AAT2856INJ-EE-T1

PRODUCT DATASHEET AAT2856 ChargePumpTM High Current Charge Pump with Dual LDO for Backlight Applications Features • Input Voltage Range: 2.7V to 5.5V • Tri-Mode Charge Pump: ▪ Drives up to Six Backlight LEDs ▪ 32 Programmable Backlight Current Settings Ranging from 115μA to 30mA ▪ 2MHz Switching Frequency • Two Linear Regulators: ▪ 200mA Output Current ▪ 200mV Dropout Voltage ▪ Output Voltage Adjustable from 1.2V to VBATTERY ▪ Output Auto-Discharge for Fast Shutdown ▪ Individual LDO Enable Inputs • Built-In Thermal Protection • Automatic Soft Start • -40°C to +85°C Temperature Range • TQFN44-28 Package General Description The AAT2856 is a highly integrated charge pump with dual linear regulators optimized for systems powered from lithium-ion/polymer batteries. The charge pump provides power for white LED backlight. Six backlight LEDs can be driven at up to 30mA. AnalogicTech’s AS2Cwire™ (Advanced Simple Serial Control™) singlewire interface is used to enable, disable, and set the current to one of 32 levels for the backlight. Backlight current matching is 1% for uniform display brightness. The AAT2856 offers two high-performance low-noise MicroPower™ low dropout (LDO) linear regulators. Both regulators use individual enable inputs and each will supply up to 200mA load current. LDO ground pin current is only 80μA, making the AAT2856 ideal for batteryoperated applications. The AAT2856 is equipped with built-in short-circuit and over-temperature protection. The soft start circuitry prevents excessive inrush current at start-up and mode transitions. The AAT2856 is available in a Pb-free TQFN44-28 package and operates over the -40°C to +85°C ambient temperature range. Applications • Camera-Enabled Mobile Devices • Digital Still Cameras • Multimedia Mobile Phones Typical Application C1 1μF C1+ C1IN CIN 4.7μF C2 1μF C2+ C2OUT COUT 2.2μF IN BL1 BL2 BL3 BL4 BL5 BL6 OUTA CBYP 0.1μF REF FBA R1A R2A COUTA 2.2μF VOUTA VOUT VBAT WLEDs OSRAM LW M673 or equivalent AAT2856 ENABLE/SET ENS EN_LDOA EN_LDOB ENA ENB AGND OUTB R2B FBB PGND R1B VOUTB COUTB 2.2μF 2856.2008.02.1.3 www.analogictech.com 1 PRODUCT DATASHEET AAT2856 AAT2856 ChargePumpTM High Current Charge Pump with Dual LDO for Backlight Applications Pin Descriptions Pin # 1 2 3 4, 5, 23, 24 6 7 8 9, 18 10 11 12 13 14, 21, 22 15 16 17 19 20 25 26 27 28 EP Symbol BL3 BL2 BL1 AGND REF FBB OUTB IN FBA OUTA C1C1+ OUT ENB C2+ C2PGND ENS BL6 BL5 ENA BL4 Description Backlight LED 3 current sink. BL3 controls the current through backlight LED 3. Connect the cathode of backlight LED 3 to BL3. If not used, connect BL3 to OUT. Backlight LED 2 current sink. BL2 controls the current through backlight LED 2. Connect the cathode of backlight LED 2 to BL2. If not used, connect BL2 to OUT. Backlight LED 1 current sink. BL1 controls the current through backlight LED 1. Connect the cathode of backlight LED 1 to BL1. If not used, connect BL1 to OUT. Analog ground. Connect AGND to PGND at a single point as close to the AAT2856 as possible. Reference output. Bypass REF to AGND with a 0.1μF or larger ceramic capacitor. Feedback input for LDO B. FBB measures the output voltage of LDO B. Connect a resistive voltage divider from the output of LDO B to FBB. FBB feedback regulation voltage is 1.2V. LDO B regulated voltage output. OUTB is the voltage output of LDO B. Bypass OUTB to AGND with a 2.2μF or larger ceramic capacitor as close to the AAT2856 as possible. Power input. Connect IN to the input source voltage. Bypass IN to PGND with a 4.7μF or larger ceramic capacitor as close to the AAT2856 as possible. Feedback input for LDO A. FBA measures the output voltage of LDO A. Connect a resistive voltage divider from the output of LDO A to FBA. FBA feedback regulation voltage is 1.2V. LDO A regulated voltage