RT7272BGSP

® RT7272B 3A, 36V, 500kHz Synchronous Step-Down Converter General Description Features The RT7272B is a high efficiency, current mode synchronous step-down DC/DC converter that can deliver up to 3A output current over a wide input voltage range from 4.5V to 36V. The device integrates a 150mΩ high side and a 80mΩ low side MOSFET to achieve high conversion efficiency up to 95%. The current mode control architecture supports fast transient response and simple compensation circuit.  4.5V to 36V Input Voltage Range  3A Output Current Internal N-MOSFETs Current Mode Control Fixed Frequency Operation : 500kHz Adjustable Output Voltage from 0.8V to 30V High Efficiency Up to 95% Stable with Low ESR Ceramic Output Capacitors Cycle-by-Cycle Current Limit Input Under Voltage Lockout Output Under Voltage Protection Thermal Shutdown Protection Adjustable Current Limit Power Saving Mode for High Efficiency at Light Load RoHS Compliant and Halogen Free A cycle-by-cycle current limit function provides protection against shorted output and an internal soft-start eliminates input current surge during start-up. The RT7272B provides complete protection functions such as input under voltage lockout, output under voltage protection, over current protection and thermal shutdown. The RT7272B is available in the thermal enhanced SOP-8 (Exposed Pad) package.              Applications Ordering Information  RT7272B  Package Type SP : SOP-8 (Exposed Pad-Option 2)   Lead Plating System G : Green (Halogen Free and Pb Free)  Note :  Richtek products are :    RoHS compliant and compatible with the current require-  ments of IPC/JEDEC J-STD-020.  Distributed Power Systems Pre-Regulator for Linear Regulators Notebook Computers Point of Load Regulator in Distributed Power System Digital Set-top Boxes Personal Digital Recorders Broadband Communications Flat Panel TVs and Monitors Vehicle Electronics Suitable for use in SnPb or Pb-free soldering processes. Simplified Application Circuit VIN BOOT VIN CIN RT7272B CB L SW VOUT R1 RLIM CC R C GND Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS7272B-05 June 2015 COUT FB RL R2 COMP is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT7272B Marking Information Pin Configurations (TOP VIEW) RT7272BGSP : Product Number 8 SW BOOT 2 EN 3 GND 4 GND RT7272B GSPYMDNN VIN 7 RLIM 6 COMP 5 FB 9 YMDNN : Date Code SOP-8 (Exposed Pad) Functional Pin Description Pin No. Pin Name 1 SW 2 BOOT 3 EN 4, 9 (Exposed Pad) Pin Function Switch Node Connect to external L-C filter. Bootstrap Supply for High Side Gate Drive. A 100nF or greater capacitor is recommended to connect from BOOT pin to SW pin. Enable Control Input. A logic-high enables the converter; a logic-low forces the device into shutdown mode. Ground. The exposed pad must be soldered to a large PCB and connected to GND for maximum thermal dissipation. Feedback Input. This pin is connected to the converter output. It is used to set the output of the converter to regulate to the desired value via an resistive divider. Compensation Node. COMP is used to compensate the regulation control loop. Connect a series RC network from COMP to GND. In some cases, an additional capacitor from COMP to GND is required. GND 5 FB 6 COMP 7 RLIM Current Limit Setting. Connect to a resistor to determine current limit. 8 VIN Power Input. The input voltage range is from 4.5V to 36V. Must bypass with a suitable large ceramic capacitor. Function Block Diagram VIN VCC Internal Regulator Oscillator Shutdown VA VCC Comparator 1.2V 0.4V Lockout Comparator - 5k EN 1.7V Slope Comp Foldback Control + - Current Sense Amplifier + - + UV Comparator RSENSE VA BOOT UV + S + R Current Comparator Q 150m Q 80m SW GND VCC 0.8V SS RLIM + +EA - FB Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 COMP is a registered trademark of Richtek Technology Corporation. DS7272B-05 June 2015 RT7272B Operation The RT7272B is a constant frequency, current mode synchronous step-down converter. In normal operation, the high side N-MOSFET is turned on when the S-R latch is set by the oscillator and is turned off when the current comparator resets the S-R latch. While the high side N-MOSFET is turned off, the low side N-MOSFET is turned on to conduct the inductor current until next cycle begins. Error Amplifier The error amplifier adjusts its output voltage by comparing