DATA SHEET AAT1401 Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control General Description Features The AAT1401 is a step-up single channel LED driver with an input voltage range of 2.7V to 5.5V. The wide input voltage range, small solution size, advanced dimming features and high efficiency is suitable for LED backlight solutions for single cell Li-ion based equipment. A precision, high voltage current sink maintains the maximum LED current set by an external resistor from 10 to 31mA. The high switching frequency supports ultra small, low cost filtering components. • Input Voltage Range: 2.7 to 5.5V • Drives up to 28V with 6 Series LEDs at 31mA • 1MHz Switching Frequency Allows Small External Components • Up to 85% Efficiency • Dimming Control Options: ▪ 32 Steps - S2Cwire Single Wire Interface ▪ Filtered PWM • Low Operating Current at 2.3mA • Shutdown Current < 1µA • Over-Voltage Protection for Open-LED Faults • Over Temperature Protection • Ultra Small, Low Profile 10-pin 1.55 x 1.15mm WLCSP Package Two dimming controls are available; 32 dimming steps using the S2Cwire™ interface, and filtered PWM control. The frequency range of the PWM dimming extends up to 100 kHz eliminating audible noise and suitable for CABC (Content Adaptive Brightness Control) applications. The device includes over-temperature protection and programmable over-voltage protection and recovers automatically when the faults are removed. The AAT1401 is available in a 10-pin wafer-level chip scale package (WLCSP) and is rated over the -40°C to +85°C temperature range. Applications • • • • • Digital Still Cameras (DSC) Mobile Handsets Netbooks and Notebooks Portable Media Players White LED Drivers Typical Application Up to 6 WLEDs D1 VIN: 2.7V–5.5V L1 10μH R1 IN CIN 4.7µF OVP AAT1401 SC PWM 2 CCOMP 56nF LX RSET 10k EN/SET PWM COMP RSET R2 VOUT: Up to 28V at 31mA COUT 0.1µF 50V CS GND PGND Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202113A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 1 DATA SHEET AAT1401 Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control Pin Descriptions Pin # Symbol A1 LX A2 A3 B1 B3 C1 IN EN/SET PGND PWM GND C3 COMP D1 D2 D3 CS RSET OVP Function Switching node of boost converter. Connect an inductor between LX and input supply (VIN); Schottky rectifier anode is connected between LX pin while cathode is connected to output capacitor. Supply input for the IC. Connect a 4.7µF 6.3V/10V ceramic capacitor from this pin to GND. Enable on/off control and S2Cwire interface input. Power ground pin. Input PWM pin. Pull high to disable the PWM dimming feature. Ground pin. Compensation pin. Connect a capacitor from this pin to GND. Compensation components are mainly related to the output capacitor valued. See the Capacitor Selection section in the Application Information section of this datasheet. Connect to the cathode of the last diode of the LED string. Connect a resistor to GND to set maximum LED current up to 31mA. Feedback pin for over-voltage protection. Pin Configuration WLCSP10 1.1 x1.5 (Top View) A1 A3 B1 B3 C1 C3 D1 2 A2 D2 D3 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202113A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 DATA SHEET AAT1401 Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control Absolute Maximum Ratings1 Symbol Description VIN VLX VCS VEN/SET,VPWM, VRSET, VCOMP, VOVP IN to GND, PGND LX to GND, PGND SINK to GND, PGND EN/SET, PWM, RSET, COMP, OVP to GND/PGND Value Units -0.3 to 6.0 -0.3 to 34 -0.3 to 28 V V V -0.3 to IN +0.3 V Value Units Thermal Information2 Symbol ΘJA PD TJ TLEAD Description Thermal Resistance Maximum Power Dissipation Maximum Junction Operating Temperature Maximum Soldering Temperature (at leads, 10 sec.) 122 820 -40 to +155 300 C/W mW O O C Recommended Operating Conditions Symbol VIN VOUT L1 FPWM-F TA Description Input Supply Voltage Boosted Output Voltage Inductor Value Input Filtered PWM Frequency Ambient Temperature Range Min 2.7 VIN + 3V 4.7 100 - 40 Typ Max Units 10 5.5 VOUT3 22 100,000 85 V V μH Hz °C 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 board. 