DATA SHEET AAT1277 1.5A Step-Up Current Regulator for Flash LEDs General Description Features The AAT1277 is a high-efficiency, high-current boost converter capable of 1.5A typical output current. It is an ideal power solution for LED photo flash applications in all single cell Li-ion powered products. • VIN Range: 2.7V to 5.5V • Dual Channel Output • Up to 1.5A Regulated Output Current (750mA per channel) • Up to 85% Efficiency with Small Inductor (1μH) • 2 MHz Switching Frequency • Separate Flash/Movie Mode Enable • Separate Flash Inhibit • User-Programmable Safety Timer • Two Resistors Set Flash and Movie Mode Current Independently • True Load Disconnect • Bypass Mode Input Current Limit 1.9A (typ.) • Over-Voltage (Open LED, Open Circuit) Protection • Short Circuit Protection • Over-Temperature Protection • Shutdown Current < 1.0μA • 18 Ball 1.5mm x 2.4mm CSP Package • -40°C to +85°C Operating Temperature Range The AAT1277 maintains output current regulation by switching the internal high-side and low-side switch transistors. The transistor switches are pulse-width modulated at a fixed frequency of 2MHz. The high switching frequency allows the use of a small inductor and output capacitor, making the AAT1277 ideally suited for small battery-powered applications. Three simple logic control inputs enable and disable flash and movie mode operation of the AAT1277. Movie-mode and Flash-mode current levels are independently fixed by two separate resistors. For Flash mode, a default timer can be used either to terminate a flash event or as a safety feature. Also included is a Flash Inhibit pin which reduces the flash current to movie-mode levels during high battery demand. One or two LEDs can be connected to the AAT1277; in the case of two LEDs the output current is matched between each diode. The AAT1277 contains a thermal management system to protect the device in the event of an output short-circuit condition. Built-in circuitry prevents excessive inrush current during start-up. The shutdown feature reduces quiescent current to less than 1.0μA. Applications • Cellphones/Smartphones • LED Photo Flash/Torch • Mobile Handsets The AAT1277 is available in a 18 ball 1.5mm x 2.4mm CSP package. Typical Application L1 1μH IN VBAT CIN 2.2μF Movie Mode Enable Flash Enable Flash Inhibit Flash LEDs SW OUT AAT1277 MEN FLEN FLINH FLOUTA FLOUTB CT RMSET 169kΩ RFSET 56.2kΩ COUT 2.2μF CT 47nF MSET FSET AGND PGND FLGND Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202087A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012 1 DATA SHEET AAT1277 1.5A Step-Up Current Regulator for Flash LEDs Pin Descriptions Ball # Symbol A1 CT A2 MEN A3 FLEN A4 AGND A5 IN A6, B3, B4 PGND B1 FSET B2, C2 B5, B6 FLGND SW C1 FLOUTA C3 FLOUTB C4 FLINH C5 MSET C6 OUT Function Flash timer control input. Connect a capacitor between CT and AGND to set maximum duration of the flash pulse. A 47nF ceramic capacitor sets the flash timer to 375ms. To disable the flash timer, connect CT to AGND. Movie mode enable pin. A low to high transition on the MEN pin initiates movie mode current level set by MSET resistor. MEN is an active high control input with a internal 200kΩ resistor to AGND. Flash enable pin. A low-to-high transition on the FLEN pin initiates a flash pulse and starts the flash timer. FLEN is an active high control input with a internal 200kΩ resistor to AGND. Analog ground pin. Connect AGND to PGND and FLGND at a single point as close to AAT1277 as possible. Power input. Connect IN to the input power supply voltage. Connect a 2.2μF or larger ceramic capacitor from IN to PGND as close as possible to AAT1277. Power ground pin. Connect PGND to AGND and FLGND at a single point as close to AAT1277 as possible. Flash mode current setting input. A 56.2kΩ resistor from FSET to AGND sets the maximum flash current available at FLOUTA and FLOUTB up to 1.5A total. Each FLOUTA