AAT3122 High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications General Description Features The AAT3122 is a low noise, constant frequency charge pump DC/DC converter that uses a dual mode load switch (1X) and fractional (1.5X) conversion to increase efficiency in white LED applications. With input voltages ranging from 2.7V to 5.5V, the device can produce an output current of up to 120mA. A low external parts count (two 1µF flying capacitors and two small bypass capacitors at VIN and OUT) makes the AAT3122 ideally suited for small battery-powered applications. • • • • • • • • • • • • • • AnalogicTech's Simple Serial Control™ (S2Cwire™) interface is used to enable, disable, and set the LED drive current with a 32-level logarithmic scale LED brightness control. The AAT3122 has a thermal management system to protect the device 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. High switching frequency enables the use of small external capacitors. A low shutdown current feature disconnects the load from VIN and reduces quiescent current to less than 1µA. The AAT3122 provides a single current source output that can be used to drive up to six LEDs at 20mA each. The AAT3122 is available in a Pb-free TSOPJW-12 package. ChargePump™ VIN 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 (S2Cwire) 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 VIN C1+ C1 1µF AAT3122 C1C2+ VOUT VBATTERY CIN 1µF COUT 1µF C2 1µF C2- EN/SET EN/SET GND 3122.2005.11.1.3 D D1 D2 D3 D4 D5 D6 1 AAT3122 High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications Pin Descriptions Pin # Symbol Function 1 2 3 4 5, 6, 7, 8 9 C2+ OUT C1C1+ D EN/SET 10 11 12 IN GND C2- Flying capacitor 2 positive terminal. Connect a 1µF capacitor between C2+ and C2-. Charge pump output. Requires 1µF bypass capacitor to ground. Flying capacitor 1 negative terminal. Flying capacitor 1 positive terminal. Connect a 1µF capacitor between C1+ and C1-. Output current source with drive capability of up to 120mA. Input control pin. Serial data interface that controls the level of output current. See Application Information for more details. Input power supply. Requires 1µF bypass capacitor to ground. Ground. Flying capacitor 2 negative terminal. Pin Configuration TSOPJW-12 (Top View) C2+ OUT C1C1+ D D 2 1 12 2 11 3 10 4 9 5 8 6 7 C2GND IN EN/SET D D 3122.2005.11.1.3 AAT3122 High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications Absolute Maximum Ratings1 Symbol VIN VOUT VEN/SET VEN/SET(MAX) IOUT2 TJ Description Input Voltage Charge Pump Output EN/SET to GND Voltage Maximum EN/SET to Input Voltage Maximum DC Output Current Operating Junction Temperature Range Value Units -0.3 to 6.0 -0.3 to 6.0 -0.3 to 6.0 0.3 150 -40 to 150 V V V V mA °C Value Units 160 625 °C/W mW Thermal Information3 Symbol ΘJA PD Description Thermal Resistance Maximum Power Dissipation (TA = 25°C)4 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 6.25mW/°C above 25°C. 3122.2005.11.1.3 3 AAT3122 High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications 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 Input Power Supply VIN Operation Range Icc ISHDN ID Charge Pump TSS FCLK ηCP EN/SET VEN(L) VEN(H) TLO THI TOFF Input Current Operating Current Shutdown Current Maximum Output Current Min Enable Threshold Low Enable Threshold High EN/SET Low Time Minimum EN/SET High Time EN/SET Off Timeout EN/SET Input Leakage Max Units 5.5 V 1.8 3.5 mA 120 1.0 132 µA mA 2.7 3.0 ≤ VIN ≤ 5.5, Active, No Load Current EN = 0 VIN = 3.5V; Code = 32 108 Soft-Start Time Clock Frequency Charge Pump Efficiency Typ VIN = 3.6V, IOUT(Total) = 120mA; Measured from IN to OUT VIN = 2.7V to 5.5V VIN = 2.7V to 5.5V 200 1000 µs kHz 93 % 0.5 1.4 0.3 75 50 -1.0 500 1.0 V V µs ns µs µA 1. The AAT3122 is guaranteed to meet performance specifications over the -40°C to +85°C operating temperature range and is assured by design, characterization, and correlation with statistical process controls. 4 3122.2005.11.1.3 AAT3122 High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications Typical Characteristics Unless otherwise noted, VIN = 3.6V, CIN = COUT = C1 = C2 = 1µF, TA = 25°C. Efficiency vs. VIN IDIODE vs. VIN 100 90 95 85 90 VDIODE = 3.3V 80 85 VDIODE = 3.4V 75 IDIODE (mA) Efficiency (%) (ID = 80mA) 80 75 VDIODE = 3.5V 70 65 VDIODE = 3.6V VDIODE = 3.3V VDIODE = 3.4V 70 65 60 55 50 60 55 45 50 40 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 2.7 5.1 2.9 3.1 3.3 3.5 VIN (V) 2.4 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 2.50 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 VIN (V) VIH and VIL vs. VIN Quiescent Current vs. VIN Quiescent Current (mA) VDIODE = 3.5V VDIODE = 3.6V 0.850 0.825 0.800 0.775 VIH 0.750 VDIODE = 3.3V 0.725 VDIODE = 3.4V 0.700 VDIODE = 3.5V 0.675 VDIODE = 3.6V 0.650 VIL 0.625 0.600 3.00 3.50 4.00 VIN (V) 3122.2005.11.1.3 4.50 5.00 5.50 2.5 3.0 3.5 4.0 4.5 5.0 5.5 VIN (V) 5 AAT3122 High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications Typical Characteristics Unless otherwise noted, VIN = 3.6V, CIN = COUT = C1 = C2 = 1µF, TA = 25°C. Turn-On to Full-Scale Charge Pump Turn-On to Full-Scale Load Switch ENSET (1V/div) ENSET (1V/div) OUT (2V/div) OUT (2V/div) VDIODE (1V/div) VDIODE (2V/div) IIN (200mA/div) IIN (100mA/div) Time (50µs/div) Time (50µs/div) Load Switch to Charge Pump (80mA) Charge Pump to Load Switch (80mA) VIN (10mV/div) VIN (20mV/div) OUT (2V/div) OUT (1V/div) VDIODE (2V/div) VDIODE (1V/div) IIN (100mA/div) IIN (200mV/div) Time (50µs/div) Time (50µs/div) 80mA Load Characteristics Turn-Off VIN 20mV/div ENSET (1V/div) VDIODE (2V/div) OUT IIN (100mA/div) VDIODE Time (200µs/div) 6 Time (1µs/div) 3122.2005.11.1.3 AAT3122 High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications Functional Block Diagram VIN Soft Start 1.5X Charge Pump 1MHz Oscillator Voltage Reference EN/SET S2Cwire Interface 5 32x8 bit ROM 8 Current Mode DAC C1+ C1C2+ C2OUT D GND Functional Description input and output voltages) and does not require user intervention to maintain maximum efficiency. 