RT8288AZSP

® RT8288A 4A, 21V 500kHz Synchronous Step-Down Converter General Description Features The RT8288A 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 Internal 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 Available in an SOP-8 (Exposed Pad) Package RoHS Compliant and Halogen Free Fault condition protection includes cycle-by-cycle current limiting and thermal shutdown. An internal soft-start minimizes external parts count and internal compensation circuitry. z z z z z z z The RT8288A requires a minimal number of readily available external components, providing a compact solution. Ordering Information RT8288A z z Applications z z Package Type SP : SOP-8 (Exposed Pad-Option 2) z z Lead Plating System Z : ECO (Ecological Element with Halogen Free and Pb free) Distributive Power Systems Battery Charger DSL Modems Pre-Regulator for Linear Regulators Pin Configurations Note : (TOP VIEW) Richtek products are : ` ` RoHS compliant and compatible with the current require- VIN ments of IPC/JEDEC J-STD-020. SW 2 SW 3 BOOT 4 Suitable for use in SnPb or Pb-free soldering processes. Marking Information 8 GND GND 7 VCC 6 FB 5 EN 9 SOP-8 (Exposed Pad) RT8288AZSP : Product Number RT8288A ZSPYMDNN YMDNN : Date Code Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS8288A-03 June 2012 is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT8288A Typical Application Circuit 1 VIN CIN 22µF Chip Enable 4 RT8288A SW 5 EN 8, 9 (Exposed Pad) VOUT (V) 5 3.3 2.5 1.8 1.5 1.2 1.05 BOOT VIN GND 2, 3 CBOOT 100nF L VOUT 6 FB RT VCC 7 R2 R1 COUT CC 0.1µF Table 1. Recommended Components Selection R1 (kΩ) R2 (kΩ) RT (kΩ) L (μH) 75 14.46 0 4.7 75 24.32 0 3.6 75 35.82 0 3.6 5 4.07 30 2 5 5.84 39 2 5 10.31 47 2 5 16.69 47 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 1 VIN 2, 3 SW 4 BOOT 5 EN 6 FB 7 VCC 8, GND 9 (Exposed Pad) Pin Function 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. 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. 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. 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. 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. Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS8288A-03 June 2012 RT8288A Function Block Diagram VIN 1.2V Shutdown Comparator + - 5k 1µA 3V + Regulator BOOT - EN Current Sense Amplifier - Ramp Generator Oscillator 500kHz + Lockout Comparator S Q + 1.7V PWM Comparator VCC Reference FB Error + Amplifier Driver R SW GND - 30pF 400k 1pF Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS8288A-03 June 2012 is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT8288A 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 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 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 1.333W 75°C/W 15°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 RDS(ON)1 -- 120 -- mΩ Lower Switch On Resistance Switch Leakage RDS(ON)2 ILEAK --- 40 0 -10 mΩ μA Current Limit Oscillator Frequency Short Circuit Frequency ILIMIT fSW VBOOT − VSW = 4.8V VFB = 0.75V VFB = 0V 5.9 425 -- 7 500 150 -575 -- A kHz kHz Maximum Duty Cycle DMAX VFB = 0.8V -- 90 -- % Minimum On Time tON -- 100 -- ns Feedback Voltage VFB 0.82 V Feedback Current IFB -- 10 50 nA Logic-High VIH 2 -- 5.5 Logic-Low VIL -- -- 0.4 VEN = 2V -- 1 -- VEN = 0V -- 0 -- EN Input Threshold Voltage Enable Current VEN = 0V, VSW = 0V or 12V 4.5V ≤ V IN ≤ 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. DS8288A-03 June 2012 RT8288A Parameter Symbol Under Voltage Lockout Threshold VUVLO Under Voltage Lockout Threshold Hysteresis ΔVUVLO Test Conditions VIN Rising VCC Regulator VCC Load Regulation ICC = 5mA Min Typ Max Unit 3.8 4 4.2 V -- 400 -- mV -- 5 -- V -- 5 -- % Soft-Start Period tSS -- 2 -- ms 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.bsolute maximum rating conditions for extended periods may remain possibility to 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. DS8288A-03 June 2012 is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT8288A Typical Operating Characteristics Reference Voltage vs. Input Voltage Efficiency vs. Output Current 0.830 100 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 0.790 0 0 0.5 1 1.5 2 2.5 3 3.5 4 4 6 8 10 14 16 18 20 22 Input Voltage (V) Output Current (A) Reference Voltage vs. Temperature Output Voltage vs. Output Current 0.84 1.240 0.83 1.235 0.82 1.230 Output Voltage (V) Reference Voltage (V) 12 0.81 0.80 0.79 0.78 1.225 1.220 1.215 1.210 0.77 1.205 0.76 1.200 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. DS8288A-03 June 2012 RT8288A Current Limit vs. Temperature Current Limit vs. Input Voltage 11 12 10 Current Limit (A) Current Limit (A) 10 8 6 4 9 8 7 6 5 2 4 VIN = 12V, VOUT = 1.22V 3 0 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) VSW (10V/Div) VSW (10V/Div) IL (2A/Div) IL (2A/Div) VIN = 12V, IOUT = 1A Time (1μs/Div) Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS8288A-03 June 2012 125 VIN = 12V, IOUT = 4A Time (1μs/Div) is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT8288A Power Off from VIN Power On from VIN VIN (10V/Div) VIN (10V/Div) VOUT (1V/Div) VOUT (1V/Div) IL (5A/Div) IL (5A/Div) VIN = 12V, VOUT = 1.22V, IOUT = 4A VIN = 12V, VOUT = 1.22V, IOUT = 4A Time (5ms/Div) Time (50ms/Div) Power On from EN Power Off from EN VEN (5V/Div) IL (5A/Div) VEN (5V/Div) IL (5A/Div) VSW (10V/Div) VSW (10V/Div) VOUT (1V/Div) VOUT (1V/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 Time (50μs/Div) is a registered trademark of Richtek Technology Corporation. DS8288A-03 June 2012 RT8288A 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. Output Voltage Setting The output voltage is set by an external resistive divider according to the following equation : VOUT = VFB ⎛⎜ 1+ R1 ⎞⎟ ⎝ R2 ⎠ 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 RT8288A R2 GND the converter starts up. Soft-Start automatically begins once the chip is enabled. During soft-start, the internal soft-start capacitor becomes charged and generates a linear ramping up voltage across the capacitor. This voltage clamps the voltage at the internal reference, causing the duty pulse width to increase slowly and in turn reduce the output surge current. Finally, the internal 1V reference takes over the loop control once the internal ramping-up voltage becomes higher than 1V. The typical soft-start time for this IC is set at 2ms. Under Voltage Lockout Threshold 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. Figure 1. Output Voltage Setting Chip Enable Operation 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 RT8288A 100nF SW Figure 2. External Bootstrap Diode Soft-Start The IC contains an internal soft-start function to prevent large inrush current and output voltage overshoot when Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS8288A-03 June 2012 The EN pin is the chip enable input. Pulling the EN pin low (2V,