output. OUTA is the voltage output of LDO A. Bypass OUTA to AGND with a 2.2μF or larger ceramic capacitor as close to the AAT2856 as possible. Negative node of charge pump capacitor 1. Connect the 1μF charge pump capacitor 1 from C1+ to C1-. Positive node of charge pump capacitor 1. Connect the 1μF charge pump capacitor 1 from C1+ to C1-. Charge pump output; supplies current to the backlight LEDs. Connect the backlight LED anodes to OUT. Bypass OUT to PGND with a 2.2μF or larger ceramic capacitor as close to the AAT2856 as possible. LDO B enable input. ENB turns on or off low dropout regulator B (LDO B). Drive ENB high to turn on LDO B; drive it low to turn it off. Positive node of charge pump capacitor 2. Connect the 1μF charge pump capacitor 2 from C2+ to C2-. Negative node of charge pump capacitor 2. Connect the 1μF charge pump capacitor 2 from C2+ to C2-. Power ground. Connect AGND to PGND at a single point as close to the AAT2856 as possible. Backlight enable and serial control input. ENS turns the backlight on/off and is the AS2Cwire input to serially control the backlightLED brightness. Backlight LED 6 current sink. BL6 controls the current through backlight LED 6. Connect the cathode of backlight LED 6 to BL6. If not used, connect BL6 to OUT. Backlight LED 5 current sink. BL5 controls the current through backlight LED 5. Connect the cathode of backlight LED 5 to BL5. If not used, connect BL5 to OUT. LDO A enable input. ENA turns on or off low dropout regulator A (LDO A). Drive ENA high to turn on LDO A; drive low to turn it off. Backlight LED 4 current sink. BL4 controls the current through backlight LED 4. Connect the cathode of backlight LED 4 to BL4. If not used, connect BL4 to OUT. Exposed paddle (bottom); connect to ground as closely as possible to the device. 2 www.analogictech.com 2856.2008.02.1.3 PRODUCT DATASHEET AAT2856 AAT2856 ChargePumpTM High Current Charge Pump with Dual LDO for Backlight Applications Pin Configuration TQFN44-28 (Top View) OUT AGND AGND BL6 BL5 ENA BL4 28 27 26 25 24 23 22 21 20 19 18 17 16 15 8 9 10 11 12 13 14 BL3 BL2 BL1 AGND AGND REF FBB 1 2 3 4 5 6 7 OUT ENS PGND IN C2C2+ ENB OUT C1+ C1OUTA FBA IN OUTB Absolute Maximum Ratings1 Symbol Description IN, OUT, BL1, BL2, BL3, BL4, BL5, BL6 Voltage to AGND C1+, C1-, C2+, C2- Voltage to AGND REF, FBB, OUTA, FBA, OUTB, ENA, ENB, ENS Voltage to AGND PGND Voltage to AGND Operating Junction Temperature Range Maximum Soldering Temperature (at leads, 10 sec) Value -0.3 to 6.0 -0.3 to VOUT + 0.3 -0.3 to VIN + 0.3 -0.3 to 0.3 -40 to 150 300 Units V V V V °C °C TJ TLEAD Thermal Information2 Symbol PD θJA Description Maximum Power Dissipation Maximum Thermal Resistance 3 Value 2 50 Units W °C/W 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 a FR4 circuit board. 3. Derate 6.25 mW/°C above 25°C ambient temperature. 2856.2008.02.1.3 www.analogictech.com 3 PRODUCT DATASHEET AAT2856 AAT2856 ChargePumpTM High Current Charge Pump with Dual LDO for Backlight Applications Electrical Characteristics1 VIN = 3.6V; CIN = 4.7μF; COUT = 2.2μF; C1 = C2 = 1μF; TA = -40°C to +85°C, unless otherwise noted. Typical values are TA = 25°C. Symbol VIN Description IN Operating Voltage Range Conditions 1X Mode, 3.0V ≤ VIN ≤ 5.5V, Active, No Load; ENL = AGND, ENS = IN 1.5X Mode, 3.0V ≤ VIN ≤ 5.5V, Active, No Load; ENL = AGND, ENS = IN 2X Mode, 3.0V ≤ VIN ≤ 5.5V, Active, No Load; ENL = AGND, ENS = IN ENA = ENB = ENS = AGND Min 2.7 Typ 0.63 1.4 2.6 140 15 200 500 2 Max 5.5 1 4 5 1.0 Units V IIN(Q) IN Operating Current mA IIN(SHDN) IN Shutdown Current TSD Over-Temperature Shutdown Threshold TSD(HYS) Over-Temperature Shutdown Hysteresis Charge Pump Section IOUT OUT Maximum Output Current VIN(TH_H) Charge Pump Mode Hysteresis fOSC Charge Pump Oscillator Frequency BL1-BL6 Backlight LED