DATA SHEET AAT1231 Step-Up DC/DC Converters for White LED Backlight Applications General Description Features The AAT1231/1231-1 are high frequency, high efficiency constant current boost converters capable of 24V maximum output voltage. Both devices are ideal power solutions for backlight applications with up to six white LEDs in series or up to twelve white LEDs in a parallel/series configuration. The input voltage is 2.7V to 5.5V for singlecell lithium-ion/polymer (Li-ion) based portable devices. • Input Voltage Range: 2.7V to 5.5V • Maximum Continuous Output 24V @ 50mA • Drives 6 LEDs in Series, 12 LEDs in Parallel / Series Configuration ▪ Constant LED Current with 6% Accuracy • Digital Control with S2Cwire Single Wire Interface ▪ 26 Discrete Steps ▪ No PWM Control Required ▪ No Additional Circuitry • Up to 82% Efficiency • Up to 2MHz Switching Frequency Allows Small External Chip Inductor and Capacitors • Hysteretic Control ▪ No External Compensation Components ▪ Excellent Load Transient Response ▪ High Efficiency at Light Loads • Integrated Soft Start with No External Capacitor • True Load Disconnect Guarantees <1.0µA Shutdown Current • Selectable Feedback Voltage Ranges for High Resolution Control of Load Current • Short-Circuit, Over-Voltage, and Over-Temperature Protection • 12-Pin TSOPJW Package • -40°C to +85°C Temperature Range The LED current is digitally controlled across a 6x operating range using Skyworks' Simple Serial Control™ (S2Cwire™) interface. Programmability across 26 discrete current steps provides high resolution, low noise, flicker-free, constant LED outputs. In programming AAT1231 operation, LED brightness increases based on the data received at the EN/SET pin. In programming AAT1231-1 operation, LED brightness decreases based on the data received at the EN/SET pin. The SEL logic pin changes the feedback voltage between two programmable ranges. The AAT1231 and the AAT1231-1 feature high current limit and fast, stable transitions for stepped or pulsed current applications. The high switching frequency (up to 2MHz) provides fast response and allows the use of ultra-small external components, including chip inductors and capacitors. Fully integrated control circuitry simplifies design and reduces total solution size. The AAT1231 and the AAT1231-1 offer a true load disconnect feature which isolates the load from the power source while in the OFF or disabled state. This eliminates leakage current, making the devices ideally suited for battery-powered applications. The AAT1231 and the AAT1231-1 are available in Pb-free, thermally-enhanced 12-pin TSOPJW packages. Applications • • • • • Digital Still Cameras (DSCs) Mobile Handsets MP3 Players PDAs and Notebook PCs White LED Drivers Typical Application L = 2.2µH C1 2.2µF PVIN LIN VIN SW PGND Li-Ion: VIN = 2.7V to 4.2V Select R3 12kΩ EN/SET SEL AGND Up to 24V/ 50mA max OSRAM LW M678 R2 226kΩ OVP AAT1231/ 1231-1 Enable/Set DS1 FB R1 (RBALLAST) 30.1Ω C2 2.2µF Capable of Driving Six LEDs in Series (see Applications Section) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 1 DATA SHEET AAT1231 Step-Up DC/DC Converters for White LED Backlight Applications Pin Descriptions Pin # Symbol 1 PVIN 2 EN/SET 3 SEL 4 5 6, 7 8 9 10 11 12 VIN N/C SW PGND AGND FB OVP LIN Function Input power pin; connected to the source of the P-channel MOSFET. Connect to the input capacitor(s). IC enable pin and S2Cwire input control to set output current. FB voltage range select. For the AAT1231, a logic LOW sets the FB voltage range from 0.1V to 0.4V; a logic HIGH sets the FB voltage range from 0.3V to 0.6V. For the AAT1231-1, a logic LOW sets the FB voltage range from 0.4V to 0.1V; a logic HIGH sets the FB voltage range from 0.6V to 0.3V. Input voltage for the converter. Connect directly to the PVIN pin. No connection. Boost converter switching node. Connect the power inductor between this pin and LIN. Power ground for the boost converter. Ground pin. Feedback pin. Connect a resistor to ground to set the maximum LED current. Feedback pin for over-voltage protection sense. Switched power input. Connect the power inductor between this pin and SW. Pin Configuration TSOPJW-12 (Top View) 2 PVIN 1 12 LIN EN/SET 2 11 OVP SEL 3 10 FB VIN 4 9 AGND N/C 5 8 PGND SW 6 7 SW Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 DATA SHEET AAT1231 Step-Up DC/DC Converters for White LED Backlight Applications Part Number Descriptions SEL Polarity Part Number HIGH LOW S2Cwire Feedback Voltage Programming AAT1231ITP AAT1231ITP-1 0.3V ≤ VFB ≤ 0.6V 0.6V ≥ VFB ≥ 0.3V 0.1V ≤ VFB ≤ 0.4V 0.4V ≥ VFB ≥ 0.1V See Table 2 See Table 3 Absolute Maximum Ratings1 TA = 25°C unless otherwise noted. Symbol PVIN, VIN SW LIN, EN/SET, SEL, FB TJ TS TLEAD Description Input Voltage Switching Node Maximum Rating Operating Temperature Range Storage Temperature Range Maximum Soldering Temperature (at leads, 10 sec) Value Units -0.3 to 6.0 28 VIN + 0.3 -40 to 150 -65 to 150 300 V V V °C °C °C Value Units 160 625 °C/W mW Thermal Information Symbol qJA PD Description Thermal Resistance Maximum Power Dissipation 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. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 3 DATA SHEET AAT1231 Step-Up DC/DC Converters for White LED Backlight Applications Electrical Characteristics1 TA = -40°C to +85°C unless otherwise noted. Typical values are at 25°C, VIN = 3.6V. Symbol Description Power Supply PVIN, VIN VOUT(MAX) IQ ISHDN IOUT DVLINEREG(FB)/ DVIN RDS(ON) L Typ Max Units 5.5 24 70 1.0 50 V V µA µA mA SEL = GND, FB = 0.1V EN/SET = GND 2.7V < VIN < 5.5V, VOUT = 24V 40 Line Regulation VIN = 2.7V to 5.5V, VFB = 0.6V 0.7 %/V 2.7 80 mW 300 µs Low Side Switch On Resistance Soft-Start Time VOVP Over-Voltage Protection Threshold Over-Voltage Hysteresis N-Channel Current Limit TJ Thermal Shutdown Threshold TJ Thermal Shutdown Hysteresis FB Min Input Voltage Range Maximum Output Voltage Operating Current Shutdown Current Maximum Continuous Output Current2 TSS ILIMIT TSD THYS SEL, EN/SET VSEL(L) VSEL(H) VEN/SET(L) VEN/SET(H) TEN/SET (LO) TEN/SET(HI) TOFF TLAT IEN/SET AAT1231 Conditions SEL Threshold Low SEL Threshold High Enable Threshold Low Enable Threshold High EN/SET Low Time EN/SET High Time EN/SET Off Timeout EN/SET Latch Timeout EN/SET Input Leakage From Enable to Output Regulation; VFB = 300mV VOUT Rising VOUT Falling 1.1 1.2 100 2.5 140 15 1.3 V mV A °C °C 0.4 V V V V µs µs µs µs µA 1.4 0.4 VEN/SET VEN/SET VEN/SET VEN/SET VEN/SET < > < > = 0.6V 1.4V 0.6V 1.4V 5V, VIN = 5V FB Pin Regulation VIN = 2.7V to 5.5V, SEL = GND, EN/SET = HIGH VIN = 2.7V to 5.5V, SEL = HIGH, EN/SET = DATA16 FB Pin Regulation VIN = 2.7V to 5.5V, SEL = GND, EN/SET = DATA16 VIN = 2.7V to 5.5V, SEL = HIGH, EN/SET = HIGH 1.4 0.3 75 75 500 500 1 -1 0.09 0.1 0.11 0.564 0.6 0.636 0.09 0.1 0.11 0.564 0.6 0.636 V AAT1231-1 FB 1. Specification over the -40°C to +85°C operating temperature range is assured by design, characterization, and correlation with statistical process controls. 