RT8279GSP

RT8279 5A, 36V, 500kHz Step-Down Converter General Description Features The RT8279 is a step-down regulator with an internal power MOSFET. It achieves 5A 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 5A Output Current z Internal Soft-Start 110mΩ Ω Internal Power MOSFET Switch Internal Compensation Minimizes External Parts Count High Efficiency up to 90% 25μ μA Shutdown Mode Fixed 500kHz Frequency Thermal Shutdown Cycle-by-Cycle Over Current Protection Wide 5.5V to 36V Operating Input Range Adjustable Output Voltage from 1.222V to 26V Available In an SOP8 (Exposed Pad) Package RoHS Compliant and Halogen Free For protection, the RT8279 provides cycle-by-cycle current limiting and thermal shutdown protection. An adjustable soft-start reduces the stress on the input source at startup. In shutdown mode, the regulator draws only 25μA of supply current. z z z z z z z z The RT8279 requires a minimum number of readily available external components, providing a compact solution. The RT8279 is available in the SOP-8 (Exposed Pad) package. Ordering Information RT8279 z z z Applications z Package Type SP : SOP-8 (Exposed Pad-Option 1) z Lead Plating System G : Green (Halogen Free and Pb Free) z z Distributive Power Systems Battery Charger DSL Modems Pre-regulator for Linear Regulators Pin Configurations (TOP VIEW) Note : Richtek products are : ` ` BOOT RoHS compliant and compatible with the current require- NC 2 ments of IPC/JEDEC J-STD-020. NC 3 Suitable for use in SnPb or Pb-free soldering processes. FB 4 GND 9 8 SW 7 VIN 6 GND 5 EN SOP-8 (Exposed Pad) Marking Information RT8279GSP : Product Number RT8279 GSPYMDNN DS8279-01 YMDNN : Date Code December 2011 www.richtek.com 1 RT8279 Typical Application Circuit 7 VIN 5.5V to 36V CIN 4.7µF/ 50V x 2 Chip Enable VIN BOOT RT8279 5 EN 1 SW 8 D1 B550A Open = Automatic Startup 6, 9 (Exposed Pad) GND CBOOT 10nF L1 VOUT CFF R1 FB 4 COUT 22µF x 2 R2 Table 1. Recommended Component Selection R1 (kΩ) R2 (kΩ) CFF (pF) L (μH) 100 100 82 6.8 100 58.6 82 10 100 31.6 82 15 100 18 82 22 VOUT (V) 2.5 3.3 5 8 COUT (μF) 22 x 2 22 x 2 22 x 2 22 x 2 Functional Pin Description Pin No. Pin Name Pin Function BOOT High Side Gate Drive Boost Input. BOOT supplies the drive for the high side N-MOSFET switch. Connect a 10nF or greater capacitor from SW to BOOT to power the high side switch. 2, 3 NC No Internal Connection. 4 FB 5 EN Feedback Input. The feedback threshold is 1.222V. Enable Input. EN is a digital input that turns the regulator on or off. Drive EN higher than 1.4V to turn on the regulator, lower than 0.4V to turn it off. For automatic startup, leave EN unconnected. 1 6, 9 (Exposed Pad) GND Ground. The exposed pad must be soldered to a large PCB and connected to GND for maximum power dissipation. 7 VIN Power Input. A suitable large capacitor should be bypassed from VIN to GND to eliminate noise on the input to the IC. 8 SW Power Switching Output. Note that a capacitor is required from SW to BOOT to power the high side switch. www.richtek.com 2 DS8279-01 December 2011 RT8279 Function Block Diagram VIN Current Sense Amplifier - Ramp Generator + BOOT EN Regulator Oscillator 500kHz S Q + Reference FB 12k Error + Amplifier - 400k 30pF Driver R PWM Comparator SW Bootstrap Control GND 13pF DS8279-01 December 2011 www.richtek.com 3 RT8279 Absolute Maximum Ratings z z z z z z z z z z (Note 1) Supply Voltage, VIN -----------------------------------------------------------------------------------------Switching Voltage, SW ------------------------------------------------------------------------------------BOOT Voltage ------------------------------------------------------------------------------------------------The Other Pins -----------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C SOP-8 (Exposed Pad) -------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) SOP-8 (Exposed Pad), θJA --------------------------------------------------------------------------------SOP-8 (Exposed Pad), θJC -------------------------------------------------------------------------------Junction Temperature ---------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) -----------------------------------------------------------------Storage Temperature Range ------------------------------------------------------------------------------ESD Susceptibility (Note 3) HBM (Human Body Mode) --------------------------------------------------------------------------------MM (Machine Mode) ----------------------------------------------------------------------------------------- Recommended