RT8055

RT8055 RICHTEK | Alldatasheet

Document overview

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Technical content

Features

zzzzz High Efficiency : Up to 95% zzzzz Low RDS(ON) Internal Switches : 100mΩΩΩΩΩ zzzzz Programmable Frequency : 300kHz to 2MHz zzzzz No Schottky Diode Required zzzzz 0.8V Reference Voltage Allows for Low Output Voltage zzzzz Forced Continuous Mode Operation zzzzz 100% Duty Cycle Operation zzzzz Input Over Voltage Protection zzzzz RoHS Compliant and Halogen Free

Applications

z Battery-Powered Equipment z Notebook Computers z Distributed Power Systems z IP Phones z Digital Cameras z 3G/3.5G Data Card General Description The RT8055 is a high efficiency synchronous, step-down DC/DC converter. Its input voltage range is from 2.6V to 5.5V and provides an adjustable regulated output voltage from 0.8V to 5V while delivering up to 3A of output current. The internal synchronous low on-resistance power switches increase efficiency and eliminate the need for an exter nal Schottky diode. The switching frequency is set by an external resistor. The 100% duty cycle provides low dropout operation extending battery life in portable systems. Current mode operation with external compensation allows the transient response to be optimized over a wide range of loads and output capacitors. The RT8055 is operated in forced continuous PWM Mode which minimizes ripple voltage and reduces the noise and RF interference. The RT8055 is available in the WDFN-10L 3x3 and SOP-8 (Exposed Pad) packages.

Ordering Information

(TOP VIEW) WDFN-10L 3x3 3A, 2MHz, Synchronous Step-Down Converter Note : Richtek products are : \ RoHS compliant and compatible with the current require- ments of IPC/JEDEC J-STD-020. \ Suitable for use in SnPb or Pb-free soldering processes. SHDN/RT GND PGND LX COMP FB VDD PVDD PVDD LX GND SHDN/RT GND LX PGND COMP FB PVDD VDD GND 4 5 SOP-8 (Exposed Pad) RT8055 Package Type QW : WDFN-10L 3x3 (W-Type) SP : SOP-8 (Exposed Pad-Option 2) Lead Plating System G : Green (Halogen Free and Pb Free) Z : ECO (Ecological Element with Halogen Free and Pb free)

©Copyright 2012 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Table 1. Recommended Component Selection

DS8055-05 November 2012 www.richtek.com ©Copyright 2012 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Functional Pin Description Pin No. WDFN-10L 3x3 SOP-8 Pin Name Pin Function 1 1 SHDN/RT Shutdown Control or Frequency Setting Input. Connect a resistor to ground from this pin sets the switching frequency. Force this pin to VDD or GND causes the device to be shut down. 11 (Exposed Pad) 9 (Exposed Pad) GND Signal Ground. All small-signal components and compensation components should be connected to this ground, which in turn connects to PGND at one point. The exposed pad must be soldered to a large PCB and connected to GND for maximum power dissipation. 3, 4 3 LX Internal Power MOSFET Switches Output. Connect this pin to the inductor. 5 4 PGND Power Ground. Connect this pin close to the negative terminal of CIN and COUT. 6, 7 5 PVDD Power Supply Input. Decouple this pin to PGND with a capacitor. 8 6 VDD Signal Supply Input. Decouple this pin to GND with a capacitor. Generally, VDD is equal to PVDD. 9 7 FB Feedback Pin. This pin receives the feedback voltage from a resistive divider connected across the output. 10 8 COMP Error Amplifier Compensation Point. The current comparator threshold increases with this control voltage. Connect external compensation elements to this pin to stabilize the control loop. Function Block Diagram Driver Control Logic OC Limit ISEN Slope Comp.OSC Output ClampEA0.8V Internal - Soft Star POR GND FB PVDD VDD PGND LX OTP VREF SD NISEN N-MOSFET ILIM 0.7V 0.4V SHDN/RT COMP

DS8055-05 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)

Electrical Characteristics

(VDD = 3.3V, T A = 25°C, unless otherwise specified) Recommended Operating Conditions (Note 4) Parameter Symbol Test Conditions Min Typ Max Unit Input Voltage Range V DD 2.6 -- 5.5 V Feedback Reference Voltage V REF 0.784 0.8 0.816 V Feedback Leakage Current I FB V FB = 3.3V -- -- 0.1 μA Active , V FB = 0.7V, Not Switching -- 500 -- μA DC Bias Current Shutdown -- -- 1 μA Output Voltage Line Regulation ΔVLINE V IN = 2.6V to 5.5V -- 0.1 -- %/V Output Voltage Load Regulation ΔVLOAD VIN = 5V, VOUT = 3.3V, IOUT = 0A to 3A -- 0.4 -- % Error Amplifier Transconductance gm -- 400 -- μA/V Current Sense Transresistance R S -- 0.4 -- Ω RT Leakage Current SHDN/RT = V IN = 5.5V -- -- 1 μA