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 linear 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 The AAT3122 requires only four external components: two 1µF ceramic capacitors for the charge pump flying capacitors (C1 and C2), one 1µF ceramic capacitor for CIN, 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 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. 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. 3122.2005.11.1.3 7 AAT3122 High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications EN/SET Serial Interface Applications Information 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 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. 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 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 transitions to a logic low state. 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. Table 1 depicts the relationship between each rising edge of the EN/SET and the output current in mA. Code IOUT (mA) Code IOUT (mA) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 3.3 3.8 4.2 4.7 5.2 6.1 6.6 7.5 8.5 9.4 10.8 11.8 13.6 15.1 16.9 18.8 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 21.2 24.0 26.8 30.1 33.9 38.1 42.4 47.5 53.6 60.2 67.3 75.8 84.7 95.1 106.8 120.0 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. Table 1: Current Level Settings. Normalized Current to Full Scale 1.0 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 Figure 1: Normalized Current Level Settings. 8 3122.2005.11.1.3 AAT3122 High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications EN/SET Timing Diagram tHI tOFF tLO EN/SET Code OFF 1 LED Selection 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 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. Device Switching Noise Performance The AAT3122 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 AAT3122 soft-start feature prevents noise transient effects associated with inrush currents 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 current source, it is difficult to measure the output voltage to derive an overall 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 3122.2005.11.1.3 2 3 OFF 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 component count, reliability, operating range, and total energy usage...not just % efficiency. Charge Pump Efficiency The AAT3122 is a fractional charge pump. The efficiency (η) can be simply defined as a linear voltage regulator 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= POUT 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= POUT V = (VOUT x IOUT)/(VIN x 1.5IOUT) = OUT PIN 1.5VIN η(%) = 100 ⎛ VOUT ⎞ ⎝1.5VIN⎠ 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 3.0mA to 120mA. Efficiency will decrease as load current drops below 0.05mA or when the level of VIN 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. 9 AAT3122 High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications 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 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 recommended over all other types of capacitors for use with the AAT3122 products. 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 capac- 10 itor 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 0.1µF are typically made from NPO or C0G materials. NPO and C0G materials typically have tight tolerance and are stable over temperature. Large capacitor values are typically composed of X7R, X5R, Z5U, or Y5V dielectric materials. 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 outputs if the die temperature rises above the thermal limit due to short-circuit conditions. 3122.2005.11.1.3 AAT3122 High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications Additional Application Circuit VIN C1+ C1 1µF C1C2+ VOUT VBATTERY CIN COUT 1µF 1µF AAT3122 C2D1 EN/SET C2 1µF D1 D2 D3 D4 D5 D6 R B* RB* RB* RB* RB* RB* EN/SET GND *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. 3122.2005.11.1.3 11 AAT3122 High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications Ordering Information Package Marking1 Part Number (Tape and Reel)2 TSOPJW-12 JEXYY AAT3122ITP-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 TSOPJW-12 2.85 ± 0.20 2.40 ± 0.10 0.10 0.20 +- 0.05 0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC 7° NOM 0.04 REF 0.055 ± 0.045 0.15 ± 0.05 + 0.10 1.00 - 0.065 0.9625 ± 0.0375 3.00 ± 0.10 4° ± 4° 0.45 ± 0.15 0.010 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. © 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 3122.2005.11.1.3