RT2805A

RT2805A RICHTEK | Alldatasheet

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Technical content

Features

zzzzz Wide Operating Input Range 5.5V to 36V zzzzz Adjustable Output Voltage from 1.222V to 26V zzzzz High Efficiency up to 90% zzzzz Internal Compensation Minimizes External Parts Count zzzzz Internal Soft-Start zzzzz 110mΩΩΩΩΩ Internal Power MOSFET Switch zzzzz 25μμμμμA Shutdown Mode zzzzz Fixed 500kHz Frequency zzzzz Thermal Shutdown zzzzz Cycle-by-Cycle Current Limit zzzzz Available In an SOP8 (Exposed Pad) Package zzzzz RoHS Compliant and Halogen Free VIN EN GND BOOT FB SW VOUT Chip Enable VIN RT2805A CBOOT COUT CIN Marking Information RT2805AGSP : Product Number YMDNN : Date CodeRT2805A GSPYMDNN Simplified Application Circuit Package Type SP : SOP-8 (Exposed Pad-Option 2) RT2805A Lead Plating System G : Green (Halogen Free and Pb Free)

DS2805A-00 November 2012www.richtek.com ©Copyright 2012 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Functional Pin Description Function Block Diagram Pin No. Pin Name Pin Function 1 BOOT Bootstrap Input for High Side Gate Driver. Connect a 10nF or greater capacitor from SW to BOOT to power the high side switch. 2, 3 NC No Internal Connection. 4 FB Feedback Input. The feedback threshold is 1.222V. 5 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. 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 connected from the VIN to GND to eliminate noise on the input to the IC. 8 SW Switch Node. Note that a capacitor is required from SW to BOOT to power the high side switch. Pin Configurations (TOP VIEW) SOP-8 (Exposed Pad) SWBOOT NC FB NC EN VIN GND 4 5 GND S Q R Driver Bootstrap Control Current Sense Amplifier Current Comparator Oscillator 500kHz Ramp Generator Regulator Reference 12k Error Amplifier 30pF400k 13pF SW BOOT FB EN VIN GND

DS2805A-00 November 2012 www.richtek.com ©Copyright 2012 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Operation The RT2805A is a constant frequency, current mode asynchronous 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 N-MOSFET is turned off, the inductor current conducts through the external diode. Error Amplifier The error amplifier adjusts its output voltage by comparing the feedback signal (V FB) with the internal 1.222V 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 150kHz for low power consumption. 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 converter is turned on when the EN pin is higher than 1.4V and turned off when the EN pin is lower than 0.4V. When the EN pin is open, it will be pulled up to logic-high by 1μA current internally. 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 5ms. Thermal Shutdown 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 30 °C, the converter will automatically resume switching.

DS2805A-00 November 2012www.richtek.com ©Copyright 2012 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)

Electrical Characteristics

Parameter Symbol Test Conditions Min Typ Max Unit TA = 25°C 1.202 1.222 1.239 Reference Voltage V REF IOUT = 0A to 5A 1.196 1.222 1.245 V High Side Switch-On Resistance R DS(ON)1 Bias Gate Driver at V IN = 5.5V -- 110 230 m Ω Low Side Switch-On Resistance R DS(ON)2 Bias Gate Driver at V IN = 5.5V -- 10 15 Ω Current Limit I LIM Voltage Mode Test 6 7.5 9 A Oscillator Frequency f OSC V FB = 0.8V 400 500 600 kHz Short Circuit Frequency V FB = 0V -- 150 -- kHz Maximum Duty Cycle D MAX V FB = 0.8V 85 90 95 % Minimum On-Time t ON Come from Maximum Duty Cycle -- 100 150 ns Under Voltage Lockout Threshold Rising V IN Rising, Check Switching -- 4.2 5 V Under Voltage Lockout Threshold Hysteresis V IN Falling, Check Switching -- 315 -- mV Logic-High V IH Let EN = 1.4V , Check I Q 1.4 -- -- EN Threshold Voltage Logic-Low V IL Let EN = 0.4V , Check I Q -- -- 0.4 V Enable Pull Up Current -- 1 -- μA Shutdown Current I SHDN V EN = 0V -- 25 45 μA Quiescent Current I Q V EN = 2V, VFB = 1.5V -- 0.6 1 mA Soft-Start Period 3 5 10 ms Thermal Shutdown T SD -- 160 -- °C (VIN = 12V, TA = −40°C to 85°C unless otherwise specified)