DS8055-05 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. 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. Guaranteed by design. Parameter Symbol Test Conditions Min Typ Max Unit ROSC = 180kΩ 1.44 1.8 2.16 Switching Frequency Adjustable Switching Frequency Range 0.3 -- 2 MHz Switch On Resistance, High R DS(ON)_P I SW = 0.3A -- 100 160 m Ω Switch On Resistance, Low R DS(ON)_N I SW = 0.3A -- 100 170 m Ω Peak Current Limit I LIM 3.5 -- -- A V DD Rising @Full Temperature 2.33 2.4 2.57 Under Voltage Lockout Threshold (Note 5) V DD Falling @Full Temperature 1.98 2.2 2.37 V Shutdown Threshold V SHDN V SHDN Rising -- V IN − 0.85 V IN − 0.4 V

DS8055-05 November 2012www.richtek.com ©Copyright 2012 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Typical Operating Characteristics Output Voltage vs. Input Voltage 3.30 3.31 3.32 3.33 3.34 3.35 3.36 Input Voltage (V) Output Voltage (V) IOUT = 0A, VOUT = 3.3V Output Voltage vs. Output Current 3.26 3.27 3.28 3.29 3.30 3.31 3.32 3.33 3.34 3.35 3.36 3.37 3.38 Output Current (A) Output Voltage (V) VIN = 5V, VOUT = 3.3V Efficiency vs. Output Current 100 Output Current (A) Efficiency (%) VIN = 5V, VOUT = 3.3V Switching Frequency vs. Temperature 1.5 1.6 1.7 1.8 1.9 2.0 2.1 -50 -25 0 25 50 75 100 125 Temperature (°C) Switching Frequency (MHz) 1 VIN = 5V, VOUT = 3.3V IOUT = 0.3A, fSW = 1.8MHz Switching Frequency vs. Input Voltage 1.5 1.6 1.7 1.8 1.9 2.0 2.1 Input Voltage (V) Switching Frequency (MHz) 1 VIN = 5V, VOUT = 3.3V IOUT = 0.3A, fSW = 1.8MHz VIN UVLO vs. Temperature 2.00 2.05 2.10 2.15 2.20 2.25 2.30 2.35 2.40 2.45 2.50 -50 -25 0 25 50 75 100 125 Temperature (°C) VIN UVLO (V) Rising Falling VOUT = 3.3V

DS8055-05 November 2012 www.richtek.com ©Copyright 2012 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Output Ripple Time (500ns/Div) VIN = 5V, VOUT = 3.3V IOUT = 0A VLX (5V/Div) VOUT (5mV/Div) Output Ripple Time (500ns/Div) VIN = 5V, VOUT = 3.3V IOUT = 3A VLX (5V/Div) VOUT (5mV/Div) Reference Voltage vs. Temperature 0.760 0.768 0.776 0.784 0.792 0.800 0.808 0.816 0.824 0.832 0.840 -50 -25 0 25 50 75 100 125 Temperature (°C) Reference Voltage (V) Output Current Limit vs. Temperature 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 -50 -25 0 25 50 75 100 125 Temperature (°C) Output Current Limit (A) VIN = 5V, VOUT = 3.3V Output Current Limit vs. Input Voltage 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 Input Voltage (V) Output Current Limit (A) VOUT = 3.3V Output Voltage vs. Temperature 3.20 3.22 3.24 3.26 3.28 3.30 3.32 3.34 3.36 3.38 3.40 -50 -25 0 25 50 75 100 125 Temperature (°C) Output Voltage (V) VIN = 5V, VOUT = 3.3V IOUT = 0A

DS8055-05 November 2012www.richtek.com ©Copyright 2012 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Power On from V IN Time (1ms/Div) VIN = 5V, VOUT = 3.3V IOUT = 0A VLX (5V/Div) VIN (2V/Div) VOUT (1V/Div) Load Transient Response Time (100 μs/Div) IOUT (1A/Div) VOUT (200mV/Div) VIN = 5V, VOUT = 3.3V IOUT = 0A to 2A Load Transient Response Time (100 μs/Div) IOUT (1A/Div) VOUT (200mV/Div) VIN = 5V, VOUT = 3.3V IOUT = 0A to 3A UVP Shutdown Time (10 μs/Div) VLX (5V/Div) VOUT (1V/Div) VIN = 5V, VOUT = 3.3V

