RT8251 RICHTEK | Alldatasheet

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Technical content

Features

zzzzz Wide Operating Input Voltage Range : 4.75V to 24V zzzzz Adjustable Output Voltage Range : 0.8V to 15V zzzzz Output Current up to 5A zzzzz 25μμμμμA Low Shutdown Current zzzzz Internal Power MOSFET : 70m ΩΩΩΩΩ zzzzz High Efficiency up to 95% zzzzz 570kHz Fixed Switching Frequency zzzzz Stable with Low ESR Output Ceramic Capacitors zzzzz Thermal Shutdown Protection zzzzz Cycle-By-Cycle Over Current Protection zzzzz RoHS Compliant and Halogen Free Pin Configurations (TOP VIEW) WQFN-16L 3x3 13141516 8765 GND VIN VIN VIN SW SW BOOT SW FB EN COMP SS VIN VIN SW SW GND SOP-8 (Exposed Pad) COMP BOOT VIN SW GND SS EN FB GND 4 5 RT8251 Lead Plating System G : Green (Halogen Free and Pb Free) Package Type QW : WQFN-16L 3x3 (W-Type) SP : SOP-8 (Exposed Pad-Option 1)

DS8251-04 February 2013 www.richtek.com ©Copyright 2013 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Pin No. WQFN-16L 3x3 SOP-8 (Exposed Pad) Pin Name Pin Function 1, 2, 3, 15, 16 2 VIN Power Input. VIN supplies the power to the IC, as well as the step-down converter switches. Connect VIN with a 4.75V to 24V power source. Connect VIN to GND with a capacitor that the capacitance is large enough to eliminate noise on the input to the IC. 17 (Exposed Pad) 9 (Exposed Pad) GND Ground. This pin is the voltage reference for the regulated output voltage. For this reason, care must be taken in its layout. This node should be placed outside of the D1 to C IN ground path to prevent switching current spikes from inducing voltage noise into the part. The exposed pad must be soldered to a large PCB and connected to GND for maximum power dissipation. 5 5 FB Feedback Input. An external resistor divider from the output to GND, tapped to the FB pin, sets the output voltage. 6 6 COMP Compensation Node. This node is the output of the transconductance error amplifier and the input to the current comparator. Frequency compensation is done at this node by connecting a series R-C to ground. 7 7 EN 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. 8 8 SS Soft-Start Control Input. SS controls the soft start period. Connect a capacitor ( ≧10nF) from SS to GND to set the soft-start period. A 10nF capacitor sets the Soft-Start period to 1ms. 9 1 BOOT Bootstrap. This capacitor C BOOT is needed to drive the power switch’s gate above the supply voltage. It is connected between the SW and BS pins to form a floating supply across the power switch driver. The voltage across C BOOT is about 5V and is supplied by the internal +5V supply when the SW pin voltage is low. 10, 11, 12, 13, 14 3 SW Power Switching Output. 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. Functional Pin Description

DS8251-04 February 2013www.richtek.com ©Copyright 2013 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Absolute Maximum Ratings (Note 1) z Power Dissipation, PD @ TA = 25°C z Package Thermal Resistance (Note 2) z ESD Susceptibility (Note 3) Recommended Operating Conditions (Note 4) Function Block Diagram VA+ UV Comparator Oscillator 570kHz Foldback Control 0.4V Internal Regulator 1.1V 1µA Shutdown Comparator Current Sense Amplifier BOOT VIN GND SW FB EN COMP 10k VA VCC VCC Slope Comp Current Comparator SS Logic - EA0.8V Gm = 820µA/V 10µA VCC