Operating Conditions z z z −0.3V to 40V −0.3V to VIN + 0.3V (VSW − 0.3V) to (VSW + 6V) −0.3V to 6V 1.333W 75°C/W 15°C/W 150°C 260°C −65°C to 150°C 2kV 200V (Note 4) Supply Voltage, VIN ------------------------------------------------------------------------------------------ 5.5V to 36V 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 Reference Voltage High Side Switch-On Resistance VREF RDS(ON)1 Low Side Switch-On Resistance RDS(ON)2 High Side Switch Leakage Current Limit Oscillator Frequency Short Circuit Frequency Maximum Duty Cycle Minimum On-Time Under Voltage Lockout Threshold Rising Under Voltage Lockout Threshold Hysteresis Logic-High EN Threshold Voltage Logic-Low Enable Pull Up Current Shutdown Current Quiescent Current Soft-Start Period Thermal Shutdown www.richtek.com 4 ILIM fOSC DMAX Test Conditions 5.5V ≤ VIN ≤ 36V VEN = 0V, VSW = 0V Duty = 90%, VBOOT−SW = 4.8V VFB = 0V VFB = 0.8V tON VIH VIL EN_hys = 350mV ISHDN IQ VEN = 0V VEN = 2V, VFB = 1.5V CSS = 0.1μF TSD Min Typ Max Unit 1.202 1.222 1.239 -110 160 V mΩ -- 10 15 Ω -6 425 -85 -7.5 500 150 90 10 9 575 -95 μA A kHz kHz % -- 100 150 ns 3.8 4.2 4.5 V -- 315 -- mV 1.4 --- --1 -0.4 -- μA --3 -- 25 0.6 5 150 45 1 8.2 -- μA mA ms °C DS8279-01 V December 2011 RT8279 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. DS8279-01 December 2011 www.richtek.com 5 RT8279 Typical Operating Characteristics Efficiency vs. Output Current Reference Voltage vs. Input Voltage 100 1.230 90 VIN = 12V VIN = 32V VIN = 36V 70 Reference Voltage (V) Efficiency (%) 80 60 50 40 30 20 10 VOUT = 5V 0 0 1 2 3 4 1.226 1.222 1.218 1.214 VOUT = 5V, IOUT = 0A 1.210 4 5 8 12 16 Output Current (A) 24 28 32 36 Output Voltage vs. Output Current 5.008 1.228 5.004 5.000 1.226 Output Voltage (V) Reference Voltage (V) Reference Voltage vs. Temperature 1.230 1.224 1.222 VIN = 12V VIN = 24V VIN = 36V 1.220 1.218 1.216 1.214 VIN = 36V VIN = 24V VIN = 12V 4.996 4.992 4.988 4.984 4.980 4.976 4.972 4.968 1.212 IOUT = 0A 1.210 -50 -25 0 25 50 75 100 4.964 VOUT = 5V 4.960 0 125 1 2 3 4 Frequency vs. Input Voltage Frequency vs. Temperature 540 530 530 520 520 Frequency (kHz) 540 510 500 490 480 470 510 500 490 480 VIN = 12V VIN = 24V VIN = 36V 470 460 460 450 450 VOUT = 5V, IOUT = 0A 440 4 8 12 16 20 24 Input Voltage (V) www.richtek.com 6 5 Output Current (A) Temperature (°C) Frequency (kHz) 20 Input Voltage (V) 28 32 VOUT = 5V 440 36 -50 -25 0 25 50 75 100 125 Temperature (°C) DS8279-01 December 2011 RT8279 Shutdown Current vs. Input Voltage 60 11 50 Shutdown Current (μA) Current Limit (A) Current Limit vs. Temperature 12 10 9 8 7 6 VIN = 12V 5 -50 -25 0 25 50 75 100 40 30 20 10 VEN = 0V 0 4 125 8 12 16 20 24 28 Temperature (°C) Input Voltage (V) Quiescent Current vs. Temperature Load Transient Response 32 36 1 Quiescent Current (mA) 0.9 VOUT (200mV/Div) 0.8 0.7 0.6 VIN = 36V VIN = 24V VIN = 12V 0.5 0.4 0.3 0.2 IOUT (2A/Div) 0.1 VIN = 12V, VOUT = 5V, IOUT = 0.2A to 5A 0 -50 -25 0 25 50 75 100 Time (100μs/Div) 125 Temperature (°C) Switching Load Transient Response VOUT (200mV/Div) VOUT (10mV/Div) VSW (10V/Div) IOUT (2A/Div) VIN = 12V, VOUT = 5V, IOUT = 2.5A to 5A Time (100μs/Div) DS8279-01 December 2011 IL (5A/Div) VIN = 12V, VOUT = 5V, IOUT = 5A Time (1μs/Div) www.richtek.com 7 RT8279 Power On from EN Power Off from EN VEN (5V/Div) VEN (5V/Div) VOUT (5V/Div) VOUT (5V/Div) IL (5A/Div) IL (5A/Div) VIN = 12V, VOUT = 5V, IOUT = 5A Time (2.5ms/Div) www.richtek.com 8 VIN = 12V, VOUT = 5V, IOUT = 5A Time (2.5ms/Div) DS8279-01 December 2011 RT8279 Application Information The RT8279 is an asynchronous high voltage buck converter that can support the input voltage range from 5.5V to 32V and the output current can be up to 5A. Output Voltage Setting The resistive divider allows the FB pin to sense the output voltage as shown in Figure 1. VOUT R1 FB RT8279 R2 GND Figure 1. Output Voltage Setting The output voltage is set by an external resistive divider according to the following equation : VOUT = VREF ⎛⎜ 1+ R1 ⎞⎟ ⎝ R2 ⎠ Where VREF is the reference voltage (1.222V typ.). Where R1 = 100kΩ. External Bootstrap Diode Connect a 10nF low ESR ceramic capacitor between the BOOT pin and SW pin. 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 RT8279. 5V BOOT RT8279 10nF SW Soft-Start The RT8279 contains an internal soft-start clamp that gradually raises the output voltage. The typical soft-start time is 5ms. Chip Enable Operation The EN pin is the chip enable input. Pull the EN pin low (1.4V,