RT7296AGJ8F

RT7296A 3A, 17V Current Mode Synchronous Step-Down Converter General Description Features The RT7296A 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  TTH Power-Save Mode against  Internal Soft-Start Function input  Input Under-Voltage Lockout under-voltage lockout, output under-voltage protection,  Output Under-Voltage Protection over-current protection, and thermal shutdown. The  Thermal Shutdown high-side mode control shorted complete output. protection and The 30m RT7296A provides functions such as PWM frequency is adjustable by the EN/SYNC pin. The RT7296A is available in the TSOT-23-8 (FC) package. Ordering Information RT7296A 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 02= : Product Code DNN : Date Code 02=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 RT7296A BOOT C3 C1 L1 VOUT SW Enable EN/SYNC PVCC C2 R3 TTH R5 R1 FB R2 C4 GND R4 Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS7296A-01 May 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT7296A Pin Configurations PVCC EN/SYNC 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 RT7296A into power saving mode under light loads. Connect to PVCC to force RT7296A into forced PWM mode. 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 0.1F 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 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. DS7296A-01 May 2015 RT7296A Function Block Diagram TTH 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 8s, the IC will shut down. resets and prepares the PWM for operation. If the input The RT7296A 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 (0.1F) between PVCC and mode, the RT7296A’s quiescent current drops to lower GND is required. than 1A. Driving the EN pin high (>1.6V) will turn on the device. Internal Soft-Start Function The RT7296A 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. DS7296A-01 May 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT7296A Over-Current Protection RT7296A provides cycle-by-cycle over current protection. When the inductor current peak value reaches current limit, IC will turn off high-side MOS to avoid over current. Under-Voltage Protection (Hiccup Mode) RT7296A 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 shut down the switching operation. The chip is automatically re-enabled when the junction temperature cools down by approximately 20C. Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 is a registered trademark of Richtek Technology Corporation. DS7296A-01 May 2015 RT7296A 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 ---------------------------------------------------------------------------------------- 4.5V 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 Test Conditions Min Typ Max Unit Shutdown Supply Current VEN = 0V -- -- 1 A Quiescent Current with no Load at DCDC Output VEN = 2V, VFB = 1V, TTH = 0.5V -- 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 440 500 580 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. DS7296A-01 May 2015 m is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT7296A Parameter EN Input Voltage Symbol 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 -- -- 8 -- s 3.7 3.9 4.1 V -- 650 -- mV -- 5 -- V VIL EN Input Current IEN EN Turn-off Delay ENtd-off Input Under-Voltage Lockout Threshold VIN Rising Test Conditions VUVLO VIN Rising Hysteresis VUVLO Unit V A VCC Regulator VCC VCC 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 = 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. www.richtek.com 6 is a registered trademark of Richtek Technology Corporation. DS7296A-01 May 2015 RT7296A Typical Application Circuit C3 0.1μF RT7296A 5 2 BOOT VIN VIN 4.5V to 17V Enable C2 0.1μF C1 22μF 6 EN/SYNC 7 PVCC R3 91k 1 TTH GND R4 4 10k Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS7296A-01 May 2015 SW FB R6 L1 10 4.7μH 3 8 VOUT R5 33k R1 40.2k R2 13k C4 44μF is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT7296A Typical Operating Characteristics Efficiency vs. Output Current Output Voltage vs. Input Voltage 100 3.60 3.55 80 VIN = 7V 3.50 3.45 70 VIN = 12V Output Voltage (V) Efficiency (%) 90 VIN = 17V 60 50 40 30 20 3.40 3.35 3.30 3.25 3.20 3.15 3.10 10 3.05 VOUT = 3.3V 0 0 0.5 1 1.5 2 2.5 VOUT = 3.3V, IOUT = 3A 3.00 4 3 5 6 7 8 Reference Voltage vs. Temperature 10 11 12 13 14 15 16 17 Output Voltage vs. Load Current 0.84 3.46 0.83 3.42 0.82 3.38 Output Voltage (V) Reference Voltage (V) 9 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 VIN = 12V, VOUT = 3.3V TTH = 3V 