the feedback signal (VFB) with the internal 0.8V reference. When the load current increases, it causes a drop in the feedback voltage relative to the reference. The error amplifier's output voltage then rises to allow higher inductor current to match the load current. Oscillator The internal oscillator runs at fixed frequency 500kHz. In short circuit condition, the frequency is reduced to 75kHz for low power consumption. Soft-Start (SS) An internal current source charges an internal capacitor to build a soft-start ramp voltage. The FB voltage will track the internal ramp voltage during soft-start interval. The typical soft-start time is 2ms. Current Setting The current limit of high side MOSFET is adjustable by an external resistor connected to the RLIM pin. The current limit range is from 2A to 6A. When the inductor current reaches the current limit threshold, the COMP voltage will be clamped to limit the inductor current. UV Comparator If the feedback voltage (VFB) is lower than 0.4V, the UV Comparator will go high to turn off the high side MOSFET. The output under voltage protection is designed to operate in Hiccup mode. When the UV condition is removed, the converter will resume switching. Thermal shutdown Internal Regulator The regulator provides low voltage power to supply the internal control circuits and the bootstrap power for high side gate driver. Enable The over temperature protection function will shut down the switching operation when the junction temperature exceeds 150°C. Once the junction temperature cools down by approximately 20°C, the converter will automatically resume switching. The converter is turned on when the EN pin is higher than 2V. When the EN pin is lower than 0.4V, the converter will enter shutdown mode and reduce the supply current to 0.5μA. Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS7272B-05 June 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT7272B Absolute Maximum Ratings (Note 1) −0.3V to 40V −0.3V to (VIN + 0.3V) −0.3V to 6V −0.3V to 40V Supply Input Voltage, VIN ----------------------------------------------------------------------------------------Switch Voltage, SW ----------------------------------------------------------------------------------------------- VBOOT − VSW --------------------------------------------------------------------------------------------------------- Other Pins Voltage ------------------------------------------------------------------------------------------------- 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 --------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------Junction Temperature ----------------------------------------------------------------------------------------------Storage Temperature Range -------------------------------------------------------------------------------------ESD Susceptibility (Note 3) HBM (Human Body Model) ---------------------------------------------------------------------------------------- Recommended Operating Conditions    2.041W 49°C/W 15°C/W 260°C 150°C −65°C to 150°C 2kV (Note 4) Supply Input Voltage, VIN ----------------------------------------------------------------------------------------- 4.5V to 36V Junction Temperature Range -------------------------------------------------------------------------------------- −40°C to 125°C Ambient Temperature Range -------------------------------------------------------------------------------------- −40°C to 85°C Electrical Characteristics (VIN = 12V, CIN = 20μF, TA = 25°C, unless otherwise specified) Parameter Symbol Shutdown Supply Current Test Conditions Min Typ Max Unit VEN = 0V -- 0.5 3 A -- 0.9 1.2 mA 0.788 0.8 0.812 V Quiescent Current IQ VEN = 3V, VFB = 0.9V Feedback Reference Voltage VREF 4.5V VIN 36V High Side Switch On-Resistance RDS(ON)1 -- 150 -- m Low Side Switch On-Resistance RDS(ON)2 -- 80 -- m -- 0 10 A 2 -- 6.3 A Min. Duty Cycle, RLIM = 57.6k 1.9 2.5 3.1 Min. Duty Cycle, RLIM = 84.5k 2.7 3.5 4.2 Min. Duty Cycle, RLIM = 137k 4.5 5.5 6.5 -- 1.5 -- High Side Switch Leakage Current VEN = 0V, VSW = 0V Upper Switch Current Limit Range UOC Upper Switch Current Limit UOC (Note 5) Lower Switch Current Limit From Drain to Source Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 A A is a registered trademark of Richtek Technology Corporation. DS7272B-05 June 2015 RT7272B Parameter Symbol Test