AAT1239-1_0810

PRODUCT DATASHEET AAT1239-1 SwitchRegTM General Description The AAT1239-1 is a high frequency, high efficiency constant current boost converter capable of driving up to ten (10) series-connected white LEDs or 40V. It is an ideal power solutions for backlight applications with up to ten white LEDs in series. The input voltage is 2.7V to 5.5V for single-cell lithium-ion/polymer (Li-ion) based portable devices. The LED current is digitally controlled across a 6x operating range using AnalogicTech’s Simple Serial Control™ (S2Cwire™) interface. Programmability across 26 discrete current steps provides high resolution, low noise, flicker-free, constant LED outputs. In programming AAT1239 operation, LED brightness increases based on the data applied at the EN/SET pin. The SEL logic pin changes the feedback voltage between two programmable ranges. The AAT1239-1 features a 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 AAT1239-1 offers 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 AAT1239-1 is available in the Pb-free, thermallyenhanced 12-pin TSOPJW package. 40V Step-Up Converter for 4 to 10 White LEDs Features • Input Voltage Range: 2.7V to 5.5V • Maximum Continuous Output 40V @ 30mA • Drives up to 10 LEDs in Series ▪ Constant LED Current with 3.5% Accuracy Over Temperature and Input Voltage Range • Digital Control with S2Cwire Single Wire Interface ▪ 26 Discrete Steps ▪ No PWM Control Required ▪ No Additional Circuitry • Up to 85% 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 < > = 0.6V 1.4V 0.6V 1.4V 5V VIN = 5V 1.4 0.3 75 75 500 500 1 -1 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 www.analogictech.com 1239-1.2008.10.1.2 PRODUCT DATASHEET AAT1239-1 AAT1239-1 SwitchRegTM Typical Characteristics (10 White LEDs; RBALLAST = 30.1Ω) 80 78 78 76 40V Step-Up Converter for 4 to 10 White LEDs Efficiency vs. LED Current Efficiency vs. LED Current (9 White LEDs; RBALLAST = 30.1Ω) VIN = 5V Efficiency (%) 76 74 72 70 68 66 2 Efficiency (%) VIN = 5V 74 72 70 68 66 VIN = 4.2V VIN = 3.6V VIN = 4.2V 4 6 8 VIN = 3.6V 10 12 14 16 18 20 2 4 6 8 10 12 14 16 18 20 ILED (mA) ILED (mA) Shutdown Current vs. Input Voltage (EN = GND) Input Voltage (top) (V) Output Voltage (middle) (V) 1.0 (10 White LEDs; RBALLAST = 30.1Ω) Feedback Voltage (bottom) (V) 4.2V 3.6V 33.2 33 32.8 0.62 0.6 0.58 Line Transient Shutdown Current (µA) 0.8 0.6 0.4 0.2 0.0 2.7 3.1 3.5 3.9 4.3 4.7 25°C 85°C -40°C 5.1 5.5 Input Voltage (V) Time (50µs/div) Accuracy ILED vs. Input Voltage (VFB = 0.6V; RBALLAST = 30.1Ω) 2.0 1.5 1.5 Accuracy ILED vs. Temperature (VFB = 0.6V; RBALLAST = 30.1Ω) Accuracy ILED (%) 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 2.7 3.2 3.7 4.2 4.7 Accuracy ILED (%) -40°C 1.0 0.5 0.0 -0.5 -1.0 -1.5 -40 25°C 85°C 5.2 5.7 -15 10 35 60 85 Input Voltage (V) Temperature (°C) 1239-1.2008.10.1.2 www.analogictech.com 5 PRODUCT DATASHEET AAT1239-1 AAT1239-1 SwitchRegTM Typical Characteristics Soft Start (10 White LEDs; VFB = 0.6V) Feedback Voltage (middle) (V) Feedback Voltage (middle) (V) EnableVoltage (top) (V) Inductor Current (bottom) (A) 0.6 0.4 0.2 0 2 1 0 0V 3.3V 40V Step-Up Converter for 4 to 10 White LEDs Soft Start (10 White LEDs; VFB = 0.3V) EnableVoltage (top) (V) Inductor Current (bottom) (A) 3.3V 0V 0.4 0.2 0 2 1 0 0V Time (200µs/div) Time (200µs/div) Shutdown (10 White LEDs; VFB = 0.6V) EnableVoltage (top) (V) Feedback Voltage (middle) (V) EnableVoltage (top) (V) Feedback Voltage (middle) (V) Inductor Current (bottom) (A) 3.3V 0V 0.6 0.4 0.2 0 0.5 0.0 3.3V 0V 0.4 0.2 0 Shutdown (10 LEDs; VFB = 0.3V) Inductor Current (bottom) (A) 0.5 0 Time (100µs/div) Time (50µs/div) Output Ripple (10 White LEDs; VIN = 3.6V; COUT = 2.2µF; ILED = 13mA) VOUT (AC Coupled) (20mV/div) VSW (20V/div) IL (500mA/div) VOUT (AC Coupled) (20mV/div) VSW (20V/div) IL (500mA/div) Output Ripple (10 White LEDs; VIN = 3.6V; COUT = 2.2µF; ILED = 20mA) Time (200ns/div) Time (200ns/div) 6 www.analogictech.com 1239-1.2008.10.1.2 PRODUCT DATASHEET AAT1239-1 AAT1239-1 SwitchRegTM Typical Characteristics Transition of LED Current (10 White LEDs; SEL = Low; ILED = 3mA to 13mA) Output Voltage (top) (V) Output Voltage (top) (V) 34 40V Step-Up Converter for 4 to 10 White LEDs Transition of LED Current (10 White LEDs; SEL = Low; ILED = 13mA to 6mA) 34 Feedback Voltage (bottom) (V) Feedback Voltage (bottom) (V) 32 30 28 0.4 0.3 0.2 0.1 0.0 32 30 0.4 0.3 0.2 0.1 0.0 Time (50µs/div) Time (50µs/div) Input Disconnect Switch Resistance vs. Input Voltage 300 280 260 240 Low Side Switch On Resistance vs. Input Voltage 120°C 100°C RDS(ON)IN (mΩ) 240 220 200 180 160 140 2.7 3.1 3.5 3.9 100°C RDS(ON)L (mΩ) 260 120°C 220 200 180 160 140 120 100 4.3 4.7 5.1 5.5 80 2.7 25°C 85°C 85°C 25°C 3.1 3.5 3.9 4.3 4.7 5.1 5.5 Input Voltage (V) Input Voltage (V) EN/SET Latch Timeout vs. Input Voltage EN/SET Latch Timeout (µs) 350 300 EN/SET Off Timeout vs. Input Voltage EN/SET Off Timeout (µs) 300 250 200 250 200 150 100 50 2.7 -40°C -40°C 85°C 25°C 25°C 85°C 150 100 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 3.1 3.5 3.9 4.3 4.7 5.1 5.5 Input Voltage (V) Input Voltage (V) 1239-1.2008.10.1.2 www.analogictech.com 7 PRODUCT DATASHEET AAT1239-1 AAT1239-1 SwitchRegTM Typical Characteristics Enable High Threshold (VIH) vs. Input Voltage Enable High Threshold (VIH) (V) 1.2 1.1 1.0 0.9 0.8 0.7 0.6 2.7 40V Step-Up Converter for 4 to 10 White LEDs Enable Low Threshold (VIL) vs. Input Voltage Enable Low Threshold (VIL) (V) 1.2 1.1 1.0 0.9 0.8 0.7 0.6 0.5 0.4 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 25°C -40°C 85°C -40°C 25°C 85°C 3.1 3.5 3.9 4.3 4.7 5.1 5.5 Input Voltage (V) Input Voltage (V) 8 www.analogictech.com 1239-1.2008.10.1.2 PRODUCT DATASHEET AAT1239-1 AAT1239-1 SwitchRegTM Functional Block Diagram 40V Step-Up Converter for 4 to 10 White LEDs PVIN LIN VIN OVP EN/SET SW Control FB Reference Output Select SEL AGND PGND Functional Description The AAT1239-1 consists 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. Soft-start 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 the level of the feedback reference voltage which is programmed through the S2Cwire interface. The SEL pin selects one of two feedback voltage ranges. In the AAT1239-1, 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. 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 some applications requiring a short duration of boosting current applying a low-to-high transition on the AAT1239-1’s SEL pin, LED current can be programmed up to 3x. The step size is determined by the programmed voltage at the FB pin where the internal default setting is 1.5x in the AAT1239-1. Control Loop The AAT1239-1 provides 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 AAT1239-1 modulates the power MOSFET switching current to maintain the programmed FB voltage. This allows the FB voltage loop to directly program the 1239-1.2008.10.1.2 www.analogictech.com 9 PRODUCT DATASHEET AAT1239-1 SwitchRegTM 40V Step-Up Converter for 4 to 10 White LEDs 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 AAT1239-1 has 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 decreased (as in the AAT1239-1; see Table 2) relative to the default FB voltage. 