RT7296EGJ8F

RT7296E 3A, 17V Current Mode Synchronous Step-Down Converter General Description Features The RT7296E is a high-efficiency, 3A current mode  6V to 17V Input Voltage Range synchronous step-down DC/DC converter with a wide  3A Output Current input voltage range from 6V to 17V. The device  Internal N-Channel MOSFETs integrates 80m low-side  Current Mode Control MOSFETs to achieve high efficiency conversion. The  Fixed Switching Frequency : 800kHz current architecture supports fast  Cycle-by-Cycle Current Limit transient response and internal compensation. A  TTH Power-Save Mode cycle-by-cycle current limit function provides protection  External Soft-Start Function against  Input Under-Voltage Lockout input  Output Under-Voltage Protection under-voltage lockout, output under-voltage protection,  Thermal Shutdown high-side mode control shorted output. complete protection and 30m The RT7296E functions such provides as over-current protection, and thermal shutdown. The Applications RT7296E is available in the TSOT-23-8 (FC) package. Ordering Information RT7296E Package Type J8F : TSOT-23-8 (FC)  Industrial and Commercial Low Power Systems  Computer Peripherals  LCD Monitors and TVs  Set-top Boxes Marking Information Lead Plating System G : Green (Halogen Free and Pb Free) 09= : Product Code DNN : Date Code 09=DNN Note : Richtek products are :  RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020.  Suitable for use in SnPb or Pb-free soldering processes. Simplified Application Circuit VIN VIN RT7296E BOOT C3 C1 L1 VOUT SW R5 PVCC C2 R3 TTH R1 FB GND R2 SS C4 C5 R4 Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS7296E-00 Augist 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT7296E Pin Configurations PVCC SS BOOT 8 7 6 5 2 3 4 VIN SW GND TTH FB (TOP VIEW) TSOT-23-8 (FC) Functional Pin Description Pin No. Pin Name Pin Function 1 TTH Transition Threshold. Connect a resistor divider to let the RT7296E into power saving mode under light loads. Connect to PVCC to force RT7296E into CCM. 2 VIN Power Input. Support 6V to17V Input Voltage. Must bypass with a suitable large ceramic capacitor at this pin. 3 SW Switch Node. Connect to external L-C filter. 4 GND System Ground. 5 BOOT Bootstrap Supply for High-Side Gate Driver. Connect a 0.1F ceramic capacitor between the BOOT and SW pins. 6 SS Soft-Start Control Input. SS control the soft-start period. Connect a capacitor from SS to GND to set the soft-start period. 7 PVCC 5V Bias Supply Output. Connect a 0.1F capacitor to ground. 8 FB Feedback Voltage Input. The pin is used to set the output voltage of the converter to regulate to the desired voltage via a resistive divider. Feedback reference = 0.8V. Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS7296E-00 Augist 2015 RT7296E Function Block Diagram TTH VIN PVCC Internal Regulator Current Sense UVLO BOOT UVLO BOOT Logic & Protection Control Power Stage & Deadtime Control + 0.4V SW UV Comparator HS Switch Current Comparator 1pF 50pF FB 0.807V 400k + EA + Oscillator LS Switch Current Comparator Current Sense Slope Compensation GND 10.5µA SS Operation Under Voltage Lockout Threshold Over Current Protection The IC includes an input Under Voltage Lockout Protection (UVLO). If the input voltage exceeds the RT7296E provides cycle-by-cycle over current limit protection. When the inductor current peak value UVLO rising threshold voltage (3.9V), the converter resets and prepares reaches current limit, IC will turn off High Side MOS to avoid over current. the PWM for operation. If the input voltage falls below the UVLO falling threshold voltage (3.25V) during normal operation, the device stops switching. The UVLO rising and falling threshold voltage includes a hysteresis to prevent noise caused reset. Under Voltage Protection (Hiccup Mode) Internal Regulator The internal regulator generates 5V power and drive internal circuit. When VIN is below 5V, PVCC will drop RT7296E provides Hiccup Mode of Under Voltage Protection (UVP). When the FB voltage drops below half of the feedback reference voltage, VFB, the UVP function will be triggered and the IC will shut down for a period of time and then recover automatically. The Hiccup Mode of UVP can reduce input current in short-circuit conditions. with VIN. A capacitor(>0.1F) between PVCC and GND is required. Thermal Shutdown Soft-Start Function from operating at excessively high temperatures. When The RT7296E provides external soft-start function. The the junction temperature is higher than 150oC, the chip soft-start function is used to prevent large inrush current while converter is being powered-up. The soft-start