AAT2842 High-Current Charge Pump with S2Cwire™ Control and Dual LDO for Backlight and Flash General Description Features The AAT2842 is a highly integrated charge pump with dual linear regulators optimized for systems operating with lithium-ion/polymer batteries. The charge pump provides power for both white LED backlight/keypad and flash. Up to four backlight LEDs can be driven at up to 30mA each and keypad LEDs can be driven using lower currents set by the S2Cwire interface. In addition, up to four flash LEDs can be driven with up to 600mA total. Two separate S2Cwire™ (Simple Serial Control™) serial digital interfaces are used to enable, disable, and set the current to one of 16 levels for both backlight and flash LEDs. Backlight/keypad and flash current settings are also controlled through external resistors for increased versatility with reduced accuracy and matching. Backlight/keypad current matching is 1% for uniform display brightness, and flash current matching is 4% for uniform power dissipation. An internal flash timer set by an external capacitor protects the flash LED should a fault occur. • • • • • • • The AAT2842 offers two high-performance MicroPower™ low dropout (LDO) linear regulators. A single enable input controls both regulators and each supplies up to 200mA to the load. Both LDOs consume only 85µA quiescent current, making them ideal for battery-operated applications. ChargePump™ VIN Range: 2.7V to 5.5V Tri-Mode Charge Pump: — Drives up to Four Backlight/Keypad and Four Flash LEDs — Separate S2Cwire Control for Backlight/Keypad and Flash Currents — Backlight/Keypad and Flash Current Set by Separate External Resistors — Flash Timer Set with External Capacitor — Up to 2MHz Switching Frequency Two Linear Regulators: — 200mA Output Current — 200mV Dropout — Output Voltage Adjustable from 1.2V to VBATTERY — Output Auto-Discharge for Fast Shutdown — 85µA Quiescent Current Built-In Thermal Protection Automatic Soft Start -40°C to +85°C Temperature Range Available in 4x4mm TQFN44-28 Package Applications • • • The AAT2842 is equipped with built-in short-circuit and over-temperature protection. The charge pump soft-start circuitry prevents excessive inrush current at start-up. The product is available in a Pb-free, space-saving TQFN44-28 package and operates over the -40°C to +85°C ambient temperature range. Camera-Enabled Mobile Devices Digital Still Cameras Multimedia Mobile Phones Typical Application C1 1μF C1+ IN CIN 4.7μF VBAT EN_BACKLIGHT EN_FLASH C2 1μF C1- C2+ AAT2842 IN BENS FENS CT BSET RSET1 CT COUT 2.2μF BL1 BL2 BL3 BL4 FL1 FL2 FL3 FL4 OUTA VOUT LDOA FSET RSET2 REF CREF R2A ENL AGND COUTA FBA VOUT LDOB OUTB EN_LDO 2842.2007.09.1.2 C2- OUT R2B FBB PGND R1A COUTB R1B 1 AAT2842 High-Current Charge Pump with S2Cwire™ Control and Dual LDO for Backlight and Flash Pin Descriptions 2 Pin # Symbol 1 BL1 2 BSET 3 FSET 4 5 AGND CT 6 REF 7 FBB 8 OUTB 9, 18 IN 10 FBA 11 OUTA 12 13 14 C1C1+ OUT 15 ENL 16 17 19 20 C2+ C2PGND FL4 21 FL3 22 FL2 23 FL1 Description 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. Backlight current setting input. A 280kΩ resistor from BSET to AGND sets the maximum backlight current to 30mA. Flash current setting input. A 280kΩ resistor from FSET to AGND sets the maximum flash current to 150mA. Analog ground. Connect AGND to PGND at a single point as close to the AAT2842 as possible. Flash timer control capacitor input. Connect a capacitor from CT to AGND to set the flash timer. A 100nF capacitor sets the timer to 1s. Reference output. For low noise operation, bypass REF to AGND with capacitor. Typically, a 0.1µF ceramic capacitor provides sufficient noise reduction. Feedback input for LDOB. FBB measures the output voltage of LDOB. Connect a resistive voltage divider from the output of LDOB to FBB. FBB feedback regulation voltage is 1.2V. LDOB regulated voltage output. OUTB is