3. Check Electrical Characteristics. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202113A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 3 DATA SHEET AAT1401 Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control Electrical Characteristics1 VIN = 3.6V, CIN = 4.7µF, COUT = 0.1µF, L = 10µH, RSET = 10KΩ, TA = -40°C to 85°C unless otherwise noted. Typical values are at TA= 25°C. Symbol VIN VOUT IQ ISHDN IQSW RDS(ON)N η Fosc TSS DMAX VOVP-T VOVPH TSD THYS VCS ICS(ACC) VRSET EN/SET VEN/SET (L) VEN/SET (H) tEN/SET(LOW) tEN/SET(HI_MIN) tEN/SET(HIMAX) tEN/SET(OFF) tEN/SET(LAT) IEN/SET (LK) PWM VPWM(L) VPWM(H) IPWM(LK) Description Input Voltage Range Maximum Output Voltage Quiescent Supply Current Input Shutdown Current Input Switching Current NMOS On-Resistance Maximum Efficiency Switching Frequency Soft-Start Time Maximum Duty Cycle OUT Over-Voltage Protection Threshold Over-Voltage Protection Hysteresis Over-Temperature Shutdown Threshold Over-Temperature Shutdown Hysteresis Current Sink Voltage Current Sink Accuracy RSET Voltage EN/SET EN/SET EN/SET Input Low Time EN/SET Minimum High Time EN/SET Maximum High Time EN/SET Input Off Timeout EN/SET Latch Timeout EN Input Leakage Logic Threshold Low Logic Threshold High PWM Input Leakage Conditions Min Typ Max Units 5.5 28 700 1 2.3 650 85 1.0 V V µA µA mA mΩ % MHz 4 ms 2.7 VENSET = VIN VENSET = 0V VENSET = VIN TA = 25°C IOUT = 31mA TA = 25°C VENSET = VIN to 95% of output regulation, CCOMP = 56nF VOVP rising IOUT = 31mA RSET = 10KΩ RSET = 10KΩ VIN = 2.7V to 5.5V VIN = 2.7V to 5.5V 430 94.0 1.1 27.9 1.2 75 155 15 500 31.0 1.206 1.3 34.1 0.4 1.4 0.3 100 VENSET = 5V, VIN = 5V -1 VPWM = 5V, VIN = 5V 1.4 -1 75 75 500 500 1 0.4 1 % V mV °C °C mV mA V V V µs ns µs µs µs µA V V µA 1. The AAT1401 is guaranteed to meet performance specification over the –40°C to +85°C operating temperature range, and is assured by design, characterization and correlation with statistical process controls. 4 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202113A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 DATA SHEET AAT1401 Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control Typical Characteristics Quiescent Current vs. Input Voltage Shutdown Current vs. Input Voltage 0.10 Shutdown Current (µA) Quiescent Current (µA) 500 480 460 440 420 85°C 25°C -40°C 400 380 2.7 3.1 3.5 3.9 4.3 4.7 5.1 0.06 0.04 0.02 3.9 4.3 4.7 RSET = 10KΩ RSET = 15KΩ RSET = 20KΩ RSET = 25KΩ RSET = 30KΩ 28 VIN = 2.7V VIN = 3.0V VIN = 3.6V VIN = 4.2V VIN = 5.0V VIN = 5.5V 2 4 6 8 24 20 16 12 8 4 0 10 12 14 16 18 20 22 24 26 28 30 32 Output Current (mA) 1 5 9 13 17 21 25 29 33 S2C Data Sink Current Accuracy vs. Temperature Sink Current Accuracy vs. Temperature (VIN = 3.6V, RSET = 15kΩ) (VIN = 3.6V, RSET = 10kΩ) 32.0 21.2 31.6 Current (mA) 22.0 20.4 19.6 18.8 18.0 -40 5.5 (VIN = 3.6V, L = 10µH) 32 0 5.1 LED Current Accuracy vs. S2C Current (mA) Efficiency (%) 3.5 Input Voltage (V) (RSET = 10KΩ, L = 10µH, 6 LEDs) Current (mA) 3.1 Efficiency vs. Output Current 90 85 80 75 70 65 60 55 50 45 40 35 30 85°C 25°C -40°C 0.00 2.7 5.5 Input Voltage (V) 