Conditions Min Typ Max Unit 450 500 550 kHz Oscillation Frequency fOSC1 Short Circuit Oscillation Frequency fOSC2 VFB = 0V -- 75 -- kHz Maximum Duty Cycle DMAX VFB = 0.7V -- 90 -- % Minimum On-Time tON -- 100 -- ns Logic-High VIH 2 -- -- Logic-Low Input Under Voltage Lockout Threshold Input Under Voltage Lockout Hysteresis VIL -- -- 0.4 3.9 4.1 4.3 V VUVLO -- 250 -- mV Thermal Shutdown TSD -- 150 -- C Thermal Shutdown Hysteresis TSD -- 20 -- C COMP to Current Sense Transconductance GCS -- 4.7 -- A/V GEA -- 1000 -- A/V Load Regulation VLOAD -- -- 0.05 %/A Line Regulation VLINE -- -- 0.1 % EN Input Voltage VUVLO VIN Rising ICOMP = ±10A Error Amplifier Transconductance VIN = 4.5V to 36V V 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. Note 5. RLIM (kΩ) = [UOC x 24.14 x (1 + 0.024 x (UOC − 3.5)) − 1.3], where UOC is desired upper switch peak current limit value. Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS7272B-05 June 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT7272B Typical Application Circuit VIN 4.5V to 36V VIN RT7272B 2 BOOT 3 EN SW 1 8 CIN 10µF x 2 Enable RL 179k 4, 9 (Exposed Pad) GND L VOUT R1 7 RLIM RLIM CB 100nF FB 5 COMP 6 COUT CC RC R2 Table 1. Suggested Component Values VOUT (V) R1 (k) R2 (k) RC (k) L (H) CC (nF) COUT (F) 12 47 3.35 47 10 2.7 22 x 2 8 27 3 36 8.2 2.7 22 x 2 5 62 11.8 24 6.8 2.7 22 x 2 3.3 75 24 16 4.7 2.7 22 x 2 2.5 25.5 12 12 3.6 2.7 22 x 2 1.2 30 60 6.8 2.2 2.7 22 x 2 Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 is a registered trademark of Richtek Technology Corporation. DS7272B-05 June 2015 RT7272B Typical Operating Characteristics Efficiency vs. Output Current 100 90 90 80 80 70 70 Efficiency (%) Efficiency (%) Efficiency vs. Output Current 100 60 VIN = VIN = VIN = VIN = 50 40 30 4.5V 12V 24V 36V VIN = VIN = VIN = VIN = 60 50 4.5V 12V 24V 36V 40 30 20 20 10 10 VOUT = 3.3V VOUT = 3.3V 0 0 0.01 0 0.1 0.5 1 1.5 2 2.5 3 Output Current (A) Output Current (A) Reference Voltage vs. Input Voltage Reference vs. Temperature 0.810 0.810 Reference Voltage (V) Reference Voltage(V) 0.808 0.805 0.803 0.800 0.798 0.795 0.805 0.800 VIN = VIN = VIN = VIN = 0.795 4.5V 12V 24V 36V 0.793 VIN = 4.5V to 36V, VOUT = 3.3V, IOUT = 0.3A VOUT = 3.3V, IOUT = 0.3A 0.790 0.790 2 9.6 17.2 24.8 32.4 -50 40 -25 0 Input Voltage(V) Output Voltage vs. Output Current 3.37 495 Switching Frequency (kHz)1 500 Output Voltage (V) 3.36 3.35 VIN = VIN = VIN = VIN = 3.33 3.32 4.5V 12V 24V 36V 3.31 3.30 50 75 100 125 Switching Frequency vs. Input Voltage 3.38 3.34 25 Temperature (°C) VOUT = 3.3V, IOUT = 0.1A to 3A 3.29 490 485 480 475 470 465 460 455 VOUT = 3.3V, IOUT = 0.3A 450 0 0.5 1 1.5 2 2.5 Output Current (A) Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS7272B-05 June 2015 3 4 8 12 16 20 24 28 32 36 Input Voltage (V) is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT7272B Current Limit vs. Temperature 8 490 7 Current Limit (A) Switching Frequency (kHz)1 Switching Frequency vs. Temperature 500 480 470 VIN = VIN = VIN = VIN = 460 4.5V 12V 24V 36V 450 6 5 4 3 VOUT = 3.3V, IOUT = 0.3A 440 VIN = 12V 2 -50 -25 0 25 50 75 100 125 -50 0 25 50 75 100 Temperature (°C) Temperature (°C) Load Transient Response Load Transient Response VOUT (200mV/Div) VOUT (200mV/Div) IOUT (2A/Div) IOUT (2A/Div) VIN = 12V, VOUT = 3.3V, IOUT = 0.3A to 3A Time (250μs/Div) Time (250μs/Div) Switching Switching VOUT (5mV/Div) VSW (5V/Div) VSW (5V/Div) IL (1A/Div) IL (2A/Div) VIN = 12V, VOUT = 3.3V, IOUT = 1.5A Time (1μs/Div) Copyright © 2015 Richtek Technology Corporation. All rights reserved. 125 VIN = 12V, VOUT = 3.3V, IOUT = 1.5A to 3A VOUT (5mV/Div) www.richtek.com 8 -25 VIN = 12V, VOUT = 3.3V, IOUT = 3A Time (1μs/Div) is a registered trademark of Richtek Technology Corporation. DS7272B-05 June 2015 RT7272B Power On from EN Power Off from EN VEN (5V/Div) VIN (5V/Div) VOUT (2V/Div) VOUT (2V/Div) IOUT (2A/Div) IOUT (2A/Div) VIN = 12V, VOUT = 3.3V, IOUT = 3A Time (2.5ms/Div) Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS7272B-05 June 2015 VIN = 12V, VOUT = 3.3V, IOUT = 3A Time (2.5ms/Div) is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT7272B Application Information Output Voltage Setting Chip Enable Operation The resistive divider allows the FB pin to sense the output voltage as shown in Figure 1. The EN pin is the chip enable input. Pulling the EN pin low (2V,