and FLOUTB channel will conduct 50% of the maximum programmed current Flash ground pin. Connect FLGND to PGND and AGND at a single point as close to AAT1277 as possible Boost converter switching node. Connect a 1μH inductor between SW and IN. Flash Output A. Connect cathode of Flash LEDA to FLOUTA. For a single flash LED, connect FLOUTA and FLOUTB together. For two flash LEDs, each output will conduct 50% of the total flash output current. Flash Output B. Connect cathode of Flash LEDB to FLOUTB. For a single flash LED, connect FLOUTB & FLOUTA together. For two flash LEDs, each output will conduct 50% of the total flash output current. Flash inhibit pin. FLINH is an active high control input with an internal 200kΩ resistor to AGND. A low-tohigh transition on the FLINH pin reduces FLOUTA and FLOUTB output currents to the preset movie-mode current level for the duration of FLINH. Strobing the FLINH pin low to high does not reset the flash timer. Movie mode current setting input. A 169kΩ resistor from MSET to AGND sets the desired movie mode current available at FLOUTA and FLOUTB to 100mA total. Each FLOUTA and FLOUTB channel will conduct 50% of the programmed current. Power output of the boost converter. Connect a 2.2μF or larger ceramic capacitor from OUT to PGND as close as possible to the AAT1277. Connect OUT to the anode(s) of the Flash LED(s). Pin Configuration CSP Ball/Pin Layout (Top View) 2 6 A6 B6 C6 5 A5 B5 C5 4 A4 B4 C4 3 A3 B3 C3 2 A2 B2 C2 1 A1 B1 C1 A B C Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202087A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012 DATA SHEET AAT1277 1.5A Step-Up Current Regulator for Flash LEDs Absolute Maximum Ratings1 (TA = 25°C unless otherwise noted.) Symbol IN, SW, OUT MEN, FLEN, FLINH, CT, MSET, FSET FLOUTA, FLOUTB TJ TA Ts TLEAD Description Maximum Rating Maximum Rating Maximum Rating Junction Temperature Range Operating Temperature Range Storage Temperature Range Maximum Soldering Temperature (at leads, 10 sec.) Value -0.3 to 6.0 VIN + 0.3 VOUT + 0.3 -40 to 150 -40 to 85 -65 to 150 300 Units V C Thermal Information2 Symbol θJA PD Description Thermal Resistance Maximum Power Dissipation3 Value Units 105.5 940 C/W mW 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. 2. Mounted on an FR4 board. 3. Derate 9.4 mW above 25°C. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202087A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012 3 DATA SHEET AAT1277 1.5A Step-Up Current Regulator for Flash LEDs Electrical Characteristics1 VIN = 3.6V; CIN = COUT = 2.2μF; L1 = 1μH; RFSET = 56.2kΩ; RMSET = 169kΩ; TA = -40°C to 85°C unless otherwise noted. Typical values are at TA = 25°C. Symbol Description Conditions Power Supply VIN Input Voltage Range Maximum Output Voltage VOUT(MAX) IIN(Q) VIN Supply Current ISHDN(MAX) VIN Shutdown Current IFL(TOTAL) Total Output Current, Flash Mode IFL FLOUTA / FLOUTB Current Accuracy IFL(MATCH) FLOUTA / FLOUTB Current Matching Tolerance IMM(LOAD) Total Output Current, Movie Mode fOSC Oscillator Switching Frequency tDEFAULT Default ON Time TSD Thermal Shutdown Threshold Thermal Shutdown Hysteresis TSD(HYS) FLEN/ MEN/FLINH Logic Control VMEN(L), VFLEN(L), MEN, FLEN, FLINH Input Low Threshold VFLINH(L) VMEN(H), MEN, FLEN, FLINH Input High Threshold VFLEN(H), VFLINH(H) RIN(LOGIC) FLINH, FLEN, MEN Input Resistance to AGND FLEN ON Delay Time tFLEN_ON FLEN OFF Delay Time tFLEN_OFF tFLINH_ON FLINH ON Delay Time tFLINH_OFF FLINH OFF Delay Time Auto Disable Function2 VLED(DETECT) Shorted LED Detection Voltage ILED(DETECT) Minimum LED Detection Current Min Typ 2.7 VFLEN = VIN, FL Load = 1.5A VFLEN = VIN, FL Load = 0A VMEN = VFLEN = VFLINH = GND IFLOUTA + IFLOUTB IMMOUTA + IMMOUTB TA = 25°C CT = 47nF Max Units 5.5 5.5 V 1.4 0.23 mA 1 1.2 -5 93 1.45 1.5 5 10 100 2.0 375 140 15 107 2.55 °C 0.4 1.4 100 VIN = 3V, ILED = 0.795μA VIN = 3V μA A % % mA MHz ms V