timing can be programmed by the external capacitor between SS pin and GND. The Chip provides a 11A charge current for the external capacitor. will shutdown the switching operation. The chip is Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS7296E-00 Augist 2015 Thermal shutdown is implemented to prevent the chip automatically re-enabled when the junction temperature cools down by approximately 20oC. is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT7296E Absolute Maximum Ratings (Note 1)  Supply Input Voltage, VIN --------------------------------------------------------------------------------------------- 0.3V to 20V  Switch Voltage, SW ------------------------------------------------------------------------------------------------------ 0.3V to VIN + 0.3V  BOOT to SW, VBOOT – SW --------------------------------------------------------------------------------------------- 0.3V to 6V  Other Pins------------------------------------------------------------------------------------------------------------------- 0.3V to 6V  Power Dissipation, PD @ TA = 25C TSOT-23-8 (FC) ---------------------------------------------------------------------------------------------------------- 1.428W  Package Thermal Resistance (Note 2) TSOT-23-8 (FC), JA --------------------------------------------------------------------------------------------------- 70C/W TSOT-23-8 (FC), JC --------------------------------------------------------------------------------------------------- 15C/W  Lead Temperature (Soldering, 10 sec.) --------------------------------------------------------------------------- 260C  Junction Temperature --------------------------------------------------------------------------------------------------- 40C to 150C  Storage Temperature Range ----------------------------------------------------------------------------------------- 65C to 150C  ESD Susceptibility (Note 3) HBM (Human Body Model) ------------------------------------------------------------------------------------------- 2kV Recommended Operating Conditions (Note 4)  Supply Input Voltage, VIN ---------------------------------------------------------------------------------------- 6V to 17V  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 Quiescent Current with no Load at DCDC Output Feedback Voltage VFB Feedback Current IFB Switch On-Resistance Min Typ Max Unit VEN = 2V, VFB = 1V, TTH = 0.5V -- 0.8 1 mA 0.799 0.807 0.815 V -- 10 50 nA VFB = 820mV High-Side RDS(ON)H -- 80 -- Low-Side RDS(ON)L -- 30 -- Under 40% duty-cycle 4.2 5 -- A From Drain to Source -- 2 -- A VFB = 0.75V -- 800 -- kHz VFB < 400mV -- 125 -- kHz VFB = 0.7V 87 92 -- % -- 60 -- ns 4.9 5.3 5.85 V -- 1.1 -- V -- 5 -- V -- 3 -- % Current Limit ILIM Low-Side Switch Current Limit Oscillation Frequency fOSC Fold-Back Frequency Maximum Duty-Cycle DMAX Minimum On-Time tON Input Under-Voltage Lockout Threshold Test Conditions VIN Rising VUVLO VIN Rising Hysteresis VUVLO PVCC Regulator VCC PVCC Load Regulation VLOAD IVCC = 5mA Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 m is a registered trademark of Richtek Technology Corporation. DS7296E-00 Augist 2015 RT7296E Parameter Symbol Test Conditions Min Typ Max Unit A Soft-Start Charge Current ISS 7.6 10.5 13.4 Thermal Shutdown Temperature TSD -- 150 -- o Thermal Shutdown Hysteresis TSD -- o -- 20 C C Note 1. Stresses listed as the above "Absolute Maximum Ratings" may cause permanent damage to the device. These are for stress ratings. 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 for extended periods may remain possibility to affect device reliability. Note 2. JA is measured at TA = 25C on a high effective thermal conductivity four-layer test board per JEDEC 51-7. JC is measured at the exposed pad of the package. Note 3. Devices are ESD sensitive. Handling precaution recommended. Note 4. The device is not guaranteed to function outside its operating conditions. Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS7296E-00 Augist 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT7296E Typical Application Circuit C3 0.1μF RT7296E 5 2 BOOT VIN VIN 6V to 17V C1 22μF R6 10 6 SS C5 22nF 7 C2 0.1μF R3 91k SW 3 VOUT Cff 22pF PVCC 1 TTH R4 10k L1 3.3μH FB 8 R5 8.2k R1 40.2k C4 44μF R2 13k GND 4 Table 1. Suggested Component Values VOUT (V) R1 (k) R2 (k) R5 (k) Cff (pF) C4 (F) L1 (H) 1.0 20.5 84.5 49.9 22 44 1.5 3.3 40.2 13 8.2 22 44 3.3 5.0 40.2 7.68 8.2 22 44 3.3 Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 is a registered trademark of Richtek Technology Corporation. DS7296E-00 Augist 2015 RT7296E Typical Operating Characteristics Efficiency vs. Output Current Output