ACT4088 Rev 1, 14-Feb-11 28V, 1.5A, 1.4MHz Step-Down DC/DC Converter in SOT23-6 FEATURES GENERAL DESCRIPTION • • • • • • • • • • • The ACT4088 is a current-mode step-down DC/DC converter that supplies up to 1.5A into 5V from a 12V input. 1.4MHz switching frequency allows the use of tiny external components, and internal loop compensation provides simple, stable power supplies with a minimum of external components. Optimized for use with ceramic input and output capacitors, the ACT4088 provides a very compact 1.5A power supply for space constrained mobile and consumer applications. Wide 4.5V to 28V Input Voltage Range 1.5A Output Current (12VIN to 5VOUT) Output Adjustable Down to 0.81V 0.3Ω Internal Power MOSFET Up to 92% Efficiency Stable with Low ESR Ceramic Output Capacitors Fixed 1.4MHz Operating Frequency Internal Soft-Start Function The ACT4088 operates over a wide input voltage range and utilizes current-mode operation to provide excellent line and load transient response while requiring no external compensation components. Fault protection includes cycle-by-cycle current limiting, frequency fold-back, hiccup mode, and thermal shutdown. Internal soft-start provides a controlled startup with no overshoot, even at light loads. Over Current Protection with Hiccup-Mode Thermal Shutdown Available in a SOT23-6 Package APPLICATIONS • • • • • • TFT LCD Monitors The ACT4088 is available in a tiny SOT23-6 package and requires very few external components. Portable DVDs, Headphones, MP3 Players, etc. Car-Powered or Battery-Powered Equipment Set-Top Boxes Telecom Power Supplies DSL and Cable Modems and Routers TYPICAL APPLICATION CIRCUIT VIN 4.5V to 28V IN BST ACT4088 ON OFF SW VOUT EN FB G Innovative PowerTM -1- www.active-semi.com Copyright © 2011 Active-Semi, Inc. ACT4088 Rev 1, 14-Feb-11 ORDERING INFORMATION PART NUMBER TEMPERATURE RANGE PACKAGE PINS ACT4088US-T -40°C to 85°C SOT23-6 6 PACKING TOP MARK TAPE & REEL FRWJ PIN CONFIGURATION SW 1 IN 2 EN 3 ACT4088 6 BST 5 G 4 FB SOT23-6 PIN DESCRIPTIONS PIN NUMBER PIN NAME 1 SW 2 IN Power supply input. Bypass this pin with a 10µF ceramic capacitor to G, placed as close to the IC as possible. 3 EN Enable Input. EN is pulled up to 5V with a 2µA current, and contains a precise 1.24V logic threshold. Drive this pin to a logic-high or leave unconnected to enable the IC. Drive to a logic-low to disable the IC and enter micro-power shutdown mode. 4 FB Feedback Input. The voltage at this pin is regulated to 0.81V. Connect to the center point of a resistive voltage-divider between OUT and G to set the output voltage. 5 G Ground and Heat sink. Connect this pin to a large, uncovered PCB copper area for best heat dissipation. 6 BST Bootstrap. This pin acts as the power supply for the high-side switch’s gate driver. Connect a 22nF capacitor between this pin and SW. Innovative PowerTM PIN DESCRIPTION Switch Output. Connect this pin to the switching end of the inductor. -2- www.active-semi.com Copyright © 2011 Active-Semi, Inc. ACT4088 Rev 1, 14-Feb-11 ABSOLUTE MAXIMUM RATINGSc PARAMETER VALUE UNIT -0.3 to 32 V SW Voltage -1 to VIN + 1 V BST Voltage VSW - 0.3 to VSW + 7 V -0.3 to 6 V Internally Limited A Junction to Ambient Thermal Resistance (θJA) 220 °C/W Maximum Power Dissipation 0.5 W Operating Junction Temperature -40 to 150 °C Storage Temperature -55 to 150 °C 300 °C IN Supply Voltage EN, FB Voltage Continuous SW Current Lead Temperature (Soldering, 10 sec) c: Do not exceed these limits to prevent damage to the device. Exposure to absolute maximum rating conditions for long periods may affect device reliability. ELECTRICAL CHARACTERISTICS (VIN = 12V, TA = 25°C, unless otherwise specified.) PARAMETER Input Voltage Under Voltage Lockout Voltage SYMBOL VIN VUVLO TEST CONDITIONS VOUT = 3.3V, ILOAD = 0A to 1.5A Input Voltage Rising MIN 4.5 4 Under Voltage Lockout Hysteresis Feedback Voltage TYP 4.2 MAX UNIT 28 V 4.49 V 250 VFB 4.75V ≤ VIN ≤ 20V, VCOMP = 1.5V 0.79 Frequency Foldback Threshold 0.81 mV 0.83 V 250 mV High-side Switch On Resistance RONH 0.300 Ω Low-side Switch On Resistance RONH 15 Ω SW Leakage VEN = 0, VSW = 0V Current Limit ILTM Switching Frequency fSW Foldback Switching Frequency Maximum Duty Cycle DMAX 1 VIN = 12V, VOUT = 5V, or EN = G, SW = G 10 1.8 1.1 1.4 µA A 1.6 MHz VFB = 0V, or FB = G 467 kHz VFB = 0.6V 92 % 75 ns Minimum On-Time EN Threshold Voltage EN Rising EN Hysteresis EN Rising EN Internal Pull-up Current 1.12 1.24 1.36 V 100 mV 2 µA Supply Current in Shutdown VEN = 0V or EN = G 15 30 µA Supply Current in Operation VEN = 2V, VFB = 1.0V 1 2 mA Thermal Shutdown Temperature 160 °C Thermal Shutdown Hysteresis 10 °C Innovative PowerTM -3- www.active-semi.com Copyright © 2011 Active-Semi, Inc. ACT4088 Rev 1, 14-Feb-11 TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 2, VIN = 12V, L = 4.7µH, C1 = 10µF, C2 = 22µF, TA = +25°C, unless otherwise specified.) Efficiency vs. Load Current Efficiency (%) 85 VIN = 18V 75 VIN = 24V 65 55 1 VOUT = 3.3V 50 0.1 1 10 Load Current (A) Load Current (A) FB Voltage vs. Temperature Oscillator Frequency vs. Temperature Oscillator Frequency (MHz) 812 808 804 ACT4088-004 1.60 ACT4088-003 816 FB Voltage (mV) VIN = 18V VIN = 24V 65 10 820 1.50 1.40 1.30 1.20 800 -40 -20 0 20 40 60 80 100 120 -40 -20 0 20 60 40 80 100 Temperature (°C) Temperature (°C) Peak Current Limit vs. Duty Cycle Shutdown Current vs. Input Voltage 2.0 Quiescent Supply Current (µA) 2.5 1.5 1.0 0.5 0.0 0 20 40 60 80 100 25 20 S 15 ly upp nt rre Cu 10 EN Pull-up Current 5 0 0 Duty Cycle Innovative PowerTM 30 120 ACT4088-006 ACT4088-005 3.0 Peak Current Limit (A) 75 55 VOUT = 5V 50 0.1 VIN = 12V 85 Efficiency (%) VIN = 12V ACT4088-002 95 ACT4088-001 95 Efficiency vs. Load Current 4 8 12 16 20 24 28 Input Voltage (V) -4- www.active-semi.com Copyright © 2011 Active-Semi, Inc. ACT4088 Rev 1, 14-Feb-11 TYPICAL PERFORMANCE CHARACTERISTICS CONT’D (Circuit of Figure 2, VIN = 12V, L = 4.7µH, C1 = 10µF, C2 = 22µF, TA = +25°C, unless otherwise specified.) Load Transient Response ACT4088-008 CH1 ACT4088-007 ILOAD = 200mA to 800mA Load Transient Response ILOAD = 200mA to 1.5A CH1 CH2 CH2 CH1: VOUT, 50mV/div CH2: ILOAD, 500mA/div TIME: 100µs/div CH1: VOUT, 50mV/div CH2: ILOAD, 500mA/div TIME: 100µs/div Start-up Waveforms ACT4088-010 CH1 ACT4088-009 ILOAD = 0mA Start-up Waveforms ILOAD = 1A CH1 CH2 CH2 CH3 CH4 CH3 CH1: VOUT, 2V/div CH2: VSW, 10V/div CH3: IL, 1A/div TIME: 200µs/div CH1: VEN, 2V/div CH2: VOUT, 2V/div CH3: VSW, 10V/div CH4: IL, 1A/div TIME: 400µs/div Steady State Switching Waveforms ACT4088-012 ACT4088-011 ILOAD = 1A CH1 Hiccup Mode Switching Waveforms CH1 CH2 CH2 CH3 CH1: VOUT, 100mV/div, (AC COUPLED) CH2: IL, 1A/div TIME: 1ms/div CH1: VOUT, 50mV/div, (AC COUPLED) CH2: VSW, 10V/div CH3: IL, 500mA/div TIME: 400ns/div Innovative PowerTM -5- www.active-semi.com Copyright © 2011 Active-Semi, Inc. ACT4088 Rev 1, 14-Feb-11 FUNCTIONAL BLOCK DIAGRAM IN CSA REGULATOR & UVLO EN BST OSCILLATOR CONTROL SOFT-START PWM Comparator ILIM Comparator HICCUP Q1 DRIVER SW REFERENCE & THERMAL SHUTDOWN COMPENSATION EA FB G in setting the ACT4088's transient response and ensuring stability. For most applications, choosing RFB1 = 49.9kΩ provides good results. For applications with output voltages of 1.8V or lower, use a larger RFB1 value such as 80.6kΩ. Once RFB1 is chosen, use the following equation to choose RFB2: FUNCTIONAL DESCRIPTION The ACT4088 is a current-mode step-down DC/DC converter that provides excellent transient response with no extra external compensation components. This device contains an internal, low-resistance, high-voltage power MOSFET, and operates at a high 1.4MHz operating frequency to ensure a compact, high-efficiency design with excellent AC and DC performance. RFB2 = RFB1 (1) ⎛ VOUT ⎞ −1⎟ ⎜ 0 . 