DATA SHEET AAT2856 High Current Charge Pump with Dual LDO for Backlight Applications General Description Features 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. Skyworks AS2Cwire™ (Advanced Simple Serial Control) single-wire 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. • 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 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 VBAT CIN 4.7µF C1 1µF C2 1µF C1+ C1IN C2+ C2OUT COUT 2.2µF IN AAT2856 ENABLE/SET ENS CBYP 0.1µF REF EN_LDOA EN_LDOB VOUT BL1 BL2 BL3 BL4 BL5 BL6 OUTA FBA ENA ENB AGND WLEDs OSRAM LW M673 or equivalent OUTB FBB PGND R2A R1A R2B R1B VOUTA COUTA 2.2µF VOUTB COUTB 2.2 µF Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202506A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • November 2, 2012 1 DATA SHEET AAT2856 High Current Charge Pump with Dual LDO for Backlight Applications Pin Descriptions Pin # Symbol 1 BL3 2 BL2 3 BL1 4, 5, 23, 24 6 AGND REF 7 FBB 8 OUTB 9, 18 IN 10 FBA 11 OUTA 12 13 C1C1+ 14, 21, 22 OUT 15 ENB 16 17 19 C2+ C2PGND 20 ENS 25 BL6 26 BL5 27 ENA 28 BL4 EP 2 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. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202506A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • November 2, 2012 DATA SHEET AAT2856 High Current Charge Pump with Dual LDO for Backlight Applications Pin Configuration TQFN44-28 (Top View) OUT AGND AGND BL6 BL5 ENA BL4 BL3 BL2 BL1 AGND AGND REF FBB 28 27 26 25 24 23 22 1 21 2 20 3 19 4 18 5 17 6 16 7 15 8 9 10 11 12 13 14 OUT ENS PGND IN C2C2+ ENB OUT C1+ C1OUTA FBA IN OUTB Absolute Maximum Ratings1 Symbol TJ TLEAD 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 Units -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 V V V V °C °C Value Units 2 50 W °C/W Thermal Information2 Symbol PD qJA Description Maximum Power Dissipation Maximum Thermal Resistance 3 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. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202506A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • November 2, 2012 3 DATA SHEET AAT2856 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 IIN(Q) Description Conditions IN Operating Voltage Range IN Operating Current 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 DI(BL_) BL1-BL6 Current Matching VBL_(TH) BL1-BL6 Charge Pump Mode Transition Threshold ENS Logic Control VENS(L) ENS Input Low Threshold 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 2 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 Typ Max Units 5.5 V 2.7 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 Address 0, Data 1; VIN - VF = 1.5V Address 12, Data 2; VIN - VF = 1.5V Address 0, Data 1; VIN - VF = 1.5V 0.63 1 1.4 4 2.6 5 1.0 Address 0, Data 1 TA = 25°C 18 VENS = VIN = 5V VIN ≥ 3.3V µA °C °C 200 500 2 mA mV MHz 20 30 22 1.4 -1.0 0.3 % mV 0.4 V V µA µs 1.0 75 ns VIN ≥ 3.3V 1.17 75 µs 500 500 µs µs 1.2 125 1.23 200 V 90 150 µA 200 OUTA, OUTB Dropout Voltage IOUT = 150mA OUTA, OUTB Power Supply Rejection Ratio IOUT = 10mA, CREF = 10nF, 1kHz mA 150 300 50 15 mV dB 0.4 1.4 REF = Open mA 1.0 50 IOUT = 1mA to 200mA ENA = ENB = IN, ENS = AGND ENA = IN, ENB = AGND or ENA = AGND, ENB = IN, ENS = AGND mA 140 15 150 OUTA, OUTB Maximum Load Current ENA, ENB Voltage Low Threshold ENA, ENB Voltage High Threshold ENA, ENB Enable Delay Min 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 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202506A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • November 2, 2012 DATA SHEET AAT2856 High Current Charge Pump with Dual LDO for Backlight Applications Typical Characteristics Backlight Efficiency vs. Input Voltage Backlight Current Matching vs. Temperature (20mA/Ch; Data 1) 100 21 Efficiency (%) LED Current (mA) 20mA/ch 90 80 70 60 50 1.6mA/ch 10.2mA/ch 40 30 2.7 3.1 3.5 3.9 4.3 4.7 5.1 Input Voltage (V) 20.5 20 19.5 19 18.5 -40 5.5 VSINK (500mV/div) VEN IOUT = 0.1mA (2V/div) 0V VOUT (2V/div) IOUT = 200mA VSINK (500mV/div) IIN (200mA/div) 0A Time (200µs/div) VSINK (500mV/div) IIN (200mA/div) IOUT = 200mA IOUT = 100mA 0V 0A (30mA/ch; Data 1) VEN (2V/div) 0V 0V VOUT (2V/div) 0V IIN (200mA/div) 0A Time (200µs/div) IOUT = 300mA Turn Off from 1.5X Mode Backlight (30mA/ch; Data 1; VIN = 2.7V) VOUT (2V/div) 0V Time (200µs/div) Turn On to 2X Mode Backlight VEN (2V/div) 85 Turn On to 1.5X Mode Backlight 0VIOUT = 100mA IIN (200mA/div) 60 IOUT = 50mA (30mA/ch; Data 1; VIN = 3.4V) IOUT = 10mA IOUT = 300mA 0V 35 Temperature (°C) Turn On to 1X Mode Backlight VOUT (2V/div) 10 IOUT = 50mA (30mA/ch; Data 1; VIN = 4.2V) IOUT = 10mA VEN IOUT = 0.1mA (2V/div) 0V -15 0V 