Voltage vs. Input Voltage 100 3.46 90 VIN = 12V 70 Output Voltage (V) Efficiency (%) 3.42 VIN = 6V 80 VIN = 17V 60 50 40 30 20 3.38 3.34 3.30 3.26 3.22 3.18 10 VOUT = 3.3V VOUT = 3.3V 0 3.14 0 0.5 1 1.5 2 2.5 3 6 7 8 Output Current (A) 10 11 12 14 15 16 17 Output Voltage vs. Output Current 3.46 0.83 3.42 0.82 3.38 Output Voltage (V) 0.84 0.81 0.80 0.79 0.78 0.77 3.34 3.30 3.26 3.22 3.18 IOUT = 1A 0.76 VIN = 12V, VOUT = 3.3V 3.14 -50 -25 0 25 50 75 100 125 0 0.5 1 1.5 2 2.5 Temperature (°C) Output Current (A) UVLO Voltage vs. Temperature Load Transient Response 5.60 3 Rising 5.40 UVLO Voltage (V) 13 Input Voltage (V) Reference Voltage vs. Temperature Reference Voltage (V) 9 VOUT (50mV/Div) 5.20 5.00 VIN = 12V, VOUT = 3.3V, L = 3.3H, IOUT = 1.5A to 3A to 1.5A 4.80 4.60 4.40 IOUT (1A/Div) Falling 4.20 VOUT = 3.3V, IOUT = 0A 4.00 -50 -25 0 25 50 75 100 Temperature (°C) Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS7296E-00 Augist 2015 125 Time (200s/Div) is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT7296E Output Ripple Voltage VOUT (20mV/Div) VIN = 12V, VOUT = 3.3V, L = 3.3H, IOUT = 3A Power On from VIN VOUT (2V/Div) VIN = 12V, VOUT = 3.3V, IOUT = 3A VIN (10V/Div) VLX (10V/Div) VLX (5V/Div) ILX (3A/Div) Time (2s/Div) Time (5ms/Div) Power Off from VIN VOUT (2V/Div) VIN = 12V, VOUT = 3.3V, IOUT = 3A VIN (10V/Div) VLX (10V/Div) ILX (3A/Div) Time (5ms/Div) Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 is a registered trademark of Richtek Technology Corporation. DS7296E-00 Augist 2015 RT7296E Application Information The RT7296E is a high voltage buck converter that can 5V support the input voltage range from 4.5V to 17V and the input voltage range from 4.5V to 17V and the output current can be up to 3A. BOOT RT7296E Output Voltage Selection SW The resistive voltage divider allows the FB pin to sense a fraction of the output voltage as shown in Figure 1. FB R5 RT7296E 100nF R1 Figure 2. External Bootstrap Diode The TTH Voltage setting VOUT R2 The TTH voltage is used to be change the transition GND threshold between power saving mode and CCM. Higher TTH voltage gets higher efficiency at light load Figure 1. Output Voltage Setting condition but larger output ripple; a lower TTH voltage For adjustable voltage mode, the output voltage is set by an external resistive voltage divider according to the following equation : can improve output ripple but degrades efficiency during light load condition. A resistor divider from PVCC (5V) of RT7296E can help to build TTH voltage, as  R1  VOUT  VFB  1    R2  shown in Figure 1. It is recommended that TTH voltage Where VFB is the feedback reference voltage (0.807V typ.). Table 2 lists the recommended resistors value for common output voltages. should be less than 0.6V. PVCC R3 Table 2. Recommended Resistors Value VOUT (V) R1 (k) R2 (k) R5 (k) 1.0 20.5 84.5 49.9 3.3 40.2 13 8.2 5.0 40.2 7.68 8.2 TTH RT7296E R4 GND Figure 1. TTH Voltage Setting External Soft-Start Capacitor External Bootstrap Diode Connect a 100nF low ESR ceramic capacitor between the BOOT pin and SW pin. 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, as shown as Figure 2, 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 (PVCC) of the RT7296E. RT7296E provides external soft-start function. The soft-start function is used to prevent large inrush current while converter is being powered-up. The soft-start timing can be programmed by the external capacitor (CSS) between SS pin and GND. The Chip provides a 11A charge current (ISS) for the external capacitor. The soft-start time (tSS, VREF is from 0V to 0.8V) can be calculated by the following formula : tSS (ms) = CSS (nF)  1.3 ISS ( A) Inductor Selection The inductor value and operating frequency determine the ripple current according to a specific input and Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS7296E-00 Augist 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT7296E output voltage. The ripple current IL increases with higher VIN and decreases with higher inductance. the load transient response as described in a later section. The output ripple, VOUT, is determined by :  V   V IL   OUT    1  OUT  VIN   f L     1 VOUT  IL   ESR   8fCOUT   Having a lower ripple current reduces not only the ESR losses in the output capacitors but also the output voltage ripple. High frequency with small ripple current can achieve highest efficiency operation. However, it requires a large inductor to achieve this goal. The output ripple will be highest at the maximum input voltage since IL increases with input voltage. Multiple capacitors placed in parallel may be needed to meet the ESR and RMS