81 V ⎝ ⎠ Setting the Output Voltage Selecting the Inductor An external voltage divider is used to set the output voltage, as well as provide a known impedance from VOUT to FB for compensation purposes. Connect a 50kΩ resistor from the output to FB to ensure stable compensation, and select the bottom resistor to provide the desired regulation voltage. The ACT4088 was optimized for use with a 4.7µH inductor. When choosing an inductor, choose one with a DC resistance of less than 250mΩ and a DC current rating that is typically 30% higher than the maximum load current. During typical operation, the inductor maintains a continuous current to output load. The inductor current has a ripple that is dependent on the inductance value. Figure 1: Output Voltage Setting VOUT Higher inductance reduces the peak-to-peak ripple current. The trade off for high inductance value is the increase in inductor core size and series resistance, and a reduction in current handling capability. RFB1 ACT4088 FB RFB2 If efficiency at light loads (such as less than 100mA) is critical in the application, a larger inductor is recommended. The feedback resistor (RFB1) interacts with the internal compensation network, and plays an important Innovative PowerTM -6- www.active-semi.com Copyright © 2011 Active-Semi, Inc. ACT4088 Rev 1, 14-Feb-11 Rectifier Diode Shutdown Control Use a Schottky diode as the rectifier to conduct current when the High-Side Power Switch is off. The Schottky diode must have current rating higher than the maximum output current and the reverse voltage rating higher than the maximum input voltage (see Figure 2). The ACT4088 enable pin provides several features for adjusting and sequencing the power supply. An internal 2µA current source pull-up, and a precision 1.24V comparator with hysteresis. With these components, a user has the flexibility of using the EN pin as: Selecting the Input Capacitor 1) A digital on/off control by pulling down the EN current source with an external open-drain transistor. The voltage at EN is internally clamped to 6V. For best performance choose a ceramic type capacitor with X5R or X7R dielectrics due to their low ESR and small temperature coefficients. However, low ESR tantalum or electrolytic types may also be used, provided that the RMS ripple current rating is higher than 50% of the output current. For most applications, a 10µF capacitor is sufficient. The input capacitor should be placed close to the IN and G pins of the IC, with shortest possible traces. In the case of tantalum or electrolytic types, connect a small parallel 0.1µF ceramic capacitor right next to the IC. 2) A sequenced power supply by tying the EN pin through a resistor to the output of another power supply. The IC will be enabled when the voltage at EN exceeds 1.24V, or a resistor divider can be used to adjust the turn-on threshold. 3) An always-on converter by floating the EN pin or pulling EN to a desired voltage with a high value (1MΩ) external resistor. EN is internally clamped at 6V and will dissipate power if an external resistor attempts to pull EN above the 6V clamp voltage. Selecting the Output Capacitor A 22µF ceramic capacitor with X5R or X7R dielectric provides the best results over a wide range of applications. 