® RT5768A 3A, 1MHz, Synchronous Step-Down Converter General Description Features The RT5768A is a high efficiency synchronous, step-down DC/DC converter. It's input voltage range from 2.7V to 5.5V that provides an adjustable regulated output voltage from 0.6V to VIN while delivering up to 3A of output current. High Efficiency : Up to 95% The internal synchronous low on resistance power switches increase efficiency and eliminate the need for an external Schottky diode. The switching frequency is fixed internally at 1MHz. The 100% duty cycle provides low dropout operation, hence extending battery life in portable systems. Current mode operation with internal compensation allows the transient response to be optimized over a wide range of loads and output capacitors. The RT5768A is available in WDFN-10L 3x3 package. Low RDS(ON) Internal Switches : 69mΩ/49mΩ at VIN = 5V Fixed Frequency : 1MHz No Schottky Diode Required Internal Compensation 0.6V Reference Allows Low Output Voltage Low Dropout Operation : 100% Duty Cycle OCP, UVP, OVP, OTP RoHS Compliant and Halogen Free Ordering Information RT5768A Applications Package Type QW : WDFN-10L 3x3 (W-Type) Lead Plating System G : Green (Halogen Free and Pb Free) Portable Instruments Battery Powered Equipment Notebook Computers Distrib uted Power Systems IP Phones Digital Cameras Pin Configurations Note : (TOP VIEW) RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. Suitable for use in SnPb or Pb-free soldering processes. LX LX LX PGOOD EN 1 2 3 4 5 GND Richtek products are : 11 10 9 8 7 6 PVIN PVIN SVIN NC FB WDFN-10L 3x3 Marking Information 8T= : Product Code 8T=YM DNN YMDNN : Date Code Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS5768A-01 June 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT5768A Typical Application Circuit RT5768A 1, 2, 3 4 PGOOD LX PGOOD R1 100k VIN CIN 10µF 9, 10 VOUT COUT PVIN CFF RFB1 8 SVIN FB 6 C1 1µF Chip Enable L RFB2 5 EN GND 11 (Exposed Pad) Table 1. Recommended Component Selection VOUT (V) RFB1 (k) RFB2 (k) CFF (pF) L (H) COUT (F) 3.3 229.5 51 22 2 22 x 2 2.5 161.5 51 22 2 22 x 2 1.8 102 51 22 1.5 22 x 2 1.5 76.5 51 22 1.5 22 x 2 1.2 51 51 22 1.5 22 x 2 1.0 34 51 22 1.5 22 x 2 Functional Pin Description Pin No. 1, 2, 3 Pin Name Pin Function LX Switch Node. Connect this pin to the inductor. 4 PGOOD Power Good Indicator. This pin is an open drain logic output that is pulled to ground when the output voltage is less than 90% of the target output voltage. Hysteresis = 5%. 5 EN Enable Control. Pull high to turn on. Do not float. 6 FB Feedback Pin. This pin receives the feedback voltage from a resistive voltage divider connected across the output. 7 NC No Internal Connection. 8 SVIN Signal Input Pin. Decouple this pin to GND with at least 1F ceramic cap. 9, 10 PVIN Power Input Pin. Decouple this pin to GND with at least 4.7F ceramic cap. 11 (Exposed Pad) GND Ground. The exposed pad must be soldered to a large PCB and connected to GND for maximum power dissipation. Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS5768A-01 June 2015 RT5768A Function Block Diagram EN EN PVIN ISEN PGOOD PGOOD Slope Com OSC VREF 0.6V EA FB OC Limit Output Clamp Driver Int-SS 0.72V OV LX Control Logic 0.54V NISEN PGOOD 0.4V POR Zero Current UV OTP SVIN Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS5768A-01 June 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT5768A Absolute Maximum Ratings (Note 1) Supply Input Voltage, PVIN, SVIN ------------------------------------------------------------------------------------LX Pin DC ----------------------------------------------------------------------------------------------------------------------------< 20ns ---------------------------------------------------------------------------------------------------------------------- Other I/O Pin Voltage ---------------------------------------------------------------------------------------------------- Power Dissipation, PD @ TA = 25°C WDFN-10L 3x3 ------------------------------------------------------------------------------------------------------------ Package Thermal Resistance (Note 2) WDFN-10L 3x3, θJA ------------------------------------------------------------------------------------------------------WDFN-10L 