RT8287AZQW

® RT8287A 4A, 21V 500kHz Synchronous Step-Down Converter General Description Features The RT8287A is a synchronous step-down regulator with an internal power MOSFET. It achieves 4A of continuous output current over a wide input supply range with excellent load and line regulation. Current mode operation provides fast transient response and eases loop stabilization. z 4A Output Current z Adjustable Soft-Start 120mΩ Ω/40mΩ Ω Internal Power MOSFET Switch Internal Compensation Minimizes External Parts Count Fixed 500kHz Frequency Thermal Shutdown Protection Cycle-by-Cycle Over Current Protection Wide 4.5V to 21V Operating Input Range Adjustable Output from 0.808V to 15V Small 14-Lead WDFN Package RoHS Compliant and Halogen Free Fault condition protection includes cycle-by-cycle current limiting and thermal shutdown. An adjustable soft-start reduces the stress on the input source at startup. z z z z z z The RT8287A requires a minimal number of readily available external components, providing a compact solution. Ordering Information RT8287A z z z Applications z Package Type QW : WDFN-14L 4x3 (W-Type) Lead Plating System Z : ECO (Ecological Element with Halogen Free and Pb free) Note : z z z Distributive Power Systems Battery Charger DSL Modems Pre-Regulator for Linear Regulators Pin Configurations Richtek products are : ` RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. ` Suitable for use in SnPb or Pb-free soldering processes. Marking Information 01 : Product Code 01 YM DNN (TOP VIEW) VIN SW SW SW SW BOOT EN 14 13 1 2 3 4 5 6 7 GND 15 12 11 10 9 8 AGND GND GND VCC SS PGOOD FB WDFN-14L 4x3 YMDNN : Date Code Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS8287A-03 June 2012 is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT8287A Typical Application Circuit 1 VIN BOOT VIN CIN 22µF RT8287A SW 6 CBOOT 0.1µF 2, 3, 4, 5 L VOUT 1.2V/4A 9 PGOOD PGOOD R3 100k 11 VCC CC 0.1µF SS 10 R1 RT FB 8 COUT CSS 47nF R2 7 EN ON/OFF AGND GND 14 12, 13, 15 (Exposed Pad) Table 1. Recommended Components Selection VOUT (V) 5 3.3 2.5 1.8 1.5 1.2 1.05 R1 (kΩ) 75 75 75 5 5 5 5 R2 (kΩ) 14.46 24.32 35.82 4.07 5.84 10.31 16.69 RT (kΩ) 0 0 0 30 39 47 47 L (μH) 4.7 3.6 3.6 2 2 2 1.5 COUT (μF) 22 x 2 22 x 2 22 x 2 22 x 2 22 x 2 22 x 2 22 x 2 Function Pin Description Pin No. Pin Name Pin Function 1 VIN Supply Input. VIN supplies the power to the IC, as well as the step-down converter switches. Drive VIN with a 4.5V to 21V power source. Bypass VIN to GND with a suitably large capacitor to eliminate noise on the input to the IC. 2, 3, 4, 5 SW Switch Node. SW is the switching node that supplies power to the output. Connect the output LC filter from SW to the output load. Note that a capacitor is required from SW to BOOT to power the high side switch. 6 BOOT High Side Gate Drive Boost Input. BOOT supplies the drive for the high side N-MOSFET switch. Connect a 100nF or greater capacitor from SW to BOOT to power the high side switch. 7 EN 8 FB 9 PGOOD 10 SS Chip Enable (Active High). For automatic start-up, connect the EN pin to VIN with a 100kΩ resistor. Feedback Input. FB senses the output voltage to regulate said voltage. Drive FB with a resistive voltage divider from the output voltage. The feedback threshold is 0.808V. Power Good Output. The output of this pin is open-drain. Power good threshold is 90% low to high and 70% high to low of regulation value. Soft-Start Control Input. SS controls the soft-start period. Connect a capacitor from SS to GND to set the soft-start period. Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS8287A-03 June 2012 RT8287A Pin No. Pin Name 11 Pin Function Bias Supply. Decouple with 0.1μF to 0.22μF capacitor. The capacitance should be no more than 0.22μF. Ground. The exposed pad must be soldered to a large PCB and connected to GND for maximum power dissipation. VCC 12, 13 GND 15 (Exposed Pad) 14 AGND Analog Ground. Connect this pin to the system ground in PCB layout. Function Block Diagram VIN 1.2V EN Shutdown Comparator + Regulator - Current Sense Amplifier - Ramp Generator + VA VA 5k VC - 1µA 3V + Oscillator 500kHz BOOT S Lockout Comparator Q + 1.7V Driver R PWM Comparator VCC PGOOD + SW Reference Error + Amplifier + - - FB VC 30pF GND 400k 10µA SS Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS8287A-03 