Outputs IBL_(MAX) BL1-BL6 Maximum Current 2 μA °C °C mA mV MHz Address 0, Data 1 TA = 25°C Address 0, Data 1; VIN - VF = 1.5V Address 12, Data 2; VIN - VF = 1.5V Address 0, Data 1; VIN - VF = 1.5V 18 20 30 150 22 1.0 mA % mV V V μA μs ns ΔI(BL_) BL1-BL6 Current Matching VBL_(TH) BL1-BL6 Charge Pump Mode Transition Threshold ENS Logic Control ENS Input Low Threshold VENS(L) VENS(H) ENS Input High Threshold IENS ENS Input Leakage Current tENS(LOW) ENS Serial Interface Low Time tENS(HI_MIN), ENS Serial Interface Minimum High Time tENS(HI_MIN) tENS(HI_MAX), ENS Serial Interface Maximum High Time tENS(HI_MAX) tENS(OFF) ENS Off Timeout tENS(LAT) ENS Serial Interface Latch Timeout Linear Regulators VFBA, VFBB IIN IOUTA(MAX), IOUTB(MAX) VOUTA(DO), VOUTB(DO) PSRRA, PSRRB VEN_(L) VEN_(H) tEN_(DLY) Output Voltage Tolerance Ground Pin Current OUTA, OUTB Maximum Load Current OUTA, OUTB Dropout Voltage OUTA, OUTB Power Supply Rejection Ratio ENA, ENB Voltage Low Threshold ENA, ENB Voltage High Threshold ENA, ENB Enable Delay 0.4 VENS = VIN = 5V VIN ≥ 3.3V 1.4 -1.0 0.3 50 VIN ≥ 3.3V 75 500 500 IOUT = 1mA to 200mA ENA = ENB = IN, ENS = AGND ENA = IN, ENB = AGND or ENA = AGND, ENB = IN, ENS = AGND 1.17 1.2 125 90 200 IOUT = 150mA IOUT = 10mA, CREF = 10nF, 1kHz 1.4 REF = Open 15 150 50 0.4 300 1.23 200 150 1.0 75 μs μs μs V μA mA mV dB V V μs 1. The AAT2856 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 www.analogictech.com 2856.2008.02.1.3 PRODUCT DATASHEET AAT2856 AAT2856 ChargePumpTM High Current Charge Pump with Dual LDO for Backlight Applications Typical Characteristics Backlight Efficiency vs. Input Voltage 100 Backlight Current Matching vs. Temperature (20mA/Ch; Data 1) 21 Efficiency (%) 80 70 60 50 40 30 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 LED Current (mA) 90 20mA/ch 20.5 20 19.5 19 18.5 -40 10.2mA/ch 1.6mA/ch -15 10 35 60 85 Input Voltage (V) Temperature (°C) Turn On to 1X Mode Backlight (30mA/ch; Data 1; VIN = 4.2V) VEN (2V/div) VOUT (2V/div) VSINK (500mV/div) IIN (200mA/div) VEN (2V/div) 0V Turn On to 1.5X Mode Backlight (30mA/ch; Data 1; VIN = 3.4V) 0V 0V 0V VOUT (2V/div) VSINK (500mV/div) 0A 0V 0V 0A IIN (200mA/div) Time (200µs/div) Time (200µs/div) Turn On to 2X Mode Backlight (30mA/ch; Data 1; VIN = 2.7V) VEN (2V/div) VOUT (2V/div) VSINK (500mV/div) IIN (200mA/div) Turn Off from 1.5X Mode Backlight (30mA/ch; Data 1) 0V 0V 0V 0A VEN (2V/div) VOUT (2V/div) IIN (200mA/div) 0V 0V 0A Time (200µs/div) Time (100µs/div) 2856.2008.02.1.3 www.analogictech.com 5 PRODUCT DATASHEET AAT2856 AAT2856 ChargePumpTM High Current Charge Pump with Dual LDO for Backlight Applications Typical Characteristics BENS, FENS High Threshold Voltage vs. Input Voltage 1.4 1.3 1.4 1.3 BENS, FENS Low Threshold Voltage vs. Input Voltage VBENS(L), VFENS(L) (V) VBENS(H), VFENS(H) (V) 1.2 1.1 1.0 0.9 0.8 0.7 0.6 0.5 2.7 3.1 3.5 3.9 -40°C 1.2 1.1 1.0 0.9 0.8 0.7 0.6 0.5 -40°C 25°C 85°C 4.3 4.7 5.1 5.5 25°C 2.7 3.1 3.5 3.9 85°C 4.3 4.7 5.1 5.5 Input Voltage (V) Input Voltage (V) BENS, FENS Latch Timeout vs. Input Voltage 260 BENS, FENS Off Timeout vs. Input Voltage 300 TBENS(LAT), TFENS(LAT) (µs) 240 220 200 180 160 140 120 100 80 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 100 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 25°C -40°C 25°C VBENS(H), VFENS(H) (V) 260 -40°C 220 25°C 85°C 180 140 Input Voltage (V) Input Voltage (V) LDOs A and B Turn On Characteristic Output Voltage Error (%) 1.0 LDOs A and B Load Regulation VEN (2V/div) 0.5 0V OUTA 0.0 VOUT (500mV/div) OUTB -0.5 0V -1.0 0.1 1 10 100 1000 Time (50µs/div) Load Current (mA) 6 www.analogictech.com 2856.2008.02.1.3 PRODUCT DATASHEET AAT2856 AAT2856 ChargePumpTM High Current Charge Pump with Dual LDO for Backlight Applications Typical Characteristics LDOs A and B Line Regulation Output