® RT6296E 2A, 17V Current Mode Synchronous Step-Down Converter General Description Features The RT6296E is a high-efficiency, 2A current mode synchronous step-down DC/DC converter with a wide input voltage range from 6V to 17V. The device integrates 100mΩ high-side and 40mΩ low-side MOSFETs to achieve high efficiency conversion. The current mode control architecture supports fast transient response and internal compensation. A cycle-by-cycle current limit function provides protection against shorted output. The RT6296E provides complete protection functions such as input undervoltage lockout, output under-voltage protection, overcurrent protection, and thermal shutdown. The RT6296E is available in the TSOT-23-8 (FC) package. 6V to 17V Input Voltage Range 2A Output Current Internal N-Channel MOSFETs Current Mode Control Fixed Switching Frequency : 800kHz Cycle-by-Cycle Current Limit TTH Power-Save Mode External Soft-Start Function Input Under-Voltage Lockout Output Under-Voltage Protection Thermal Shutdown Applications Ordering Information RT6296E Package Type J8F : TSOT-23-8 (FC) Lead Plating System G : Green (Halogen Free and Pb Free) Industrial and Commercial Low Power Systems Computer Peripherals LCD Monitors and TVs Set-top Boxes Marking Information 0C= : Product Code Note : 0C=DNN Richtek products are : DNN : Date Code 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 RT6296E BOOT C3 C1 L1 VOUT SW R5 PVCC C2 R1 FB R3 TTH GND R2 SS C4 C5 R4 Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS6296E-00 August 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT6296E 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 RT6296E into power saving mode under light loads. Connect to PVCC to force RT6296E 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 0.1F 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 0.1F 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. DS6296E-00 August 2015 RT6296E Function Block Diagram TTH VIN PVCC Internal Regulator Current Sense UVLO BOOT UVLO BOOT Logic & Protection Control 0.4V Power Stage & Deadtime Control + UV Comparator HS Switch Current Comparator 1pF 50pF FB 0.807V 400k + EA + Oscillator SW LS Switch Current Comparator Slope Compensation Current Sense 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 UVLO rising threshold voltage (5.3V), the converter resets and prepares RT6296E provides cycle-by-cycle over current limit protection. When the inductor current peak value 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 (4.2V) during normal operation, the device stops switching. The UVLO rising and falling threshold voltage includes a hysteresis to prevent noise caused reset. Internal Regulator The internal regulator generates 5V power and drive internal circuit. When VIN is below 5V, PVCC will drop with VIN. A capacitor (>0.1μF) between PVCC and GND is required. Soft-Start Function The RT6296E 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 between SS pin and GND. The Chip provides a 10.5μA charge current for the external capacitor. Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS6296E-00 August 2015 Under Voltage Protection (Hiccup Mode) RT6296E 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. Thermal Shutdown Thermal shutdown is implemented to prevent the chip from operating at excessively high temperatures. When the junction temperature is higher than 150°C, the chip will shutdown the switching operation. The chip is automatically re-enabled when the junction temperature cools down by approximately 20°C. is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT6296E Absolute Maximum Ratings (Note 1) Supply Input Voltage, VIN ------------------------------------------------------------------------------------------Switch Voltage, SW -------------------------------------------------------------------------------------------------BOOT to SW, VBOOT − SW ------------------------------------------------------------------------------------------Other Pins --------------------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C −0.3V to 20V −0.3V to VIN + 0.3V −0.3V to 6V −0.3V to 6V TSOT-23-8 (FC) -------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) TSOT-23-8 (FC), θJA -------------------------------------------------------------------------------------------------TSOT-23-8 (FC), θJC -------------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) --------------------------------------------------------------------------Junction Temperature ------------------------------------------------------------------------------------------------Storage Temperature Range ---------------------------------------------------------------------------------------ESD Susceptibility (Note 3) HBM (Human Body Model) ------------------------------------------------------------------------------------------ 1.428W Recommended Operating Conditions 70°C/W 15°C/W 260°C −40°C to 150°C −65°C to 150°C 2kV (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 -- 100 -- Low-Side RDS(ON)L -- 40 -- Under 40% duty-cycle 3 4.5 -- 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. DS6296E-00 August 2015 RT6296E 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 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 highly thermal conductive four-layer test board. 