0.08 31.2 30.8 30.4 -15 10 35 Temperature (°C) 60 30.0 -40 85 -15 10 35 60 85 Temperature (°C) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202113A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 5 DATA SHEET AAT1401 Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control Typical Characteristics Startup Time vs. CCOMP LED Current Accuracy vs. Input Voltage (6 WLEDs) (VIN = 3.6V, RSET = 15KΩ) 21.2 15 12 20.4 tSU (ms) Current (mA) 20.8 20.0 19.6 6 3 19.2 18.8 2.7 9 0 3.1 3.5 3.9 4.3 4.7 5.1 10 5.5 Input Voltage (V) 0.9 0.9 0.8 VEN(L) (V) VEN(H) (V) 1.0 0.8 0.7 85°C 25°C -40°C 0.6 0.5 3.9 4.3 4.7 5.1 50 60 70 80 0.6 85°C 25°C -40°C 0.4 5.5 2.7 3.1 3.5 3.9 4.3 4.7 Input Voltage (V) NMOS RDS(ON)N vs. Input Voltage 85°C 25°C -40°C RDS(ON) (mΩ) 900 800 700 600 500 400 2.7 3.1 3.5 3.9 4.3 Input Voltage (V) 6 4.7 5.1 100 0.7 0.5 Input Voltage (V) 1000 90 EN Input Low Threshold Voltage vs. Input Voltage 1.0 3.5 40 CCOMP (nF) 1.1 3.1 30 EN Input High Threshold Voltage vs. Input Voltage 2.7 20 5.5 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202113A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 5.1 5.5 DATA SHEET AAT1401 Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control Typical Characteristics PWM Input Low Threshold Voltage vs. Input Voltage 1.1 1.0 1.0 0.9 0.9 0.8 VPWM(L) (V) VPWM(H) (V) PWM Input High Threshold Voltage vs. Input Voltage 0.8 0.7 85°C 25°C -40°C 0.6 0.5 2.7 3.1 3.5 3.9 4.3 4.7 5.1 0.6 85°C 25°C -40°C 0.5 0.4 5.5 Input Voltage (V) 2.7 3.1 1.25 3.9 4.3 4.7 5.1 5.5 Input Voltage (V) OVP Low Threshold Voltage vs. Input Voltage 85°C 25°C -40°C 1.23 1.20 85°C 25°C -40°C 1.16 VOVP(L) (V) 1.21 1.19 1.17 1.12 1.08 1.04 1.15 1.00 2.7 3.1 3.5 3.9 4.3 4.7 5.1 Input Voltage (V) 5.5 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 Input Voltage (V) Startup Waveform Turn Off (VIN = 3.6V; CIN = 4.7μF, COUT = 0.1μF, CCOMP = 56nF, RSET = 10KΩ, 6 LEDs) EN (5V/div) 3.5 OVP High Threshold Voltage vs. Input Voltage VOVP(H) (V) 0.7 (VIN = 3.6V; CIN = 4.7μF, COUT = 0.1μF, CCOMP = 56nF, RSET = 10KΩ, 6 LEDs) EN 0 (5V/div) 0 VOUT (10V/div) 0 IIN 0 (100mA/div) VOUT 0 (20V/div) IIN 0 (200mA/div) ILED (20mA/div) 0 ILED (20mA/div) Time (2ms/div) 0 Time (100µs/div) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202113A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 7 DATA SHEET AAT1401 Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control Typical Characteristics Operation Waveform Operation Waveform (VIN = 3.6V; CIN = 4.7μF, COUT = 0.1μF, CCOMP = 56nF, RSET = 10KΩ, 6 WLEDs) VLX (20V/div) IINDUCTOR (500mA/div) VOUT (AC) (500mV/div) (VIN = 3.6V; CIN = 4.7μF, COUT = 0.1μF,CCOMP = 56nF, RSET = 10KΩ, PWM = 50kHz, 50% Duty Cycle, 6 WLEDs) VLX (20V/div) 0 IINDUCTOR (500mA/div) 0 0 0 VOUT (AC) (50mV/div) 0 0 ILED (20mA/div) 0 ILED (20mA/div) 0 Time (1µs/div) LED Current Transient LED Current Transition (VIN = 3.6V; CIN = 4.7μF, COUT = 0.1μF, CCOMP = 56nF, RSET = 10KΩ, PWM = 10KHz, Duty Cycle = 100% to 50%, 31mA to 15mA) PWM (5V/div) VOUT (20V/div) (VIN = 3.6V; CIN = 4.7μF, COUT = 0.1μF, CCOMP = 56nF, RSET = 10KΩ, PWM = 10KHz, Duty Cycle = 50% to 100%, 31mA to 15mA) PWM (5V/div) VOUT (10V/div) 0 IIN (200mA/div) 0 ILED (20mA/div) 0 IIN (100mA/div) ILED (20mA/div) 0 Time (1ms/div) ILED (20mA/div) 0 0 Time (1ms/div) (VIN = 3.6V; CIN = 4.7μF, COUT = 0.1μF, CCOMP = 56nF, RSET = 10KΩ, S2Cwire Data 16 to 1) EN/SET (5V/div) VOUT (20V/div) 0 0 0 0 IIN (200mA/div) 0 ILED (20mA/div) 0 0 0 Time (1ms/div) 8 0 LED Current Transient by S2Cwire (VIN = 3.6V; CIN = 4.7μF, COUT = 0.1μF, CCOMP = 56nF, RSET = 10KΩ, S2Cwire Data 1 to 16) IIN (200mA/div) 