RT7296F 3A, 17V Current Mode Synchronous Step-Down Converter General Description Features The RT7296F is a high-efficiency, 3A current mode 4.5V to 17V Input Voltage Range synchronous step-down DC/DC converter with a wide 3A Output Current input voltage range from 4.5V 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 : 500kHz current architecture supports fast Synchronous to External Clock : 200kHz to 2MHz transient response and internal compensation. A Cycle-by-Cycle Current Limit cycle-by-cycle current limit function provides protection Internal Soft-Start Function against Power Save mode at light load input Power Good Indicator under-voltage lockout, output under-voltage protection, Input Under-Voltage Lockout over-current protection, and thermal shutdown. The Output Under-Voltage Protection PWM frequency is adjustable by the EN/SYNC pin. The Thermal Shutdown high-side mode control shorted complete output. protection and The 30m RT7296F functions such provides as RT7296F is available in the TSOT-23-8 (FC) package. Ordering Information RT7296F Package Type J8F : TSOT-23-8 (FC) Lead Plating System G : Green (Halogen Free and Pb Free) Applications Industrial and Commercial Low Power Systems Computer Peripherals LCD Monitors and TVs Set-top Boxes Marking Information Note : Richtek products are : 08= : Product Code DNN : Date Code 08=DNN 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 RT7296F BOOT C3 C1 L1 VOUT SW Enable EN/SYNC R5 PVCC C2 R3 PG Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS7296F-00 July 2015 R1 FB R2 C4 GND is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT7296F Pin Configurations PVCC EN/SYNC BOOT 8 7 6 5 2 3 4 VIN SW GND PG FB (TOP VIEW) TSOT-23-8 (FC) Functional Pin Description Pin No. Pin Name Pin Function 1 PG Power Good Output. This pin is an open drain which can be connected to PVCC by a resistor. If output voltage achieve 90% of the normal voltage, the PG pin will go high after 400s delay. 2 VIN Power Input. Support 4.5V 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 EN/SYNC Enable Control Input. High = Enable. Apply an external clock to adjust the switching frequency. If using pull high resistor connected to VIN, the recommended value range is 60k to 300k. 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. DS7296F-00 July 2015 RT7296F Function Block Diagram PG VIN PVCC Internal Regulator Current Sense UVLO BOOT UVLO Shutdown Comparator - EN/SYNC 1.4V + 0.4V + BOOT Logic & Protection Control Power Stage & Deadtime Control SW - UV Comparator HS Switch Current Comparator 1pF 50pF 400k FB 0.807V Internal SS + EA + Oscillator LS Switch Current Comparator Current Sense GND Slope Compensation Operation Under-Voltage Lockout Threshold Operating Frequency and Synchronization The IC includes an input Under Voltage Lockout The internal oscillator runs at 500kHz (typ.) when the Protection (UVLO). If the input voltage exceeds the EN/SYNC pin is at logic-high level (>1.6V). If the EN UVLO rising threshold voltage (3.9V), the converter pin is pulled to low-level over 8s, the IC will shut down. resets and prepares the PWM for operation. If the input The RT7296F can be synchronized with an external voltage falls below the UVLO falling threshold voltage clock ranging from 200kHz to 2MHz applied to the (3.25V) during normal operation, the device stops EN/SYNC pin. The external clock duty cycle must be switching. The UVLO rising and falling threshold from 20% to 80% with logic-high level = 2V and voltage includes a hysteresis to prevent noise caused logic-low level = 0.8V. reset. Internal Regulator Chip Enable The internal regulator generates 5V power and drive The EN pin is the chip enable input. Pulling the EN pin internal circuit. When VIN is below 5V, PVCC will drop low (<1.1V) will shut down the device. During shutdown with VIN. A capacitor (>0.1F) between PVCC and mode, the RT7296F’s quiescent current drops to lower GND is required. than 1A. Driving the EN pin high (>1.6V) will turn on the device. Internal Soft-Start Function The RT7296F provides internal soft-start function. The soft-start function is used to prevent large inrush current while converter is being powered-up. The soft-start time (VFB from 0V to 0.8V) is 1.5ms. Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS7296F-00 July 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT7296F 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 = 25C TSOT-23-8 (FC) ---------------------------------------------------------------------------------------------------------- 1.428W Package Thermal Resistance (Note 2) TSOT-23-8 (FC), JA --------------------------------------------------------------------------------------------------- 70C/W TSOT-23-8 (FC), JC --------------------------------------------------------------------------------------------------- 15C/W Lead Temperature (Soldering, 10 sec.) --------------------------------------------------------------------------- 260C Junction Temperature --------------------------------------------------------------------------------------------------- 40C to 150C Storage Temperature Range ----------------------------------------------------------------------------------------- 65C to 150C ESD Susceptibility (Note 3) HBM (Human Body Model) ------------------------------------------------------------------------------------------- 2kV Recommended Operating Conditions (Note 4) Supply Input Voltage, VIN ---------------------------------------------------------------------------------------4.5V to 17V Junction Temperature Range ---------------------------------------------------------------------------------------- 40C to 125C Ambient Temperature Range ---------------------------------------------------------------------------------------- 40C to 85C Electrical Characteristics (VIN = 12V, TA = 25C, unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max Unit Shutdown Supply Current VEN = 0V -- 7 -- A Quiescent Current with no Load at DCDC Output VEN = 2V, VFB = 1V -- 0.8 1 mA 0.799 0.807 0.815 V -- 10 50 nA Feedback Voltage VFB Feedback Current IFB Switch On-Resistance VFB = 820mV High-Side RDS(ON)H -- 80 -- Low-Side RDS(ON)L -- 30 -- -- -- 1 A Under 40% duty-cycle 4.2 5 -- A From Drain to Source -- 2 -- A 440 500 570 kHz 200 -- 2000 kHz VFB < 400mV -- 125 -- kHz VFB = 0.7V 90 95 -- % -- 60 -- ns Switch Leakage Current Limit VEN = 0V, VSW = 0V ILIM Low-Side Switch Current Limit Oscillation Frequency fOSC SYNC Frequency Range f SYNC Fold-Back Frequency Maximum Duty-Cycle DMAX Minimum On-Time tON VFB = 0.75V Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 m is a registered trademark of Richtek Technology Corporation. DS7296F-00 July 2015 RT7296F Parameter EN Input Voltage Symbol Test Conditions Min Typ Max Logic-High VIH 1.2 1.4 1.6 Logic-Low 1.1 1.25 1.4 VEN = 2V -- 2 -- VEN = 0V -- 0 -- VIL Unit V A EN Input Current IEN EN Turn-off Delay ENtd-off -- 8 -- s Power-Good Rising Threshol PGvth-Hi -- 0.9 -- VFB Power-Good Falling Threshol PGvth-Lo -- 0.85 -- VFB Power-Good Delay PGTd -- 0.4 -- ms Power-Good Sink Current Capability VPG -- -- 0.4 V Power-Good Leakage Current IPG-LEAK -- -- 1 A 3.7 3.9 4.1 V -- 650 -- mV -- 5 -- V Input Under-Voltage Lockout Threshold VIN Rising VUVLO Sink 4mA VIN Rising Hysteresis VUVLO PVCC Regulator VCC PVCC Load Regulation VLOAD IVCC = 5mA -- 3 -- % Soft-Start Time tSS FB from 0V to 0.8V -- 1.5 -- ms 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 = 25C 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. DS7296F-00 July 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT7296F Typical Application Circuit VIN 4.5V to 17V C1 22μF C3 0.1μF RT7296F 5 2 BOOT VIN 6 Enable EN/SYNC SW R6 L1 10 4.7μH 3 VOUT Cff 7 C2 0.1μF PVCC R3 100k 1 PG FB 8 R5 16k GND 4 15pF R1 40.2k R2 13k C4 44μF Table 1. Suggested Component Values VOUT (V) R1 (k) R2 (k) R5 (k) Cff (pF) C2 (F) C4 (F) L1 (H) 1.0 20.5 84.5 82 15 0.1 44 2.2 3.3 40.2 13 16 15 0.1 44 4.7 5.0 40.2 7.68 16 15 0.1 44 4.7 Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 is a registered trademark of Richtek Technology Corporation. DS7296F-00 July 2015 RT7296F Typical Operating Characteristics Output Voltage vs. Input Voltage Efficiency vs. Output Current 3.46 100 3.42 80 VIN = 4.5V 70 VIN = 12V 60 VIN = 17V Output Voltage(V) Efficiency (%) 90 50 40 30 20 3.38 3.34 3.30 3.26 3.22 3.18 10 VOUT = 3.3V 0 IOUT = 3A 3.14 0 0.5 1 1.5 2 2.5 3 4 5 6 7 8 Output Current (A) Output Voltage vs. Output Current 0.84 3.46 0.83 3.42 0.82 3.38 Output Voltage (V) Reference Voltage (V) 10 11 12 13 14 15 16 17 Input Voltage (V) Reference Voltage vs. Temperature 0.81 0.80 0.79 0.78 3.34 3.30 3.26 3.22 3.18 0.77 VIN = 12V, VOUT = 3.3V IOUT = 1A 3.14 0.76 -50 -25 0 25 50 75 100 0 125 0.5 1 Temperature (°C) 2 2.5 3 EN Threshold vs. Temperature 1.50 4.20 1.45 EN Threshold (V) 4.40 4.00 Rising 3.80 3.60 1.40 Rising 1.35 1.30 1.25 3.40 Falling 3.20 1.5 Output Current (A) UVLO Voltage vs. Temperature UVLO Voltage (V) 9 Falling 1.20 VOUT = 3.3V, IOUT = 0A VOUT = 3.3V, IOUT = 0A 1.15 3.00 -50 -25 0 25 50 75 100 Temperature (°C) Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS7296F-00 July 2015 125 -50 -25 0 25 50 75 100 125 Temperature (°C) is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT7296F Load Transient Response Output Ripple Voltage VOUT VOUT (50mV/Div) (20mV/Div) VLX IOUT (1A/Div) (5V/Div) VIN = 12V, VOUT = 3.3V, IOUT = 1.5A to 3A to 1.5A, L = 4.7H VIN = 12V, VOUT = 3.3V, IOUT = 3A, L = 4.7H Time (200s/Div) Time (1s/Div) Power On from EN Power Off from EN VOUT VOUT (2V/Div) (2V/Div) VEN VEN (2V/Div) (2V/Div) VLX VLX (10V/Div) (10V/Div) ILX ILX (3A/Div) (3A/Div) VIN = 12V, VOUT = 3.3V, IOUT = 3A Time (2ms/Div) Time (2ms/Div) Power On from VIN Power Off from VIN VOUT VOUT (2V/Div) (2V/Div) VIN VIN (10V/Div) (10V/Div) VLX (10V/Div) VLX (10V/Div) ILX ILX (3A/Div) (3A/Div) VIN = 12V, VOUT = 3.3V, IOUT = 3A Time (5ms/Div) Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 VIN = 12V, VOUT = 3.3V, IOUT = 3A VIN = 12V, VOUT = 3.3V, IOUT = 3A Time (5ms/Div) is a registered trademark of Richtek Technology Corporation. DS7296F-00 July 2015 RT7296F Application Information The RT7296F 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 BOOT current can be up to 3A. RT7296F SW Output Voltage Selection The resistive voltage divider allows the FB pin to sense Figure 2. External Bootstrap Diode a fraction of the output voltage as shown in Figure 1. FB R5 RT7296F 100nF Inductor Selection R1 VOUT The inductor value and operating frequency determine R2 the ripple current according to a specific input and GND output voltage. The ripple current ΔIL increases with higher VIN and decreases with higher inductance. Figure 1. Output Voltage Setting by an external resistive voltage divider according to the V V IL OUT 1 OUT VIN f L following equation : Having a lower ripple current reduces not only the ESR For adjustable voltage mode, the output voltage is set R1 VOUT VFB 1 R2 losses in the output capacitors but also the output voltage ripple. High frequency with small ripple current Where VFB is the feedback reference voltage (0.8V can achieve highest efficiency operation. However, it typ.). Table 2 lists the recommended resistors value for requires a large inductor to achieve this goal. common output voltages. For the ripple current selection, the value of IL = 0.3 Table 2. Recommended Resistors Value (IMAX) will be a reasonable starting point. The largest VOUT (V) R1 (k) R2 (k) R5 (k) ripple current occurs at the highest VIN. To guarantee 1.0 20.5 84.5 82 that the ripple current stays below the specified 3.3 40.2 13 16 maximum, the inductor value should be chosen 5.0 40.2 7.68 16 according to the following equation : 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 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. is lower than 5.5V or duty ratio is higher than 65% .The CIN and COUT Selection bootstrap diode can be a low cost one such as IN4148 The input capacitance, CIN, is needed to filter the or BAT54. The external 5V can be a 5V fixed input from trapezoidal current at the source of the top MOSFET. system or a 5V output (PVCC) of the RT7296F. To prevent large ripple current, a low ESR input Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS7296F-00 July 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT7296F capacitor sized for the maximum RMS current should ceramic capacitors with trace inductance can also lead be used. The RMS current is given by : to significant ringing. IRMS IOUT(MAX) VOUT VIN VIN 1 VOUT Thermal Considerations For continuous operation, do not exceed absolute 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 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, VOUT, is determined by : VOUT 1 IL ESR 8fCOUT 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 ambient thermal resistance, θJA, is layout dependent. For TSOT-23-8 (FC) package, the thermal resistance, θJA, is 70°C/W on a standard four-layer 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 thermal test board. The maximum power dissipation at TA = 25°C can be calculated by the following formula : 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 TJ(MAX) and thermal resistance, θJA. The derating curve in Figure 3 allows the designer to see the effect of rising ambient temperature on the maximum power dissipation. 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 Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 is a registered trademark of Richtek Technology Corporation. DS7296F-00 July 2015 RT7296F Layout Considerations Maximum Power Dissipation (W)1 1.5 Four-Layer PCB For best performance of the RT7296F, the following 1.2 layout guidelines must be strictly followed. Input capacitor must be placed as close to the IC as 0.9 possible. 0.6 SW should be connected to inductor by wide and short trace. Keep sensitive components away from 0.3 this trace. 0.0 0 25 50 75 100 125 Keep every trace connected to pin as wide as possible for improving thermal dissipation. Ambient Temperature (°C) Figure 3. 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 6 SW 2 PVCC 7 EN/SYNC GND VIN VOUT CIN COUT COUT PG 8 BOOT 5 SW CIN R2 The feedback components must be connected as close to the device as possible. PVCC Css 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 3. PCB Layout Guide Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS7296F-00 July 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 11 RT7296F 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. DS7296F-00 July 2015