0V 0A Time (100µs/div) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202506A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • November 2, 2012 5 DATA SHEET AAT2856 High Current Charge Pump with Dual LDO for Backlight Applications Typical Characteristics BENS, FENS Low Threshold Voltage vs. Input Voltage BENS, FENS High Threshold Voltage vs. Input Voltage 1.4 1.4 1.3 -40°C 1.2 VBENS(L), VFENS(L) (V) VBENS(H), VFENS(H) (V) 1.3 1.1 1.0 0.9 0.8 25°C 0.7 85°C 0.6 0.5 2.7 3.1 3.5 3.9 4.3 4.7 5.1 85°C 25°C 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 300 VBENS(H), VFENS(H) (V) TBENS(LAT), TFENS(LAT) (µs) 0.7 BENS, FENS Off Timeout vs. Input Voltage 25°C IOUT = 300mA 200 -40°C IOUT = 200mA 180 IOUT = 100mA 140 0.8 Input Voltage (V) IOUT = 50mA 220 160 0.9 IOUT = 0.1mA 240 1.0 0.5 5.5 BENS, FENS Latch Timeout vs. Input Voltage IOUT = 10mA -40°C 1.1 0.6 Input Voltage (V) 260 1.2 25°C 120 260 25°C -40°C 220 85°C 180 140 100 80 2.7 3.1 3.5 3.9 4.3 4.7 5.1 100 2.7 5.5 Input Voltage (V) 4.3 4.7 5.1 5.5 LDOs A and B Load Regulation 0V 0V Time (50µs/div) 3.9 Input Voltage (V) Output Voltage Error (%) VOUT (500mV/div) 3.5 LDOs A and B Turn On Characteristic VEN (2V/div) 3.1 1.0 0.5 OUTA 0.0 OUTB -0.5 -1.0 0.1 1 10 100 1000 Load Current (mA) IOUT = 50mA 6 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com IOUT = 10mA 202506A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • November 2, 2012 IOUT = 0.1mA IOUT = 300mA DATA SHEET AAT2856 High Current Charge Pump with Dual LDO for Backlight Applications Typical Characteristics LDOs A and B Output Voltage vs. Temperature 1.5 1.0 0.5 Output Voltage (%) Output Voltage Error (%) LDOs A and B Line Regulation OUTA 0 OUTB -0.5 -1.0 2.7 3.1 3.5 3.9 4.3 4.7 5.1 Output Voltage (V) 3.2 3.0 0 -0.5 -1 -15 IOUT = 10mA IOUT = 0.1mA IOUT = 200mA IOUT = 200mA IOUT = 100mA 2.4 VOUT (AC Coupled) (20mV/div) 2.2 2.0 2.7 2.8 2.9 3.0 3.1 60 85 IOUT = 50mA (10mA Load) VIN = 3.6V VIN (250mV/div) IOUT = 300mA 2.8 35 LDOs A and B Line Transient Response IOUT = 50mA = 0.1mA IOUTIOUT = 100mA 2.6 10 Temperature (°C) LDOs A and B Dropout Characteristics IOUT = 10mA 0.5 -1.5 -40 5.5 Input Voltage (V) 1 IOUT = 300mA I = 200mA VINOUT = 3.1V IOUT = 100mA 3.2 Input Voltage (V) Time (50µs/div) LDOs A and B Load Transient Response (10mA to 200mA Load Step) IOUT (100mA/div) IOUT = 200mA VOUT (AC Coupled) (100mV/div) Time (50µs/div) VIN = 3.1V Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202506A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • November 2, 2012 7 DATA SHEET AAT2856 High Current Charge Pump with Dual LDO for Backlight Applications Functional Block Diagram IN IN C1+ C1C2+ OUTA 1X/1.5X/2X Tri-mode Charge Pump FBA VREF C2- OUTB FBB VREF REF ENA To LDO A OUT ENB To LDO B BL1 BL2 Control Logic ENS BL3 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. 8 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. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202506A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • November 2, 2012 DATA SHEET AAT2856 High Current Charge Pump with Dual LDO for Backlight Applications AS2Cwire Serial Interface AS2Cwire Serial Interface Addressing 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. Address ENS Rising Edges 0 1 2 3 17 18 19 20 12 29 15 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. Address ENS Rising Edges 0 1 2 3 17 18 19 20 12 29 15 32 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. 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. 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. 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 Data THI TLO TLAT TLAT EN/SET 1 Address 2 17 18 1 0 2... n <= 16 1 Data Reg 1 0 Data Reg 2 0 n Figure 1: AS2Cwire Serial Interface Timing. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202506A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • November 2, 2012 9 DATA SHEET AAT2856 High Current Charge Pump with Dual LDO for Backlight Applications Data 30mA Max (mA) 20mA Max (mA) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 30.0 27.9 26.1 24.2 21.0 19.2 17.3 15.0 12.7 10.9 8.1 6.2 4.4 3.5 2.6 0 20.0 19.0 17.8 16.5 14.3 13.0 11.8 10.2 8.5 7.3 5.4 4.1 2.9 2.2 1.6 0 30 30mA FS 25 20 15 20mA FS 10 5 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Data Code Figure 2: Data Code for Address 0-3 vs. Backlight Current Level. Maximum Backlight Current (Address 12) There are two separate current level scales that apply to Addresses 0-2: 20mA and 30mA. According to the Maximum Backlight Current setting at Address 12, only one of the two scales can be active at any given time and never both. By default, the 20mA scale is active on startup. To change to the 30mA scale, or go back to the 20mA scale, write to Address 12. Table 2: Data for the Backlight Current Level, Addresses 0-3. Data Main Current On Sub Current On Current (µA) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 No No No No No No No No Yes Yes Yes Yes Yes Yes Yes Yes No No No No Yes Yes Yes Yes No No No No Yes Yes Yes Yes 0 0 0 0 95 500 950 1900 95 500 950 1900 95 500 950 1900 Table 3: Low-Level Backlight Current, Address 3, FS = 20mA Range. 