.5 volts, the theoretical efficiency is 95%. Due to internal switching losses and IC quiescent cur- rent consumption, the actual efficiency can be meas- ured at 93%. These figures are in close agreement for output load conditions from 3.0mA to 120mA. Efficiency will decrease as load current drops below 0.05mA or when the level of V IN approaches VOUT. Refer to the Typical Characteristics section for measured plots of efficiency versus input voltage and output load current for the given charge pump output voltage options. AAT3122 High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications 3122.2005.11.1.3 9 EN/SET Timing Diagram EN/SET Code 1 2 3 OFFOFF tHI tLO tOFF

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 per- formance. Optimum performance will be obtained when low ESR ceramic capacitors are used. In general, low ESR may be defined as less than 100mΩ. When choosing the four capacitors, a capacitor value of 1µF is a good starting point. 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 recom- mended over all other types of capacitors for use with the AAT3122 products. Ceramic capacitors offer many advantages over their tantalum and alu- minum electrolytic counterparts. A ceramic capaci- tor 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 impor- tant characteristic to consider when selecting a capacitor. ESR is a resistance internal to a capac- itor that is caused by the leads, internal connec- tions, size or area, material composition, and ambi- ent temperature. Capacitor ESR is typically meas- ured 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 0.1µF are typically made from NPO or C0G materials. NPO and C0G materials typically have tight tolerance and are stable over tempera- ture. Large capacitor values are typically com- posed of X7R, X5R, Z5U, or Y5V dielectric materi- als. Large ceramic capacitors, typically greater than 2.2µF, are often available in low-cost Y5V and Z5U dielectrics, but large capacitors are not required in the AAT3122 application. 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 AAT3122 has a thermal protection circuit that will shut down the charge pump and current out- puts if the die temperature rises above the thermal limit due to short-circuit conditions. AAT3122 High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications 10 3122.2005.11.1.3

High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications 3122.2005.11.1.3 11 Additional Application Circuit *In some applications, white LED forward voltages (VF) can vary significantly. Ballast resistors between the LED cathodes and ground are recommended for balancing the forward voltage differences. The ballast resistor value may be approxiamted by the following equation: RB = (VIN(MIN))1.5 - (VF(MAX) + 250mV) IF(MAX) VF(MAX) = Maximum expected LED forward voltage at the given maximum forward current level. Refer to the LED manufacturers’ datasheet for maximum VF specifications. IF(MAX) = Maximum forward current used to drive an individual LED. VIN(MIN) = Minimum input supply voltage for the application. RB = Ballast resistor value in ohms. CIN 1µF VBATTERY COUT 1µF EN/SET 1µF 1µF D2 D3 D4 D5 VIN VOUT C1+ C1- C2+ C2- EN/SET GND AAT3122

High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications 12 3122.2005.11.1.3 Advanced Analogic Technologies, Inc. 830 E. Arques Avenue, Sunnyvale, CA 94085 Phone (408) 737-4600 Fax (408) 737-4611

Ordering Information

Package Information

All dimensions in millimeters. 0.20 + 0.10 - 0.05 0.055 ± 0.045 0.45 ± 0.15 7° NOM 4° ± 4° 3.00 ± 0.10 2.40 ± 0.10 2.85 ± 0.20 0.15 ± 0.05 0.9625 ± 0.0375 1.00 + 0.10 - 0.065

0.04 REF

0.010 2.75 ± 0.25 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 Marking 1 Part Number (Tape and Reel)2 TSOPJW-12 JEXYY AAT3122ITP-T1 © 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 con- trol 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. 1. XYY = assembly and date code. 2. Sample stock is generally held on part numbers listed in BOLD.