AAT3157 High Efficiency 1X/1.5X/2X Charge Pump For White LED Applications General Description Features The AAT3157 is a low noise, constant frequency charge pump DC/DC converter that uses a trimode load switch (1X), fractional (1.5X), and doubling (2X) conversion to maximize efficiency for white LED applications. The AAT3157 is capable of driving up to three channels of LEDs at 20mA per channel from a 2.7V to 5.5V input. The current sinks may be operated individually or in parallel for driving higher current LEDs. A low external parts count (two 1μF flying capacitors and two small 1μF capacitors at IN and OUTCP) make this part ideally suited for small, battery-powered applications. • • • • • • • • • • • • AnalogicTech's S2Cwire™ (Simple Serial Control™) serial digital input is used to enable, disable, and set current for each LED with 16 settings down to 50μA. The low-current mode supply current can be as low as 50μA to save power. Each output of the AAT3157 is equipped with builtin protection for output short-circuit and auto-disable for load short-circuit conditions. Built-in softstart circuitry prevents excessive inrush current during start-up. A low-current shutdown feature disconnects the load from the input and reduces quiescent current to less than 1μA. ChargePump™ VIN Range: 2.7V to 5.5V Fully Programmable Current with Single Wire — 16 Current Levels — Four Low Current Settings Down to 50µA Low IQ (50µA) for Low Current Mode Tri-Mode 1X, 1.5X, and 2X Charge Pump for Maximum Efficiency and VF Coverage Drives up to Three Channels of LEDs No Inductors, Low Noise Operation 1MHz Constant Switching Frequency Small Application Circuit Built-In Thermal Protection Automatic Soft Start IQ <1µA in Shutdown 2.85x3.0mm TSOPJW-12 Package Applications • • • • Color (RGB) Lighting Programmable Current Sinks White LED Backlighting White Photo Flash for Digital Still Cameras The AAT3157 is available in a Pb-free, space-saving 2.85x3.0mm 12-pin TSOPJW package. Typical Application C1+ C2+ C2 1µF C1 1µF C2- C12.7V to 5.5V IN CIN 1µF OUTCP D1 AAT3157 GND D2 D3 COUT 1µF D1 D2 EN/SET 3157.2006.05.1.2 EN/SET D3 1 AAT3157 High Efficiency 1X/1.5X/2X Charge Pump For White LED Applications Pin Descriptions Pin # Symbol Function 1 D3 Current sink input #3. 2 D2 Current sink input #2. 3 D1 Current sink input #1. 4 GND 5 IN 6 C2- Flying capacitor 2 negative terminal. 7 C2+ Flying capacitor 2 positive terminal. Connect a 1µF capacitor between C2+ and C2-. 8 OUTCP 9 C1- Flying capacitor 1 negative terminal. 10 C1+ Flying capacitor 1 positive terminal. Connect a 1µF capacitor between C1+ and C1-. 11 EN/SET 12 N/C Ground. Input power supply. Requires 1µF capacitor connected between this pin and ground. Charge pump output to drive load circuit. Requires 1µF capacitor connected between this pin and ground. S2Cwire serial interface control pin. No connection. Pin Configuration TSOPJW-12 (Top View) D3 D2 D1 GND IN C2- 2 1 12 2 11 3 10 4 9 5 8 6 7 N/C EN/SET C1+ C1OUTCP C2+ 3157.2006.05.1.2 AAT3157 High Efficiency 1X/1.5X/2X Charge Pump For White LED Applications Absolute Maximum Ratings1 Symbol VIN VEN/SET IOUT2 TJ TLEAD Description Value Units -0.3 to 6 -0.3 to VIN + 0.3 150 -40 to 150 300 V V mA °C °C Description Value Units Maximum Power Dissipation4 Maximum Thermal Resistance 0.625 160 W °C/W Input Voltage to GND EN/SET Voltage to GND Maximum DC Output Current Operating Junction Temperature Range Maximum Soldering Temperature (at leads, 10 sec) Thermal Information3 Symbol PD θJA 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. 3157.2006.05.1.2 3 AAT3157 High Efficiency 1X/1.5X/2X Charge Pump For White LED Applications Electrical Characteristics1 CIN = COUT = C1 = C2 = 1.0µF; TA = -40°C to +85°C, unless otherwise noted. Typical values are TA = 25°C, VIN = 3.6V. Symbol Description Conditions Input Power Supply VIN Operation Range ICC ISHDN IDX Operating Current Min Typ Max Units 5.5 1 V 0.3 1 3 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 50µA Setting, 1X Mode VEN/SET = 0V ISET = 20mA, TA = 25°C VF:D1:D3 = 3.6V Shutdown Current ISINK Average Current Accuracy I(D-Match) Current Matching2 1X to 1.5X or 1.5X to 2X Transition VTH Threshold at Any ISINK Pin Charge Pump Section TSS Soft-Start Time FCLK Clock Frequency EN/SET VEN(L) Enable Threshold Low VIN = 2.7V VEN(H) Enable Threshold High VIN = 5.5V 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 mA 1 50 18 20 0.5 1 22 1 150 mV 100 1000 µs kHz 0.4 1.4 0.3 75 50 -1 µA µA mA % 75 500 500 1 V V µs ns µs µs µs µA 1. The AAT3157 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. 