V 200 200 10 93 5 1.45 795 kΩ μs V μA 1. The AAT1277 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. Guranteed by Design 4 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202087A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012 PRODUCT DATASHEET DATA SHEET AAT1277 SwitchRegTM 1.5A Step-Up Step-Up Current Current Regulator Regulator for for Flash Flash LEDs LEDs 1.5A Flash Mode Efficiency vs. Input Voltage 100 90 320mA, VF = 2.91V 540mA, VF = 3.00V 700mA, VF = 3.04V 900mA, VF = 3.04V 1500mA, VF = 3.15V 1200mA, VF = 3.27V 80 204mA 104mA 52mA 85 Efficiency (%) 90 Efficiency (%) Movie Mode Efficiency vs. Input Voltage 70 60 50 80 75 70 65 60 55 50 2.7 40 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 3.1 3.5 Shutdown Current vs. Input Voltage 4.7 5.1 5.5 Quiescient Current vs. Input Voltage (VMEN = VFLEN = VFLINH = 0V) ( VFLEN = VIN; IFLOUTA = IFLOUTB = 0mA) 350 0.03 300 0.025 250 0.02 IIN(Q) (µA) Shutdown Current (μA) 4.3 Input Voltage (V) Input Voltage (V) 0.015 0.01 2.7 200 150 100 0.005 25°C -40°C 3.1 3.5 3.9 4.3 4.7 5.1 85C 50 25C -40C 0 0 5.5 2.7 3.1 3.5 Input Voltage (V) 1 0.5 0 -0.5 -1 -1.5 FL1 FL2 10 35 60 85 Output Current Accuracy (%) 2 1.5 -15 4.3 4.7 5.1 5.5 Flash and Movie Modes Current Matching vs. Temperature (VIN = 3.6V; IFLOUTA = IFLOUTB = 50mA) -2 -40 3.9 Input Voltage (V) Movie Mode Current Accuracy vs. Temperature Output Current Accuracy (%) 3.9 (VIN = 3.6V) 0.8 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 Movie Mode Flash Mode -0.8 -40 -15 10 35 60 85 Temperature (°C) Temperature (°C) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202087A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012 5 PRODUCT DATASHEET DATA SHEET AAT1277 SwitchRegTM 1.5A Step-Up Step-Up Current Current Regulator Regulator for for Flash Flash LEDs LEDs 1.5A Flash LED Current Accuracy vs. Temperature Flash ON Delay Time vs. Input Voltage (IFLOUTA = IFLOUTB = 750mA; COUT = 2.2μF; L = 1μH) 320 2 1.5 1 0.5 0 -0.5 -1 -1.5 FL1 FL2 -2 -40 -15 10 35 60 Flash ON Delay Time (μs) Output Current Accuracy (%) (VIN= 3.6V; IFLOUTA= IFLOUTB= 750mA) 280 240 200 160 120 80 85C 40 25C -40C 0 85 2.7 3.1 3.5 Temperature (C) 3.9 4.3 4.7 5.1 5.5 Input Voltage (V) Flash ON Time vs. Input Voltage Flash Timeout Delay vs. CT Capacitor (IFLOUTA = IFLOUTB = 750mA; CT = 47nF; COUT = 2.2μF; L = 1μH) (IFLOUTA = IFLOUTB = 750mA/ch; VIN = 3.6V) 440 1200 Flash Timeout (ms) Flash ON Time (ms) 420 400 380 360 340 320 85C 300 1000 800 600 400 200 25C -40C 280 2.7 3.1 3.5 3.9 4.3 4.7 5.1 0 0 5.5 20 40 Movie Mode LED Accuracy (%) (IFLOUTA = IFLOUTB = 50mA; COUT = 2.2μF; L = 1μH) 10 8 6 4 2 0 -2 -4 -6 -8 3.1 3.5 3.9 4.3 Input Voltage (V) 6 100 120 140 4.7 5.1 5.5 Oscillator Frequency Accuracy vs. Temperature Oscillator Frequency Accuracy (%) Movie Mode Current Accuracy vs. Input Voltage 2.7 80 CT Capacitor (nF) Input Voltage (V) -10 60 (VIN = 3.6V; FOSC = 2MHz) 4 3 2 1 0 -1 -2 -3 -4 -40 -15 10 35 60 Temperature (°C) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202087A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012 85 PRODUCT DATASHEET DATA SHEET AAT1277 SwitchRegTM 1.5A Step-Up Step-Up Current Current Regulator Regulator for for Flash Flash LEDs LEDs 1.5A Oscillator Frequency (MHz) Oscillator Frequency vs. Input Voltage (TA = 25°C) Flash Mode Output Ripple (IFLOUT = 1.5A; VIN = 4V; L = 1μH) 2.4 2.3 VOUT (AC Coupled) (50mV/div) 2.2 2.1 2 VINDUCTOR (2V/div) 1.9 0V 1.8 IINDUCTOR (50mA/div) 1.7 1.6 2.7 3.1 3.5 3.9 4.3 4.7 5.1 1.65A 5.5 Time (200ns/div) Input Voltage (V) Movie Mode Line Transient Movie Mode Turn On Characteristic (IFLOUT = 206mA; VIN = 4.2V to 3.6V) (IFLOUTA = IFLOUTB = 50mA; COUT = 2.2μF; VIN = 3.6V; L= 1μH) VMEN 5V/div 4.2V VIN (500mV/div) 3.6V VOUT 2V/div VFLx 2V/div IFL (AC Coupled) (50mA/div) IFLx 100mA/div 0V 0V 0V 0A Time (100μs/div) Time (50μs/div) Movie Mode to Flash Turn On Characteristic Flash Turn