3x3, θJC ------------------------------------------------------------------------------------------------------ Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------------ Junction Temperature ---------------------------------------------------------------------------------------------------- Storage Temperature Range ------------------------------------------------------------------------------------------- ESD Susceptibility (Note 3) HBM (Human Body Model) ---------------------------------------------------------------------------------------------MM (Machine Model) ---------------------------------------------------------------------------------------------------- −0.3V to 6.5V Recommended Operating Conditions −0.3V to 6.8V −2.5V to 9V −0.3V to 6.5V 1.429W 70°C/W 8.2°C/W 260°C 150°C −65°C to 150°C 2kV 200V (Note 4) Supply Input Voltage, PVIN, SVIN ------------------------------------------------------------------------------------- 2.7V to 5.5V Junction Temperature Range -------------------------------------------------------------------------------------------- −40°C to 125°C Ambient Temperature Range -------------------------------------------------------------------------------------------- −40°C to 85°C Electrical Characteristics (VIN = 3.3V, TA = 25°C, unless otherwise specified) Parameter Symbol Min Typ Max Unit 0.594 0.6 0.606 V -- 0.1 0.4 A Active , VFB = 0.7V, Not Switching -- 110 140 Shutdown -- -- 1 Output Voltage Line Regulation VIN = 2.7V to 5.5V IOUT = 0A -- 0.3 -- %/V Output Voltage Load Regulation IOUT = 0A to 3A 1 -- 1 % -- -- 1 A 0.8 1 1.2 MHz Feedback Reference Voltage VREF Feedback Leakage Current IFB DC Bias Current Test Conditions Switch Leakage Current Switching Frequency A Switch On Resistance, High RDS(ON)_P VIN = 5V -- 69 -- m Switch On Resistance, Low RDS(ON)_N VIN = 5V -- 49 -- m P-MOSFET Current Limit ILIM 4 -- -- A Under Voltage Lockout Threshold VUVLO VIN Rising 2.2 2.4 2.6 VIN Falling 2 2.2 2.4 Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 V is a registered trademark of Richtek Technology Corporation. DS5768A-01 June 2015 RT5768A Parameter Min Typ Max VIH 1.6 -- -- VIL -- -- 0.4 -- 500 -- k -- 150 -- C -- 20 -- C 500 -- -- s -- 100 -- VOUT Over Voltage Protection (Latch-Off, Delay Time = 10s) 115 120 130 % VOUT Under Voltage Lock Out (Latch-Off) 57 66 75 % 85 90 -- % -- 5 -- % Logic-High EN Input Threshold Voltage Logic-Low Symbol Test Conditions EN Pull Low Resistance Over Temperature Protection TSD Over Temperature Protection Hysteresis Soft-Start Time tSS VOUT Discharge Resistance Power Good Measured FB, With Respect to VREF Power Good Hysteresis Unit 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. Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS5768A-01 June 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT5768A Typical Operating Characteristics Efficiency vs. Load Current Efficiency vs. Load Current 100 100 90 80 VIN = 3.3V VIN = 5V 80 70 Efficiency (%) Efficiency (%) 90 VIN = 4.2V VIN = 5V 60 50 40 30 20 70 60 50 40 30 20 10 10 VOUT = 3.3V 0 VOUT = 1.8V 0 0 0.5 1 1.5 2 2.5 3 0 0.5 1 Load Current (A) 2.5 3 1.820 90 1.815 70 Output Voltage (V) VIN = 3.3V VIN = 5V 80 Efficiency (%) 2 Output Voltage vs. Output Current Efficiency vs. Load Current 100 60 50 40 30 20 1.810 1.805 1.800 VIN = 5V 1.795 VIN = 3.3V 1.790 1.785 10 VOUT = 1.05V VOUT = 1.8V 0 1.780 0 0.5 1 1.5 2 2.5 3 0 0.5 1 1.5 2 2.5 3 Output Current (A) Load Current (A) Current Limit vs. Temperature Current Limit vs. Input Voltage 7.0 7.0 6.5 6.5 6.0 6.0 Current Limit (A) Current Limit (A) 1.5 Load Current (A) 5.5 5.0 4.5 4.0 3.5 VIN = 5V 5.5 VIN = 3.3V 5.0 4.5 4.0 3.5 VOUT = 1.05V 3.0 VOUT = 1.05V 3.0 2.5 3 3.5 4 4.5 5 Input Voltage (V) Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 5.5 -50 -25 0 25 50 75 100 125 Temperature (°C) is a registered trademark of Richtek Technology Corporation. DS5768A-01 June 2015 RT5768A RDS(ON) vs. Temperature Load Transient Response 90 85 80 Ω) RDS(ON) (mΩ VOUT (50mV/Div) P-MOSFET 75 70 65 60 55 IOUT (2A/Div) 50 45 N-MOSFET 40 VIN = 5V VIN = 5V, VOUT = 1.8V, IOUT = 0.5A to 3A 35 -50 -25 0 25 50 75 100 Time (50μs/Div) 125 Temperature (°C) Load Transient Response VOUT (50mV/Div) Switching VOUT (5mV/Div) VLX (5V/Div) IOUT (2A/Div) VIN = 5V, VOUT = 1.8V, IOUT = 1.5A to 3A ILX (1A/Div) VIN = 5V, VOUT = 1.8V, IOUT = 1.5A Time (50μs/Div) Time (500ns/Div) Switching Over Voltage Protection VOUT (5mV/Div) VLX (5V/Div) VOUT (1V/Div) ILX (2A/Div) VLX (2V/Div) VIN = 5V, VOUT = 1.8V, IOUT = 3A Time (500ns/Div) Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS5768A-01 June 2015 VIN = 5V, VOUT = 1.8V, IOUT = 1A Time (10μs/Div) is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT5768A Under Voltage Protection Over Current Protection VIN = 5V, VOUT = 1.8V VIN = 5V, VOUT = 1.8V VOUT (1V/Div) VOUT (1V/Div) ILX (5A/Div) VLX (2V/Div) VLX (2V/Div) Time (5μs/Div) Time (2.5μs/Div) Power On from VIN Power Off from VIN VIN (2V/Div) VIN (2V/Div) VOUT (1V/Div) VOUT (1V/Div) ILX (2A/Div) ILX (2A/Div) VOUT = 1.8V, IOUT = 3A Time (2.5ms/Div) Time (2.5ms/Div) Power On from EN Power Off from EN VEN (5V/Div) VEN (5V/Div) VOUT (1V/Div) VOUT (1V/Div) ILX (2A/Div) ILX (2A/Div) VIN = 5V, VOUT = 1.8V, IOUT = 3A Time (200μs/Div) Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 VOUT = 1.8V, IOUT = 3A VIN = 5V, VOUT = 1.8V, IOUT = 3A Time (40μs/Div) is a registered trademark of Richtek Technology Corporation. DS5768A-01 June 2015 RT5768A Application Information The RT5768A is a single-phase buck converter. It provides single feedback loop, current mode control with fast transient response. An internal 0.6V reference allows the output voltage to be precisely regulated for low output voltage applications. A fixed switching frequency (1MHz) oscillator and internal compensation are integrated to minimize external component count. Protection features include over current protection, under voltage protection, over voltage protection and over temperature protection. UVLO Protection Output Voltage Setting Inductor Selection Connect a resistive voltage divider at the FB between VOUT and GND to adjust the output voltage. The output voltage is set according to the following equation : R VOUT = VREF 1 + FB1 R FB2 where VREF is 0.6V (typ.). The switching frequency (on-time) and operating point (% ripple or LIR) determine the inductor value as shown below: VOUT RFB1 FB RFB2 GND Figure 1. Setting VOUT with a Voltage Divider Chip Enable and Disable The RT5768A has input Under Voltage Lockout protection (UVLO). If the input voltage exceeds the UVLO rising threshold voltage (2.4V typ.), the converter resets and prepares the PWM for operation. If the input voltage falls below the UVLO falling threshold voltage during normal operation, the device will stop switching. The UVLO rising and falling threshold voltage has a hysteresis to prevent noise-caused reset. L= VOUT VIN VOUT fSW LIR ILOAD(MAX) VIN where LIR is the ratio of the peak-to-peak ripple current to the average inductor current. Find a low loss inductor having the lowest possible DC resistance that fits in the allotted dimensions. Ferrite cores are often the best choice, although powdered iron is inexpensive and can work well at 200kHz. The core must be large enough not to saturate at the peak inductor current (IPEAK) : IPEAK = ILOAD(MAX) + LIR ILOAD(MAX) 2 The EN pin allows for power sequencing between the controller bias voltage and another voltage rail. The RT5768A remains in shutdown if the EN pin is lower than 400mV. When the EN pin rises above the VEN trip point, the RT5768A begins a new initialization and soft-start cycle. The calculation above serves as a general reference. To further improve transient response, the output inductor can be further reduced. This relation should be considered along with the selection of the output capacitor. Internal Soft-Start Input Capacitor Selection The RT5768A provides an internal soft-start function to prevent large inrush current and output voltage overshoot when the converter starts up. The soft-start (SS) automatically begins once the chip is enabled. During softstart, the internal soft-start capacitor becomes charged and generates a linear ramping up voltage across the capacitor. This voltage clamps the voltage at the FB pin, causing PWM pulse width to increase slowly and in turn reduce the output surge current. The internal 0.6V reference takes over the loop control once the internal ramping-up voltage becomes higher than 0.6V. High quality ceramic input decoupling capacitor, such as X5R or X7R, with values greater than 20μF are recommended for the input capacitor. The X5R and X7R ceramic capacitors are usually selected for power regulator capacitors because the dielectric material has less capacitance variation and more temperature stability. Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS5768A-01 June 2015 Voltage rating and current rating are the key parameters when selecting an input capacitor. Generally, selecting an input capacitor with voltage rating 1.5 times greater than the maximum input voltage is a conservatively safe design. is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT5768A The input capacitor is used to supply the input RMS current, which can be approximately calculated using the following equation : IIN_RMS = ILOAD VOUT VOUT 1 VIN VIN The next step is selecting a proper capacitor for RMS current rating. One good design is using more than one capacitor with low equivalent series resistance (ESR) in parallel to form a capacitor bank. The input capacitance value determines the input ripple voltage of the regulator. The input voltage ripple can be approximately calculated using the following equation : VIN = IOUT(MAX) 0.25 CIN fSW For example, if IOUT_MAX = 3A, CIN = 20μF, fSW = 1MHz, the input voltage ripple will be 37.5mV. Output Capacitor Selection The output capacitor and the inductor form a low pass filter in the buck topology. In steady state condition, the ripple current flowing into/out of the capacitor results in ripple voltage. The output voltage ripple (VP-P) can be calculated by the following equation : 1 VP_P = LIR ILOAD(MAX) ESR + 8 COUT fSW When load transient occurs, the output capacitor supplies the load current before the controller can respond. Therefore, the ESR will dominate the output voltage sag during load transient. The output voltage undershoot (VSAG) can be calculated by the following equation : VSAG = ILOAD ESR For a given output voltage sag specification, the ESR value can be determined. Another parameter that has influence on the output voltage sag is the equivalent series inductance (ESL). The rapid change in load current results in di/dt during transient. Therefore, the ESL contributes to part of the voltage sag. Using a capacitor with low ESL can obtain better transient performance. Generally, using several capacitors connected in parallel can have better transient performance than using a single capacitor for the same total ESR. Unlike the electrolytic capacitor, the ceramic capacitor has relatively low ESR and can reduce the voltage deviation Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 during load transient. However, the ceramic capacitor can only provide low capacitance value. Therefore, use a mixed combination of electrolytic capacitor and ceramic capacitor to obtain better transient performance. Power Good Output (PGOOD) PGOOD is an open-drain type output and requires a pullup resistor. PGOOD is actively held low in soft-start, standby, and shutdown. It is released when the output voltage rises above 90% of nominal regulation point. The PGOOD signal goes low if the output is turned off or is 10% below its nominal regulation point. Under Voltage Protection (UVP) The output voltage can be continuously monitored for under voltage. When under voltage protection is enabled, both UGATE and LGATE gate drivers will be forced low if the output is less than 66% of its set voltage threshold. The UVP will be ignored for at least 3ms (typ.) after start up or a rising edge on the EN threshold. Toggle EN threshold or cycle VIN to reset the UVP fault latch and restart the controller. Over Voltage Protection (OVP) The RT5768A is latched once OVP is triggered and can only be released by toggling EN threshold or cycling VIN. There is a 10μs delay built into the over voltage protection circuit to prevent false transition. Over Current Protection (OCP) The RT5768A provides over current protection by detecting high side MOSFET peak inductor current. If the sensed peak inductor current is over the current limit threshold (4A typ.), the OCP will be triggered. When