Voltage Error (%) 1.0 1.5 LDOs A and B Output Voltage vs. Temperature Output Voltage (%) 1 0.5 0 -0.5 -1 -1.5 -40 0.5 OUTA 0 OUTB -0.5 -1.0 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 -15 10 35 60 85 Input Voltage (V) Temperature (°C) LDOs A and B Dropout Characteristics 3.2 LDOs A and B Line Transient Response (10mA Load) VIN = 3.6V VIN (250mV/div) Output Voltage (V) 3.0 2.8 2.6 2.4 2.2 2.0 2.7 IOUT = 100mA IOUT = 200mA VOUT (AC Coupled) (20mV/div) 2.8 2.9 3.0 3.1 3.2 VIN = 3.1V Input Voltage (V) Time (50µs/div) LDOs A and B Load Transient Response (10mA to 200mA Load Step) IOUT = 200mA IOUT (100mA/div) VOUT (AC Coupled) (100mV/div) Time (50µs/div) 2856.2008.02.1.3 www.analogictech.com 7 PRODUCT DATASHEET AAT2856 AAT2856 ChargePumpTM High Current Charge Pump with Dual LDO for Backlight Applications Functional Block Diagram IN IN C1+ C1C2+ C2- OUTA 1X/1.5X/2X Tri-mode Charge Pump FBA VREF OUTB FBB VREF REF OUT BL1 BL2 BL3 Control Logic ENA ENB To LDO A To LDO B ENS BL4 BL5 BL6 AGND PGND Functional Description The AAT2856 is a highly integrated backlight LED driver with two LDO linear regulators. The charge pump LED driver drives backlight LEDs from a 2.7V to 5.5V input voltage. The LDO regulators are operated from the same input voltage range and produce regulated output voltages as low as 1.2V. LED Drivers The LEDs are driven from an internal charge pump that, depending on the battery voltage and LED forward voltage, drives LEDs directly from the supply voltage (1X or bypass mode) or steps up the supply voltage by a factor of 1.5 (1.5X mode) or 2 (2X mode). The charge pump requires only two tiny 1μF ceramic capacitors, providing a more compact solution than typical inductor-based stepup converter solutions. Each individual LED is driven by a current sink to AGND, allowing individual current control with high accuracy over a wide range of input voltages and LED forward voltages while maintaining high efficiency. The charge pump is controlled by the voltage across the LED current sinks. When any one of the active current sinks begins to dropout, the charge pump goes to the next higher mode (from 1X to 1.5X or from 1.5X to 2X mode) to maintain sufficient LED voltage for constant LED current. The AAT2856 continuously monitors the LED forward voltages and uses the input voltage to determine when to reduce the charge pump mode for better efficiency. There is also a 500mV mode-transition hysteresis that prevents the charge pump from oscillating between charge pump modes. The backlight LED current levels are dynamically controllable by the AS2Cwire single-wire interface. The backlight section has multiple current level scales and the maximum current level is fixed at 20mA or 30mA, depending on the scale chosen through programming. If any one of the backlight or flash current sinks is not used, connect that current sink to OUT. The current controller monitors the sink voltage and, if it is connected to OUT, then the controller determines that the current sink is not used or that the LED is shorted. In either case, the controller turns off the affected current sink. 8 www.analogictech.com 2856.2008.02.1.3 PRODUCT DATASHEET AAT2856 ChargePumpTM High Current Charge Pump with Dual LDO for Backlight Applications AS2Cwire Serial Interface Addressing Address 0 1 2 3 12 15 AS2Cwire Serial Interface The AAT2856 is dynamically programmable by the AS2Cwire single-wire interface. AS2Cwire records rising edges detected at the ENS pin to address and load the data registers. AS2Cwire latches data or address after the ENS input has been held high for time tLAT (500μs). Address or data is differentiated by the number of ENS rising edges. Since the data registers are 4 bits each, the differentiating number of pulses is 24 or 16, so that Address 0 is