On Characteristic (IFLOUTA= IFLOUTB = 50mA to 750mA; COUT = 1.0uF; VIN = 3.6V; L= 1μH) (IFLOUTA = IFLOUTB = 750mA; COUT = 2.2μF; VIN = 3.6V; L = 1μH) VFLEN 5V/div 0V VOUT 1V/div 3.0 VOUT 2V/div 0V VFLx 2V/div VFLx 1V/div IFLx 1A/div VFLEN 5V/div IFLx 1A/div 0A Time (100us/div) 0V 0V 0V 0V Time (100us/div) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202087A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012 7 PRODUCT DATASHEET DATA SHEET AAT1277 SwitchRegTM 1.5A Step-Up Step-Up Current Current Regulator Regulator for for Flash Flash LEDs LEDs 1.5A Flash Inhibit Turn On Characteristic Flash Mode Timing (IFLOUTA = IFLOUTB = 750mA to 50mA; COUT = 2.2μF; VIN = 3.6V; L = 1μH) (IFLOUTA = IFLOUTB = 750mA; COUT = 2.2μF; VIN = 3.6V; L = 1μH) VFLEN 5V/div VFLEN 5V/div 0V VOUT 1V/div 3.3 VOUT 2V/div VFLx 1V/div 0V VFLx 2V/div 0A IFLx 1A/div IFLx 1A/div 0V 0V 0V 0V Time (100ms/div) Time (100us/div) Movie Mode Ripple MEN, FLEN, FLINH Logic Threshold High vs Input Voltage (IFLOUTA = IFLOUTB = 50mA; COUT = 2.2μF; VIN = 3.1V; L = 1μH) 1.2 1.1 VSW 2V/div ISW 200mA/div VMEN, VFLEN, VFLNH (V) VOUT 20mV/div AC Coupling 0V 0A 1 0.9 0.8 0.7 0.6 25C 0.5 85C -40C 0.4 2.7 3.1 3.5 Time (500ns/div) 4.3 4.7 5.1 5.5 Input Voltage (V) MEN, FLEN, FLINH Logic Threshold Low vs Input Voltage MEN, FLEN, FLINH Input Pull Down Resistance vs Temperature 1.2 400 1.1 350 RMEN, RFLEN, RFLNH (kΩ) VMEN, VFLEN, VFLNH (V) 3.9 1 0.9 0.8 0.7 0.6 25C 0.5 85C 300 250 200 150 100 50 -40C 0.4 2.7 0 3.1 3.5 3.9 4.3 Input Voltage (V) 8 4.7 5.1 5.5 -40 -15 10 35 60 Temperature (°C) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202087A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012 85 DATA SHEET AAT1277 1.5A Step-Up Current Regulator for Flash LEDs Functional Block Diagram IN OUT SW FLOUTA FLOUTB MEN FLEN Control FLINH MSET FSET CT Functional Description The AAT1277 is a boost converter with a current regulated output designed to drive high current white LEDs used in camera flash applications. The AAT1277 has two channels to accurately regulate the current flow through two separate white LEDs. There are two basic modes of operation in the AAT1277; a Flash mode controlled by the FLEN pin and movie mode controlled through the MEN pin. Flash Mode By strobing the FLEN input pin low-to-high, a flash pulse and the internal timer are initiated. The maximum flash current in the AAT1277 is set by an external resistor, RFSET. The flash timer will terminate the flash current regardless of the status of the FLEN pin. This can be either used as a simple flash timing pulse or can be used as a safety timer in the event of a control logic malfunction to prevent the LED from overheating. The maximum flash time is determined by an external timing capacitor connected to the CT pin. It is not recommended for the flash duration to be set longer than 1s. If the safety timer is not needed in the application, it can be disabled by connecting the CT pin directly to AGND. After a flash event has expired via the flash timer, both AGND PGNDFLGND MEN and FLEN must be cycled to a logic low state to reset the flash timer. The AAT1277 has two LED current sources which share the output current equally. For a single white LED application, the two current sources can be connected together to apply full output current into the LED. In two LED applications, each diode can be connected to its corresponding current source (FLOUTA or FLOUTB) and the output current will be shared. In applications where only one LED is connected to either FLOUTA or FLOUTB, the unused current sink must be directly connected to OUT, thereby disabling that channel. Flash Inhibit Function In mobile GSM systems where the phone remains in constant contact with the base station by regular communication, a FLINH pin is provided to prevent both the camera flash and PA transmission pulses from occurring simultaneously. This avoids potential dips to the Li-ion battery voltage below the system’s undervoltage lockout threshold (UVLO). During a flash event, strobing the FLINH pin low-to-high reduces the LED current to the default movie-mode current level for the duration of FLINH. Strobing FLINH high-to-low instructs the AAT1277 to revert the flash LED current to its maximum level, assuming that the FLEN pin is still active (HIGH) and the flash timer has not expired. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202087A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012 9 DATA SHEET AAT1277 1.5A Step-Up Current Regulator for Flash LEDs Movie Mode The movie mode is enabled when the MEN input pin transitions from low to high and will remain on until input is pulled back to a low logic level. The movie-mode current level is set by an external resistor connected between MSET and AGND. Channel current outputs (FLOUTA and FLOUTB) in movie mode operate in the same manner as they do in flash mode, only at a current level as set by the RMSET resistor. The flash timer function is disabled in movie mode to permit constant LED illumination.The FLEN signal takes priority over movie-mode operation. Over-Temperature Protection Thermal protection disables the AAT1277 when internal power dissipation becomes excessive when operating. The junction over-temperature threshold is 140°C with 15°C of temperature hysteresis. The output voltage automatically recovers when the over-temperature fault condition is removed. Over-Voltage Protection (Open LED, Open Circuit) The AAT1277’s output voltage is limited by internal overvoltage protection (OVP) circuitry, which prevents damage to the AAT1277 from open LED or open circuit conditions. During an open circuit, the output voltage rises and reaches 5.5V (typical), and the OVP circuit disables the switching, preventing the output voltage from rising higher. Once the open circuit condition is removed, switching will resume and the controller will return to normal operation. Auto-Disable Feature The AAT1277 is equipped with an auto-disable feature for each LED channel. After the IC is enabled and started up, a test current of 1mA (typical) is forced through each sink channel. The channel will be disabled if the voltage of that particular sink pin does not drop to a certain threshold. This feature is very convenient for disabling an unused channel or during an LED fail-short event. This small test current should be added to the set output current in both flash and movie mode conditions. Timing Diagrams MEN FLEN IFLOUTA = IFLOUTB = IMM OFF t= 0 t= n Figure 1: Movie Mode Timing Diagram. 10 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202087A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012 DATA SHEET AAT1277 1.5A Step-Up Current Regulator for Flash LEDs MEN FLEN IFLOUTA = IFLOUTA = IFL OFF t = t CT t= 0 Figure 2: Diagram of Flash Mode When Flash Event Does Not Exceed Flash Timer TFLASH < TCT. MEN FLEN IFLOUTA = IFLOUTA = IFL OFF t= 0 t = t CT Figure 3: Diagram of Flash Mode Timing When Flash Event is Terminated by Flash Timer TFLASH ≥ TCT. MEN FLEN IFLOUTA = IFLOUTA = IFL IFLOUTA = IFLOUTA = IMM OFF MM=ON t= 0 t = t CT Figure 4: Diagram of Movie Mode Followed by Flash Mode When Flash Event is Terminated Before Flash Timer TFLASH < TCT1,2. 1. FLEN must be pulled low after a flash time out period to reset the flash timer. 2. Movie mode will not re-enable until FLEN returns low after flash time. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202087A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012 11 DATA SHEET AAT1277 1.5A Step-Up Current Regulator for Flash LEDs MEN FLEN IFLOUTA = IFLOUTA = IFL IFLOUTA = IFLOUTA = IMM OFF MM = ON t= 0 t = t CT Flash Timer Reset Next Flash Event Figure 5: Diagram of Movie Mode Followed by Flash Mode When Flash Event is Terminated by Flash Timer TFLASH < TCT. (Note: Both MEN and FLEN must return to a logic low state to reset the flash timer before the system can execute another flash or movie mode event.) MEN FLEN FLINH IFLOUTA = IFLOUTA = IFL IFLOUTA = IFLOUTA = IMM OFF MM=ON t=0 t = t CT Figure 6: Diagram of Movie Mode Followed By Flash Mode With Flash Inhibit During Flash Event TFLASH < TCT. (Note: The flash current is reduced to the movie mode current for the duration of FLINH). 