DS2805A-00 November 2012 www.richtek.com ©Copyright 2012 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. 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. The EVB board copper area is 70mm 2. 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. is a registered trademark of Ric htek Technology Corporation. Table 1. Recommended Component Selection

DS2805A-00 November 2012 www.richtek.com ©Copyright 2012 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Typical Operating Characteristics Frequency vs. Temperature 440 450 460 470 480 490 500 510 520 530 540 -50 -25 0 25 50 75 100 125 Temperature (°C) Frequency (kHz ) VOUT = 5V VIN = 12V VIN = 24V VIN = 36V Frequency vs. Input Voltage 440 450 460 470 480 490 500 510 520 530 540 4 8 12 16 20 24 28 32 36 Input Voltage (V) Frequency (kHz ) VOUT = 5V, IOUT = 0A Reference Voltage vs. Temperature 1.210 1.212 1.214 1.216 1.218 1.220 1.222 1.224 1.226 1.228 1.230 -50 -25 0 25 50 75 100 125 Temperature (°C) Reference Voltage (V) IOUT = 0A VIN = 12V VIN = 24V VIN = 36V Output Voltage vs. Output Current 4.960 4.964 4.968 4.972 4.976 4.980 4.984 4.988 4.992 4.996 5.000 5.004 5.008 012345 Output Current (A) Output Voltage (V) VOUT = 5V VIN = 36V VIN = 24V VIN = 12V Reference Voltage vs. Input Voltage 1.210 1.214 1.218 1.222 1.226 1.230 4 8 12 16 20 24 28 32 36 Input Voltage (V) Reference Voltage (V) VOUT = 5V, IOUT = 0A Efficiency vs. Output Current 100 012345 Output Current (A) Efficiency (%) VOUT = 5V VIN = 12V VIN = 32V VIN = 36V

DS2805A-00 November 2012www.richtek.com ©Copyright 2012 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Current Limit vs. Temperature -50 -25 0 25 50 75 100 125 Temperature (°C) Current Limit (A) VIN = 12V Shutdown Current vs. Input Voltage 4 8 12 16 20 24 28 32 36 Input Voltage (V) Shutdown Current (μA) VEN = 0V Quiescent Current vs. Temperature 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 -50 -25 0 25 50 75 100 125 Temperature (°C) Quiescent Current (mA) VIN = 36V VIN = 24V VIN = 12V Load Transient Response Time (100 μs/Div) VOUT (200mV/Div) IOUT (2A/Div) VIN = 12V, VOUT = 5V, IOUT = 0.2A to 5A Load Transient Response Time (100 μs/Div) VOUT (200mV/Div) IOUT (2A/Div) VIN = 12V, VOUT = 5V, IOUT = 2.5A to 5A Switching Time (1 μs/Div) VOUT (10mV/Div) IL (5A/Div) VIN = 12V, VOUT = 5V, IOUT = 5A VSW (10V/Div)

DS2805A-00 November 2012 www.richtek.com ©Copyright 2012 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Power Off from EN Time (2.5ms/Div) VEN (5V/Div) IL (5A/Div) VIN = 12V, VOUT = 5V, IOUT = 5A VOUT (5V/Div) Power On from EN Time (2.5ms/Div) VEN (5V/Div) IL (5A/Div) VIN = 12V, VOUT = 5V, IOUT = 5A VOUT (5V/Div)

©Copyright 2012 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. 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. ringing that would indicate a stability problem. trapezoidal current at the source of the high side MOSFET. Table 2. Suggested Inductors for Typical 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.

©Copyright 2012 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Figure 3. Reference Circuit with Snubber and Enable Timing Control the junction to ambient thermal resistance. on the standard JEDEC 51-7 four-layers thermal test board. guide, please refer to the section of Layout Consideration.

©Copyright 2012 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Figure 6. PCB Layout Guide Table 3. Suggested Capacitors for CIN and COU T Table 4. Suggested Diode

9 CIN

components away from this trace.

DS2805A-00 November 2012 www.richtek.com 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. Outline Dimension 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