2. Maximum continuous output current increases with reduced output voltage, but may vary depending on operating efficiency and thermal limitations. 4 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 V DATA SHEET AAT1231 Step-Up DC/DC Converters for White LED Backlight Applications Typical Characteristics Efficiency vs. LED Current Efficiency vs. LED Current (4 White LEDs; RBALLAST = 30.1Ω) (5 White LEDs; RBALLAST = 30.1Ω) 85 83 VIN = 5V 82 83 Efficiency (%) Efficiency (%) 84 82 81 80 VIN = 4.2V VIN = 3.6V 79 78 VIN = 4.2V 79 VIN = 3.6V 78 77 75 2 4 6 8 10 12 14 16 18 20 LED Current (mA) 2 4 6 8 10 12 14 16 18 20 18 20 LED Current (mA) Efficiency vs. LED Current Efficiency vs. LED Current (6 White LEDs; RBALLAST = 30.1Ω) (12 White LEDs; RBALLAST = 30.1Ω) 84 81 83 80 VIN = 5V 78 VIN = 4.2V 77 76 75 VIN = 5V 82 79 Efficiency (%) Efficiency (%) 80 76 77 VIN = 3.6V 81 80 79 VIN = 4.2V 78 77 VIN = 3.6V 76 74 75 73 74 2 4 6 8 10 12 14 16 18 20 LED Current (mA) 2 4 6 8 10 12 14 16 LED Current (mA) Shutdown Current vs. Input Voltage Feedback Voltage vs. Temperature (EN = GND) (RBALLAST = 30.1Ω) 700 Feedback Voltage (mV) 1.0 Shutdown Current (µA) VIN = 5V 81 0.8 0.6 85°C 0.4 25°C 0.2 0.0 2.7 -40°C 600 500 400 300 200 100 0 3.1 3.5 3.9 4.3 Input Voltage (V) 4.7 5.1 -40 5.5 -15 10 35 60 85 Temperature (°C) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 5 DATA SHEET AAT1231 Step-Up DC/DC Converters for White LED Backlight Applications Typical Characteristics Accuracy ILED vs. Temperature Accuracy ILED vs. Input Voltage (VFB = 0.6V; RBALLAST = 30.1Ω) 1.0 2.0 0.8 1.5 Accuracy ILED (%) Accuracy ILED (%) (VFB = 0.6V; RBALLAST = 30.1Ω) 0.5 0.3 0.0 -0.3 -0.5 -40°C 0.5 0.0 85°C -0.5 25°C -1.0 -1.5 -0.8 -2.0 -1.0 -40 -15 10 35 60 2.7 85 Temperature (°C) 3.2 3.7 4.2 4.7 Line Transient Shutdown (6 White LEDs; RBALLAST = 30.1Ω) (VFB = 0.6V; ILED = 20mA) 20.6 20.4 20.2 0.8 0.6 0.4 Enable Voltage (V) (top) Feedback Voltage (V) (middle) 3.6V 20.8 5.7 2.5V 0V 0.6 0.4 0.2 0 0.5 0.0 Time (50µs/div) Time (50µs/div) Output Ripple Output Ripple (6 White LEDs; ILED = 13mA) (6 White LEDs; ILED = 20mA) VOUT (DC Offset 20.7V) (20mV/div) VOUT (DC Offset 19.8V) (50mV/div) 20 20 VLX (V) VLX (V) 0 0.5 0.5 IL (A) IL (A) 0 Time (400ns/div) 6 0 0 Time (200ns/div) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 Inductor Current (A) (bottom) 4.2V 5.2 Input Voltage (V) Feedback Voltage (bottom) (V) Input Voltage (top) (V) Output Voltage (middle) (V) 1.0 DATA SHEET AAT1231 Step-Up DC/DC Converters for White LED Backlight Applications Typical Characteristics AAT1231 Soft Start AAT1231 Soft Start with S2Cwire (6 White LEDs; VFB = 0.3V) 0.4 0.2 0 2 1 0 Enable Voltage (top) (V) Feedback Voltage (middle) (V) 0V 2.5V 0V 0.2 0 2 1 0 Time (50µs/div) Time (100µs/div) AAT1231-1 Soft Start AAT1231-1 Soft Start with S2Cwire (6 White LEDs; VFB = 0.6V) 0.4 0.2 0 1 0 0.6 0V 0.4 0.2 0 1 0 Time (50µs/div) Time (100µs/div) Transition of LED Current Transition of LED Current (6 White LEDs; SEL = Low; ILED = 13.3mA to 6.6mA) (6 White LEDs; SEL = Low; ILED = 3.3mA to 13.3mA) 18 0.4 0.3 0.2 0.1 0.0 Time (20µs/div) Output Voltage (top) (V) 20 22 20 18 0.4 0.3 0.2 0.1 0.0 Feedback Voltage (bottom) (V) 22 Feedback Voltage (bottom) (V) Output Voltage (top) (V) Enable Voltage (top) (V) Feedback Voltage (middle) (V) 0V 2.5V Inductor Current (bottom) (A) 2.5V Inductor Current (bottom) (A) Enable Voltage (top) (V) Feedback Voltage (middle) (V) (6 White LEDs; VFB = 0.3V) 0.6 Inductor Current (bottom) (A) 2.5V Inductor Current (bottom) (A) Enable Voltage (top) (V) Feedback Voltage (middle) (V) (6 White LEDs; VFB = 0.6V) Time (20µs/div) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 7 DATA SHEET AAT1231 Step-Up DC/DC Converters for White LED Backlight Applications Typical Characteristics EN/SET Off Timeout vs. Input Voltage 300 350 300 EN/SET Off Timeout (µs) EN/SET Latch Timeout (µs) EN/SET Latch Timeout vs. Input Voltage 25°C -40°C 250 85°C 200 150 100 -40°C 200 85°C 150 100 50 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 Input Voltage (V) 2.7 3.1 3.5 4.7 5.1 5.5 1.2 1.1 1.1 -40°C -40°C 1.0 1.0 0.9 0.9 VIH (V) VIL (V) 4.3 EN/SET High Threshold vs. Input Voltage 1.2 0.8 0.7 85°C 25°C 0.6 25°C 85°C 0.8 0.7 0.6 0.5 0.5 0.4 2.7 3.1 3.5 3.9 4.3 4.7 5.1 0.4 2.7 5.5 Input Voltage (V) 3.1 3.5 3.9 4.3 4.7 5.1 5.5 Input Voltage (V) Low Side Switch On Resistance vs. Input Voltage Input Disconnect Switch Resistance vs. Input Voltage 160 300 280 140 120°C 120 RDS(ON)IN (mΩ) RDS(ON)L (mΩ) 3.9 Input Voltage (V) EN/SET Low Threshold vs. Input Voltage 100°C 100 80 25°C 260 120°C 100°C 240 220 200 180 85°C 60 25°C 85°C 160 40 2.5 3 3.5 4 4.5 Input Voltage (V) 8 25°C 250 5 5.5 140 2.5 6 3 3.5 4 4.5 5 Input Voltage (V) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 5.5 6 DATA SHEET AAT1231 Step-Up DC/DC Converters for White LED Backlight Applications Functional Block Diagram LIN PVIN VIN OVP EN/SET FB SW Reference Output Select Control SEL AGND Functional Description The AAT1231 and the AAT1231-1 consist of a DC/DC boost controller, an integrated slew rate controlled input disconnect MOSFET switch, and a high voltage MOSFET power switch. A high voltage rectifier, power inductor, output capacitor, and sense resistors are required to implement a DC/DC constant current boost converter. The input disconnect switch is activated when a valid input voltage is present and the EN/SET pin is pulled high. The slew rate control on the P-channel MOSFET ensures minimal inrush current as the output voltage is charged to the input voltage, prior to the switching of the N-channel power MOSFET. Monotonic turn-on is guaranteed by the integrated soft-start circuitry. Softstart eliminates output voltage overshoot across the full input voltage range and all loading conditions. The maximum current through the LED string is set by the ballast resistor and the feedback voltage of the IC. The output current may be programmed by adjusting PGND the level of the feedback reference voltage which is programmed through the S2Cwire interface. The SEL pin selects one of two feedback voltage ranges. For the AAT1231 and with a LOW logic level applied to the SEL pin, the FB pin voltage can be programmed from 0.1V to 0.4V. With a logic HIGH applied to the SEL pin, the FB pin voltage