0 LED Current Transient by S2Cwire EN/SET (5V/div) VOUT (20V/div) Time (1µs/div) Time (1ms/div) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202113A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 DATA SHEET AAT1401 Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control Functional Block Diagram LX PGND IN Control OVP OVP OSC REF COMP RSET CS EN/SET Interface PWM GND Functional Description Soft Start / Enable The AAT1401 is a small size, high efficiency, current mode controlled step-up converter LED driver for up to 6 white LEDs. It is available with up to 28V output voltage to allow up to 6 series connected LEDs to be driven with currents up to 31mA. The device uses a single current sink to regulate the LED current by controlling the output voltage. The maximum LED current is programmed by an external resistor with range from 10mA to 31mA. The LED current dimming is controlled via one of two options, using either the S2Cwire 32-step single-wire interface or PWM control. The AAT1401 is enabled by EN/SET pulled to high after power on with a certain delay time. Internal soft start circuitry limits the input inrush current and eliminates output voltage overshoot. When ENSET is pulled low the AAT1401 enters a low-power, non-switching state. The total input current during shutdown is less than 1μA. An external diode limits VOUT to the level of VIN during shutdown. The diode consumes a small amount of additional input current depending on the OVP resistor divider value. The over-voltage protection function is designed to protect the boost converter during the fault of the open circuit of the LED string. The over-temperature function is targeted to protect the converter if an over-temperature fault occurs. The AAT1401 will recover to normal operation automatically when the OVP or OTP fault is removed. Over-Temperature Protection Thermal protection disables the AAT1401 when internal dissipation becomes excessive. Thermal protection disables the power MOSFET. The junction over-temperature threshold is 155°C with 15°C of temperature hysteresis. The output voltage automatically recovers when the over-temperature fault condition is removed. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202113A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 9 DATA SHEET AAT1401 Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control Over-Voltage Protection S2Cwire™ Serial Interface Over-voltage protection prevents damage to the AAT1401's LX pin during open-circuit or high output voltage conditions. An over-voltage event is defined as a condition where the voltage on the OVP pin exceeds the over-voltage protection threshold (VOVP-T). When VOVP has reached the threshold limit, the converter stops switching and the output voltage decays. Switching resumes when the lower hysteresis limit of VOVP is reached, thereby maintaining an average output voltage between the upper and lower OVP thresholds. The LED current magnitude can be controlled by the EN/ SET pin using the S2Cwire interface. The interface records rising edges of the EN/SET pin and decodes them into 32 individual current level settings. Code 1 is full scale (maximum LED current), and Code 32 is 2% of the full scale. The modulo 32 interface wraps states back to state 1 after the 32nd clock. The counter can be clocked at speeds up to 1MHz, so intermediate states are not visible. The first rising edge of EN/SET enables the IC and initially sets the output LED current to full scale after 500µs tLAT. Once the final clock cycle is input for the desired brightness level, the EN/SET pin should be