the voltage output of low dropout regulator B. Bypass OUTB to AGND with a 2.2µF or larger ceramic capacitor as close to the AAT2842 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 AAT2842 as possible. Feedback input for LDOA. FBA measures the output voltage of LDOA. Connect a resistive voltage divider from the output of LDOA to FBA. FBA feedback regulation voltage is 1.2V. LDOA regulated voltage output. OUTA is the voltage output of low dropout regulator A. Bypass OUTA to AGND with a 2.2µF or larger ceramic capacitor as close to the AAT2842 as possible. Negative node of charge pump capacitor 1. Positive node of charge pump capacitor 1. Connect a 1µF ceramic capacitor from C1+ to C1-. Charge pump output. OUT is the output of the charge pump and supplies current to the backlight and flash LEDs. Connect the backlight and flash LED anodes to OUT. Bypass OUT to PGND with a 2.2µF or larger capacitor as close to the AAT2842 as possible. LDO enable input. ENL turns on or off the low dropout regulators. Drive ENL high to turn on the regulators, drive it low to turn them off. Positive node of charge pump capacitor 2. Connect a 1µF ceramic capacitor from C2+ to C2-. Negative node of charge pump capacitor 2. Power ground. Connect AGND to PGND at a single point as close to the AAT2842 as possible. Flash LED 4 current sink. FL4 controls the current through Flash LED 4. Connect the cathode of Flash LED 4 to FL4. If not used, connect FL4 to OUT. Flash LED 3 current sink. FL3 controls the current through Flash LED 3. Connect the cathode of Flash LED 3 to FL3. If not used, connect FL3 to OUT. Flash LED 2 current sink. FL2 controls the current through Flash LED 2. Connect the cathode of Flash LED 2 to FL2. If not used, connect FL2 to OUT. Flash LED 1 current sink. FL1 controls the current through Flash LED 1. Connect the cathode of Flash LED 1 to FL1. If not used, connect FL1 to OUT. 2842.2007.09.1.2 AAT2842 High-Current Charge Pump with S2Cwire™ Control and Dual LDO for Backlight and Flash Pin Descriptions (continued) Pin # Symbol 24 FENS 25 BENS 26 BL4 27 BL3 28 BL2 Description Flash enable and serial control input. FENS is the on/off control for the flash and the S2Cwire input to serially control the flash LED brightness relative to the maximum current set by the resistor at FSET. Backlight enable and serial control input. BENS is the on/off control for the backlight and the S2Cwire input to serially control the backlight LED brightness relative to the maximum current set by the resistor at BSET. 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. 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. Exposed paddle (bottom); connect to PGND as closely as possible to the device. EP Pin Configuration TQFN44-28-0.4 (Top View) TQFN44-28-0.45 (Top View) 27 26 25 24 23 FL2 FL1 FENS BENS BL4 BL3 BL2 FL2 FL1 FENS BENS BL4 BL3 BL2 28 BL1 BSET FSET AGND CT REF FBB 22 28 1 21 2 20 3 19 4 18 5 17 6 16 7 15 8 9 10 11 12 13 14 FL3 FL4 PGND IN C2C2+ ENL BL1 BSET FSET AGND CT REF FBB 27 26 25 24 23 22 1 21 2 20 3 19 4 18 5 17 6 16 15 7 8 9 10 11 12 13 FL3 FL4 PGND IN C2C2+ ENL 14 OUT C1+ C1OUTA FBA IN OUTB OUT C1+ C1OUTA FBA IN OUTB N.B. Not recommended for new designs. 2842.2007.09.1.2 3 AAT2842 High-Current Charge Pump with S2Cwire™ Control and Dual LDO for Backlight and Flash Absolute Maximum Ratings1 Symbol TJ TLEAD Description IN, OUT, FL1, FL2, FL3, FL4, BL1, BL2, BL3, BL4 Voltage to AGND C1+, C1-, C2+, C2- Voltage to AGND BSET, FSET, CT, FBB, OUTA, FBA, OUTB, ENL, REF, FENS, BENS 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 V V -0.3 to VIN + 0.3 V -0.3 to 0.3 -40 to 150 300 V °C °C Value Units 2 50 W °C/W Thermal Information2 Symbol PD θJA Description 3 Maximum Power Dissipation Maximum Thermal Resistance 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 an FR4 circuit board. 3. Derate 20mW°C above 40°C ambient temperature. 