4) Line UVLO. If desired, to achieve a UVLO voltage that is higher than the internal UVLO, an external resistor divider from VIN to EN to GND can be used to disable the ACT4088 until a higher input voltage is achieved. For example, it is not useful for a converter with 9V output to start up with a 4.2V input voltage, as the output cannot reach regulation. To enable the ACT4088 when the input voltage reaches 12V, a 9kΩ/1kΩ resistor divider from IN to GND can be connected to the EN pin. Both the precision 1.2V threshold and 80mV hysteresis are multiplied by the resistor ratio, providing a proportional 6.67% hysteresis for any startup threshold. For the example of a 12V enable threshold, the turn off threshold would be 11.2V. The output capacitor also needs to have low ESR to keep low output voltage ripple. The output ripple voltage is: VRIPPLE = IOUTMAX K RIPPLE RESR + VIN 2 8 × fSW LCOUT (2) where IOUTMAX is the maximum output current, KRIPPLE is the ripple factor (typically 20% to 30%), RESR resistance is the ESR of the output capacitor, fSW is the switching frequency, L is the inductor value, and COUT is the output capacitance. In the case of ceramic output capacitors, RESR is very small and does not contribute to the ripple. In the case of tantalum or electrolytic type, the ripple is dominated by RESR multiplied by the ripple current. In that case, the output capacitor is chosen to have sufficiently low due to ESR, typically choose a capacitor with less than 50mΩ ESR. 5) Power supply sequencing. By connecting a small capacitor from EN to GND, the 2µA current source and 1.24V threshold can provide a stable and predictable delay between startup of multiple power supplies. For example, a startup delay of roughly 10mS is provided using 150nF, and roughly 20mS by using 330nF. The EN current source is active anytime an input supply is applied, so disabling the IC or resetting the delay requires an external open-drain pull-down device to reset the capacitor and hold the EN pin low for shutdown. External Bootstrap Diode An external bootstrap diode (D2 in Figure 2) is recommended if the input voltage is less than 5.5V or if there is a 5V system rail available. This diode helps strengthen gate drive at lower input voltages, resulting in lower on-resistance and higher efficiency. Low cost diodes, such as 1N4148 or BAT54, are suitable for this application. Innovative PowerTM -7- www.active-semi.com Copyright © 2011 Active-Semi, Inc. ACT4088 Rev 1, 14-Feb-11 Soft-Start Frequency Foldback The ACT4088 provides an internal soft-start feature, which ramps the output voltage and output current are from 0 to the full value over 0.5 milliseconds. This feature prevents output voltage overshoot at light loads as well as to prevent large inrush currents upon startup. The soft-start circuitry is internally reset anytime the IC is disabled using the EN pin, as well as if the IC reaches hiccup mode or thermal shutdown. In all of these cases, soft-start provides a smooth, controlled restart after the fault is removed. The voltage at FB is monitored by a comparator to detect an extreme output overload condition. If the voltage at the FB pin falls to below 0.3V, the internal oscillator slows to a decreased frequency of 467kHz, 33% of the nominal value. This prevents the inductor current from rising excessively during a dead-short condition, potentially resulting in inductor saturation. Figure 2: ACT4088 Typical 5V/1.5A Output Application Innovative PowerTM -8- www.active-semi.com