identified by 17 rising edges, Address 1 by 18 rising edges, Address 2 by 19 rising edges, etc. Data is set to any number of rising edges between 1 and 16. A typical write protocol is a burst of ENS rising edges identifying a particular address, followed by a pause with ENS held high for the tLAT timeout period, then a burst of rising edges signifying data, and another tLAT timeout after the data has been sent. Once an address is set, multiple writes to that address are allowed since the address is not reset after each write. Address edges are needed when changing the address, or writing to an address other than the default after shutdown. Address 0 is the default address after shutdown. If the part is enabled with only data edges and no address, then Address 0 will be programmed and backlight channels BL1-BL6 will turn-on according to the number of data edges applied. When ENS is held low for a time longer than tOFF (500μs), the AAT2856 enters shutdown mode and draws less than 1μA of current from IN. At shutdown, the data and address registers are reset to 0. Table 1a contains the AS2Cwire serial interface address functionality when independent channel control is disabled (independent channel control is disabled by default) and conversely Table 1b contains the AS2Cwire serial interface address functionality when independent channel control is enabled. Address THI TLO TLAT ENS Rising Edges 17 18 19 20 29 32 Function Backlight Current BL1-BL6 Main Backlight Current BL1-BL5 Sub Backlight Current BL6 Low Current Backlight Maximum Backlight Current Scale BL1-BL6 Backlight Independent Channel Control Table 1a: AS2Cwire Serial Interface Addressing with Independent Channel Control Disabled. ENS Rising Edges 17 18 19 20 29 32 Address 0 1 2 3 12 15 Function Not Applicable Backlight Current BL1-BL6 BL3-BL6 On/Off Control BL1-BL2 On/Off Control Maximum Backlight Current Scale BL1-BL6 Not Applicable Table 1b: AS2Cwire Serial Interface Addressing with Independent Channel Control Enabled. Backlight Current Control (Address 0-3) Use Addresses 0-3 to program all six backlight LED channels. All six backlight channels are programmed to the same current level by writing Address 0 followed by any Data between 1 and 16. To program only the main channels BL1 through BL5, use Address 1. Similarly, use Address 2 to program only the sub channel BL6 independently. Data TLAT EN/SET 1 2 17 18 1 2... n 500μs). The functionality of the maximum backlight current scale (Address 12) is unmodified by the enabling of independent channel control. The LDO enables are always independent of AS2Cwire programming. Data 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Table 7: Address 3 with Independent Channel Control Enabled: BL1 and BL2 On/Off Control. Low Dropout Regulators The AAT2856 includes two independent LDO linear regulators. The regulators operate from a 2.7V to 5.5V input voltage at IN. The AAT2856 supplies separate LDO enable inputs (ENA and ENB) to control individually the operation of the LDOs. The LDO output voltages are set through resistive voltage dividers from the output (OUTA or OUTB) to the feedback input (FBA or FBB). The regulator controls the output voltage such that the voltage divider output is at the 1.2V feedback threshold. The low 200mV dropout voltage at 200mA load current allows the regulator to maintain output voltage regulation. Each LDO regulator can supply up to 200mA continuous current to the load. They include current limiting and thermal overload protection to prevent damage to the load or to the LDOs. BL6 Off Off Off Off Off Off Off Off On On On On On On On On BL5 Off Off Off Off On On On On Off Off Off Off On On On On BL4 Off Off On On Off Off On On Off Off On On Off Off On On BL3 Off On Off On Off On Off On Off On Off On Off On Off On Table 6: Address 2 with Independent Channel Control Enabled: BL3-BL6 On/Off Control. 