10 35 IBLED (mA) The AAT2856 incorporates additional circuitry that optimizes performance for exceptionally low backlight current settings. A separate address is used to activate this circuitry. To program the low current settings with improved performance and efficiency, write to Address 3. Unlike Addresses 0-2, which have current level settings according to Table 2 and Figure 2, Address 3 possesses a separate set of current levels described by the Low Current Backlight settings found in Table 3. Since only one of the scales can be active at any given time, the 20mA and 30mA scales cannot be mixed between main and sub. When setting Address 12 to the 30mA scale, only current levels from that scale can be mixed between main and sub. When changing maximum current scales, the data remains constant regardless of scale. When the maximum current scale is changed, the previously stored data value will remain constant but the current value will change due to the different current values on the separate maximum current scales. Data Maximum Current Scale 1 2 20mA 30mA Table 4: Address 12 Maximum Current Scale. Backlight Independent Channel Control (Address 15) The AAT2856 has a unique independent channel control mode whereby individual backlight LED channels can be enabled and disabled to form a custom arrangement of active channels. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202506A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • November 2, 2012 DATA SHEET AAT2856 High Current Charge Pump with Dual LDO for Backlight Applications To enable independent channel control mode, write Data 8 to Address 15. To exit individual mode control, the AAT2856 state machine can be reset by strobing ENS low and holding ENS low longer than the AS2Cwire’s tOFF latch time. Data Individual Backlight Control 8 On Table 5: Address 15, Independent Backlight Control. With independent channel control enabled, the functionality of Addresses 2 and 3 will conform to what is described in Tables 8 and 9. Also Address 0 is no longer applicable after independent channel control has been enabled. As indicated by the possible settings listed in the tables, any combination of backlight channels can be enabled and disabled. The original functionality (Sub Backlight Current BL6 and Low Current Backlight) of Addresses 2 and 3 are no longer available unless the internal state machine has been reset to default mode operation (when ENS is logic low for >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 BL6 BL5 BL4 BL3 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Off Off Off Off Off Off Off Off On On On On On On On On Off Off Off Off On On On On Off Off Off Off On On On On Off Off On On Off Off On On Off Off On On Off Off On On Off On Off On Off On Off On Off On Off On Off On Off On Data BL2 BL1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Off Off Off Off Off Off Off Off On On On On On On On On Off Off Off Off On On On On Off Off Off Off On On On On 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. Table 6: Address 2 with Independent Channel Control Enabled: BL3-BL6 On/Off Control. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202506A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • November 2, 2012 11 DATA SHEET AAT2856 High Current Charge Pump with Dual LDO for Backlight Applications Applications Information R2 Standard 1% Values (R1 = 120K) 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) VOUT(A/B) R2(A/B) FB(A/B) VREF(A/B) = 1.2V VOUT (V) R2 (W) 2.8 2.5 2.0 1.8 1.5 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. R1(A/B) η= 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. R2 = R1(VOUT - 1.2V) 1.2V 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. POUT PIN 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= VF VF · ILED ≈ VIN · IIN VIN 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= 12 VF VF · ILED = VIN · 1.5IIN 1.5 · VIN Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202506A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • November 2, 2012 DATA SHEET AAT2856 High Current Charge Pump with Dual LDO for Backlight Applications 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. 