4 2842.2007.09.1.2 AAT2842 High-Current Charge Pump with S2Cwire™ Control and Dual LDO for Backlight and Flash Electrical Characteristics1 VIN = 3.6V; CIN = 4.7µF; COUT = 2.2µF; C1 = C2 = 1.0µF; RBSET = RFSET = 280kΩ; TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = 25°C. Symbol VIN IIN(Q) Description Conditions IN Operating Voltage Range IN Operating Current IIN(SHDN) IN Shutdown Current Over-Temperature Shutdown TSD Threshold Over-Temperature Shutdown TSD(HYS) Hysteresis Charge Pump Section IOUT OUT Maximum Output Current VIN(TH_H) Charge Pump Mode Hysteresis fOSC Charge Pump Oscillator Frequency tSS Charge Pump Soft-Start Delay Backlight LED Outputs, S2Cwire Data = 1 IBL_(MAX) BL1-BL4 Maximum Current ΔI(BL_) BL1-BL4 Current Matching2 BL1-BL4 Charge Pump Mode VBL_(TH) Transition Threshold VBSET RBSET Pin Voltage Backlight LED Outputs, S2Cwire Data = 7 IBL_(MAX) BL1-BL4 Maximum Current ΔI(BL_) BL1-BL4 Current Matching2 BL1-BL4 Charge Pump Mode VBL_(TH) Transition Threshold Flash LED Outputs, S2Cwire Data = 1 IFL_(MAX) FL1-FL4 Maximum Current ΔI(FL_) FL1-FL4 Current Matching2 FL1-FL4 Charge Pump Mode VFL_(TH) Transition Threshold VFSET RFSET Pin Voltage Min Typ Max Units 2.7 1X Mode, 3.0V ≤ VIN ≤ 5.5V, Active, No Load; ENL = AGND, FENS = BENS = IN 1.5X Mode, 3.0V ≤ VIN ≤ 5.5V, Active, No Load; ENL = AGND, FENS = BENS = IN 2X Mode, 3.0V ≤ VIN ≤ 5.5V, Active, No Load; ENL = AGND, FENS = BENS = IN RBSET = 280kΩ, Data 1, 1X Mode ENL = BENS = FENS = AGND, TA = 25°C 3.0 50 5.0 27 8.6 °C 15 °C 600 350 mA mV 2 MHz 350 µs 30 0.5 150 33 1 9.6 150 1 300 0.7 mA % mV V 10.6 2 mA % mV 165 4 mA % mV 60 135 µA µA 140 0.7 VIN - VF = 1.5V VIN - VF = 1.5V mA 5.0 OUT = 0V to VBAT VIN - VF = 1.5V VIN - VF = 1.5V V 1.0 Data 1 VIN - VF = 1.5V VIN - VF = 1.5V 5.5 V 1. The AAT2842 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. 2842.2007.09.1.2 5 AAT2842 High-Current Charge Pump with S2Cwire™ Control and Dual LDO for Backlight and Flash Electrical Characteristics1 VIN = 3.6V; CIN = 4.7µF; COUT = 2.2µF; C1 = C2 = 1.0µF; RBSET = RFSET = 280kΩ; TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = 25°C. Symbol Enable/Set VBENS(L), VFENS(L) VBENS(H), VFENS(H) IBENS, IFENS TBENS(L), TFENS(L) Description Conditions Min Typ BENS, FENS Low Threshold BENS, FENS High Threshold BENS, FENS Input Leakage Current Units 0.4 V 1.4 VBENS or VFENS = VIN = 5V BENS, FENS Low Time TBENS(H-MIN), BENS, FENS Minimum TFENS(H-MIN) High Time TBENS(H-MAX), BENS, FENS Maximum TFENS(H-MAX) High Time TBENS(OFF), BENS, FENS Off Timeout TFENS(OFF) TBENS(LAT), BENS, FENS Latch Timeout TFENS(LAT) Linear Regulators VFBA, VFBB FB Voltage Tolerance IIN IN Operating Current OUTA, OUTB Maximum Load IOUTA(MAX), IOUTB(MAX) Current VOUTA(DO), OUTA, OUTB Dropout Voltage VOUTB(DO) ENL Enable Low Voltage VENL(L) Threshold ENL Enable High Voltage VENL(H) Threshold tENL(DLY) ENL Enable Delay ROUTA(DCHG), OUTA, OUTB Auto-Discharge ROUTA(DCHG) Resistance PSRRA, OUTA, OUTB Power Supply Rejection Ratio PSRRB Max V -1 1 µA 0.3 75 µs 50 IOUT = 1mA to 200mA ENL = IN, BENS = FENS = AGND 1.17 1.2 85 ns 75 µs 500 µs 500 µs 1.23 150 V µA 200 IOUT = 150mA mA 150 1.4 REF = Open IOUT =10mA, CREF = 10nF, 1kHz 300 mV 0.4 V V 15 µs 20 Ω 50 dB 1. The AAT2842 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. 6 2842.2007.09.1.2 AAT2842 High-Current Charge Pump with S2Cwire™ Control and Dual LDO for Backlight and Flash Typical Characteristics VIN = 3.6V; CIN = 4.7µF; COUT = 2.2µF; C1 = C2 = 1.0µF; RBSET = RFSET = 280kΩ; TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = 25°C. Backlight Efficiency vs. Supply Voltage Flash Efficiency vs. Supply Voltage 100 100 Efficiency (%) 90 80 70 60 7.5mA/ch VF = 3.1V 50 40 2.1mA/ch VF = 2.9V 90 Efficiency (%) 30mA/ch VF = 3.7V 80 70 150mA total VF = 2.9V 60 50 200mA total VF = 2.9V 40 30 300mA total VF = 3.0V 30 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 