current handling requirement. Dry tantalum, special polymer, aluminum electrolytic and ceramic capacitors are all available in surface mount packages. Special polymer capacitors offer very low ESR value. However, it provides lower capacitance density than other types. Although Tantalum capacitors For the ripple current selection, the value of IL = 0.3(IMAX) will be a reasonable starting point. The largest 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 :  VOUT   VOUT  L  1     f  IL(MAX)   VIN(MAX)     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. have the highest capacitance density, it is important to only use types that pass the surge test for use in switching power supplies. Aluminum electrolytic capacitors have significantly higher ESR. However, it can be used in cost-sensitive applications for ripple current rating and long term reliability considerations. 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. CIN and COUT Selection The input capacitance, CIN, is needed to filter the Thermal Considerations trapezoidal current at the source of the top MOSFET. To prevent large ripple current, a low ESR input 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 capacitor sized for the maximum RMS current should be used. The RMS current is given by : IRMS  IOUT(MAX) VOUT VIN VIN 1 VOUT difference between junction and ambient temperature. The maximum power dissipation can be calculated by the following formula : This formula has a maximum at VIN = 2VOUT, where IRMS = IOUT/2. This simple worst-case condition is PD(MAX) = (TJ(MAX)  TA) / JA commonly used for design because even significant deviations do not offer much relief. where TJ(MAX) is the maximum junction temperature, TA is the ambient temperature, and JA is the junction to 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 COUT is determined by the required Effective Series Resistance (ESR) to minimize voltage ripple. Moreover, the amount of bulk capacitance is also a key for COUT selection to ensure that the control loop is stable. Loop stability can be checked by viewing Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 ambient thermal resistance. For recommended operating condition specifications, the maximum junction temperature is 125C. The junction to ambient thermal resistance, JA, is layout dependent. For TSOT-23-8 (FC) package, the thermal resistance, JA, is 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 is a registered trademark of Richtek Technology Corporation. DS7296E-00 Augist 2015 RT7296E following formula : Layout Considerations PD(MAX) = (125C  25C) / (70C/W) = 1.428W for TSOT-23-8 (FC) package For best performance of the RT7296E, the following layout guidelines must be strictly followed. The maximum power dissipation depends on the operating ambient temperature for fixed TJ(MAX) and thermal resistance, JA. The derating curve in Figure 4 allows the designer to see the effect of rising ambient temperature on the maximum power dissipation.  possible.  SW should be connected to inductor by wide and short trace. Keep sensitive components away from this trace. 1.6 Maximum Power Dissipation (W)1 Input capacitor must be placed as close to the IC as Four-Layer PCB  1.4 Keep every trace connected to pin as wide as possible for improving thermal dissipation. 1.2 1.0 0.8 0.6 0.4 0.2 0.0 0 25 50 75 100 125 Ambient Temperature (°C) Figure 4. Derating Curve of Maximum Power Dissipation SW should be connected to inductor by Wide and short trace. Keep sensitive components away from this trace. Suggestion layout trace wider for thermal. R1 FB VOUT 4 3 SW 2 6 7 PVCC GND VIN VOUT CIN COUT COUT TTH 8 BOOT Css SS 5 SW CIN R2 PVCC The feedback components must be connected as close to the device as possible. GND Via can help to reduce power trace and improve thermal dissipation. Input capacitor must be placed as close to the IC as possible. Suggestion layout trace wider for thermal. Figure 4. PCB Layout Guide Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS7296E-00 Augist 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 11 RT7296E Outline Dimension Dimensions In Millimeters Symbol Dimensions In Inches Min. Max. Min. Max. A 0.700 1.000 0.028 0.039 A1 0.000 0.100 0.000 0.004 B 1.397 1.803 0.055 0.071 b 0.220 0.380 0.009 0.015 C 2.591 3.000 0.102 0.118 D 2.692 3.099 0.106 0.122 e 0.585 0.715 0.023 0.028 H 0.080 0.254 0.003 0.010 L 0.300 0.610 0.012 0.024 TSOT-23-8 (FC) Surface Mount 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. Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 12 is a registered trademark of Richtek Technology Corporation. DS7296E-00 Augist 2015