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 100mW. 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. 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. 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 (qJA) 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 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202506A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • November 2, 2012 13 DATA SHEET AAT2856 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. Figure 3: Example PCB Layout. Button(s) Pushed 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 SW1 SW2 SW3 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. 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 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202506A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • November 2, 2012 DATA SHEET AAT2856 High Current Charge Pump with Dual LDO for Backlight Applications Evaluation Board Schematics DC+ 1 2 J1 3 VIN C12 100µF 100µF (optional) lab supply bypass D1 VOUT D2 D3 D4 D5 C3 2.2µF D6 J2 0 ENA 22 U1 AAT2856 OUT 23 AGND BL6 24 AGND ENA 25 PGND 19 4 AGND IN 18 5 AGND C2- 17 6 REF C2+ 16 7 FBB ENB 15 8 9 10 11 12 13 ENS C2 1.0µF C4 4.7µF OUT BL1 C1+ 20 3 C1- 21 ENS OUTA OUT BL2 FBA BL3 2 IN 1 OUTB C8 0.1µF 26 BL5 27 BL4 28 ENB 14 VOUT OUTB Programmed for 2.8V output by default R2 78.7k R1 59k C5 2.2µF C1 1.0µF C6 2.2µF R4 29.4k R4 (Ω), R3 = 59k VOUT A/B(V) R2 (Ω), R1 = 59k 1.2 1.8 2.8 1.5 2.5 3.3 R3 59k C7 2.2µF OUTA Programmed for 1.8V output by default R4 short, R5 open (R2 short, R1 open) 29.4K 78.7K 14.7K 63.4K 105K Figure 6: AAT2856 Section Schematic. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202506A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • November 2, 2012 15 DATA SHEET AAT2856 High Current Charge Pump with Dual LDO for Backlight Applications U3 AAT4296 VIN 1 C11 0.1µF 2 3 4 IN OUT3 OUT2 OUT4 OUT1 OUT5 EN/SET GND 8 7 6 5 J3 ENA J4 ENB ENA ENB R5 100K (Opt) R6 100K (Opt) VIN VIN R8 R9 R10 1K 1K 1K U2 1 2 3 SW1 4 SW2 VDD GP5 GP4 GP3 VSS GP0 GP1 GP2 8 7 6 C10 1µF 5 PIC12F675 R7 330 LED7 RED SW3 ENS DC- Figure 7: MCU and I/O Expander Section Schematic. Evaluation Board Component Listing Component Part# Description Manufacturer 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 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 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 Skyworks Microchip Skyworks OSRAM Murata Murata Murata Murata AVX Vishay Vishay Vishay Vishay Vishay Vishay Sullins Electronics Chicago Miniature Lamp ITT Industries 16 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202506A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • November 2, 2012 DATA SHEET AAT2856 High Current Charge Pump with Dual LDO for Backlight Applications Ordering Information Package Marking1 Part Number (Tape and Reel)2 TQFN44-28-0.4 YFXYY AAT2856INJ-EE-T1 Skyworks Green™ products are compliant with all applicable legislation and are halogen-free. For additional information, refer to Skyworks Definition of Green™, document number SQ04-0074. Package Information3 TQFN44-28-0.4 Pin 1 Dot by Marking C0.3 2.600 ± 0.050 4.000 ± 0.050 Detail "A" 4.000 ± 0.050 2.600 ± 0.050 Top View Bottom View 0.400 ± 0.050 0.430 ± 0.050 0.750 ± 0.050 Side View 0.230 ± 0.050 0.203 REF 0.050 ± 0.050 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. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202506A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • November 2, 2012 17 DATA SHEET AAT2856 High Current Charge Pump with Dual LDO for Backlight Applications Copyright © 2012 Skyworks Solutions, Inc. All Rights Reserved. Information in this document is provided in connection with Skyworks Solutions, Inc. (“Skyworks”) products or services. These materials, including the information contained herein, are provided by Skyworks as a service to its customers and may be used for informational purposes only by the customer. Skyworks assumes no responsibility for errors or omissions in these materials or the information contained herein. Skyworks may change its documentation, products, services, specifications or product descriptions at any time, without notice. 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Additional information, including relevant terms and conditions, posted at www.skyworksinc.com, are incorporated by reference. 18 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202506A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • November 2, 2012