2. Current matching is defined as the deviation of any sink current from the average of all active channels. 4 3157.2006.05.1.2 AAT3157 High Efficiency 1X/1.5X/2X Charge Pump For White LED Applications Typical Characteristics CIN = COUT = C1 = C2 = 1.0µF; TA = 25°C, VIN = 3.6V, unless otherwise noted. Turn-On to 1X Mode Efficiency vs. Supply Voltage (VIN = 4.2V; 20mA/ch Load) 100 Efficiency (%) 90 EN/SET (2V/div) 80 70 VOUT (2V/div) 60 5mA/ch VF = 2.7V 50 10mA/ch VF = 3.1V VSINK (2V/div) 20mA/ch VF = 3.4V 40 IIN (100mA/div) 30 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 μs/div) Time (100μ Supply Voltage (V) Turn-On to 1.5X Mode Turn-On to 2X Mode (VIN = 3.5V; 20mA/ch Load) (VIN = 2.8V; 20mA/ch Load) EN/SET (2V/div) EN/SET (2V/div) VOUT (2V/div) VSINK (2V/div) VOUT (2V/div) VSINK (2V/div) IIN (100mA/div) IIN (200mA/div) Time (100µs/div) Time (100µs/div) Turn-Off to 1.5X Mode Diode Current vs. Temperature (VIN = 3.5V; 20mA/ch Load) (20mA/ch) Diode Current (mA) 22.0 EN/SET (2V/div) VLED (1V/div) IIN (100mA/div) 21.5 21.0 ID1 20.5 ID2 20.0 19.5 ID3 19.0 18.5 18.0 -40 Time (100µs/div) 3157.2006.05.1.2 -25 -10 5 20 35 50 65 80 Temperature (°°C) 5 AAT3157 High Efficiency 1X/1.5X/2X Charge Pump For White LED Applications Typical Characteristics CIN = COUT = C1 = C2 = 1.0µF; TA = 25°C, VIN = 3.6V, unless otherwise noted. Input Ripple vs. Input Voltage Line Response (20mA/ch Load) 14.0 20mA/ch Input Ripple (mV) 12.0 10.0 4.0V VIN (500mV/div) 14mA/ch 3.6V 8.0 VOUT (100mV/div) 6.0 10mA/ch 4.0 ILED (10mA/div) 2.0 0.0 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 Input Voltage (V) Time (1ms/div) Load Characteristics Load Characteristics (VIN = 3.7V; 1.5X Mode; 20mA/ch Load) (VIN = 2.7V; 2X Mode; 20mA/ch Load) VIN (20mV/div) VIN (20mV/div) VOUT (50mV/div) VOUT (50mV/div) ILED (10mA/div) ILED (10mA/div) Time (500ns/div) Time (500ns/div) Load Characteristics EN/SET Latch Timeout vs. Input Voltage EN/SET Latch Timeout (µs) (VIN = 3.3V; 1.5X Mode; 10mA/ch Load) VIN (20mV/div) VOUT (50mV/div) ILED (10mA/div) 350 300 250 -40°C 200 150 100 25°C 85°C 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 Time (500ns/div) 6 Input Voltage (V) 3157.2006.05.1.2 AAT3157 High Efficiency 1X/1.5X/2X Charge Pump For White LED Applications Typical Characteristics CIN = COUT = C1 = C2 = 1.0µF; TA = 25°C, VIN = 3.6V, unless otherwise noted. EN/SET Off Timeout vs. Input Voltage Enable Threshold High vs. Input Voltage 300 Enable Threshold High (V) EN/SET Off Timeout (µs) 350 -40°C 250 200 150 25°C 85°C 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 Input Voltage (V) 1.4 1.2 -40°C 1.0 0.8 25°C 0.6 85°C 0.4 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 Input Voltage (V) Enable Threshold Low (V) Enable Threshold Low vs. Input Voltage 1.4 1.2 1.0 -40°C 0.8 25°C 0.6 85°C 0.4 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 Input Voltage (V) 3157.2006.05.1.2 7 AAT3157 High Efficiency 1X/1.5X/2X Charge Pump For White LED Applications Functional Block Diagram C1+ C1- C2+ C2- 1X, 1.5X, 2X Charge Pump IN OUTCP Soft Start Control 1MHz Oscillator Voltage Reference 6 x 16 bit ROM EN/SET S2Cwire Interface D/A D1 D/A D2 D/A D3 GND Functional Description The AAT3157 is a tri-mode load switch (1X) and high efficiency (1.5X or 2X) charge pump device intended for white LED backlight 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 AAT3157 charge pump is enabled when any of the three 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 AAT3157 requires only four external components: two 1µF ceramic capacitors for the charge pump flying capacitors (C1 and C2), one 1µF ceramic input capacitor (CIN), and one 0.33µF to 1µF ceramic charge pump output capacitor (COUT). 