held high to maintain the device output current at the programmed level. The device is disabled 500μs after the EN/SET pin enters a logic low state. The EN/SET timing is designed to accommodate a wide range of data rates from 20kHz to 1MHz. LED Current Setting The maximum LED current is determined by the RSET resistor value. With a fixed 1.2V voltage on RSET, the LED maximum current is a linear ratio to the current flowing through RSET. ILED = VSET · 258 RSET After the first rising edge of EN/SET, the boost converter is enabled and reaches full capacity after the soft-start time. Exact counts of clock pulses for the desired current level should be entered on the EN/SET pin with a single burst of clocks. The counter refreshes each time a new clock input to the EN/SET pin is detected. A constant current is maintained as long as EN/SET remains in a logic high state. To save power, the boost converter is switched off after EN/SET has remained in the low state for at least the tOFF timeout period as shown in Figure 1. The LED dimming is controlled via one of two options, either using the 32-step S2Cwire single-wire interface via the EN/SET pin or PWM control with varied duty cycle up to 100kHz frequency. 32 S2Cwire rising-edge steps set the LED current from 100% to 2% percentage of the maximum LED current value when PWM control is disabled by pulling the PWM pin high. S2Cwire can also be used to set maximum LED current along with a PWM signal to dim the LED lighting from 100% to 1% of duty cycle. S2Cwire Serial Interface Timing THI TLO TOFF T LAT EN/SET 1 Data Reg 2 n-1 n ≤ 32 0 n 0 Figure 1: S2Cwire Timing Diagram. 10 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202113A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 DATA SHEET AAT1401 Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control Application Information Figure 2 illustrates the LED current value at different S2Cwire code settings when RSET is 15kΩ with a maximum LED current of 20mA. The maximum LED current is determined by value of the external resistor RSET from 10mA to 31mA. The value of RSET is determined by the voltage of RSET and the LED current, and can be calculated by: V · 258 RSET = SET ILED 22 20 18 16 ILED (mA) LED Current Setting 14 12 10 8 6 Maximum LED Current (mA) RSET (kΩ) 31 20 15 12 10 10 15 20 25 30 Table 1: Examples of Standard 1% RSET Values for Setting Maximum LED Current Levels. LED current dimming is controlled either via the S2Cwire single-wire interface through the EN/SET pin in 32 steps or via PWM control with varied duty cycle up to 100kHz frequency. The S2Cwire interface programs the LED current from the maximum LED current set by RSET to 2% of the maximum LED current as shown in Table 2. S2Cwire Data LED Current (% IMAX) S2Cwire Data LED Current (% IMAX) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 100 97 94 90 87 84 81 77 74 71 68 65 61 58 55 52 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 48 45 42 39 35 32 29 26 23 19 16 13 10 6 3 2 4 2 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 ILED (mA) Figure 2: S2Cwire Dimming Control at Maximum LED Current (20mA max). Filtered PWM Dimming The AAT1401 provides a PWM input as an additional means of providing dimming control for CABC applications. The LED current reduces percentage linearly as the duty cycle decreasing. Frequencies of up to 100kHz can be applied. To avoid output flicker and noise, the input control PWM frequency is filtered by the low pass filter composed of the error amplifier and the external compensation capacitor. Figure 3 shows the LED current dimming controlled by varying the PWM duty cycle at RSET = 15kΩ. 20 18 16 14 ILED (mA) Where VSET = 1.2V. Table 1 lists examples of standard 1% metal film RSET values for different maximum LED current requirements. 