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 AAT1239-1 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 increasing the peak inductor current, resulting in higher average current in the inductor and LED string(s). Alternatively, when the VFB is reduced, the controller responds by decreasing the peak inductor current, resulting in lower average current in the inductor and LED string(s). 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 AAT1239-1 provides 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 40V. Current Limit and Over-Temperature Protection 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. Thermal protection disables the AAT1239-1 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. Over-Voltage Protection Over-voltage protection prevents damage to the AAT1239-1 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 overvoltage 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. 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 Under-Voltage Lockout 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. 10 www.analogictech.com 1239-1.2008.10.1.2 PRODUCT DATASHEET AAT1239-1 SwitchRegTM Application Information Over-Voltage Protection 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 40V (VOUT(MAX)). The value of R3 should be selected from 10kΩ to 20kΩ to minimize losses without degrading noise immunity. 40V Step-Up Converter for 4 to 10 White LEDs Assume R3 = 12kΩ and VOUT(MAX) = 40V. Selecting 1% resistor for high accuracy, this results in R2 = 374kΩ (rounded to the nearest standard value). The minimum OVP threshold can be calculated: VOUT(OVP_MIN) = VOVP(MIN) · = 35.4V ⎛ R2 ⎞ +1 ⎝ R3 ⎠ 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. R2 = R3 · ⎛ VOUT(MAX) ⎞ -1 ⎝ VOVP ⎠ VOUT(MAX) < VOUT(OVP_MIN) In some cases, this may disallow configurations with high LED forward voltage (VFLED) and/or greater than ten series white LEDs. VFLED unit-to-unit tolerance can be as high as +15% of nominal for white LED devices. VOUT AAT1239-1 R2 OVP GND R3 COUT 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 Figure 1: Over-Voltage Protection Circuit. Over Voltage Protection Pin (top) (V) Inductor Current (bottom)(A) 1.238V 1.142V 40 30 4 2 0 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 ten series white LED string and VOVP = 40V. 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. Output Voltage (middle) (V) Time (4ms/div) Figure 2: Over-Voltage Protection Open Circuit Response (No LED). 