8 The three constant current sink inputs (D1 to D3) can drive three individual LEDs with a maximum current of 20mA each. The unused sink inputs must be connected to OUTCP, otherwise the part will operate only in 2X charge pump mode. The S2Cwire serial interface enables the AAT3157 and sets the current sink magnitudes. Constant Current Output Level Settings The constant current sink levels for D1 to D3 are set via the serial interface according to a logarithmic scale for the first 12 codes and a separate low-current scale for the last four codes. For the first 12 codes, each code is approximately 1.5dB lower than the previous code. In this manner, LED brightness appears linear with each increasing code count. Because the inputs D1 to D3 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 AAT3157 are programmable, no PWM (pulse width modulation) or 3157.2006.05.1.2 AAT3157 High Efficiency 1X/1.5X/2X Charge Pump For White LED Applications 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. additional control circuitry is needed to control LED brightness. This feature greatly reduces the burden 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 AAT3157 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. When EN/SET is held low for an amount of time greater than TOFF, the AAT3157 enters into shutdown mode and draws less than 1µA from VIN. The internal data register is reset to zero during shutdown. S2Cwire Serial Interface The current level magnitude is controlled by AnalogicTech's Simple Serial Control (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. Data Output (mA/Ch) Data Output (mA/Ch) 1 2 3 4 5 6 7 8 20.0 17.0 14.0 12.0 10.0 8.6 7.0 6.0 9 10 11 12 13 14 15 16 5.0 4.2 3.4 2.8 1.0 0.5 0.1 0.05 Auto-Disable Feature The AAT3157 is equipped with an auto-disable feature for each LED channel. After the IC is enabled and started up, a test current of 100µA (typical) is forced through each sink channel. The channel will be disabled if the voltage of that particular SINK pin does not drop to certain threshold. This feature is very convenient for disabling an unused channel or during an LED fail-short event. Thermal Protection The AAT3157 has a thermal protection circuit that will shut down the charge pump if the die temperature rises above the thermal limit, as would be the case during a short circuit of the OUTCP pin. Table 1: Current Level Settings. S2Cwire Serial Interface Timing T HI T LO TOFF TLAT EN/SET 1 Data Reg 3157.2006.05.1.2 2 n 1 n <= 16 n 0 9 AAT3157 High Efficiency 1X/1.5X/2X Charge Pump For White LED Applications Applications Information Although the AAT3157 is designed for driving white LEDs, the device also can be used to drive most types of LEDs with forward voltage specifications ranging from 2.0V to 4.7V. 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. Since the D1 to D3 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 AAT3157 make it capable of driving LEDs with forward voltages as high as 4.7V at full current from an input supply as low as 3.0V. Outputs can be paralleled to drive high-current LEDs without complication. Device Switching Noise Performance The AAT3157 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 AAT3157 soft-start feature prevents noise transient effects associated with inrush currents during start-up of the charge pump circuit. 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 100mΩ. A value of 1µF for all four capacitors is a good starting point 10 when choosing capacitors. If the LED current sources are programmed only 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 AAT3157. 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 to 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 0.1µF 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 2.2µF) are often available in lowcost Y5V and Z5U dielectrics, but capacitors greater than 1µF are not typically required for AAT3157 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. 3157.2006.05.1.2 AAT3157 High Efficiency 1X/1.5X/2X Charge Pump For White LED Applications Ordering Information Package Marking1 Part Number (Tape and Reel)2 TSOPJW-12 QWXYY AAT3157ITP-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 + 0.10 - 0.05 2.40 ± 0.10 0.20 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. 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 3157.2006.05.1.2 11