12 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202087A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012 DATA SHEET AAT1277 1.5A Step-Up Current Regulator for Flash LEDs LED Selection The AAT1277 is specifically designed to drive white flash LEDs (typical forward voltage of 2.5V to 4.0V). Since the FLOUTA and FLOUTB input current sinks are matched with low voltage dependence; the LED-to-LED brightness will be matched regardless of the individual LED forward voltage (VF) levels. Flash Mode Current FLOUTA and FLOUTB can be programmed up to a maximum total flash current of 1.5A or up to 750mA per channel. The output currents in FLOUTA and FLOUTB are equal. The maximum flash current in each FLOUTA and FLOUTB is set by the RFSET resistor. For the desired flash current in each output, the resistor value can be calculated using the following equation: RFSET = 56.2kΩ · 750mA IFLOUTX A flash event is initiated by asserting the FLEN pin. A flash event is automatically terminated when FLEN is deasserted or if the safety timer terminates before the FLEN pin is de-asserted. Any time that the FLINH pin is asserted, the default movie-mode current level will appear at both FLOUTA and FLOUTB. The default moviemode current level will be maintained on FLOUTA and FLOUTB as long as the FLINH and FLEN pins are asserted, and the safety timer continues to run. event and fail to pull the FLEN input low after a flash event. The flash timer may also be used to strobe the flash relay in the timer to turn the flash off after a preset time determined by the CT capacitor. This feature eliminates the need for an external housekeeping baseband controller to contain a safety or delay routine. The flash time T can be calculated by the following equation: T = 7.98s/μF · CT (μF) Where T is in seconds and CT is in μF. For example, using a 47nF capacitor at CT sets the flash timeout to: Flash Timeout = 7.98s/μF · 47nF = 375ms The relationship between the flash safety timeout and the capacitance of the timer capacitor is illustrated in Figure 7. 1200 Flash Timeout (ms) Applications Information 1000 800 600 400 200 0 0 20 40 60 80 100 120 140 CT Capacitor (nF) Figure 7: Flash Safety Timeout vs. Timer Capacitor. Movie Mode Current The AAT1277 movie mode current settings can be programmed by the external resistor RMSET. 169kΩ · 50mA RMSET = IMMOUTX Flash Timer The AAT1277 flash timer function is programmed by an external timing capacitor, CT. The primary purpose of the flash timer is a safety function to prevent damage to the flash LED should a system error occur during a flash Shutdown The current sink devices (FLOUTA and FLOUTB) are the power returns for all loads, there si no leakage current through load if the current sink devices are disabled. When FLEN and MEN are both held at logic low level, the AAT1277 is disabled and draws less than 1uA of leakage current from VIN. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202087A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012 13 DATA SHEET AAT1277 1.5A Step-Up Current Regulator for Flash LEDs Selecting the Boost Inductor The AAT1277 controller utilizes PWM control and the switching frequency is fixed. To maintain 2MHz maximum switching frequency and stable operation, a 1μH inductor is recommended. Manufacturer’s specifications list both the inductor DC current rating, which is a thermal limitation, and peak inductor current rating, which is determined by the saturation characteristics. Measurements at full load and high ambient temperature should be performed to ensure that the inductor does not saturate or exhibit excessive temperature rise. The inductor (L) is selected to avoid saturation at minimum input voltage and maximum output load conditions. Worst-case peak current occurs at minimum input voltage (maximum duty cycle) and maximum load. Bench measurements are recommended to confirm actual IPEAK and to ensure that the inductor does not saturate at maximum LED current and minimum input supply voltage. The RMS current flowing through the boost inductor is equal to the DC plus AC ripple components. Under worst case RMS conditions, the current waveform is critically continuous. The resulting RMS calculation yields worst case inductor loss. The RMS current value should be compared against the inductor manufacturer’s temperature rise, or thermal derating guidelines: IRMS = IPEAK 3 For a given inductor type, smaller inductor size leads to an increase in DCR winding resistance and, in most cases, increased thermal impedance. Winding resistance degrades boost converter efficiency and increases the inductor’s operating temperature: recommended to ensure good capacitance stability over the full operating temperature range. The output capacitor is selected to maintain the output load without significant voltage droop (∆VOUT) during the power switch ON interval. A 1μF ceramic output capacitor is recommended (see Table 2). Typically, 6.3V or 10V rated capacitors are required for this flash LED boost output. Ceramic capacitors selected as small as 0603 are available which meet these requirements. MLC capacitors exhibit significant capacitance reduction with applied voltage. Output ripple measurements should confirm that output voltage drop and operating stability are within acceptable limits. Voltage derating can minimize this factor, but results may vary with package size and among specific manufacturers. To maintain stable operation at full load, the output capacitor should be selected to maintain ∆VOUT between 100mV and 200mV. The boost converter input current flows during both ON and OFF switching intervals. The input ripple current is less than the output ripple and, as a result, less input capacitance is required. PCB Layout Guidelines Boost converter performance can be adversely affected by poor layout. Possible impact includes high input and output voltage ripple, poor EMI performance, and reduced operating efficiency. Every attempt should be made to optimize the layout in order to minimize parasitic PCB effects (stray resistance, capacitance, and inductance) and EMI coupling from the high frequency SW node. A suggested PCB layout for the AAT1277 1.5A step-up regulator is shown in Figures 4 and 5. The following PCB layout guidelines should be considered: 1. PLOSS(INDUCTOR) = I2RMS · DCR Selecting the Boost Capacitors In general, it is good design practice to place a decoupling capacitor (input capacitor) between the IN and GND pins. An input capacitor in the range of 2.2μF to 10μF is recommended. A larger input capacitor in this application may be required for stability, transient response, and/or ripple performance. The high output ripple inherent in the boost converter necessitates the use of low impedance output filtering. Multi-layer ceramic (MLC) capacitors provide small size and adequate capacitance, low parasitic equivalent series resistance (ESR) and equivalent series inductance (ESL), and are well suited for use with the AAT1277 boost regulator. MLC capacitors of type X7R or X5R are 14 2. 3. 4. 