2.7 2.8 2.9 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4.0 4.1 4.2 Supply Voltage (V) Supply Voltage (V) Turn On to 1X Mode Backlight Turn On to 1.5X Mode Backlight (30mA/ch; Data 1; VIN = 4.2V) (30mA/ch; Data 1; VIN = 3.5V) EN (2V/div) EN (2V/div) OUT (2V/div) OUT (2V/div) VSINK (500mV/div) VSINK (500mV/div) IIN (100mA/div) IIN (200mA/div) Time (200µs/div) Time (200µs/div) Turn On to 2X Mode Backlight Turn Off from 1.5X Mode Backlight (30mA/ch; Data 1; VIN = 3.2V) (30mA/ch; Data 1) EN (2V/div) EN (2V/div) OUT (2V/div) OUT (2V/div) VSINK (500mV/div) IIN (200mA/div) IIN (200mA/div) Time (200µs/div) 2842.2007.09.1.2 Time (100µs/div) 7 AAT2842 High-Current Charge Pump with S2Cwire™ Control and Dual LDO for Backlight and Flash Typical Characteristics VIN = 3.6V; CIN = 4.7µF; COUT = 2.2µF; C1 = C2 = 1.0µF; RBSET = RFSET = 280kΩ; TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = 25°C. BENS, FENS High Threshold Voltage vs. Supply Voltage 1.2 1.2 -40°C 1.1 VBENS(L), VFENS(L) (V) 1.1 VBENS(H), VFENS(H) (V) BENS, FENS Low Threshold Voltage vs. Supply Voltage 1.0 0.9 0.8 0.7 85°C 0.6 25°C 0.5 0.4 0.3 0.9 0.8 0.7 25°C 85°C 0.6 0.5 0.4 0.3 0.2 0.2 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 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 VIN (V) VIN (V) BENS, FENS Latch Timeout vs. Supply Voltage BENS, FENS Off Timeout vs. Supply Voltage 500 350 -40°C 300 25°C 250 85°C 200 TBENS(OFF), TFENS(OFF) (µs) 400 TBENS(LAT), TFENS(LAT) (µs) -40°C 1.0 450 400 350 300 -40°C 250 200 25°C 85°C 150 150 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 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 VIN (V) VIN (V) LDOs A and B Turn On Characteristic Output Voltage Accuracy (%) LDOs A and B Line Regulation ENL (2V/div) VOUT (500mV/div) 1.00 0.50 OUTA 0.00 OUTB -0.50 -1.00 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 (50µs/div) 8 Input Voltage (V) 2842.2007.09.1.2 AAT2842 High-Current Charge Pump with S2Cwire™ Control and Dual LDO for Backlight and Flash Typical Characteristics VIN = 3.6V; CIN = 4.7µF; COUT = 2.2µF; C1 = C2 = 1.0µF; RBSET = RFSET = 280kΩ; TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = 25°C. LDOs A and B Load Regulation LDOs A and B Line Transient Response Output Voltage Accuracy (%) (10mA Load) 1.00 VIN (400mV/div) 0.50 OUTA VIN = 4.2V 0.00 VIN = 3.7V OUTB -0.50 -1.00 0.1 1 10 100 VOUT (10mV/div) 1000 Load Current (mA) Time (40µs/div) LDOs A and B Load Transient Response (10mA to 200mA Load Step) IOUT (100mA/div) IOUT = 200mA VOUT (100mV/div) Time (20µs/div) 2842.2007.09.1.2 9 AAT2842 High-Current Charge Pump with S2Cwire™ Control and Dual LDO for Backlight and Flash Functional Block Diagram IN IN C1+ C1C2+ OUTA LDO A Tri-Mode Charge Pump (1X/1.5X/2X) FBA OUTB C2- LDO B FBB 1.2V VREF ENL To LDO A&B REF OUT BL1 BL2 BENS BL3 FENS Control Logic CT BL4 FL1 BSET FL2 FSET FL3 FL4 AGND PGND Functional Description The AAT2842 is a highly integrated LED driver with two LDO linear regulators. The charge pump LED driver simultaneously drives the backlight and flash LEDs from a 2.7V to 5.5V input voltage. The LDO regulators operate 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 the LED directly from the input voltage (1X mode) or steps the input voltage up by a factor of 1.5 (1.5X mode) or 2 (2X mode). The charge pump requires only two tiny ceramic capac- 10 itors, making a more compact solution than an inductor-based step-up converter solution. Each individual LED is driven by a current sink to GND 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 starts 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 and keep constant LED current. The AAT2842 continuously monitors the LED forward voltages, and the input voltage determines when to reduce the charge pump mode for better efficiency. There is also a 350mV mode-transition hysteresis that prevents the charge pump from oscillating between modes. 