1239-1.2008.10.1.2 www.analogictech.com 11 PRODUCT DATASHEET AAT1239-1 SwitchRegTM Over-Voltage Protection Cold Temperature Apply Self-Recovery 40V Step-Up Converter for 4 to 10 White LEDs 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): VOUT (5V/div) ILED (200mA/div) RBALLAST = Figure 3: Over-Voltage Protection Constant Voltage Operation (10 White LEDs; ILED = 20mA; R2 = 12kΩ; R3 = 374kΩ). While OVP is active, the maximum LED current programming error (ΔILED) is proportional to voltage error across an individual LED (ΔVFLED). VFB 0.6 = = 30Ω ≈ 30.1Ω ILED(MAX) 0.020 RBALLAST (Ω) Maximum ILED Current (mA) 30 25 20 15 10 5 SEL = High 20.0 24.3 30.1 40.2 60.4 121.0 SEL = Low 13.3 16.2 20.0 26.7 40.2 80.6 (N · VFLED(TYP) - VOUT(OVP_MIN) - VFB) ΔVFLED = N To minimize the ΔILED 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 45V under worstcase operating conditions. Table 1: Maximum LED Current and RBALLAST Resistor Values (1% Resistor Tolerance). Typical white LEDs are driven at maximum continuous currents of 15mA to 20mA. The maximum number 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. VSW(MAX) = VOVP(MAX) · ⎛ R3 ⎞ + 1 + VF + VRING ⎝ R2 ⎠ VOUT(OVP_MIN) = VOVP(TYP) · ⎛ R2 ⎞ +1 ⎝ R3 ⎠ VF = -Schottky Diode DS1 forward voltage at turn-OFF VRING = Voltage ring occurring at turn-OFF N= (VOUT(OVP_MIN) - VFB(MAX)) VFLED(MAX) LED Selection and Current Setting The AAT1239-1 is 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. The ballast resistor (RBALLAST) value can be calculated as follows: Figure 4 shows the schematic of using ten LEDs in series. Assume VFLED @ 20mA = 3.5V (typical) from LW M673 (OSRAM) datasheet. VOUT(OVP_MIN) = 1.2V · ⎛ 374kΩ ⎞ + 1 = 38.6V ⎝ 10.4kΩ ⎠ N= 38.6V - 0.6V 3.5V ≈ 10.9 Therefore, under these typical operating conditions, ten LEDs can be used in series. RBALLAST = VFB(MAX) ILED(MAX) 12 www.analogictech.com 1239-1.2008.10.1.2 PRODUCT DATASHEET AAT1239-1 SwitchRegTM 40V Step-Up Converter for 4 to 10 White LEDs DS1 L1 2.2μH D1 LED D6 LED JP1 1 2 3 VCC R4 10K U1 1 2 3 4 5 6 C1 2.2μF Enable JP2 1 2 3 VIN EN SEL VP N/C SW LIN OVP FB GND PGND SW 12 11 10 9 8 7 R2 374K R3 12K D2 LED D3 LED D4 LED D5 LED C2 2.2μF D7 LED D8 LED D9 LED D10 LED AAT1239-1 TSOP12JW R1 30.1 Select C1 10V 0603 X5R 2.2μF GRM188R60J225KE01D C2 50V 1206 X7R 2.2μF GRM31CR71H225KA88 L1 2.2μH SD3814-2R2 or SD3110-2R2 DS1 SS16L D1-D10 LW M673 White LED other alternatives: more stability at 40V: C2 50V 1206 X7R 4.7μF GRM31CR71H475K under 20V application: C2 25V 0805 X7R 2.2μF GRM21BR71E225KA73L Figure 4: AAT1239-1 White LED Boost Converter Schematic. LED Brightness Control The AAT1239-1 uses 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 AAT1239-1 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 20 15 10 Default SEL=HIGH SEL=LOW 5 0 1 4 7 10 13 16 S2Cwire Data Register Figure 5: Programming AAT1239-1 LED Current with RBALLAST = 30.1Ω. 1239-1.2008.10.1.2 www.analogictech.com 13 PRODUCT DATASHEET AAT1239-1 SwitchRegTM 40V Step-Up Converter for 4 to 10 White LEDs rising edges of the EN/SET input and decodes them into 16 individual states. Each state corresponds to a reference feedback voltage setting on the FB pin, as shown in Table 2. Alternatively, toggling the SEL logic pin from low to high implements stepped or pulsed LED currents by increasing the FB pin voltage. Figure 6 illustrates the SELECT pin scaling factor, defined as the LED current with SEL=HIGH divided by the LED current with SEL=LOW. In the AAT1239-1, the possible scaling factors are 3.0x to 1.5x with the internal default setting of 1.5x. 3. 5 S2Cwire Serial Interface Timing 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 AAT1239-1 is disabled. When the AAT1239-1 is disabled, the register is reset to its default value. In the AAT1239-1, the FB pin voltage is set to 0.3V if the EN/SET pin is subsequently pulled HIGH. Select Pin Scaling Factor (Low to High) 3. 