June 2012 1pF is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT8287A Absolute Maximum Ratings z z z z z z z z z z (Note 1) Supply Input Voltage, VIN ---------------------------------------------------------------------------------Switch Voltage, SW ----------------------------------------------------------------------------------------Boot Voltage, BOOT ----------------------------------------------------------------------------------------Other Pins -----------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C WDFN-14L 4x3 -----------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) WDFN-14L 4x3, θJA -----------------------------------------------------------------------------------------WDFN-14L 4x3, θJC -----------------------------------------------------------------------------------------Junction Temperature ---------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) -----------------------------------------------------------------Storage Temperature Range ------------------------------------------------------------------------------ESD Susceptibility (Note 3) HBM (Human Body Model) --------------------------------------------------------------------------------- Recommended Operating Conditions z z z −0.3V to 26V −0.3V to (VIN + 0.3V) (SW − 0.3V) to (SW + 6V) −0.3V to 6V 1.667W 60°C/W 7°C/W 150°C 260°C −65°C to 150°C 2kV (Note 4) Supply Input Voltage, VIN ---------------------------------------------------------------------------------- 4.5V to 21V Junction Temperature Range ------------------------------------------------------------------------------- −40°C to 125°C Ambient Temperature Range ------------------------------------------------------------------------------- −40°C to 85°C Electrical Characteristics (VIN = 12V, TA = 25°C unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max Unit Shutdown Current ISHDN VEN = 0 -- 0 1 μA Quiescent Current IQ VEN = 2V, VFB = 1V -- 0.7 -- mA Upper Switch On Resistance R DS(ON)1 -- 120 -- mΩ Lower Switch On Resistance R DS(ON)2 -- 40 -- mΩ Switch Leakage ILEAK VEN = 0V, VSW = 0V or 12V -- 0 10 μA Current Limit ILIMIT VBOOT − VSW = 4.8V 6.2 7 -- A Oscillator Frequency fSW VFB = 0.75V 425 500 575 kHz VFB = 0V -- 150 -- kHz VFB = 0.8V -- 90 -- % -- 100 -- ns 0.82 V nA Short Circuit Frequency Maximum Duty Cycle D MAX Minimum On Time tON Feedback Voltage VFB Feedback Current IFB -- 10 50 Logic-High VIH 2 -- 5.5 Logic-Low VIL -- -- 0.4 VEN = 2V -- 1 -- VEN = 0V -- 0 -- EN Threshold Voltage Enable Current 4.5V ≤ VIN ≤ 21V Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 0.796 0.808 V μA is a registered trademark of Richtek Technology Corporation. DS8287A-03 June 2012 RT8287A Parameter Symbol Min Typ Max Unit Power Good Rising Threshold -- 90 -- % Power Good Falling Threshold -- 70 -- % Power Good Delay -- 20 -- μs -- -- 0.4 V -- 10 -- nA 3.8 4 4.2 V -- 400 -- mV -- 5 -- V ICC = 5mA -- 5 -- % CSS = 47nF -- 4.7 -- ms Power Good Sink Current Capability Test Conditions Sink 4mA Power Good Leakage Current Under Voltage Lockout Threshold Under Voltage Lockout Threshold Hysteresis VUVLO VIN Rising ΔVUVLO VCC Regulator VCC Load Regulation Soft-Start Period tSS Thermal Shutdown TSD -- 150 -- °C Thermal Shutdown Hysteresis ΔTSD -- 30 -- °C Note 1. Stresses beyond those listed “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions may affect device reliability. Note 2. θJA is measured at TA = 25°C on a high effective thermal conductivity four-layer test board per JEDEC 51-7. θJC is measured at the exposed pad of the package. Note 3. Devices are ESD sensitive. Handling precaution is recommended. Note 4. The device is not guaranteed to function outside its operating conditions. Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS8287A-03 June 2012 is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT8287A Typical Operating Characteristics Efficiency vs. Output Current Reference Voltage vs. Input Voltage 100 0.830 90 VIN = 12V 0.825 Reference Voltage (V) Efficiency (%) 80 VIN = 21V 70 60 50 40 30 20 0.820 0.815 0.810 0.805 0.800 0.795 10 VOUT = 1.22V, IOUT = 0A to 4A 0 0.790 0 0.5 1 1.5 2 2.5 3 3.5 4 4 6 8 10 Output Current (A) 14 16 18 20 22 Input Voltage (V) Reference Voltage vs. Temperature Output Voltage vs. Output Current 0.84 1.226 0.83 1.224 0.82 1.222 Output Voltage (V) Reference Voltage (V) 12 0.81 0.80 0.79 0.78 1.220 1.218 1.216 1.214 0.77 1.212 0.76 1.210 VIN = 12V, VOUT = 1.22V, IOUT = 0A to 4A -50 -25 0 25 50 75 100 0 125 0.5 1 1.5 Temperature (°C) Switching Frequency vs. Input Voltage 2.5 3 3.5 4 Switching Frequency vs. Temperature 550 550 525 525 Switching Frequency (kHz)1 Switching Frequency (kHz)1 2 Output Current (A) 500 475 450 425 400 375 500 475 450 425 400 375 VOUT = 1.22V, IOUT = 0.8A VIN = 12V, VOUT = 1.22V, IOUT = 1A 350 350 4 6 8 10 12 14 16 18 20 Input Voltage (V) Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 22 -50 -25 0 25 50 75 100 125 Temperature (°C) is a registered trademark of Richtek Technology Corporation. DS8287A-03 June 2012 RT8287A Current Limit vs. Input Voltage Current Limit vs. Temperature 12 11 10 Current Limit (A) Current Limit (A) 10 8 6 4 9 8 7 6 5 2 4 VIN = 12V, VOUT = 1.22V 0 3 4 6 8 10 12 14 16 18 20 22 -50 -25 0 25 50 75 100 Input Voltage (V) Temperature (°C) Load Transient Response Load Transient Response VOUT (200mV/Div) VOUT (200mV/Div) IOUT (2A/Div) IOUT (2A/Div) VIN = 12V, VOUT = 1.22V, IOUT = 1A to 4A VIN = 12V, VOUT = 1.22V, IOUT = 0A to 4A Time (100μs/Div) Time (100μs/Div) Output Voltage Ripple Output Voltage Ripple VOUT (50mV/Div) VOUT (50mV/Div) VLX (10V/Div) VLX (10V/Div) IL (2A/Div) IL (2A/Div) VIN = 12V, IOUT = 1A Time (1μs/Div) Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS8287A-03 June 2012 125 VIN = 12V, IOUT = 4A Time (1μs/Div) is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT8287A Power Off from VIN Power On from VIN VIN (10V/Div) VIN (10V/Div) VOUT (1V/Div) VOUT (1V/Div) VPGOOD (5V/Div) IL (5A/Div) VPGOOD (5V/Div) IL (5A/Div) VIN = 12V, VOUT = 1.22V, IOUT = 4A Time (5ms/Div) Time (50ms/Div) Power On from EN Power Off from EN VEN (5V/Div) VEN (5V/Div) VOUT (1V/Div) VOUT (1V/Div) VPGOOD (5V/Div) IL (5A/Div) VPGOOD (5V/Div) IL (5A/Div) VIN = 12V, VOUT = 1.22V, IOUT = 4A Time (2.5ms/Div) Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 VIN = 12V, VOUT = 1.22V, IOUT = 4A VIN = 12V, VOUT = 1.22V, IOUT = 4A Time (50μs/Div) is a registered trademark of Richtek Technology Corporation. DS8287A-03 June 2012 RT8287A Application Information The IC is a synchronous high voltage buck converter that can support the input voltage range from 4.5V to 21V and the output current can be up to 4A. Soft-Start The output voltage is set by an external resistive divider according to the following equation : The IC contains an external soft-start clamp that gradually raises the output voltage. The soft-start timing is programmed by the external capacitor between SS pin and GND. The chip provides an internal 10μA charge current for the external capacitor. If 47nF capacitor is used to set the soft-start, the period will be 4.7ms (typ.). VOUT = VFB ⎛⎜ 1+ R1 ⎞⎟ ⎝ R2 ⎠ Under Voltage Lockout Threshold Output Voltage Setting where VFB is the feedback reference voltage 0.808V (typical). The resistive divider allows the FB pin to sense a fraction of the output voltage as shown in Figure 1. VOUT R1 FB RT8287A R2 GND Figure 1. Output Voltage Setting External Bootstrap Diode Connect a 100nF low ESR ceramic capacitor between the BOOT pin and SW pin as shown in Figure 2. This capacitor provides the gate driver voltage for the high side MOSFET. It is recommended to add an external bootstrap diode between an external 5V and BOOT pin for efficiency improvement when input voltage is lower than 5.5V or duty ratio is higher than 65% .The bootstrap diode can be a low cost one such as IN4148 or BAT54. The external 5V can be a 5V fixed input from system or a 5V output of the IC. Note that the external boot voltage must be lower than 5.5V. 5V BOOT RT8287A 100nF SW The IC includes an input Under Voltage Lockout Protection (UVLO). If the input voltage exceeds the UVLO rising threshold voltage (4.2V), the converter resets and prepares the PWM for operation. If the input voltage falls below the UVLO falling threshold voltage (3.8V) during normal operation, the device stops switching. The UVLO rising and falling threshold voltage includes a hysteresis to prevent noise caused reset. Chip Enable Operation The EN pin is the chip enable input. Pulling the EN pin low (2V,