can be programmed from 0.3V to 0.6V. In the AAT1231-1, the SEL function is inverted in that the FB pin voltage can be programmed from 0.4V to 0.1V with a logic LOW applied to the SEL pin and 0.6V to 0.3V with a logic HIGH applied to the SEL pin. Regardless of which device is chosen, the feedback voltage can be set to any one of 16 current levels within each FB range, providing high-resolution control of the LED current, using the single-wire S2Cwire control. For torch and flash applications where a short duration, pulsed load is desired, applying a low-to-high transition on the AAT1231’s SEL pin produces a 1.5x to 3.0x LED current step. In the AAT1231-1 on the other hand, the LED current step for a low-to-high transition on the SEL Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 9 DATA SHEET AAT1231 Step-Up DC/DC Converters for White LED Backlight Applications pin can be programmed from 3.0x to 1.5x. In both products, the step size is determined by the programmed voltage at the FB pin where the internal default setting is 3.0x in the AAT1231 and 1.5x in the AAT1231-1. Control Loop The AAT1231/1231-1 provide the benefits of current mode control with a simple hysteretic output current loop providing exceptional stability and fast response with minimal design effort. The device maintains exceptional constant current regulation, transient response, and cycle-by-cycle current limit without additional compensation components. The AAT1231/1231-1 modulate the power MOSFET switching current to maintain the programmed FB voltage. This allows the FB voltage loop to directly program the required inductor current in order to maintain the desired LED current. The switching cycle initiates when the N-channel MOSFET is turned ON and current ramps up in the inductor. The ON interval is terminated when the inductor current reaches the programmed peak current level. During the OFF interval, the input current decays until the lower threshold, or zero inductor current, is reached. The lower current is equal to the peak current minus a preset hysteresis threshold, which determines the inductor ripple current. The peak current is adjusted by the controller until the LED output current requirement is met. The magnitude of the feedback error signal determines the average input current. Therefore, the AAT1231/1231-1 controller implements a programmed current source connected to the output capacitor, parallel with the LED string and ballast resistor. There is no right-half plane zero, and loop stability is achieved with no additional compensation components. An increase in the feedback voltage (VFB) results in an increased error signal sensed across the ballast resistor (R1). The controller responds by decreasing the peak inductor current, resulting in lower average current in the inductor and LED string(s). Alternatively, when the VFB is reduced, the controller responds by increasing the peak inductor current, resulting in higher average current in the inductor and LED string(s). 10 Under light load conditions, the inductor OFF interval current goes below zero and the boost converter enters discontinuous mode operation. Further reduction in the load current results in a corresponding reduction in the switching frequency. The AAT1231/1231-1 provide pulsed frequency operation which reduces switching losses and maintains high efficiency under light load conditions. Operating frequency varies with changes in the input voltage, output voltage, and inductor size. Once the boost converter has reached continuous mode, further increases in the LED current will not significantly change the operating frequency. A small 2.2µH (±20%) inductor is selected to maintain high frequency switching (up to 2MHz) and high efficiency operation for outputs up to 24V. Soft Start / Enable The input disconnect switch is activated when a valid input voltage is present and the EN/SET pin is pulled high. The slew rate control on the P-channel MOSFET ensures minimal inrush current as the output voltage is charged to the input voltage, prior to switching of the N-channel power MOSFET. Monotonic turn-on is guaranteed by the built-in soft-start circuitry. Soft start eliminates output current overshoot across the full input voltage range and all loading conditions. After the soft start sequence has terminated, the initial LED current is determined by the internal, default FB voltage across the external ballast resistor at the FB pin. Additionally, the AAT1231 and the AAT1231-1 have been designed to offer the system designer two choices for the default FB voltage based on the state of the SEL pin. Changing the LED current from its initial default setting is easy by using the S2Cwire single wire serial interface; the FB voltage can be increased (as in the AAT1231; see Table 2) or decreased (as in the AAT1231-1; see Table 3) relative to the default FB voltage. Some applications may require the output to be active when a valid input voltage is present. In these cases, add a 10kW resistor between the VIN, VP, and EN/SET pins to avoid startup issues. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 DATA SHEET AAT1231 Step-Up DC/DC Converters for White LED Backlight Applications Current Limit and Over-Temperature Protection Application Information The switching of the N-channel MOSFET terminates when a current limit of 2.5A (typical) is exceeded. This minimizes power dissipation and component stresses under overload and short-circuit conditions. Switching resumes when the current decays below the current limit. Over-Voltage Protection Thermal protection disables the AAT1231/1231-1 when internal dissipation becomes excessive. Thermal protection disables both MOSFETs. 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. OVP Protection with Open Circuit Failure The OVP protection circuit consists of a resistor network tied from the output voltage to the OVP pin (see Figure 1). To protect the device from open circuit failure, the resistor divider can be selected such that the over-voltage threshold occurs prior to the output reaching 24V (VOUT(MAX)). The value of R3 should be selected from 10kW to 20kW to minimize losses without degrading noise immunity. R2 = R3 · Over-Voltage Protection Under-Voltage Lockout AAT1231/1231-1 R2 COUT OVP R3 GND Figure 1: Over-Voltage Protection Circuit. 