2856.2008.02.1.3 www.analogictech.com 11 PRODUCT DATASHEET AAT2856 ChargePumpTM High Current Charge Pump with Dual LDO for Backlight Applications R2 Standard 1% Values (R1 = 120K) VOUT (V) 2.8 2.5 2.0 1.8 1.5 Applications Information LDO Output Voltage Programming The output voltages for LDOA and LDOB are programmed by an external resistor divider network. As shown below, the selection of R1 and R2 is a straight forward matter. R1 is chosen by considering the tradeoff between the feedback network bias current and resistor value. Higher resistor values allow stray capacitance to become a larger factor in circuit performance whereas lower resistor values increase bias current and decrease efficiency. OUT(A/B) R2(A/B) FB(A/B) VREF(A/B) = 1.2V R1(A/B) VOUT(A/B) R2 (Ω) 160K 130K 79.6K 60.4K 30.1K Table 8: Example Output Voltages and Corresponding Resistor Values. Device Power Efficiency The AAT2856 power conversion efficiency depends on the charge pump mode. By definition, device efficiency is expressed as the output power delivered to the LEDs divided by the total input power consumed. η= POUT PIN To select appropriate resistor values, first choose R1 such that the feedback network bias current is less than 10μA. Then, according to the desired VOUT, calculate R2 according to the equation below. An example calculation follows. An R1 value of 120K is chosen, resulting in a small feedback network bias current of 1.2V/120K = 10μA. The desired output voltage is 1.8V. From this information, R2 is calculated from the equation below. When the input voltage is sufficiently greater than the LED forward voltages, 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. By simplifying the conditions such that the LEDs have uniform VF, the power conversion efficiency can be approximated by: η= R2 = R1(VOUT - 1.2V) 1.2V VF VF · ILED ≈ VIN · IIN VIN The result is R2 = 60K. Since 60K is not a standard 1%-value, 60.4K is selected. From this example calculation, for VOUT = 1.8V, use R1 = 120K and R2 = 60.4K. Example output voltages and corresponding resistor values are provided in Table 8. Selection of set resistor values outside of the typical application must be carefully evaluated to ensure that the application’s performance requirements can still be met. Due to the very low 1X mode quiescent current, the input current nearly equals the total output current delivered to the LEDs. Further, the low-resistance bypass switch introduces negligible voltage drop from input to output. The AAT2856 further maintains optimized performance and efficiency by detecting when the input voltage is not sufficient to sustain LED drive current. The device automatically switches to 1.5X mode when the input voltage drops too low in relation to the LED forward voltages. 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: η= VF VF · ILED = VIN · 1.5IIN 1.5 · VIN 12 www.analogictech.com 2856.2008.02.1.3 PRODUCT DATASHEET AAT2856 ChargePumpTM High Current Charge Pump with Dual LDO for Backlight Applications 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 are often available in lowercost dielectrics, but capacitors greater than 10μF are not typically required for AAT2856 applications. Capacitor area is another contributor to ESR. Capacitors that are physically larger will have a lower ESR when compared to an equivalent material smaller capacitor. These larger devices can improve circuit performance when compared to an equal value capacitor in a smaller package size. Similarly, when the input falls further, such that 1.5X mode can no longer sustain LED drive 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 current. For ideal conversion, the 2X mode efficiency is given by: η= VF VF · ILED = VIN · 2IIN 2 · VIN LED Selection The AAT2856 is designed to drive high-intensity white LEDs. It is particularly suitable for LEDs with an operating forward voltage in the range of 1.5V to 4.2V. The charge pump can also drive other loads that have similar characteristics to white LEDs. For various load types, the AAT2856 provides a high-current, programmable ideal constant current source. 