Copyright © 2011 Active-Semi, Inc. ACT4088 Rev 1, 14-Feb-11 Figure 3: ACT4088 Optimized for Minimal External Components The ACT4088 with provides excellent AC and DC results across a wide range of external component combinations. The circuit of Figure 3 can be used to generate a 5V output from a 12V input utilizing a smaller (i.e. lower-cost) output capacitor while maintaining good performance. Figure 4: Figure 5: Circuit of Figure 3 (ILOAD = 150mA to 850mA) Circuit of Figure 3 (ILOAD = 1A) ACT4088-014 ACT4088-013 Circuit of Figure 3 ILOAD = 150mA to 850mA Circuit of Figure 3 ILOAD = 1A CH1 CH1 CH2 CH2 CH1: ILOAD, 500mA/div CH2: VOUT, 100mV/div (AC Coupled) TIME: 200µs/div Innovative PowerTM CH1: VSW, 10V/div CH2: VOUT, 20mV/div (AC Coupled) TIME: 400ns/div -9- www.active-semi.com Copyright © 2011 Active-Semi, Inc. ACT4088 Rev 1, 14-Feb-11 Hiccup Mode If the ACT4088 transitions from normal operation to a severe overload condition (the voltage at FB falls below 0.3V), the controller automatically enters "Hiccup Mode" to provide maximum protection to the system. In hiccup mode, the IC stops switching, clears the soft-start circuitry, then attempts to restart. If the overload condition has been removed, the IC will start up normally and continue regulating. In the case of a sustained overload, however, the IC will attempt to regulate for a period of time equal to 3x the soft-start period (1.5ms). If the overload condition persists until the end of this period, the IC will begin another hiccup cycle. This hiccup-mode control scheme minimizes power dissipation during severe overload conditions, and ensures that the ACT4088 responds quickly to instantaneous severe overload conditions while providing immunity to false hiccups that may occur with a heavily loaded output. Thermal Shutdown The ACT4088 automatically turns off when the IC junction temperature exceeds 160°C, and reenables when the IC junction temperature drops by 10°C (typ). PC Board Layout The high current paths at G, IN and SW should be placed very close to the device with short, direct and wide traces. The input capacitor needs to be as close as possible to the IN and G pins. The external feedback resistors should be placed next to the FB pin. Keep the switch node traces short and away from the feedback network and use shielded inductors. Innovative PowerTM - 10 - www.active-semi.com Copyright © 2011 Active-Semi, Inc. ACT4088 Rev 1, 14-Feb-11 PACKAGE OUTLINE SOT23-6 PACKAGE OUTLINE AND DIMENSIONS D θ b 0.2 SYMBOL DIMENSION IN INCHES MAX MIN MAX A - 1.450 - 0.057 A1 0.000 0.150 0.000 0.006 A2 0.900 1.300 0.035 0.051 b 0.300 0.500 0.012 0.020 c 0.080 0.220 0.003 0.009 L1 MIN L E E1 DIMENSION IN MILLIMETERS c e A A2 A1 e1 D 2.900 BSC 0.114 BSC E 1.600 BSC 0.063 BSC E1 2.800 BSC 0.110 BSC e 0.950 BSC 0.037 BSC e1 1.900 BSC 0.075 BSC L 0.300 0.600 0.012 0.024 θ 0° 8° 0° 8° Active-Semi, Inc. reserves the right to modify the circuitry or specifications without notice. Users should evaluate each product to make sure that it is suitable for their applications. Active-Semi products are not intended or authorized for use as critical components in life-support devices or systems. Active-Semi, Inc. does not assume any liability arising out of the use of any product or circuit described in this datasheet, nor does it convey any patent license. Active-Semi and its logo are trademarks of Active-Semi, Inc. For more information on this and other products, contact [email protected] or visit http://www.active-semi.com. ® is a registered trademark of Active-Semi. Innovative PowerTM - 11 - www.active-semi.com Copyright © 2011 Active-Semi, Inc.