1.224V 1.168V 26 24 22 2 1 0 Output Voltage (middle) (V) Internal bias of all circuits is controlled via the VIN input. Under-voltage lockout (UVLO) guarantees sufficient VIN bias and proper operation of all internal circuitry prior to soft start. VOUT Over Voltage Protection Pin (top) (V) Inductor Current (bottom (A) Over-voltage protection prevents damage to the AAT1231/1231-1 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 Threshold Limit (VOVP = 1.2V typical). When the voltage on the OVP pin has reached the threshold limit, the converter stops switching and the output voltage decays. Switching resumes when the voltage on the OVP pin drops below the lower hysteresis limit, maintaining an average output voltage between the upper and lower OVP thresholds multiplied by the resistor divider scaling factor. VOUT(MAX) -1 VOVP Time (5ms/div) Figure 2: Over-Voltage Protection Open Circuit Response (No LED). Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 11 DATA SHEET AAT1231 Step-Up DC/DC Converters for White LED Backlight Applications Assume R3 = 12kW and VOUT(MAX) = 24V. Selecting 1% resistor for high accuracy, this results in R2 = 226kW (rounded to the nearest standard value). The minimum OVP threshold can be calculated: VOUT(OVP_MIN) = VOVP(MIN) · R2 +1 R3 = 21.8V OVP Constant Voltage Operation Cold Temperature Applied ILED (10mA/div) To avoid OVP detection and subsequent reduction in the programmed output current (see following section), the maximum operating voltage should not exceed the minimum OVP set point. VOUT(MAX) < VOUT(OVP_MIN) In some cases, this may disallow configurations with high LED forward voltage (VFLED) and/or greater than five series white LEDs. VFLED unit-to-unit tolerance can be as high as +15% of nominal for white LED devices. OVP Constant Voltage Operation Under closed loop constant current conditions, the output voltage is determined by the operating current, LED forward voltage characteristics (VFLED), quantity of series connected LEDs (N), and the feedback pin voltage (VFB). VOUT = VFB + N · VFLED When the rising OVP threshold is exceeded, switching is stopped and the output voltage decays. Switching automatically restarts when the output drops below the lower OVP hysteresis voltage (100mV typical) and, as a result, the output voltage increases. The cycle repeats, maintaining an average DC output voltage proportional to the average of the rising and falling OVP levels (multiplied by the resistor divider scaling factor). High operating frequency and small output voltage ripple ensure DC current and negligible flicker in the LED string(s). The waveform in Figure 3 shows the output voltage and LED current at cold temperature with a six series white LED string and VOVP = 19.4V. As shown, the output voltage rises as a result of the increased VFLED which triggers the OVP constant voltage operation. Self heating of the LEDs triggers a smooth transition back to constant current control. 12 Self-Recovery VOUT (5V/div) ILED Time (1s/div) Figure 3: Over-Voltage Protection Constant Voltage Operation (6 White LEDs; ILED = 13mA; R2 = 182kW; R3 = 12kW). While OVP is active, the maximum LED current programming error (DILED) is proportional to voltage error across an individual LED (DVFLED). ∆VFLED = (N · VFLED(MAX) - VOUT(OVP_MIN) - VFB) N To minimize the DILED error, the minimum OVP voltage (VOUT(OVP_MIN)) may be increased, yielding a corresponding increase in the maximum OVP voltage (VOUT(OVP_MAX)). Measurements should confirm that the maximum switching node voltage (VSW(MAX)) is less than 28V under worstcase operating conditions. VSW(MAX) = VOVP(MAX) · R3 + 1 + VF + VRING R2 VF = ‑Schottky Diode DS1 forward voltage at turn-OFF VRING = Voltage ring occurring at turn-OFF LED Selection and Current Setting The AAT1231/1231-1 are well suited for driving white LEDs with constant current. Applications include main and sub-LCD display backlighting, and color LEDs. The LED current is controlled by the FB voltage and the ballast resistor. For maximum accuracy, a 1% tolerance resistor is recommended. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 DATA SHEET AAT1231 Step-Up DC/DC Converters for White LED Backlight Applications The ballast resistor (RBALLAST) value can be calculated as follows: RBALLAST = VFB(MAX) ILED(MAX) where: VFB(MAX) = 0.4V when SEL = Low VFB(MAX) = 0.6V when SEL = High i.e., for a maximum LED current of 20mA (SEL = High): RBALLAST = VFB ILED(MAX) 0.6 = = 30Ω ≈ 30.1Ω 0.020 Typical white LEDs are driven at maximum continuous currents of 15mA to 20mA. For maximum output, two parallel strings of six series LEDs are used. A total output current of 30mA or 40mA is required (15mA to 20mA in each string). The maximum quantity of series connected LEDs is determined by the minimum OVP voltage of the boost converter (VOUT(OVP_MIN)), minus the maximum feedback voltage (VFB(MAX)) divided by the maximum LED forward voltage (VFLED(MAX)). VFLED(MAX) can be estimated from the manufacturers’ datasheet at the maximum LED operating current. VOUT(OVP_MIN) = VOVP(MIN) · N= RBALLAST (W) Maximum ILED Current (mA) SEL = High SEL = Low 50 40 35 30 25 20 15 10 5 12.1 15.0 16.9 20.0 24.3 30.1 40.2 60.4 121.0 8.06 10.0 11.3 13.3 16.2 20.0 26.7 40.2 80.6 Table 1: Maximum LED Current and RBALLAST Resistor Values (1% Resistor Tolerance). R2 +1 R3 (VOUT(OVP_MIN) - VFB(MAX)) VFLED(MAX) Figure 4 shows the schematic of using six LEDs in series. Assume VFLED @ 20mA = 3.5V (typical) from LW M673 (OSRAM) datasheet. VOUT(OVP_MIN) = 1.1V · N= 226kΩ + 1 = 21.82V 12kΩ 21.82V - 0.6V 3.5V ≈ 6.1 Therefore, under typical operating conditions, six LEDs can be used in series. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 13 DATA SHEET AAT1231 Step-Up DC/DC Converters for White LED Backlight Applications VIN = 2.7V to 5.5V R4 10K 1 1 2 2 3 3 4 5 Enable JP2 6 VIN EN SEL VP N/C SW 1 LIN OVP FB GND PGND SW VOUT = 24V/20mA 2.2µH U1 AAT1231/1231-1 JP1 C1 2.2µF DS1 L1 R2 226K 12 11 D2 LED 10 9 R3 12K 8 C2 2.2µF D3 LED 7 TSOP12JW D4 LED 2 3 D1 LED R1 D6 D5 30.1Ω LED LED Select U1 AAT1231/1231-1 TSOPJW-12 L1 2.2µH SD3814-2R2 C1 2.2µF 10V 0603 C2 2.2µF 25V 0805 D1-D6 LW M673 White LED DS1 30V 0.2A BAT42W SOD-123 R1 30.1 0603 R2 226K 0603 R3 12K 0603 R4 10K 0603 Figure 4: AAT1231/1231-1 White LED Boost Converter Schematic. LED Brightness Control The AAT1231 and the AAT1231-1 use S2Cwire programming to control LED brightness and does not require PWM (pulse width modulation) or additional control circuitry. This feature greatly reduces the burden on a microcontroller or system IC to manage LED or display brightness, allowing the user to “set it and forget it.” With its high-speed serial interface (1MHz data rate), the output current of the AAT1231 and the AAT1231-1 can be changed successively to brighten or dim the LEDs in smooth transitions (i.e., to fade out) or in abrupt steps, giving the user complete programmability and real-time control of LED