0 2. 5 2. 0 (Default) 1. 5 1. 0 1 4 7 10 13 16 S2Cwire Data Register S2Cwire Feedback Voltage Programming The FB pin voltage is set to the default level at initial powerup. The AAT1239-1 is programmed through the S2Cwire interface. Table 2 illustrates FB pin voltage programming for the AAT1239-1. 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 of the AAT1239-1, 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. Figure 6: AAT1239-1 SEL Pin Scaling Factor: ILED (SEL = High) Divided by ILED (SEL = Low). S2Cwire Serial Interface AnalogicTech’s S2Cwire single wire serial interface is a proprietary high-speed single-wire interface available only from AnalogicTech. The S2Cwire interface records THI TLO T LAT TOFF EN/SET 1 2 n-1 n ≤ 16 Data Reg 0 n-1 0 Figure 7: AAT1239-1 S2Cwire Timing Diagram to Program the Output Voltage. 14 www.analogictech.com 1239-1.2008.10.1.2 PRODUCT DATASHEET AAT1239-1 SwitchRegTM Rising Clock Edges/Data Register 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 40V Step-Up Converter for 4 to 10 White LEDs SEL = Low Reference Voltage (V) 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 SEL = High Reference Voltage (V) 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 LED Current (mA); RBALLAST = 30.1Ω 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 LED Current (mA); RBALLAST = 30.1Ω 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 2: AAT1239-1 S2Cwire Reference Feedback Voltage Control Settings With RBALLAST = 30.1Ω (Assumes Nominal Values)*. Selecting the Schottky Diode To ensure minimum forward voltage drop and no recovery, high voltage Schottky diodes are considered the best choice for the AAT1239-1 boost converter. 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 (θJA) 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. 40V rated Schottky diodes are recommended for outputs less than 30V, while 60V rated Schottky diodes are recommended for outputs greater than 35V. The switching period is divided between ON and OFF time intervals. 1 = TON + TOFF FS 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. Duty cycle is defined as the ON time divided by the total switching interval. D= TON TON + TOFF = TON ⋅ FS *All table entries are preliminary and subject to change without notice. 1239-1.2008.10.1.2 www.analogictech.com 15 PRODUCT DATASHEET AAT1239-1 SwitchRegTM 40V Step-Up Converter for 4 to 10 White LEDs high efficiency under light load. The rectifier reverse current increases dramatically at elevated temperatures. 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)). Selecting the Boost Inductor The AAT1239-1 controller utilizes 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 and switching loss, but results 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. For higher efficiency in Li-ion battery applications (VIN from 3.0V to 4.2V) and stable operation, increasing the inductor size up to 10μH is recommended. Figure 15 and 16 show the special enhanced efficiency application. A better estimate of DMAX is possible once VF is known. V - VIN(MIN) DMAX = OUT VOUT 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. DMAX = (VOUT + VF - VIN(MIN)) (VOUT + VF) TJ(DIODE) = TAMB + θJA · PLOSS(DIODE) Output diode junction temperature should be maintained