12 10 8 6 4 2 0 100 90 80 70 60 50 40 30 20 10 0 PWM Duty Cycle (%) Figure 3: Filtered PWM Dimming Duty Cycle vs. Maximum LED Current (20mA max). Table 2: S2Cwire Dimming Control Current Settings. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202113A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 11 DATA SHEET AAT1401 Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control Capacitor Selection A compensation capacitor CCOM is used for step-up converter loop compensation, soft startup time control, and PWM digital signal filtering. Loop compensation requires matching values for CCOM, COUT, ILED, and VOUT: COUT ILED < CCOM 30 · 10-6 · VOUT The AAT1401 can drive up to 6 white LEDs with forward voltages up to 4V each. In a worst case with VF of 4V, a COUT value of 0.1µF, and LED maximum current of 20mA, the value of CCOM should be higher than 3.6nF. CCOM > COUT · 30 · VOUT 0.1 · 30 · 24 (nF) = (nF) = 3.6nF ILED 20 A higher value for CCOM lengthens the soft startup time. The relationship between CCOM and startup time is almost linear, with startup time x 105 magnification of CCOM; thus 56nF CCOM leads to a soft startup time of 5.6ms. Table 3 gives several examples of minimum CCOM values at different COUT and ILED and the step-up converter's operation stable. Values of 56nF for CCOM and 0.1µF for COUT are suitable in most cases. COUT (µF) VOUT (V) CCOM_MIN (nF) 31 31 20 20 10 10 0.1 1 0.1 1 0.1 1 24 24 24 24 24 24 2.3 23 3.6 36 7.2 72 Inductor Selection Inductor value, saturation current and DCR is most important parameter in selecting an inductor for AAT1401. The suitable inductance range for the AAT1401 is 4.7µH to 22µH. Higher inductance lowers the step-up converter's RMS current value. Together with lower DCR value of the inductor, it makes the total inductor power loss become much lower. Considering inductor size and cost, 10µH inductance is most suitable. Figure 4 illustrates AAT1401 efficiency at different inductance with similar DCR value. Efficiency (%) ILED (mA) 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 as input, output and compensation capacitors in the AAT1401 step-up converter LED driver application. MLC capacitors of type X7R or X5R are recommended to ensure good capacitance stability over the full operating temperature range. A 4.7µF/6.3V input capacitor is recommended and a 0.1µF/50V output capacitor is suitable as noted above. Table 4 lists some recommended capacitors for use with the AAT1401. Table 3: Minimum CCOM Values vs. ILED and COUT (Step-Up Converter Operation Stable). 90 86 82 78 74 70 66 62 58 54 50 46 42 38 34 30 4.7µH 10µH 22µH 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 ILED (mA) Figure 4: AAT1401 Efficiency at Different Inductance with Similar DCR (VIN = 3.6V). Manufacturer Part Number Value (µF) Voltage (V) Temperature Range Case Size Murata GRM188R60J475K GRM188R71H104KA93 4.7 0.1 6.3 50 X5R X7R 0603 0603 Table 4: Examples of AAT1401 Input and Output Capacitor Selection. 12 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202113A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 DATA SHEET AAT1401 Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control Considering the inductor copper loss, the inductor DCR value together with the RMS current value flowing through the inductor leads to inductor conduction loss and also affects total efficiency. Larger DCR leads to larger conduction loss and decreases total efficiency. The inductor conduction loss can be estimated as shown in the equation: 1 · (I2L_MAX + I2L_MIN + IL_MAX · IL_MIN) · DCR 3 Efficiency (%) IL_MAX and IL_MIN are the inductor peak current and minimum current. Figure 5 shows DCR effects on efficiency with a 10µH inductor. 