brightness. LED Current (mA) 25 SEL = HIGH 10 (Default) SEL = LOW 5 0 1 4 7 20 SEL=HIGH (Default) 15 10 SEL=LOW 5 0 1 4 7 10 13 S2Cwire Data Register Figure 6: Programming AAT1231-1 LED Current with RBALLAST = 30.1W. 10 13 16 S2Cwire Data Register Figure 5: Programming AAT1231 LED Current with RBALLAST = 30.1W. 14 16 Alternatively, toggling the SEL logic pin from low to high implements stepped or pulsed LED currents by increasing the FB pin voltage. Figures 7 and 8 illustrate the SELECT pin scaling factor, defined as the LED current with SEL=HIGH divided by the LED current with SEL=LOW. For the AAT1231, scaling factors from 1.5x to 3.0x are possible, depending on the S2Cwire data register (default = 3.0x). In the AAT1231-1, the possible scaling factors are 3.0x to 1.5x with the internal default setting of 1.5x. 20 15 LED Current (mA) 25 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 DATA SHEET AAT1231 Select Pin Scaling Factor (High to Low) Step-Up DC/DC Converters for White LED Backlight Applications individual states. Each state corresponds to a reference feedback voltage setting on the FB pin, as shown in Table 2. 3.5 (Default) 3.0 2.5 S2Cwire Serial Interface Timing 2.0 The S2Cwire single wire serial interface data can be clocked-in at speeds up to 1MHz. After data has been submitted, EN/SET is held high to latch the data for a period TLAT. The FB pin voltage is subsequently changed to the level as defined by the state of the SEL logic pin. When EN/SET is set low for a time greater than TOFF, the AAT1231/1231-1 is disabled. When either the AAT1231 or the AAT1231-1 is disabled, the register is reset to its default value. In the AAT1231, the default register value sets the FB pin voltage to 0.6V if the EN/SET pin is subsequently pulled HIGH. In the AAT1231-1, the FB pin voltage is set to 0.3V under the same condition. 1.5 1.0 1 4 7 10 13 16 S2Cwire Data Register Figure 7: AAT1231 SEL Pin Scaling Factor: ILED (SEL = High) Divided by ILED (SEL = Low). Select Pin Scaling Factor (Low to High) 3. 5 3. 0 2. 5 S2Cwire Feedback Voltage Programming 2. 0 (Default) The FB pin voltage is set to the default level at initial powerup. The AAT1231 and the AAT1231-1 are programmed through the S2Cwire interface. Table 2 illustrates FB pin voltage programming for the AAT1231 and Table 3 illustrates FB pin voltage programming for the AAT1231-1. The rising clock edges applied at the EN/SET pin determine the FB pin voltage. If a logic LOW is applied at the SEL pin, the default feedback voltage range for the AAT1231 is 0.1V to 0.4V; for a logic HIGH condition at the SEL pin, the default feedback voltage range is 0.3V to 0.6V. Conversely, if a logic LOW is applied at the SEL pin of the AAT1231-1, the default feedback voltage range becomes 0.4V to 0.1V and 0.6V to 0.3V for a logic HIGH condition at the SEL pin. 1. 5 1. 0 1 4 7 10 13 16 S2Cwire Data Register Figure 8: AAT1231-1 SEL Pin Scaling Factor: ILED (SEL = High) Divided by ILED (SEL = Low). S2Cwire Serial Interface Skyworks' S2Cwire single wire serial interface is a proprietary high-speed single-wire interface available only from Skyworks. The S2Cwire interface records rising edges of the EN/SET input and decodes them into 16 THI TLO TOFF T LAT EN/SET 1 Data Reg 2 n-1 0 n ≤ 16 n 0 Figure 9: AAT1231/1231-1 S2Cwire Timing Diagram to Program the Output Voltage. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 15 DATA SHEET AAT1231 Step-Up DC/DC Converters for White LED Backlight Applications SEL = Low SEL = High Rising Clock Edges/Data Register Reference Voltage (V) LED Current (mA); RBALLAST = 30.1W Reference Voltage (V) LED Current (mA); RBALLAST = 30.1W 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 0.1 (default) 0.12 0.14 0.16 0.18 0.20 0.22 0.24 0.26 0.28 0.30 0.32 0.34 0.36 0.38 0.40 3.32 3.99 4.65 5.32 5.98 6.64 7.31 7.97 8.64 9.30 9.97 10.63 11.30 11.96 12.62 13.29 0.3 (default) 0.32 0.34 0.36 0.38 0.40 0.42 0.44 0.46 0.48 0.50 0.52 0.54 0.56 0.58 0.60 9.97 10.63 11.30 11.96 12.62 13.29 13.95 14.62 15.28 15.95 16.61 17.28 17.94 18.60 19.27 19.93 Table 2: AAT1231 S2Cwire Reference Feedback Voltage Control Settings with RBALLAST = 30.1Ω (Assume Nominal Values). SEL = Low SEL = High Rising Clock Edges/Data Register Reference Voltage (V) LED Current (mA); RBALLAST = 30.1W Reference Voltage (V) LED Current (mA); RBALLAST = 30.1W 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 0.4 (default) 0.38 0.36 0.34 0.32 0.30 0.28 0.26 0.24 0.22 0.20 0.18 0.16 0.14 0.12 0.10 13.29 12.62 11.96 11.30 10.63 9.97 9.30 8.64 7.97 7.31 6.64 5.98 5.32 4.65 3.99 3.32 0.6 (default) 0.58 0.56 0.54 0.52 0.50 0.48 0.46 0.44 0.42 0.40 0.38 0.36 0.34 0.32 0.30 19.93 19.27 18.60 17.94 17.28 16.61 15.95 15.28 14.62 13.95 13.29 12.62 11.96 11.30 10.63 9.97 Table 3: AAT1231-1 S2Cwire Reference Feedback Voltage Control Settings With RBALLAST = 30.1Ω (Assumes Nominal Values). 16 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 DATA SHEET AAT1231 Step-Up DC/DC Converters for White LED Backlight Applications To ensure minimum forward voltage drop and no recovery, high voltage Schottky diodes are considered the best choice for the AAT1231/1231-1 boost converters. The output diode is sized to maintain acceptable efficiency and reasonable operating junction temperature under full load operating conditions. Forward voltage (VF) and package thermal resistance (qJA) are the dominant factors to consider in selecting a diode. The diode non-repetitive peak forward surge current rating (IFSM) should be considered for high pulsed load applications, such as camera flash. IFSM rating drops with increasing conduction period. Manufacturers’ datasheets should be consulted to verify reliability under peak loading conditions. The diode’s published current rating may not reflect actual operating conditions and should be used only as a comparative measure between similarly rated devices. 20V rated Schottky diodes are recommended for outputs less than 15V, while 30V rated Schottky diodes are recommended for outputs greater than 15V. The switching period is divided between ON and OFF time intervals. 