2842.2007.09.1.2 AAT2842 High-Current Charge Pump with S2Cwire™ Control and Dual LDO for Backlight and Flash The backlight and flash LED currents are controlled by a combination of an external programming resistor from BSET (for backlight) or FSET (for flash) to AGND and the backlight or flash serial S2Cwire interface BENS or FENS. The programming resistor sets the maximum LED current for each channel, and the serial S2Cwire interface controls the LED current relative to the maximum. To drive backlight LEDs with optimal absolute accuracy and channel-to-channel matching, the maximum output current is set to 30mA with a 280kΩ resistor connected at the BSET pin of the AAT2842. The AAT2842 features separate control interfaces for the backlight and flash current control. The backlight current features 16 current steps, each as a percentage of the maximum backlight current set by the BSET resistance. The flash has 16 current level settings, again as a percentage of the maximum flash current set by the FSET resistance (see Tables 1 and 2). Initiating a flash current also initiates the flash timer which is programmed via an external capacitor CT. Calculate the flash time T by the following equation: T = 10 · CT Using Backlight LED Outputs for Low-Current LED Applications The AAT2842's backlight current outputs can be programmed to drive lower current LEDs, such as those used for keypad applications. For best low-current accuracy and matching, the preferred method is to use a 280kΩ resistor for RBSET and then set the desired current output using the product's S2Cwire interface, as shown in Table 1. If any one of the current sinks is not used, connect the unused current sink to OUT. The current controller monitors the current sink voltage and, if it is connected to OUT, then it is assumed that the current sink is not used or that the LED is shorted, and the controller turns off that current sink. S2Cwire Serial Interface The S2Cwire serial interface records rising edges of the EN/SET pin and decodes them into 16 different states. The S2Cwire 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. 2842.2007.09.1.2 where T is in seconds and CT is in µF. For example, for a 0.1µF capacitor: T = 10 · 0.1μF = 1s To disable the flash timer, connect CT to AGND. Data BL% of BSET 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 100 82 70 59 49.2 41.0 33.0 28.2 23.5 18.7 15.4 12.3 7.7 4.1 2.4 0.2 Table 1: Backlight Current Register: BL1-BL4 (RBSET = 280kΩ). 11 AAT2842 High-Current Charge Pump with S2Cwire™ Control and Dual LDO for Backlight and Flash Data FL% of FSET 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 100 81 72 66 60 52.5 46.2 41.4 36.6 31.7 28.5 25.0 21.7 18.4 16.7 15.0 Table 2: Flash Current Register: FL1-FL4 (RFSET = 280kΩ). Applications Information LDO Output Voltage Programming The output voltages for LDOA and LDOB are programmed by an external resistor divider network. As shown in Figure 2, the selection of R1 and R2 is a straightforward 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 = 1.2V R1(A/B) Shutdown Since the sink switches are the only power returns for all loads, there is no leakage current when all of the sink switches are disabled. To activate the shutdown mode, hold both the BENS and FENS inputs low for longer than TBENS(OFF) or TFENS(OFF) (500µs). In this state, the AAT2842 typically draws less than 1µA from the input. Data and address registers are reset to 0 in shutdown. Low Dropout Regulators The AAT2842 includes two LDO linear regulators. The regulators run from the same 2.7V to 5.5V input voltage as the charge pump. The regulators use a single on/off control input, ENL. The LDO output voltages are set through a resistive voltage divider from the output (OUTA or OUTB) to the feedback input (FBA or FBB). The ratio of resistor values determines the