DS8251-04 February 2013 www.richtek.com ©Copyright 2013 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Parameter Symbol Test Conditions Min Typ Max Unit Feedback Reference Voltage V FB 4.75V ≦ VIN ≦ 24V 0.784 0.8 0.816 V High-Side Switch-On Resistance R DS(ON)1 -- 70 -- m Ω Low-Side Switch-On Resistance R DS(ON)2 -- 15 -- Ω High-Side Switch Leakage V EN = 0V, VSW = 0V -- -- 10 μA Current Limit I LIM Duty = 85%; V BOOT−SW = 4.8V -- 6.8 -- A Current Sense Transconductance G CS Output Current to V COMP -- 4.6 -- A/V Error Amplifier Tansconductance gm ΔIC = ±10μA -- 920 -- μA/V Oscillator Frequency f SW 420 570 720 kHz Short Circuit Oscillation Frequency V FB = 0V -- 185 -- kHz Maximum Duty Cycle D MAX V FB = 0.7V -- 85 -- % Minimum On-Time t ON -- 100 -- ns UVLO Threshold Rising -- 4.1 -- V UVLO Threshold Hysteresis -- 200 -- mV Logic Low V IL -- -- 0.4 EN Input Voltage Logic High V IH 1.4 -- 5.5 V Enable Pull Up Current V EN = 0V -- 1 -- μA Shutdown Current I SHDN V EN = 0V -- 25 -- μA Quiescent Current I Q V EN = 2V, VFB = 1V -- 0.8 1 mA Soft-Start Current I SS V SS = 0V -- 10 -- μA Soft-Start Period C SS = 10nF -- 1 -- ms Thermal Shutdown T SD -- 150 -- °C

Electrical Characteristics

(VIN = 12V, TA = 25°C unless otherwise specified) 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. θ JA is measured at T A = 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.

DS8251-04 February 2013www.richtek.com ©Copyright 2013 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Typical Operating Characteristics Output Voltag Deviation vs. Load Current -1.5 -0.5 0.5 1.5 0.001 0.01 0.1 1 10 Load Current (A) Output Voltage Deviation (%) 1 VOUT = 3.3V VIN = 24V VIN = 12V VIN = 5V Reference Voltage vs. Temperature 0.786 0.791 0.796 0.801 0.806 0.811 0.816 -50 -25 0 25 50 75 100 125 Temperature (°C) Reference Voltage (V) VIN = 12V Output Voltage Deviation vs. Input Voltage -1.5 -0.5 0.5 1.5 4 6.5 9 11.5 14 16.5 19 21.5 24 Input Voltage (V) Output Voltage Deviation (%) 1 VOUT = 3.3V IOUT = 5A IOUT = 3A IOUT = 0A Efficiency vs. Load Current 100 Load Current (A) Efficiency (%) VIN = 12V VOUT = 3.3V VIN = 24V Efficiency vs. Load Current 100 Load Current (A) Efficiency(%) VOUT = 5V VIN = 12V VIN = 24V Quiescent Current vs. Temperature 0.2 0.4 0.6 0.8 1.2 -50 -25 0 25 50 75 100 125 Temperature (°C) Quiescent Current (mA ) VIN = 12V

DS8251-04 February 2013 www.richtek.com ©Copyright 2013 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Load Transient Response Time (100 μs/Div) IOUT (2A/Div) VOUT (200mV/Div) VIN = 12V, VOUT = 3.3V IOUT = 0A to 5A Load Transient Response Time (100 μs/Div) IOUT (2A/Div) VOUT (200mV/Div) VIN = 12V, VOUT = 3.3V IOUT = 2.5A to 5A Current Limit vs. Duty Cycle 5.7 6.3 6.9 7.5 8.1 8.7 9.3 0 1 02 03 04 05 06 07 08 09 0 1 0 0 Duty Cycle (%) Peak Current (A) Switching Frequency vs. Input Voltage 550 560 570 580 590 600 610 4 6.5 9 11.5 14 16.5 19 21.5 24 Input Voltage (V) Switcing Frequency (kHz) 1 VOUT = 3.3V, IOUT = 1A Switching Frequency vs. Temperature 510 530 550 570 590 610 630 -50 -25 0 25 50 75 100 125 Temperature (°C) Switching Frequenc (kHz) 1 11 VOUT = 3.3V, IOUT = 1A VIN = 12V VIN = 24V Output Ripple Time (1 μs/Div) ISW (2A/Div) VOUT (10mV/Div) VIN = 12V VOUT = 3.3V IOUT = 5A VSW (10V/Div)