1 = TON + TOFF FS The maximum duty cycle can be estimated from the relationship for a continuous mode boost converter. Maximum duty cycle (DMAX) is the duty cycle at minimum input voltage (VIN(MIN)). DMAX = IAVG(OFF) = Duty cycle is defined as the ON time divided by the total switching interval. D= TON TON + TOFF = TON ⋅ FS IOUT 1 - DMAX The following curves show the VF characteristics for different Schottky diodes (100°C case). The VF of the Schottky diode can be estimated from the average current during the off time. 10000 B340LA MBR0530T 1000 ZHCS350 100 BAT42W 10 0.00 During the ON time, the N-channel power MOSFET is conducting and storing energy in the boost inductor. During the OFF time, the N-channel power MOSFET is not conducting. Stored energy is transferred from the input battery and boost inductor to the output load through the output diode. VOUT - VIN(MIN) VOUT The average diode current during the OFF time can be estimated. Forward Current (mA) Selecting the Schottky Diode 0.10 0.20 0.30 0.40 0.50 0.60 0.70 Forward Voltage (V) The average diode current is equal to the output current. IAVG(TOT) = IOUT The average output current multiplied by the forward diode voltage determines the loss of the output diode. PLOSS(DIODE) = IAVG(TOT) · VF = IOUT · VF For continuous LED currents, the diode junction temperature can be estimated. TJ(DIODE) = TAMB + θJA · PLOSS(DIODE) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 17 DATA SHEET AAT1231 Step-Up DC/DC Converters for White LED Backlight Applications Manufacturer Part Number Rated Forward Current (A) Diodes, Inc. Diodes, Inc. ON Semi Zetex Central Semi B340LA BAT42W MBR0530T ZHCS350 CMDSH2-3 3 0.2 0.5 0.35 0.2 Non-Repetitive Peak Surge Current (A) Rated Voltage (V) Thermal Resistance (qJA, °C/W) Case 70.0 4.0 5.5 4.2 1.0 40 30 30 40 30 25 500 206 330 500 SMA SOD-123 SOD-123 SOD-523 SOD-323 Table 4: Typical Surface Mount Schottky Rectifiers for Various Output Levels. The AAT1231 and the AAT1231-1 controllers utilize hysteretic control and the switching frequency varies with output load and input voltage. The value of the inductor determines the maximum switching frequency of the boost converter. Increased output inductance decreases the switching frequency, resulting in higher peak currents and increased output voltage ripple. To maintain 2MHz maximum switching frequency and stable operation, an output inductor sized from 1.5µH to 2.7µH is recommended. A better estimate of DMAX is possible once VF is known. DMAX = (VOUT + VF - VIN(MIN)) (VOUT + VF) Where VF is the Schottky diode forward voltage. If not known, it can be estimated at 0.5V. 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 completed to ensure that the inductor does not saturate or exhibit excessive temperature rise. 18 Switching Frequency (MHz) Selecting the Boost Inductor The output inductor (L) is selected to avoid saturation at minimum input voltage, maximum output load conditions. Peak current may be estimated using the following equation, assuming continuous conduction mode. Worst-case peak current occurs at minimum input voltage (maximum duty cycle) and maximum load. Switching frequency (FS) can be estimated from the curves and assumes a 2.2µH inductor. 2.0 VIN = 3.0V VOUT = 18V 1.8 VIN = 3.0V VOUT = 15V 1.6 VIN = 3.6V VOUT = 18V VIN = 3.6V VOUT = 15V 1.4 1.2 1.0 0.8 0.6 VIN = 2.7V VOUT = 18V 0.4 40 VIN = 2.7V VOUT = 15V 50 60 70 80 90 100 Output Current (mA) Switching Frequency (MHz) Output diode junction temperature should be maintained below 110ºC, but may vary depending on application and/or system guidelines. The diode qJA can be minimized with additional PCB area on the cathode. PCB heat-sinking the anode may degrade EMI performance. The reverse leakage current of the rectifier must be considered to maintain low quiescent (input) current and high efficiency under light load. The rectifier reverse current increases dramatically at elevated temperatures. 2.0 1.8 VIN = 3.0V VOUT = 12V 1.6 VIN = 3.0V VOUT = 10V VIN = 3.6V VOUT = 12V VIN = 3.6V VOUT = 10V 1.4 1.2 1.0 0.8 VIN = 2.7V VOUT = 10V 0.6 VIN = 2.7V VOUT = 12V 0.4 40 50 60 70 80 90 Output Current (mA) IPEAK = IOUT D · VIN(MIN) + MAX (1 - DMAX) (2 · FS · L) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 100 DATA SHEET AAT1231 Step-Up DC/DC Converters for White LED Backlight Applications At light load and low output voltage, the controller reduces the operating frequency to maintain maximum operating efficiency. As a result, further reduction in output load does not reduce the peak current. Minimum peak current can be estimated from 0.5A to 0.75A. At high load and high output voltages, the switching frequency is somewhat diminished, resulting in higher IPEAK. Bench measurements are recommended to confirm actual IPEAK and ensure that the inductor does not saturate at maximum LED current and minimum input 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 manufacturer’s temperature rise, or thermal derating, guidelines. ing applied to the LIN node (non-switching) can improve the inductor’s thermal capability. PCB heatsinking may degrade EMI performance when applied to the SW node (switching) of the AAT1231/1231-1. Shielded inductors provide decreased EMI and may be required in noise sensitive applications. Unshielded chip inductors provide significant space savings at a reduced cost compared to shielded (wound and gapped) inductors. In general, chip-type inductors have increased winding resistance (DCR) when compared to shielded, wound varieties. Inductor Efficiency Considerations The efficiency for different inductors is shown in Figure 7 for six white LEDs in series. Smaller inductors yield increased DCR and reduced operating efficiency. 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. Efficiency (%) 80 77 Cooper SD3814-2R2 (77mΩ) Cooper SD3110-2R2 (161mΩ) 74 71 68 65 2 5 8 11 14 17 20 LED Current (mA) PLOSS(INDUCTOR) = IRMS2 · DCR To ensure high reliability, the inductor case temperature should not exceed 100ºC. In some cases, PCB heatsink- Manufacturer Sumida www.sumida.com Cooper Electronics www.cooperet.com Murata www.murata.com Taiyo Yuden www.t-yuden.com Figure 10: AAT1231/1231-1 Efficiency for Different Inductor Types (VIN = 3.6V; Six White LEDs in Series). Inductance (µH) Maximum DC ISAT Current (mA) DCR (mW) Size (mm) LxWxH Type CDRH2D11-2R2 2.2 780 78 3.2x3.2x1.2 Shielded SD3814-2R2 SD3110-2R2 LQH3NPN2R2NG0 LQM2HPN2R2MG0 NR3010T-2R2M 2.2 2.2 2.2 2.2 2.2 1900 910 1250 1300 1100 77 161 164 80 95 4.0x4.0x1.4 3.1x3.1x1.0 3.0x3.0x1.0 2.5x2.0x1.0 3.0x3.0x1.0 CBC2016T2R2M 2.2 750 200 2.0x1.6x1.6 CBC2518T2R2M 2.2 510 90 2.5x1.8x1.8 Shielded Shielded Chip Coil Shield Chip Coil Shield Shielded Chip Non-Shielded Shielded Part Number Table 5: Recommended Inductors for Various Output Levels (Select IPEAK < ISAT). Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 19 DATA SHEET AAT1231 Step-Up DC/DC Converters for White LED Backlight Applications Selecting the Boost Capacitors The high output ripple inherent in the boost converter necessitates 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 AAT1231/1231-1 boost regulator. MLC capacitors of type X7R or X5R are recommended to ensure good capacitance stability over the full operating temperature range. The output capacitor is sized to maintain the output load without significant voltage droop (DVOUT) during the power switch ON interval, when the output diode is not conducting. A ceramic output capacitor from 2.2µF to 4.7µF is recommended (see Table 5). Typically, 25V rated capacitors are required for the 24V maximum boost output. Ceramic capacitors sized as small as 0805 are available which meet these requirements. MLC capacitors exhibit significant capacitance reduction with applied voltage. Output ripple measurements should confirm that output voltage droop and operating stability are acceptable. Voltage derating can minimize this factor, but results may vary with package size and among specific manufacturers. Output capacitor size can be estimated at a switching frequency (FS) of 500kHz (worst case). COUT = IOUT · DMAX FS · ∆VOUT To maintain stable operation at full load, the output capacitor should be sized to maintain DVOUT between 100mV and 200mV. 20 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 AAT1231/1231-1 boost converter is shown in Figures 10 and 11. The following PCB layout guidelines should be considered: 1. Minimize the distance from Capacitor C1 and C2 negative terminal to the PGND pins. This is especially true with output capacitor C2, which conducts high ripple current from the output diode back to the PGND pins. 2. Minimize the distance between L1 to DS1 and switching pin SW; minimize the size of the PCB area connected to the SW pin. 3. Maintain a ground plane and connect to the IC PGND pin(s) as well as the GND terminals of C1 and C2. 4. Consider additional PCB area on DS1 cathode to maximize heatsinking capability. This may be necessary when using a diode with a high VF and/or thermal resistance. 5. To avoid problems at startup, add a 10kW resistor between the VIN, VP and EN/SET pins (R4). This is critical in applications requiring immunity from input noise during “hot plug” events, e.g. when plugged into an active USB port. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 DATA SHEET AAT1231 Step-Up DC/DC Converters for White LED Backlight Applications Manufacturer Part Number Value (µF) Voltage Rating Temp Co Case Size Murata Murata Murata Murata Murata GRM188R60J225KE19 GRM188R61A225KE34 GRM219R61E225KA12 GRM21BR71E225KA73L GRM21BR61E475KA12 2.2 2.2 2.2 2.2 4.7 6.3 10 25 25 25 X5R X5R X5R X7R X5R 0603 0603 0805 0805 0805 Table 6: Recommended Ceramic Capacitors. Figure 11: AAT1231/1231-1 Evaluation Board Top Side Layout (with six LEDs and microcontroller). Figure 12: AAT1231/1231-1 Evaluation Board Bottom Side Layout (with six LEDs and microcontroller). Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 21 DATA SHEET AAT1231 Step-Up DC/DC Converters for White LED Backlight Applications VCC R7 1K R8 330 D7 RED Up 02 4 1 3 5 Down 02 4 1 3 5 Select 02 4 1 3 5 R6 1K R5 1K C3 1µF U2 1 SW3 2 3 4 SW2 S2Cwire Microcontroller VDD GP5 GP4 GP3 VSS GP0 GP1 GP2 8 7 6 R9 330 5 PIC12F675 D8 GREEN (Select indicator) SW1 R4 10K J2 DC- J3 DC+ DS1 Schottky L1 J1 1 2 3 2.2µH U1 VCC 1 JP1 2 3 4 C1 2.2µF 5 6 VIN EN SEL VP N/C SW LIN OVP FB GND PGND SW VOUT R2 226K 12 11 10 R3 12K 9 8 7 AAT1231/1231-1 R1 D6 D5 30.1 LED LED D1 LED D2 LED D3 LED AAT1231/1231-1 White LED Driver C2 2.2µF D4 LED U1 Skyworks AAT1231/1231-1 TSOPJW-12 package U2 PIC12F675 C1 GRM188R60J225KE01 C2 GRM21BR71E225KA73 C3 GRM216R61A105KA01 R1 30.1W, 1%, 1/4W; 0603 R2 226kW, 1%, 1/4W; 0603 R3 12.1kW, 1%, 1/4W; 0603 R4 10kW, 5%, 1/4W; 0603 R5, R6, R7 1KW, 5%, 1/4W; 0805 R8, R9 330W, 5%, 1/4W; 0805 JP1 0W, 5%; 0805 DS1 BAT42W L1 Cooper Electronics 2.2µH SD3814-2R2 D1-D6 White Hyper-Bright LED LW M673 D7 Red LED 1206 D8 Green LEC 1206 SW1 - SW3 SPST, 5mm J1, J2, J3 Conn. Header, 2mm Figure 13: AAT1231/1231-1 Evaluation Board Schematic (with six LEDs and microcontroller). 22 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 DATA SHEET AAT1231 Step-Up DC/DC Converters for White LED Backlight Applications Additional Applications Efficiency vs. LED Current L = 2.2µH C1 2.2µF LIN VIN SW 85 R2 187kΩ C2 2.2µF OVP R3 12kΩ ENSET SEL FB AGND VIN = 5V 84 AAT1231/ 1231-1 PGND (4 White LEDs; RBALLAST = 30.1Ω) Efficiency (%) Li-Ion VIN = 2.7V to 5.5V PVIN DS1 Up to 24V/ 50mA max 83 82 81 80 VIN = 4.2V VIN = 3.6V 79 78 30.1Ω 20mA 77 2 4 6 8 10 12 14 16 18 20 18 20 LED Current (mA) Figure 14: Four LEDs In Series Configuration. Efficiency vs. LED Current L = 2.2µH C1 2.2µF LIN VIN SW 83 82 AAT1231/ 1231-1 PGND (5 White LEDs; RBALLAST = 30.1Ω) R2 196kΩ C2 2.2µF Efficiency (%) Li-Ion VIN = 2.7V to 5.5V PVIN DS1 Up to 24V/ 50mA max OVP R3 12kΩ ENSET SEL AGND FB VIN = 5V 81 80 VIN = 4.2V 79 VIN = 3.6V 78 77 76 30.1Ω 20mA 75 2 4 6 8 10 12 14 16 LED Current (mA) Figure 15: Five LEDs In Series Configuration. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 23 DATA SHEET AAT1231 Step-Up DC/DC Converters for White LED Backlight Applications Efficiency vs. LED Current L = 2.2µH C1 2.2µF LIN VIN SW 81 80 VIN = 5V AAT1231/ 1231-1 R2 226kΩ OVP PGND (6 White LEDs; RBALLAST = 30.1Ω) Up to 24V/ 50mA max C2 2.2µF Efficiency (%) Li-Ion VIN = 2.7V to 5.5V PVIN DS1 R3 12kΩ EN/SET SEL FB AGND 30.1Ω 79 78 VIN = 4.2V 77 76 75 VIN = 3.6V 74 20mA 73 2 4 6 8 10 12 14 16 18 20 18 20 LED Current (mA) Figure 16: Six LEDs In Series Configuration. L = 2.2µH C1 2.2µF PVIN LIN VIN SW (12 White LEDs; RBALLAST = 30.1Ω) 84 83 AAT1231/ 1231-1 PGND Efficiency vs. LED Current Up to 24V/ 50mA max R2 226kΩ OVP C2 2.2µF R3 12kΩ EN/SET SEL AGND FB 30.1Ω VIN = 5V 82 Efficiency (%) Li-Ion VIN = 2.7V to 5.5V DS1 81 80 79 VIN = 4.2V 78 77 VIN = 3.6V 76 20mA 75 30.1Ω 20mA 74 2 4 6 8 10 12 14 16 LED Current (mA) Figure 17: Twelve LEDs In Series/Parallel Configuration. 