below 110ºC, but may vary depending on application and/or system guidelines. The diode θJA 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 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. Manufacturer Taiwan Semiconductor Co., Ltd. Diodes, Inc Zetex Part Number SS16L SS15L SS14L B340LA ZHCS350 Rated Forward Current (A) 1.1 3 0.35 Non-Repetitive Peak Surge Current (A) 30 30 30 70.0 4.2 Rated Voltage (V) 60 50 40 40 40 Thermal Resistance (θJA, °C/W) 45 45 45 25 330 Size (mm) (LxWxH) 3.8x1.9x1.43 3.8x1.9x1.43 3.8x1.9x1.43 5.59x2.92x2.30 1.7x0.9x0.8 Case Sub SMA Sub SMA Sub SMA SMA SOD523 Table 3: Typical Surface Mount Schottky Rectifiers for Various Output Levels. 16 www.analogictech.com 1239-1.2008.10.1.2 PRODUCT DATASHEET AAT1239-1 AAT1239-1 SwitchRegTM 40V Step-Up Converter for 4 to 10 White LEDs be compared against the manufacturer’s temperature rise, or thermal derating, guidelines. 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. IRMS = IPEAK 3 IPEAK = IOUT D · VIN(MIN) + MAX (1 - DMAX) (2 · FS · L) 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. 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 PLOSS(INDUCTOR) = IRMS2 · DCR To ensure high reliability, the inductor case temperature should not exceed 100ºC. In some cases, PCB heatsinking 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 AAT1239-1. 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. Manufacturer Sumida www.sumida.com Part Number CDRH2D14-2R2 CDRH2D14-4R7 CDRH4D22/HP-4R7 CDRH3D18-100NC SD3814-2R2 SD3110-2R2 SD3118-4R7 SD3118-100 NP03SB-2R0M NR3010T-2R2M NP03SB4R7 NP03SB100M Inductance (μH) 2.2 4.7 4.7 10 2.2 2.2 4.7 10 2 2.2 4.7 10 Maximum DC ISAT Current (mA) 1500 1000 2200 900 1900 910 1020 900 1900 1100 1200 800 DCR (mΩ) 75 135 66 164 77 161 162 295 32 95 47 100 Size (mm) LxWxH 3.2x3.2x1.55 3.2x3.2x1.55 5.0x5.0x2.4 4.0x4.0x2.0 4.0x4.0x1.0 3.1x3.1x1.0 3.1x3.1x1.8 3.1x3.1x1.8 4.0x4.0x1.8 3.0x3.0x1.0 4.0x4.0x1.8 4.0x4.0x1.8 Type Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Cooper Electronics www.cooperet.com Taiyo Yuden www.t-yuden.com Table 4: Recommended Inductors for Various Output Levels (Select IPEAK < ISAT). 1239-1.2008.10.1.2 www.analogictech.com 17 PRODUCT DATASHEET AAT1239-1 SwitchRegTM Inductor Efficiency Considerations The efficiency for different inductors is shown in Figure 8 for ten white LEDs in series. Smaller inductors yield increased DCR and reduced operating efficiency. 75 CDRH5D16F-2R2 (29mΩ) 40V Step-Up Converter for 4 to 10 White LEDs 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 (ΔVOUT) 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, 50V rated capacitors are required for the 40V maximum boost output. Ceramic capacitors sized as small as 0805 or 1206 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). Efficiency (%) 72 SD3814-2R2 (77mΩ) 69 66 63 2 5 8 11 14 17 20 LED Current (mA) Figure 8: AAT1239-1 Efficiency for Different Inductor Types (VIN = 3.6V; Ten White LEDs in Series). COUT = IOUT · DMAX FS · ΔVOUT 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 AAT1239-1 boost regulator. MLC capacitors of type X7R or X5R are To maintain stable operation at full load, the output capacitor should be sized to maintain ΔVOUT between 100mV and 200mV. The boost converter input current flows during both ON and OFF switching intervals. The input ripple current is less than the output ripple and, as a result, less input capacitance is required. Manufacturer Murata Murata Murata Murata Murata Part Number GRM188R60J225KE19 GRM188R61A225KE34 GRM21BR71E225KA73L GRM31CR71H225KA88 GRM31CR71H475K Value (μF) 2.2 2.2 2.2 2.2 4.7 Voltage Rating 6.3 10 25 50 50 Temp Co X5R X5R X7R X7R X7R Case Size 0603 0603 0805 1206 1206 Table 5: Recommended Ceramic Capacitors. 