90 86 82 78 74 70 66 62 58 54 50 46 42 38 34 30 VOUT · ILED VIN · η Inductor peak-to-peak current ripple: IL_PP = VIN · (VOUT - VIN) VOUT · L · f Inductor peak current: PL_LOSS = I2L_RMS · DCR = DC input current: IIN = IL_PEAK = IIN + IL_PP VOUT · ILED VIN · (VOUT - VIN) = + 2 VIN · η 2 · VOUT · L · f For example, for a white LED with 3.2V VF and 20mA current at 82% efficiency, the inductor peak current is IL_PEAK = 3.2 · 6 · 0.02 3.6 · (3.2 · 6 - 3.6) + = 276mA 3.6 · 0.82 2 · 3.2 · 6 · 10µ · 1M Table 5 gives some examples of recommended inductors for use with the AAT1401. OVP Setting 10µH DCR 235mΩ 3.2x3.2x1.55mm 10µH DCR164mΩ 4.0x4.0x2.0mm 10µH DCR 36mΩ 8.3x8.3x3.0mm 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 Over-voltage protection is designed to protect the step-up converter from a LED string open fault. The OVP threshold is 1.2V. For 6 white LEDs with VF up to 4V, the resistor divider values for R1 and R2 can be calculated by: ILED (mA) R1 = Figure 5: Inductor DCR Effects on Total Efficiency with 10µH at 3.6V VIN. Inductor saturation current is also a key parameter in selecting an inductor. For the step-up converter, the peak inductor current is the DC input current plus half the inductor peak-to-peak current ripple. Manufacturer Sumida Murata Coilcraft Coiltronics VOUT - 1 · R2 VOVP_TH Higher resistor divider values decrease the power loss on the resistors. The total resistor value for 24V VOUT should be less than 2.4MΩ for better noise immunity. Values of 1MΩ for resistor R1 and 51kΩ for resistor R2 are recommended. Part Number Inductance (µH) Maximum DC ISAT Current (mA) DCR (mΩ, typ) Size (mm) LxWxH Type CDRH3D18-100 CDRH3D23-220 LQH44PN100MP0L LQH44PN220MP0L EPL2014-103MLC LPS4012-223MLC SD18-100-R 10 22 10 22 10 22 10 900 550 1150 800 600 790 982 164 219 160 370 440 600 158 4.0x4.0x2.0 3.9x3.9x2.5 4.0x4.0x1.65 4.0x4.0x1.65 2.1x2.2x1.0 4.1x4.1x1.2 5.8x5.8x1.8 Shielded Shielded Non-shielded Non-shielded Shielded Shielded Shielded Table 5: Example of AAT1401 Inductor Selection. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202113A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 13 DATA SHEET AAT1401 Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control Rectifier Diode Selection An external rectifier diode is required for the non-synchronous step-up converter. A low VF Schottky diode is recommended. The diode voltage rating should be higher than the OVP voltage. For an AAT1401 driving 6 white LEDs with up to 4V forward voltage, the diode voltage rating should be higher than 24V. Select a diode with DC rated current equal to the input current to allow an adequate margin for safe use. Manufacturer Diodes Central TSC Printed Circuit Board Layout Recommendations For best performance of the AAT1401, the following guidelines should be followed when designing the PCB layout: 1. Make the power trace as short and wide as possible, including the input/output power lines and switching node, etc. 2. Make sure the ground bump connected to the printed circuit board with large copper area for better thermal dissipation. 