DS8251-04 February 2013www.richtek.com ©Copyright 2013 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Power On from EN Time (250 μs/Div) VOUT (2V/Div) VEN (5V/Div) VIN = 12V, VOUT = 3.3V, IOUT = 5A Power Off from EN Time (25 μs/Div) VOUT (2V/Div) VEN (5V/Div) VIN = 12V, VOUT = 3.3V, IOUT = 5A

©Copyright 2013 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. more detail please refer to Table 4. trapezoidal current at the source of the high side MOSFET. deviations do not offer much relief. meet size or height requirements in the design. capacitor, please refer to table 3 for more detail. for COUT selection to ensure that the control loop is stable. response as described in a later section. capacitors are all available in surface mount packages. Special polymer capacitors offer very low ESR value. pass the surge test for use in switching power supplies. Table 2. Suggested Inductors for Typical

©Copyright 2013 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. ringing that would indicate a stability problem. refer to the section of Layout Consideration. Figure 5. Reference Circuit with Snubber and Enable Timing Control and temperature difference between junction to ambient. the junction to ambient thermal resistance.

©Copyright 2013 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Figure 9. PCB Layout Guide for WQFN Package \` Connect feedback network behind the output capacitors. behind the output capacitors. and Figure 10 for reference. as close as to the IC as possible. as close to the device as possible.

©Copyright 2013 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Figure 10. PCB Layout Guide for PSOP-8 Package components away from this trace. Table 3. Suggested Capacitors for CIN and COUT Table 4. Suggested Diode

DS8251-04 February 2013 www.richtek.com ©Copyright 2013 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Outline Dimension A D E L be SEE DETAIL A Dimensions In Millimeters Dimensions In Inches Symbol Min Max Min Max A 0.700 0.800 0.028 0.031 A1 0.000 0.050 0.000 0.002 A3 0.175 0.250 0.007 0.010 b 0.180 0.300 0.007 0.012 D 2.950 3.050 0.1 16 0.120 D2 1.300 1.750 0.051 0.069 E 2.950 3.050 0.1 16 0.120 E2 1.300 1.750 0.051 0.069 e 0.500 0.020 L 0.350 0.450 0.014 0.018 W-Type 16L QFN 3x3 Package Note : The configuration of the Pin #1 identifier is optional, but must be located within the zone indicated. DETAIL A Pin #1 ID and Tie Bar Mark Options 2 2

www.richtek.com DS8251-04 February 2013 Richtek Technology Corporation 5F, No. 20, Taiyuen Street, Chupei City Hsinchu, Taiwan, R.O.C. Tel: (8863)5526789 Richtek products are sold by description only. Richtek reserves the right to change the circuitry and/or specifications without notice at any time. Customers should obtain the latest relevant information and data sheets before placing orders and should verify that such information is current and complete. Richtek cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Richtek product. Information furnish ed by Richtek is believed to be accurate and reliable. However, no responsibility is assumed by Richtek or its subsidiaries for its use; nor for any infringeme nts of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of R ichtek or its subsidiaries. A BJ F H M C D I Y X EXPOSED THERMAL PAD (Bottom of Package) 8-Lead SOP (Exposed Pad) Plastic Package Dimensions In Millimeters Dimensions In Inches Symbol Min Max Min Max A 4.801 5.004 0.189 0.197 B 3.810 4.000 0.150 0.157 C 1.346 1.753 0.053 0.069 D 0.330 0.510 0.013 0.020 F 1.194 1.346 0.047 0.053 H 0.170 0.254 0.007 0.010 I 0.000 0.152 0.000 0.006 J 5.791 6.200 0.228 0.244 M 0.406 1.270 0.016 0.050 X 2.000 2.300 0.079 0.091 Option 1 Y 2.000 2.300 0.079 0.091 X 2.100 2.500 0.083 0.098 Option 2 Y 3.000 3.500 0.118 0.138