DS8055-05 November 2012www.richtek.com ©Copyright 2012 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. This formula has a maximum at V IN = 2V OUT, where IRMS = I OUT/2. This simple worst-case condition is commonly used for design because even significant deviations do not offer much relief. Choose a capacitor rated at a higher temperature than required. Several capacitors may also be paralleled to meet size or height requirements in the design. The selection of C OUT is determined by the effective series resistance (ESR) that is required to minimize voltage ripple and load step transients, as well as the amount of bulk capacitance that is necessary to ensure that the control loop is stable. Loop stability can be checked by viewing the load transient response as described in a later section. The output ripple, ΔV OUT, is determined by : V V VII OUT IN IN OUTOUT(MAX)RMS −= ⎡ +Δ≤Δ OUT LOUT 8fC 1ESRIV This keeps the maximum output current relatively constant regardless of duty cycle. Short Circuit Protection When the output is shorted to ground, the inductor current decays very slowly during a single switching cycle. A current runaway detector is used to monitor inductor current. As current increasing beyond the control of current loop, switching cycles will be skipped to prevent current runaway from occurring. Inductor Selection The inductor value and operating frequency determine the ripple current according to a specific input and output voltage. The ripple current ΔI L increases with higher VIN and decreases with higher inductance. OUT OUTL IN VVI = 1 fL V OUT OUT L(MAX) IN(MAX) VVL = 1fI V Having a lower ripple current reduces not only the ESR losses in the output capacitors but also the output voltage ripple. However, it requires a large inductor to achieve this goal. For the ripple current selection, the val ue of ΔIL = 0.4(IMAX) will be a reasonable starting point. The large st ripple current occurs at the highest VIN. To guarantee that the ripple current stays below the specified maximum, the inductor value should be chosen according to the following equation : The inductor's current rating (caused a 40°C temperature rising from 25 °C ambient) should be greater than the maximum load current and its saturation current should be greater than the short circuit peak current limit. C IN and COUT Selection The input capacitance, C IN, is needed to filter the trapezoidal current at the source of the top MOSFET. To prevent large ripple voltage, a low ESR input capacitor sized for the maximum RMS current should be used. RMS current is given by : The output ripple is highest at maximum input voltage since ΔI L increases with input voltage. Multiple capacitors placed in parallel may be needed to meet the ESR and RMS current handling requirements. Dry tantalum, special polymer, aluminum electrolytic and ceramic capacitors are all available in surface mount packages. Special polymer capacitors offer very low ESR but have lower capacitance density than other types. Tantalum capacitors have the highest capacitance density but it is important to only use types that have been surge tested for use in switching power supplies. Aluminum electrolytic capacitors have significantly higher ESR but can be used in cost-sensitive applications provided that consideration is given to ripple current ratings and long term reliability. Ceramic capacitors have excellent low ESR characteristics but can have a high voltage coefficient and audible piezoelectric effects. The high Q of ceramic capacitors with trace inductance can also lead to significant ringing. Using Ceramic Input and Output Capacitors Higher values, lower cost ceramic capacitors are now becoming available in smaller case sizes. Their high ripple current, high voltage rating and low ESR make them ideal for switching regulator applications. However, care must be taken when these capacitors are used at the input and output. When a ceramic capacitor is used at the input

©Copyright 2012 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. on the maximum power dissipation. Figure 3. Derating Curve of Maximum Power Dissipation \` Flood all unused areas on all layers with copper. \` Connect the FB pin directly to the feedback resistors.

©Copyright 2012 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Table 2. Inductors Table 3. Capacitors for CIN and COUT Figure 4. PCB Layout Guide resistor divider must be connected between VOUT and GND.

DS8055-05 November 2012 www.richtek.com ©Copyright 2012 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Outline Dimension 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 2.300 2.650 0.091 0.104 E 2.950 3.050 0.1 16 0.120 E2 1.500 1.750 0.059 0.069 e 0.500 0.020 L 0.350 0.450 0.014 0.018 W-Type 10L DFN 3x3 Package 1 122 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 D E A L be SEE DETAIL A

DS8055-05 November 2012www.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. 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