5. Minimize the distance from capacitor CIN and COUT’s negative terminals to the PGND pins. This is especially true with output capacitor COUT, which conducts high ripple current from the output to the PGND pins. Minimize the distance under the inductor between IN and switching pin SW; minimize the size of the PCB area connected to the SW pin. Maintain a ground plane and connect to the IC PGND pin(s) as well as the PGND connections of CIN and COUT. Consider additional PCB exposed area for the flash LEDs to maximize heatsinking capability. This may be necessary when using high current application and long flash duration application. Connect the exposed paddle (bottom of the die) to either PGND or GND. Connect AGND, FLGND to GND as close as possible to the package. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202087A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012 DATA SHEET AAT1277 1.5A Step-Up Current Regulator for Flash LEDs Manufacturer Part Number Inductance (μH) Saturated Rated Current (A) DCR (mΩ) Size (mm) LxWxH Cooper Bussmann Cooper Bussmann Cooper Bussmann Sumida Coilcraft SD3812-1R0-R SDH3812-1R0-R SD10-1R0-R CDH38D11/S LPS4012-102NLC 1 1 1 1 1 2.69 3 2.25 2.8 2.5 48 45 44.8 48.8 60 4.0x4.0x1.2 3.8x3.8x1.2 5.2x5.2x1.0 4.0x4.0x1.2 4.1x4.1x1.2 Type Shielded Shielded Shielded Shielded Shielded Drum Drum Drum Drum Drum Core Core Core Core Core Table 1: Typical Suggested Surface Mount Inductors. Manufacturer Murata Part Number Capacitance (μF) Voltage Rating (V) Temp Co. Case Size GRM185R60J225KE26 GRM188R71A225KE15 GRM21BR70J225KA01 GRM21BR71A225KA01 GRM219R61A475KE19 2.2 2.2 2.2 2.2 4.7 6.3 10 6.3 10 10 X5R X7R X7R X7R X5R 0603 0603 0805 0805 0805 GRM21BR71A106KE51 10 10 X7R 0805 Table 2: Typical Suggested Surface Mount Capacitors. *Denotes the default value. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202087A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012 15 DATA SHEET AAT1277 1.5A Step-Up Current Regulator for Flash LEDs VIN J1 VIN SW1 1 3 R3 2 4 100k FLINH J2 SW2 1 3 R4 100k VIN 2 4 FLEN J3 VIN SW3 1 3 R5 JP1 0 JP2 0 D1 D2 100k VIN U1 2 4 A1 A2 A3 A4 A5 B5, B6 A6, B3, B4 MEN L1 1μH C4 1μF VOUT C1 2.2μF CT FSET MEN FLOUTA FLEN FLGND AGND FLOUTB IN FLINH SW MSET PGND OUT AAT1277 CSP-18 C3 47nF GND D1, D2 L1 C1, C2 C3 B1 C1 B2, C2 C3 C4 C5 C6 R2 169k R1 56.2k C2 2.2μF Seoul Semi FOW401-Z4S CooperBussmann SD3812-1R0-R, 1μH, 2.69A, 48mΩ Murata GRM188R71A225KE15 2.2μF, 0603, X7R, 10V Murata GRM155R71A473KA01, 47nH, 0402, X7R, 10V Figure 8: AAT1277 Evaluation Board Schematic. Figure 9: AAT1277 Evaluation Board Top Side Layout. 16 Figure 10: AAT1277 Evaluation Board Bottom Side Layout. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202087A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012 DATA SHEET AAT1277 1.5A Step-Up Current Regulator for Flash LEDs Component Part Number U1 AAT1277IUT SW1 – SW3 R1 R2 R3, R4, R5 JP1, JP2 C1, C2 C3 L1 D1-D2 PTS645TL50 Chip Resistor Chip Resistor Chip Resistor Chip Resistor GRM188R71A225KE15 GRM155R71A473KA01 SD3812-1R0-R LXCL-PWF4 Description 1.5A Step-Up Current Regulator for Flash LEDs; 18 ball 1.5mm x 2.4mm CSP package Switch, SPST, 5mm 56.2kΩ, 1%, 1/4W; 0402 169kΩ, 1%, 1/4W; 0402 100kΩ, 1%, 1/4W; 0603 0Ω, 5%, 1/4W; 0603 2.2μF, 10V, X7R, 0603 47nF, 10V, X7R, 0402 Drum Core, 1μH, 2.69A, 48mΩ White Flash LED Manufacturer Skyworks ITT Industries Vishay Vishay Vishay Vishay Murata Murata Cooper Bussmann Lumileds, Philips Table 3: AAT1277 Evaluation Board Bill of Materials. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202087A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012 17 DATA SHEET AAT1277 1.5A Step-Up Current Regulator for Flash LEDs Ordering Information Package Marking1 Part Number (Tape and Reel)2 CSP-18 M6XYY AAT1277IUT-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 Information CSP-18 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. 18 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202087A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 21, 2012 DATA SHEET AAT1277 1.5A Step-Up Current Regulator for Flash LEDs 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. 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