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. DS6296E-00 August 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT6296E Typical Application Circuit C3 0.1µF RT6296E 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 PVCC 1 TTH R4 10k L1 4.7µH 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 2.2 3.3 40.2 13 8.2 22 44 4.7 5.0 40.2 7.68 8.2 22 44 4.7 Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 is a registered trademark of Richtek Technology Corporation. DS6296E-00 August 2015 RT6296E Typical Operating Characteristics Output Voltage vs. Input Voltage Efficiency vs. Output Current 3.46 100 3.42 Efficiency (%) Output Voltage (V) VIN = 4.5V VIN = 12V VIN = 17V 80 60 40 3.38 3.34 3.30 3.26 3.22 20 3.18 VOUT = 3.3V, IOUT = 2A VOUT = 3.3V 3.14 0 0 0.25 0.5 0.75 1 1.25 1.5 1.75 4 2 5 6 7 Reference Voltage vs. Temperature 9 10 11 12 13 14 15 16 17 Output Voltage vs. Output Current 0.84 3.46 0.83 3.42 0.82 3.38 Output Voltage (V) Reference Voltage (V) 8 Input Voltage (V) Output Current (A) 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 Temperature (°C) 0.25 0.5 0.75 1 1.25 1.5 1.75 2 Output Current (A) UVLO Voltage vs. Temperature Load Transient Response 5.60 UVLO Voltage (V) 5.40 Rising VOUT (50mV/Div) Falling IOUT (1A/Div) 5.20 5.00 4.80 4.60 4.40 4.20 VOUT = 3.3V, IOUT = 0A VIN = 12V, VOUT = 3.3, IOUT = 1A to 2A to 1A, L = 4.7μH 4.00 -50 -25 0 25 50 75 100 125 Time (200μs/Div) Temperature (°C) Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS6296E-00 August 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT6296E Power On from VIN Output Ripple Voltage VOUT (20mV/Div) VOUT (2V/Div) VIN (10V/Div) VLX (10V/Div) VLX (5V/Div) VIN = 12V, VOUT = 3.3, IOUT = 2A, L = 4.7μH Time (1μs/Div) ILX (2A/Div) VIN = 12V, VOUT = 3.3, IOUT = 2A Time (5ms/Div) Power Off from VIN VIN = 12V, VOUT = 3.3, IOUT = 2A VOUT (2V/Div) VIN (10V/Div) VLX (10V/Div) ILX (2A/Div) Time (5ms/Div) Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 is a registered trademark of Richtek Technology Corporation. DS6296E-00 August 2015 RT6296E Application Information The RT6296E is a high voltage buck converter that can 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. 5V BOOT Output Voltage Selection RT6296E 100nF SW The resistive voltage divider allows the FB pin to sense a fraction of the output voltage as shown in Figure 1. Figure 2. External Bootstrap Diode FB RT6296E R5 R1 VOUT The TTH Voltage setting R2 GND Figure 1. Output Voltage Setting For adjustable voltage mode, the output voltage is set by an external resistive voltage divider according to the following equation : R1 VOUT VFB 1 R2 The TTH voltage is used to be change the transition threshold between power saving mode and CCM. Higher TTH voltage gets higher efficiency at light load condition but larger output ripple; a lower TTH voltage can improve output ripple but degrades efficiency during light load condition. A resistor divider from PVCC (5V) of RT6296E can help to build TTH voltage, as shown in Figure 3. It is recommended that TTH voltage should be less than 0.6V. PVCC Where VFB is the feedback reference voltage (0.807V typ.). Table 2 lists the recommended resistors value for common output voltages. R3 TTH RT6296E R4 GND 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 External Soft-Start Capacitor 5.0 40.2 7.68 8.2 RT6296E provides external soft-start function. The softstart 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 11μA 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 : 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 RT6296E. Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS6296E-00 August 2015 Figure 3. TTH Voltage Setting tSS (ms) = CSS (nF) 1.3 ISS ( A) is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT6296E Inductor Selection The inductor value and operating frequency determine the ripple current according to a specific input and output voltage. The ripple current ΔIL increases with higher VIN and decreases with higher inductance. V V IL OUT 1 OUT f L V IN 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. For the ripple current selection, the value of ΔIL = 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. CIN 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 current, a low ESR input capacitor sized for the maximum RMS current should be used. The RMS current is given by : IRMS IOUT(MAX) VOUT VIN VIN 1 VOUT This formula has a maximum at VIN = 2VOUT, where IRMS = IOUT/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 COUT is determined by the required Effective Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 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 the load transient response as described in a later section. The output ripple, ΔVOUT, is determined by : 1 VOUT IL ESR 8fCOUT The output ripple will be highest at the maximum input voltage since ΔIL 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 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. Thermal 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 : PD(MAX) = (TJ(MAX) − TA) / θJA where TJ(MAX) is the maximum junction temperature, TA is the ambient temperature, and θJA is the junction to ambient thermal resistance. For recommended operating condition specifications, the maximum junction temperature is 125°C. The junction to is a registered trademark of Richtek Technology Corporation. DS6296E-00 August 2015 RT6296E ambient thermal resistance, θJA, is layout dependent. For TSOT-23-8 (FC) package, the thermal resistance, θJA, 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 following formula : Layout Considerations For best performance of the RT6296E, the following layout guidelines must be strictly followed. PD(MAX) = (125°C − 25°C) / (70°C/W) = 1.428W for TSOT-23-8 (FC) package The maximum power dissipation depends on the operating ambient temperature for fixed T J(MAX) and thermal resistance, θJA. The derating curve in Figure 4 allows the designer to see the effect of rising ambient temperature on the maximum power dissipation. Input capacitor must be placed as close to the IC as possible. SW should be connected to inductor by wide and short trace. Keep sensitive components away from this trace. Keep every trace connected to pin as wide as possible for improving thermal dissipation. Maximum Power Dissipation (W)1 1.6 Four-Layer PCB 1.4 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 5. PCB Layout Guide Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS6296E-00 August 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 11 RT6296E Outline Dimension Symbol Dimensions In Millimeters 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. www.richtek.com 12 DS6296E-00 August 2015