LDO output voltage. The low 200mV dropout voltage at 200mA load current allows the regulator to maintain output voltage regulation. Each LDO regulator can supply a continuous load current up to 200mA. Both LDOs include current limiting and thermal overload protection to prevent damage to the load or to the LDOs. 12 Figure 2: Selection of External Resistors. To select appropriate resistor values, first choose R1 such that the feedback network bias current is reasonable. Then, according to the desired VOUT, calculate R2 according to the equation below. An example calculation follows. R1 is chosen to be 120K, 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 3. 2842.2007.09.1.2 AAT2842 High-Current Charge Pump with S2Cwire™ Control and Dual LDO for Backlight and Flash R2 Standard 1% Values (R1 = 120K) VOUT (V) R2 (Ω) 2.8 2.5 2.0 1.8 1.5 160K 130K 79.6K 60.4K 30.1K RFSET = This is illustrated graphically in Figure 4. Maximum Flash LED Current vs. RFSET 180 Table 3: Example Output Voltages and Corresponding Resistor Values. The value of RBSET determines the maximum LED current level for the backlight section. In the typical application, selecting RBSET = 280kΩ results in 30mA/channel LED current. From this reference point, the maximum current level can be modified by calculating an alternative RBSET value: RBSET = 30mA · 280kΩ IBLED(MAX) This is illustrated graphically in Figure 3. Maximum Backlight LED Current vs. RBSET 35 IBLED (mA) 30 25 160 140 IFLED (mA) Altering the Maximum LED Current Level from 30mA for Backlight and 150mA for Flash 150mA · 280kΩ IFLED(MAX) 120 100 80 60 40 20 0 100 200 300 400 500 600 700 800 900 1000 1100 RFSET (kΩ Ω) Figure 4: Maximum Flash Current vs. RFSET. 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. Brightness Control Using the BSET and FSET Pins An alternative method can be used for brightness control of the flash and/or backlight sections by utilizing the corresponding set resistor pin. By using a digital I/O port or DAC output, an alternative brightness control technique can be created for each lighting section, as shown in Figure 5. 20 15 10 AAT2842 5 0 100 200 300 400 500 600 700 800 900 1000 1100 RBSET (kΩ Ω) Figure 3: Maximum LED Current vs RBSET. Similarly, the value of RFSET determines the maximum LED current level for the flash section. In the typical application, selecting RFSET = 280kΩ results in 150mA/channel LED current. From this reference point, the maximum current level can be modified by calculating an alternative RFSET value: 2842.2007.09.1.2 HI/LO or VDAC R2 B/FSET R1 Figure 5: Brightness Control Using Either BSET or FSET Resistor Pin. 13 AAT2842 High-Current Charge Pump with S2Cwire™ Control and Dual LDO for Backlight and Flash Using an additional resistor to connect the BSET pin with a digital output provides a LO/HI control. When the digital output is asserted high, the resulting brightness level for the backlighting section is LO and the individual LED current levels are: Device Power Efficiency The AAT2842 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. VIO⎞ ⎛ 0.7V ILED(LO) = 12 · 103 R // R - R ⎝ 1 2 2⎠ The same can be applied to the FSET pin. When the digital output is asserted high, the resulting brightness level for the flash section is LO and the individual LED current levels are: VIO⎞ ⎛ 0.7V ILED(LO) = 60 · 103 R // R - R ⎝ 1 2 2⎠ When the digital output is asserted low, the resulting brightness level for the backlighting section is HI and the individual LED current levels are: ⎛ 0.6V ⎞ ILED(HI) = 12 · 103 R // R ⎝ 1 2⎠ The same can be applied to the FSET pin. When the digital output is asserted low, the resulting brightness level for the flash section is HI and the individual LED current levels are: ⎛ 0.6V ⎞ ILED(HI) = 60 · 103 R // R ⎝ 1 2⎠ Additionally, the output from a digital-to-analog converter can be used with either SET pin to control