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 3 illustrates an example 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. The junction-to-ambient thermal resistance (θJA) for the connection 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. 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 to the AGND and PGND pins. It is good practice to connect the GND pins to the exposed paddle area with traces as shown in the example. The flying capacitors C1 and C2 should close to the IC. Trace length should be minimize path resistance and potential input and output capacitors should also close to the chip as possible. be connected kept short to coupling. The be placed as 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. Ceramic composition capacitors are highly recommended over all other types of capacitors for use with the AAT2856. 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 nonpolarized. 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. 2856.2008.02.1.3 www.analogictech.com 13 PRODUCT DATASHEET AAT2856 ChargePumpTM High Current Charge Pump with Dual LDO for Backlight Applications supply connection by positioning the J1 jumper to the ON position. A red LED indicates that power is applied. The Enables of both LDOs are connected with jumpers J3 and J4. These terminals must be connected to the external source to turn on/off the LDOs. When applying external enable signals, consideration must be given to the voltage levels. The externally applied voltages cannot exceed the supply voltage that is applied to the IN pins of the device (DC+). The LDO loads can be connected directly to the evaluation board. For adequate performance, be sure to connect the load between OUTA/OUTB and DC- as opposed to some other GND in the system. Button(s) Pushed SW1 Figure 3: Example PCB Layout. Evaluation Board User Interface The user interface for the AAT2856 evaluation board is provided through 4 buttons and a number of connection terminals. The board is operated by supplying external power and pressing individual buttons or button combinations. The table below indicates the function of each button or button combination. To power-on the board, connect a power supply or battery to the DC- and DC+ terminals. Make the board’s Description [Push/Release once] Increment the number of EN/SET edges, but the backlight current is decreased (dimmer). If held down, autocycle through the settings. [Push/Release once] Decrement the number of EN/SET edges, but the backlight current is increased (brighter). If held down, autocycle through the settings. [Push/Release once] Toggle between 20mA and 30mA maximum current. SW2 SW3 Table 9: AAT2856 Evaluation Board User Interface1. Evaluation Board Layout Figure 4: AAT2856 Evaluation Board Layout Top Side. Figure 5: AAT2856 Evaluation Board Layout Bottom Side. 1. The enable for LDOA and LDOB are manually set externally. 14 www.analogictech.com 2856.2008.02.1.3 PRODUCT DATASHEET AAT2856 AAT2856 ChargePumpTM High Current Charge Pump with Dual LDO for Backlight Applications Evaluation Board Schematics DC+ 1 2 3 VIN J1 C12 100μF 100μF (optional) lab supply bypass C3 2.2μF VOUT D1 D2 D3 D4 D5 D6 J2 0 ENA 28 27 26 25 24 23 22 U1 AAT2856 AGND 1 2 3 4 5 6 AGND OUT BL4 BL5 ENA BL6 BL3 BL2 BL1 AGND AGND REF FBB OUTB OUTA OUT FBA C1+ C1IN OUT ENS PGND IN C2C2+ ENB 21 20 19 18 17 16 15 ENS C2 1.0μF C4 4.7μF C8 0.1μF 7 ENB 8 9 10 11 12 13 14 VOUT OUTB R2 78.7k Programmed for 2.8V output by default R1 59k C5 2.2μF C6 2.2μF R4 29.4k R4 (Ω), R3 = 59k R2 (Ω), R1 = 59k R4 short, R5 open (R2 short, R1 open) 29.4K 78.7K 14.7K 63.4K 105K R3 59k C7 2.2μF Programmed for 1.8V output by default OUTA C1 1.0μF VOUT A/B(V) 1.2 1.8 2.8 1.5 2.5 3.3 Figure 6: AAT2856 Section Schematic. 