24 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 DATA SHEET AAT1231 Step-Up DC/DC Converters for White LED Backlight Applications Multi-String White LED Configurations for Digital Photo Frame Applications (3S7P: 3 in series per string with 7 strings in parallel) is shown in Figure 18. A scalable schematic and PCB layout are illustrated in Figures 19 through 21. The AAT1231 and AAT1231-1 can be configured to light up as many as thirty-two white LEDs (WLED). This solution is scalable, flexible and good for digital photo frame applications with multi-strings of WLEDs. Efficiency vs. Total LED Current (21 White LEDs [3 in Series, 7 in Parallel]; RBALLAST = 4.32Ω) 90 The multi-string WLED configuration can be composed of many different parallel/series combinations, such as 6S2P, 6S3P, 5S4P, 5S5P, 5S6P, 4S7P, 4S8P, 3S9P, and 3S10P. ‘S’ is defined as the number of WLEDs in a series per string. ‘P’ is defined as the number of strings of WLEDs that are connected from the output voltage (VOUT) to the ballast resistor, or in parallel. To match the “brightness” of each separate string of WLEDs, each string must have the same number of WLEDs in them. The over-voltage protection (OVP) should also be adjusted according to the maximum feedback voltage plus the maximum forward voltage (VF) of each WLED multiplied by the total number of WLEDs in any of the parallel strings of WLEDs. The efficiency of one configuration VIN = 5V VIN = 4.2V VIN = 3.6V Efficiency (%) 85 80 75 70 65 20 40 60 80 100 140 160 Total LED Current (mA) Figure 18: Efficiency of the 3S7P Multi-String Configuration. VCC R8 1k R6 1k D12 RED R5 1k R4 1k 1 2 3 4 SW3 Up SW2 Down U2 VDD GP5 GP4 GP3 C3 1µF VSS GP0 GP1 GP2 8 7 6 5 R7 1k PIC12F675 D11 GREEN (Select indicator) SW1 Select R9 10k DC- DC+ J2 J1 1 VOUT 2 3 VCC JP1 C1 2.2µF J3 DS1 D Schottky L1 1 2 3 4 5 6 U1 VIN EN SEL VP N/C SW 2.2µH LIN OVP FB GND PGND SW JP2 R2 220K 12 11 10 9 8 7 R3 12.1K AAT1231 TSOPJW-12 R1 C2 2.2µF D1a LED D2a LED D3a LED D1b LED D2b LED D3b LED D4a LED D5a LED D6a LED D1c LED D2c LED D3c LED D4b LED D5b LED D6b LED D7a LED D8a LED D1d LED D2d LED D3d LED D4c LED D5c LED D6c LED D7b LED D8b LED D9a LED D10a LED D1e LED D2e LED D3e LED D4d LED D5d LED D6d LED D7c LED D8c LED D9b LED D10b LED D1f LED D2f LED D3f LED D4e LED D5e LED D6e LED D7d LED D8d LED D9c LED D10c LED C1 10V 0603 X5R 2.2µF GRM188R60J225KE01 C2 25V 0805 X7R 2.2µF GRM21BR71E225KA73 DS1 B340LA L1 2.2µH SD10-2R2, SD12-2R2, SD18-2R2 D1a-D10c White LED Figure 19: Multi-String WLED Application Schematic. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 25 DATA SHEET AAT1231 Step-Up DC/DC Converters for White LED Backlight Applications Figure 20: Top Layer of the Multi-String WLED Application. The ballast resistor R1 is calculated based on the total number of WLED strings and the total WLED current required from the AAT1231 or AAT1231-1. The value of the ballast resistor for each application is listed in Table 7. Figure 21: Bottom Layer of the Multi-String WLED Application. Number of Parallel Strings Total LED Current (A) R1 (Ω) 1% Tolerance 10 9 8 7 6 5 4 3 2 1 0.20 0.18 0.16 0.14 0.12 0.10 0.08 0.06 0.04 0.02 3.01 3.32 3.74 4.32 4.99 6.04 7.50 10.0 15.0 30.1 Table 7: Ballast Resistor Values for Multi-String WLED Applications. 26 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 DATA SHEET AAT1231 Step-Up DC/DC Converters for White LED Backlight Applications Ordering Information Package LED Current Control Marking1 Part Number (Tape and Reel)2 TSOPJW-12 TSOPJW-12 Increasing Decreasing SDXYY TUXYY AAT1231ITP-T1 AAT1231ITP-1-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 TSOPJW-12 2.85 ± 0.20 2.40 ± 0.10 0.20 + 0.10 - 0.05 0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC 7° NOM 0.055 ± 0.045 All dimensions in millimeters. 0.04 REF 0.15 ± 0.05 + 0.10 1.00 - 0.065 0.9625 ± 0.0375 3.00 ± 0.10 4° ± 4° 0.45 ± 0.15 0.010 2.75 ± 0.25 1. XYY = assembly and date code. 2. Sample stock is generally held on part numbers listed in BOLD. Copyright © 2012 Skyworks Solutions, Inc. All Rights Reserved. Information in this document is provided in connection with Skyworks Solutions, Inc. (“Skyworks”) products or services. These materials, including the information contained herein, are provided by Skyworks as a service to its customers and may be used for informational purposes only by the customer. Skyworks assumes no responsibility for errors or omissions in these materials or the information contained herein. Skyworks may change its documentation, products, services, specifications or product descriptions at any time, without notice. Skyworks makes no commitment to update the materials or information and shall have no responsibility whatsoever for conflicts, incompatibilities, or other difficulties arising from any future changes. No license, whether express, implied, by estoppel or otherwise, is granted to any intellectual property rights by this document. Skyworks assumes no liability for any materials, products or information provided hereunder, including the sale, distribution, reproduction or use of Skyworks products, information or materials, except as may be provided in Skyworks Terms and Conditions of Sale. THE MATERIALS, PRODUCTS AND INFORMATION ARE PROVIDED “AS IS” WITHOUT WARRANTY OF ANY KIND, WHETHER EXPRESS, IMPLIED, STATUTORY, OR OTHERWISE, INCLUDING FITNESS FOR A PARTICULAR PURPOSE OR USE, MERCHANTABILITY, PERFORMANCE, QUALITY OR NON-INFRINGEMENT OF ANY INTELLECTUAL PROPERTY RIGHT; ALL SUCH WARRANTIES ARE HEREBY EXPRESSLY DISCLAIMED. SKYWORKS DOES NOT WARRANT THE ACCURACY OR COMPLETENESS OF THE INFORMATION, TEXT, GRAPHICS OR OTHER ITEMS CONTAINED WITHIN THESE MATERIALS. SKYWORKS SHALL NOT BE LIABLE FOR ANY DAMAGES, INCLUDING BUT NOT LIMITED TO ANY SPECIAL, INDIRECT, INCIDENTAL, STATUTORY, OR CONSEQUENTIAL DAMAGES, INCLUDING WITHOUT LIMITATION, LOST REVENUES OR LOST PROFITS THAT MAY RESULT FROM THE USE OF THE MATERIALS OR INFORMATION, WHETHER OR NOT THE RECIPIENT OF MATERIALS HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. Skyworks products are not intended for use in medical, lifesaving or life-sustaining applications, or other equipment in which the failure of the Skyworks products could lead to personal injury, death, physical or environmental damage. Skyworks customers using or selling Skyworks products for use in such applications do so at their own risk and agree to fully indemnify Skyworks for any damages resulting from such improper use or sale. Customers are responsible for their products and applications using Skyworks products, which may deviate from published specifications as a result of design defects, errors, or operation of products outside of published parameters or design specifications. Customers should include design and operating safeguards to minimize these and other risks. Skyworks assumes no liability for applications assistance, customer product design, or damage to any equipment resulting from the use of Skyworks products outside of stated published specifications or parameters. Skyworks, the Skyworks symbol, and “Breakthrough Simplicity” are trademarks or registered trademarks of Skyworks Solutions, Inc., in the United States and other countries. Third-party brands and names are for identification purposes only, and are the property of their respective owners. Additional information, including relevant terms and conditions, posted at www.skyworksinc.com, are incorporated by reference. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012 27