the brightness level. The result is like the equations above, where VIO is replaced with VDAC. Using the flash section as an example: VDAC⎞ ⎛ 0.7V ILED = 60 · 103 R // R - R ⎝ 1 2 2 ⎠ 14 η= 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 · ILED VF ≈ 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 AAT2842 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 · ILED VF ≈ VIN · 1.5IIN 1.5 · VIN 2842.2007.09.1.2 AAT2842 High-Current Charge Pump with S2Cwire™ Control and Dual LDO for Backlight and Flash 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 · ILED VF ≈ VIN · 2IIN 2 · VIN LED Selection The AAT2842 is designed to drive high-intensity white LEDs. It is particularly suitable for LEDs with an operating forward voltage in the range of 4.2V to 1.5V. The charge pump device can also drive other loads that have similar characteristics to white LEDs. For various load types, the AAT2842 provides a highcurrent, 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 100mΩ. Ceramic composition capacitors are highly recommended over all other types of capacitors for use 2842.2007.09.1.2 with the AAT2842. Ceramic capacitors offer many advantages over their tantalum and aluminum electrolytic counterparts. A ceramic capacitor typically has very low ESR, is lowest cost, has a smaller PCB footprint, and is non-polarized. Low ESR ceramic capacitors help maximize charge pump transient response. Since ceramic capacitors are non-polarized, they are not prone to incorrect connection damage. Equivalent Series Resistance ESR is an important characteristic to consider when selecting a capacitor. ESR is a resistance internal to a 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 lower-cost dielectrics, but capacitors greater than 10µF are not typically required for AAT2842 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. 15 AAT2842 High-Current Charge Pump with S2Cwire™ Control and Dual LDO for Backlight and Flash Evaluation Board Layout Figure 2: AAT2842 Evaluation Board Top Layer. Evaluation Board User Interface The user interface for the AAT2842 evaluation board is provided through four buttons and a number of connection terminals. The board is operated by supplying external power and pressing individual buttons or button combinations. Table 4 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. Close the board supply connection by positioning the J1 jumper to the ON position. A red LED indicates that power is applied. 16 Figure 3: AAT2842 Evaluation Board Bottom Layer. The evaluation board is flexible so that the user can disconnect the enable lines from the microcontroller and apply external enable signals. By removing the jumpers from J2, J3, and/or J4, external enable signals can be applied to the board. External enable signals must be applied to Pin 1 of each J2, J3, or J4 terminal. 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. 2842.2007.09.1.2 AAT2842 High-Current Charge Pump with S2Cwire™ Control and Dual LDO for Backlight and Flash Button(s) Pushed1 Description DATA Increment the data setting for the most recently activated mode. With backlight or movie mode activated, hold down the button to auto-cycle through the brightness levels. Toggle ON/OFF the backlighting section. Set the brightness level using the DATA button (defaults to Data 1). Decrement the brightness setting for backlight mode. Hold down to auto-cycle. Toggle ON/OFF movie mode illumination. Set the brightness level using the DATA button (defaults to Data 10). Decrement the brightness setting for movie mode. Hold down to auto-cycle. Generate a flash pulse. Pulse duration is the lesser of 2 seconds or the CT value result. Set the brightness level using the DATA button (defaults to Data 1). Toggle ON/OFF the LDOs. Reset. Clear all data and bring all enable lines low. LIGHT LIGHT+DATA MOVIE MOVIE+DATA FLASH DATA+FLASH LIGHT+MOVIE+FLASH