2856.2008.02.1.3 www.analogictech.com 15 PRODUCT DATASHEET AAT2856 AAT2856 ChargePumpTM High Current Charge Pump with Dual LDO for Backlight Applications VIN 1 2 U3 AAT4296 C11 0.1μF IN OUT3 OUT2 OUT4 OUT1 OUT5 EN/SET GND 8 7 6 5 3 4 J3 J4 ENA ENA ENB ENB R6 100K (Opt) VIN VIN R8 R9 R10 1K 1K 1K U2 1 2 R5 100K (Opt) SW1 SW2 SW3 3 4 VDD GP5 GP4 GP3 PIC12F675 VSS GP0 GP1 GP2 8 7 6 5 C10 1μF R7 330 LED7 RED ENS DC- Figure 7: MCU and I/O Expander Section Schematic. Evaluation Board Component Listing Component U1 U2 U3 D1-D6 C1, C2, C10 C3, C5, C6, C7 C4 C8, C11 C12 R8-R10 R7 R5, R6 R4 R2 R1, R3 J1-J4 LED7 SW1-SW3 Part# AAT2856INJ-EE-T1 PIC12F675 AAT4296IJS-1-T1 LW M673 GRM18x GRM18x GRM18x GRM18x TAJBx Chip Resistor Chip Resistor Chip Resistor Chip Resistor Chip Resistor Chip Resistor PRPN401PAEN CMD15-21SRC/TR8 PTS645TL50 Description High Eff. 1X/1.5X/2X CP for White LED, Dual LDO 8-bit CMOS, FLASH MCU; 8-pin PDIP I/O Expander Mini TOPLED White LED; SMT 1.0μF, 10V, X5R, 0603, Ceramic 2.2μF, 10V, X5R, 0603, Ceramic 4.7μF, 10V, X5R, 0603, Ceramic 0.1μF, 16V, X7R, 0603, Ceramic 100μF, 10V, 10μA, Tantalum 1K, 5%, 1/4W; 1206 330, 5%, 1/4W; 1206 100K, 5%, 1/10W; 0603 29.4K, 1%, 1/10W; 0603 78.7K, 1%, 1/10W; 0603 59K, 1%, 1/10W; 0603 Conn. Header, 2mm Zip Red LED; 1206 Switch Tact, SPST, 5mm Manufacturer AnalogicTech Microchip AnalogicTech OSRAM Murata Murata Murata Murata AVX Vishay Vishay Vishay Vishay Vishay Vishay Sullins Electronics Chicago Miniature Lamp ITT Industries 16 www.analogictech.com 2856.2008.02.1.3 PRODUCT DATASHEET AAT2856 AAT2856 ChargePumpTM High Current Charge Pump with Dual LDO for Backlight Applications Ordering Information Package TQFN44-28-0.4 Marking1 YFXYY Part Number (Tape and Reel)2 AAT2856INJ-EE-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/about/quality.aspx. Package Information3 TQFN44-28-0.4 Pin 1 Dot by Marking Detail "A" 2.600 ± 0.050 C0.3 4.000 ± 0.050 4.000 ± 0.050 2.600 ± 0.050 Top View Bottom View 0.400 ± 0.050 0.430 ± 0.050 0.750 ± 0.050 0.230 ± 0.050 0.203 REF 0.050 ± 0.050 Side View Pin 1 Indicator Detail "A" All dimensions in millimeters. 1. XYY = assembly and date code. 2. Sample stock is generally held on part numbers listed in BOLD. 3. The leadless package family, which includes QFN, TQFN, DFN, TDFN and STDFN, has exposed copper (unplated) at the end of the lead terminals due to the manufacturing process. A solder fillet at the exposed copper edge cannot be guaranteed and is not required to ensure a proper bottom solder connection. 2856.2008.02.1.3 www.analogictech.com 17 PRODUCT DATASHEET AAT2856 AAT2856 ChargePumpTM High Current Charge Pump with Dual LDO for Backlight Applications Advanced Analogic Technologies, Inc. 3230 Scott Boulevard, Santa Clara, CA 95054 Phone (408) 737-4600 Fax (408) 737-4611 © 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. Except as provided in AnalogicTech’s terms and conditions of sale, AnalogicTech assumes no liability whatsoever, and AnalogicTech disclaims any express or implied warranty relating to the sale and/or use of AnalogicTech products including liability or warranties relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right. In order to minimize risks associated with the customer’s applications, adequate design and operating safeguards must be provided by the customer to minimize inherent or procedural hazards. 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. 18 www.analogictech.com 2856.2008.02.1.3