OCP is tripped, the RT5768A will keep the over current threshold level until the over current condition is removed. Thermal Shutdown (OTP) The device implements an internal thermal shutdown function when the junction temperature exceeds 150°C. The thermal shutdown forces the device to stop switching when the junction temperature exceeds the thermal shutdown threshold. Once the die temperature decreases below the hysteresis of 20°C, the device reinstates the power up sequence. is a registered trademark of Richtek Technology Corporation. DS5768A-01 June 2015 RT5768A Thermal Considerations Layout Considerations For continuous operation, do not exceed absolute maximum junction temperature. The maximum power dissipation depends on the thermal resistance of the IC package, PCB layout, rate of surrounding airflow, and difference between junction and ambient temperature. The maximum power dissipation can be calculated by the following formula : Layout is very important in high frequency switching converter design. The PCB can radiate excessive noise and contribute to converter instability with improper layout. Certain points must be considered before starting a layout using the RT5768A. PD(MAX) = (TJ(MAX) − TA) / θJA the traces of the main current paths as short and wide as possible. Put the input capacitor as close as possible to the device 70°C/W on a standard JEDEC 51-7 four-layer thermal test board. The maximum power dissipation at TA = 25°C can be calculated by the following formulas : PD(MAX) = (125°C − 25°C) / (70°C/W) = 1.429W for WDFN-10L 3x3 package The maximum power dissipation depends on the operating ambient temperature for fixed T J(MAX) and thermal resistance, θJA. The derating curves in Figure 2 allow the designer to see the effect of rising ambient temperature on the maximum power dissipation. 2.0 Four-Layer PCB 1.6 LX node encounters high frequency voltage swings so it should be kept in a small area. Keep sensitive components away from the LX node to prevent stray capacitive noise pick-up. Ensure all feedback network connections are short and direct. Place the feedback network as close to the chip as possible. The GND pin and Exposed Pad should be connected to a strong ground plane for heat sinking and noise protection. An example of PCB layout guide is shown in Figure 3. for reference. The output capacitor must be placed near the IC. COUT LX LX VOUT LX RPGOOD PGOOD VIN EN REN 1 2 3 4 5 Input capacitor must be placed as close to the IC as possible. GND 11 LX should be connected to inductor by wide and short trace. Keep sensitive components away from this trace. 1.2 0.8 10 9 8 7 6 PVIN PVIN SVIN NC FB CIN1 CIN2 R2 R1 VOUT For recommended operating condition specifications, the maximum junction temperature is 125°C. The junction to ambient thermal resistance, θJA, is layout dependent. For WDFN-10L 3x3 packages, the thermal resistance, θJA, is pins (VIN and GND). GND where TJ(MAX) is the maximum junction temperature, TA is the ambient temperature, and θJA is the junction to ambient thermal resistance. Maximum Power Dissipation (W)1 Make The voltage divider must be connected as close to the device as possible. Figure 3. PCB Layout Guide 0.4 0.0 0 25 50 75 100 125 Ambient Temperature (°C) Figure 2. Derating Curve of Maximum Power Dissipation Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS5768A-01 June 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 11 RT5768A Outline Dimension D2 D L E E2 1 e SEE DETAIL A b 2 1 2 1 A A1 A3 DETAIL A Pin #1 ID and Tie Bar Mark Options Note : The configuration of the Pin #1 identifier is optional, but must be located within the zone indicated. Symbol Dimensions In Millimeters Dimensions In Inches 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 0.116 0.120 D2 2.300 2.650 0.091 0.104 E 2.950 3.050 0.116 0.120 E2 1.500 1.750 0.059 0.069 e L 0.500 0.350 0.020 0.450 0.014 0.018 W-Type 10L DFN 3x3 Package Richtek Technology Corporation 14F, No. 8, Tai Yuen 1st 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 furnished 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 infringements 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 Richtek or its subsidiaries. www.richtek.com 12 DS5768A-01 June 2015