18 www.analogictech.com 1239-1.2008.10.1.2 PRODUCT DATASHEET AAT1239-1 AAT1239-1 SwitchRegTM 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 AAT1239-1 boost converter is shown in Figures 9 and 10. 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. 40V Step-Up Converter for 4 to 10 White LEDs 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 10kΩ 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. 2. Figure 9: AAT1239-1 Evaluation Board Top Side Layout (with ten LEDs and microcontroller). Figure 10: AAT1239-1 Evaluation Board Bottom Side Layout (with ten LEDs and microcontroller). 1239-1.2008.10.1.2 www.analogictech.com 19 PRODUCT DATASHEET AAT1239-1 AAT1239-1 SwitchRegTM 40V Step-Up Converter for 4 to 10 White LEDs VCC S2Cwire Microcontroller R8 330Ω R7 1k R6 1k R5 1k 1 2 U2 PIC12F675 C3 0.1μF VDD GP5 GP4 GP3 VSS GP0 GP1 GP2 8 7 6 5 S1 Select S2 Down S3 Up 3 4 D12 Red R9 330Ω D11 Green JP2 R4 10k JP3 DC- DC+ U1 AAT1239-1 L1 10μH 12 DS1 Schottky VOUT R2 374k R3 12k JP4 D1 WLED D2 WLED D3 WLED D4 WLED AAT1239-1 White LED Driver C2 2.2μF C 10μF VCC 123 JP1 1 2 VIN EN 3 SEL 4 LIN 11 OVP 10 FB GND 8 PGND SW 7 9 C1 4.7μF 5 6 VP N/C SW R1 30.1Ω D10 WLED D9 WLED D8 WLED D7 D6 WLED WLED D5 WLED Figure 11: AAT1239-1 Evaluation Board Schematic (with ten LEDs and microcontroller). 20 www.analogictech.com 1239-1.2008.10.1.2 PRODUCT DATASHEET AAT1239-1 AAT1239-1 SwitchRegTM Additional Applications Efficiency vs. LED Current L1 2.2μH DS1 Schottky R2 158k C2 2.2μF Up to 17V/ 30mA max D1 LED 40V Step-Up Converter for 4 to 10 White LEDs (4 White LEDs; RBALLAST = 30.1Ω) 84 83 82 PVIN Li-Ion VIN = 2.7V to 5.5V C1 2.2μF LIN VIN = 5V Efficiency (%) VIN SW AAT1239-1 OVP D2 LED D3 LED D4 LED R3 12k 81 80 79 78 77 76 75 74 2 4 6 8 10 12 14 16 18 20 PGND EN/SET SEL FB AGND R1 30.1Ω 20mA VIN = 4.2V VIN = 3.6V ILED (mA) Figure 12: Four LEDs In Series Configuration. Efficiency vs. LED Current L1 2.2μH DS1 Schottky R2 287k C2 2.2μF Up to 30V/ 30mA max D1 LED (8 White LEDs; RBALLAST = 30.1Ω) VIN = 5V 80 78 PVIN Li-Ion VIN = 2.7V to 5.5V C1 2.2μF LIN Efficiency (%) VIN SW AAT1239-1 OVP D2 LED D3 LED D4 LED D5 LED 76 74 72 70 68 66 2 4 6 8 10 12 14 16 18 20 R3 12k PGND EN/SET SEL FB AGND R1 30.1Ω 20mA D8 LED D7 LED D6 LED VIN = 4.2V VIN = 3.6V ILED (mA) Figure 13: Eight LEDs In Series Configuration. Efficiency vs. LED Current L1 2.2μH DS1 Schottky R2 324k C2 2.2μF Up to 34V/ 30mA max D1 LED (9 White LEDs; RBALLAST = 30.1Ω) 78 76 VIN = 5V PVIN Li-Ion VIN = 2.7V to 5.5V C1 2.2μF LIN VIN SW AAT1239-1 OVP Efficiency (%) D2 LED D3 LED D4 LED D5 LED R3 12k 74 72 70 68 66 PGND EN/SET SEL FB AGND R1 30.1Ω 20mA D9 LED D8 LED D7 LED D6 LED VIN = 4.2V VIN = 3.6V 2 4 6 8 10 12 14 16 18 20 ILED (mA) Figure 14: Nine LEDs In Series Configuration. 