Table 4: Evaluation Board User Interface. Evaluation Board Schematics VOUT D1 D2 D3 D4 D5 D6 ENBL ENFL 22 FL2 7 23 6 DC+ BL1 FL3 BSET FL4 FSET PGND AGND IN CT C2C2+ FBB ENL 21 20 19 J1 VIN 18 17 C2 1.0μF 16 15 OUT C4 4.7μF 3 2 C12 100μF optional 100μF lab supply bypass 1 ENL 14 13 12 11 10 9 8 C9 1.0μF C1+ C1OUTA REF FBA IN OUTB C8 1.0μF 24 5 25 4 FL1 FENS BENS 2 R10 280K CTRL_CT 26 BL4 BL3 BL2 1 3 R9 280K 27 28 280K yields 30mA/ch max backlighting 280K yields 150mA/ch max flash U1 AAT2842 VOUT OUTB Programmed for 2.8V output by default R11 160K C6 2.2μF C1 1.0μF C3 2.2μF C5 2.2μF R12 120K OUTA R13 60.4K C7 2.2μF Programmed for 1.8V output by default R14 120K Figure 4: AAT2842 Section Schematic. 1. The “+” indicates that these buttons are pressed and released together. 2842.2007.09.1.2 17 AAT2842 High-Current Charge Pump with S2Cwire™ Control and Dual LDO for Backlight and Flash VIN C11 0.1μF J2 ENBL J3 ENFL J4 ENL ENBL U3 1 IN 2 NC 3 NC 4 OUT3 8 7 OUT2 6 OUT1 5 ENFL EN/SET GND AAT4291 ENL R6 R7 R8 100K 100K 100K VIN VIN R1 R2 R3 R4 1K 1K 1K 1K DATA SW1 LIGHT SW2 MOVIE SW3 FLASH SW4 U2 1 2 3 4 VDD GP5 GP4 GP3 8 VSS 7 GP0 GP1 6 5 GP2 PIC12F675 C10 0.1μF R5 330 LED7 RED CTRL_CT DC- Figure 5: MCU and I/O Expander Section Schematic. 18 2842.2007.09.1.2 AAT2842 High-Current Charge Pump with S2Cwire™ Control and Dual LDO for Backlight and Flash Evaluation Board Component Listing Component U1 U2 U3 D1 - D4 D5, D6 C1, C2, C10 C3, C5, C6, C7 C4 C8, C9, C11 C12 R1 - R4 R5 R6 - R8 R9, R10 R11 R12, R14 R13 J1 - J4 LED7 SW1 - SW4 2842.2007.09.1.2 Part Number AAT2842INJ-EE-T1, AAT2842IBJ-EE-T1 PIC12F675 AAT4291IJS-1-T1 LW M673 LXCL-PWF1 GRM18x GRM18x GRM18x GRM18x TAJBx Chip Resistor Chip Resistor Chip Resistor Chip Resistor Chip Resistor Chip Resistor Chip Resistor PRPN401PAEN CMD15-21SRC/TR8 PTS645TL50 Description Manufacturer 2 High-Current Charge Pump with S Cwire Control and Dual LDO for Backlight and Flash 8-bit CMOS, FLASH MCU; 8-pin PDIP I/O Expander Mini TOPLED White LED; SMT Luxeon Flash LED 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%, 1/4W; 1206 280K, 1%, 1/10W; 0603 160K, 1%, 1/10W; 0603 120K, 1%, 1/10W; 0603 60.4K, 1%, 1/10W; 0603 Conn. Header, 2mm Zip Red LED; 1206 Switch Tact, SPST, 5mm AnalogicTech Microchip AnalogicTech OSRAM Lumileds Murata Murata Murata Murata AVX Vishay Vishay Vishay Vishay Vishay Vishay Vishay Sullins Electronics Chicago Miniature Lamp ITT Industries 19 AAT2842 High-Current Charge Pump with S2Cwire™ Control and Dual LDO for Backlight and Flash Ordering Information Package Marking1 Part Number (Tape and Reel)2 TQFN44-28-0.45 TQFN44-28-0.4 TGXYY XUXYY AAT2842IBJ-EE-T1 AAT2842INJ-EE-T1 Comments Not recommended for new designs Recommended for new designs 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. Legend Voltage Code 1.2 E 1. XYY = assembly and date code. 2. Sample stock is generally held on part numbers listed in BOLD. 20 2842.2007.09.1.2 AAT2842 High-Current Charge Pump with S2Cwire™ Control and Dual LDO for Backlight and Flash Package Information1 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 0.230 ± 0.050 0.203 REF 0.050 ± 0.050 Side View Pin 1 Indicator Detail "A" All dimensions in millimeters. 1. 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. 2842.2007.09.1.2 21 AAT2842 High-Current Charge Pump with S2Cwire™ Control and Dual LDO for Backlight and Flash TQFN44-28-0.45 N.B.: Not recommended for new designs. Index Area (D/2 x E/2) 2.60 ± 0.05 4.00 ± 0.05 Detail "A" 4.00 ± 0.05 2.60 ± 0.05 Top View Bottom View 0.45 ± 0.05 0.35 ± 0.05 0.75 ± 0.05 0.203 ± 0.025 0.05 ± 0.05 0.18 ± 0.05 Side View Pin 1 Indicator 0.425 ± 0.050 Detail "A" All dimensions in millimeters. © 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. Advanced Analogic Technologies, Inc. 3230 Scott Boulevard, Santa Clara, CA 95054 Phone (408) 737- 4600 Fax (408) 737- 4611 22 2842.2007.09.1.2