3. Put the input and output capacitor close to the IC as close as possible to get the best filter result. Part Number Maximum DC Blocking Voltage VR (V) Maximum DC Forward Current IF (mA) Non-repetitive Peak Forward Surge Current IFSM (A) Forward Voltage VF (V) Case Size WxLxH (mm) SDM20U40 SD103BW CMDSH2-3 SS13L SS14L 40 30 30 30 40 250 350 200 1100 1100 1.0 1.5 1.0 30 30 0.37@20mA 0.37@20mA 0.32@15mA [email protected] [email protected] SOD523 SOD123 SDD323 Sub SMA Sub SMA 0.9x1.7x0.65 1.7x3.85x1.35 1.35x2.6x1.0 1.9x3.8x1.43 1.9x3.8x1.43 Table 6: Example of Typical Rectifier Diode. 14 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202113A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 DATA SHEET AAT1401 Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control Schematic and Layout DS1 SDM20U40 L1 10µH R1 1M U1 AAT1401IUQ J1 VIN DC+ CIN 4.7µF DC- A2 A1 LX D1 R2 51k D3 OVP PWM D2 A3 EN/SET B3 PWM VIN R3 51k AAT1401 White LED Driver IN J2 D3 C3 COMP D2 RSET CCOM 56nF D4 C1 GND B1 PGND RSET 15k COUT 0.1μF/50V D1 CS D6 D5 R4 51k V_MCU S2Cwire/PWM Microcontroller PWM EN/SET S2C R7 R8 R9 1k 1k 1k U2 1 2 3 4 UP PIC12F675 VDD GP5 GP4 GP3 VSS GP0 GP1 GP2 C1 0.1µF 8 7 R6 51k 6 5 R5 1k LED1 Red VMCU DOWN 3 2 1 J3 CYCLE Figure 6: AAT1401 Evaluation Board Schematic. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202113A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 15 DATA SHEET AAT1401 Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control Figure 7: AAT1401 Evaluation Board Top Side Layout. Figure 8: AAT1401 Evaluation Board Top Side Layout (detail). Figure 9: AAT1401 Evaluation Board Bottom Side Layout. 16 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202113A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 DATA SHEET AAT1401 Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control Component Part Number Description Manufacturer U1 U2 R1 R2, R3, R4, R6 RSET R5, R7, R8, R9 CIN COUT C1 CCOM D1, D2, D3, D4, D5, D6 DS1 L1 LED1 CYCLE, UP, DOWN AAT1401 PIC12F675 RC0603FR-071ML RC0603FR-0751KL RC0603FR-0715KL RC0603FR-071KL GRM188R60J475K GRM188R71H104K GRM188R71C104K GRM188R71C563K High Efficiency Serial LED Driver for 6 White LEDs 8-Pin Flash-Based 8-Bit CMOS Microcontroller Res 1MΩ 1/10W 1% 0603 SMD Res 51KΩ 1/10W 1% 0603 SMD Res 15KΩ 1/10W 1% 0603 SMD Res 1KΩ 1/10W 1% 0603 SMD Cap Ceramic 4.7μF 0603 X5R 6.3V 10% Cap Ceramic 0.1μF 0603 X7R 50V 10% Cap Ceramic 0.1μF 0603 X7R 16V 10% Cap Ceramic 0.056μF 0603 X7R 16V 10% Skyworks Microchip RS-0805UW 20mA White LED 0805 Realstar SDM20U40 CDRH3D18-100NC 0805KRCT 6*6*5 Surface Mount Schottky Barrier Diode Power Inductor 10μH 0.9A SMD Red LED 0805 12V 50mA Pushbutton Diodes Sumida HB E-LT Yageo Murata Table 7: AAT1401 Evaluation Board Bill of Materials (BOM). Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202113A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 17 DATA SHEET AAT1401 Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control Ordering Information Package Maximum # of LEDs Interface Marking1 Part Number (Tape and Reel)2 WLCSP-10 6 S2C, Filtered PWM F4YY AAT1401IUQ-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 WLCSP-10 1.145 ± 0.035 ø 0.2 (Ref.) Pin A1 indication 0.800 BSC 0.300 0.100 0.300 1.545 ± 0.035 Line_2 0.400 BSC 1.200 BSC 0.200 BSC Line_1 0.100 Bottom View Top View 0.380 ± 0.025 0.200 ± 0.025 0.070 ± 0.035 0.650 ± 0.085 0.265 ± 0.015 Side View End View All dimensions in millimeters. 1. YY = date code. 2. Sample stock is generally held on part numbers listed in BOLD. 18 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202113A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 DATA SHEET AAT1401 Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control 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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