1239-1.2008.10.1.2 www.analogictech.com 21 PRODUCT DATASHEET AAT1239-1 AAT1239-1 SwitchRegTM L1 10μH 40V Step-Up Converter for 4 to 10 White LEDs 90.0 DS1 R2 374kΩ C2 2.2μF D1 D2 D3 D4 D5 D6 87.5 PVIN Li-Ion VIN = 3.0V to 4.2V C1 4.7μF LIN SW Efficiency (%) 85.0 82.5 80.0 77.5 75.0 72.5 70.0 2 4 6 8 10 12 14 16 18 20 VIN AAT1239-1 R3 12kΩ OVP PGND EN/SET SEL C1 10V 0805 X5R 4.7μF GRM219R61A475KE19 C2 50V 1206 X7R 2.2μF GRM31CR71H225KA88 L1 10μH CDRH3D18-100NC DS1 SS16L FB D10 D9 D8 D7 AGND R1 30.1Ω 20mA VIN = 3.0V VIN = 3.6V VIN = 4.2V IOUT (mA) Figure 15: Enhanced Efficiency Configuration for Li-ion Battery Ten WLEDs Series-Connected Application. L1 4.7μH 85.0 DS1 82.5 D2 D3 D4 D5 D12 D13 D14 D15 D16 D17 D18 D19 D20 Li-Ion VIN=3.0V to 4.2V C1 4.7μF VIN SW AAT1239 -1 OVP R3 12kΩ C2 2.2μF Efficiency (%) PVIN LIN R2 374kΩ D1 D11 80.0 77.5 75.0 72.5 70.0 67.5 65.0 5 10 15 20 25 30 35 40 PGND EN/SET SEL FB AGND R1 15Ω 40mA D6 D7 D8 VIN = 3.0V VIN = 3.6V VIN = 4.2V C1 10V 0805 X5R 4.7μF GRM219R61A475KE19 C2 50V 1206 X7R 2.2μF GRM31CR71H225KA88 L1 4.7μH CDRH4D22/HP-4R7 DS1 SS16L D9 D10 IOUT (mA) Figure 16: Enhanced Efficiency Configuration for Li-ion Battery, Two Branch, Ten WLEDs Series-Connected Application. 22 www.analogictech.com 1239-1.2008.10.1.2 PRODUCT DATASHEET AAT1239-1 AAT1239-1 SwitchRegTM Ordering Information Package TSOPJW-12 40V Step-Up Converter for 4 to 10 White LEDs Marking1 ZLXYY Part Number (Tape and Reel)2 AAT1239ITP-1-T1 All AnalogicTech products are offered in Pb-free packaging. The term “Pb-free” means semiconductor products that are in compliance with current RoHS standards, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. For more information, please visit our website at http://www.analogictech.com/about/quality.aspx. Package Information TSOPJW-12 0.10 0.20 + 0.05 - 2.40 ± 0.10 0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC 2.85 ± 0.20 7° NOM 3.00 ± 0.10 0.9625 ± 0.0375 + 0.10 1.00 - 0.065 0.04 REF 0.15 ± 0.05 4° ± 4° 0.010 0.055 ± 0.045 0.45 ± 0.15 2.75 ± 0.25 All dimensions in millimeters. 1. XYY = assembly and date code. 2. Sample stock is generally held on part numbers listed in BOLD. Advanced Analogic Technologies, Inc. 3230 Scott Boulevard, Santa Clara, CA 95054 Phone (408) 737-4600 Fax (408) 737-4611 © Advanced Analogic Technologies, Inc. AnalogicTech cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an AnalogicTech product. No circuit patent licenses, copyrights, mask work rights, or other intellectual property rights are implied. AnalogicTech reserves the right to make changes to their products or specifications or to discontinue any product or service without notice. Except as provided in AnalogicTech’s terms and conditions of sale, AnalogicTech assumes no liability whatsoever, and AnalogicTech disclaims any express or implied warranty relating to the sale and/or use of AnalogicTech products including liability or warranties relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right. In order to minimize risks associated with the customer’s applications, adequate design and operating safeguards must be provided by the customer to minimize inherent or procedural hazards. Testing and other quality control techniques are utilized to the extent AnalogicTech deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily performed. AnalogicTech and the AnalogicTech logo are trademarks of Advanced Analogic Technologies Incorporated. All other brand and product names appearing in this document are registered trademarks or trademarks of their respective holders. 1239-1.2008.10.1.2 www.analogictech.com 23