0.76 3.14 -50 -25 0 25 50 75 100 125 0 0.5 1 2 2.5 3 EN Threshold vs. Temperature 1.50 4.20 1.45 EN Threshold (V) UVLO Voltage (V) UVLO Voltage vs. Temperature 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 Load Current (A) Temperature (°C) 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. www.richtek.com 8 125 -50 -25 0 25 50 75 100 125 Temperature (°C) is a registered trademark of Richtek Technology Corporation. DS7296A-01 May 2015 RT7296A Load Transient Response Output Ripple Voltage VOUT VOUT (100mV/Div) (20mV/Div) IOUT (1A/Div) VIN = 12V, VOUT = 3.3V, IOUT = 1.5A to 3A to 1.5A, L = 4.7H VLX (5V/Div) Time (200s/Div) Time (2s/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 VIN = 12V, VOUT = 3.3V, IOUT = 3A Time (5ms/Div) Time (500s/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. DS7296A-01 VIN = 12V, VOUT = 3.3V, IOUT = 3A, L = 4.7H May 2015 VIN = 12V, VOUT = 3.3V, IOUT = 3A Time (5ms/Div) is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT7296A Application Information The RT7296A 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. RT7296A SW Output Voltage Selection The resistive voltage divider allows the FB pin to sense a fraction of the output voltage as shown in Figure 1. FB R5 RT7296A 100nF Figure 2. External Bootstrap Diode The TTH Voltage setting R1 VOUT The TTH voltage is used to be change the transition R2 threshold between power saving mode and CCM. GND 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 can improve output ripple but degrades efficiency by an external resistive voltage divider according to the during light load condition. A resistor divider from PVCC following equation : (5V) of RT7296A can help to build TTH voltage, as  R1  VOUT  VFB  1    R2  shown in Figure 3. It is recommended that TTH voltage should be less than 0.6V. Where VFB is the feedback reference voltage (0.8V PVCC typ.). Table 1 lists the recommended resistors value for R3 TTH RT7296A common output voltages. Table1. Recommended Resistors Value VOUT (V) R1 (k) R2 (k) R5 (k) 1.0 20.5 82 82 3.3 40.2 13 33 5.0 40.2 7.68 33 R4 GND Figure 3. TTH Voltage Setting Inductor Selection The inductor value and operating frequency determine External Bootstrap Diode the ripple current according to a specific input and Connect a 100nF low ESR ceramic capacitor between output voltage. The ripple current ΔIL increases with the BOOT pin and SW pin. This capacitor provides the higher VIN and decreases with higher inductance. gate driver voltage for the high side MOSFET. It is recommended to add an external bootstrap diode  V   V IL   OUT    1  OUT  f  L V    IN  between an external 5V and BOOT pin, as shown as Having a lower ripple current reduces not only the ESR Figure 2, for efficiency improvement when input voltage losses in the output capacitors but also the output is lower than 5.5V or duty ratio is higher than 65% .The voltage ripple. High frequency with small ripple current bootstrap diode can be a low cost one such as IN4148 can achieve highest efficiency operation. However, it or BAT54. The external 5V can be a 5V fixed input from requires a large inductor to achieve this goal. system or a 5V output (PVCC) of the RT7296A. Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 is a registered trademark of Richtek Technology Corporation. DS7296A-01 May 2015 RT7296A For the ripple current selection, the value of IL = 0.3 voltage since IL increases with input voltage. Multiple (IMAX) will be a reasonable starting point. The largest capacitors placed in parallel may be needed to meet ripple current occurs at the highest VIN. To guarantee the ESR and RMS current handling requirement. Dry that the ripple current stays below the specified tantalum, special polymer, aluminum electrolytic and maximum, the inductor value should be chosen ceramic capacitors are all available in surface mount according to the following equation : packages. Special polymer capacitors offer very low  VOUT   VOUT  L  1   f  IL(MAX)   VIN(MAX)     ESR value. However, it provides lower capacitance The inductor's current rating density than other types. Although Tantalum capacitors (caused a 40°C have the highest capacitance density, it is important to temperature rising from 25°C ambient) should be only use types that pass the surge test for use in greater than the maximum load current and its switching saturation current should be greater than the short capacitors have significantly higher ESR. However, it circuit peak current limit. can be used in cost-sensitive applications for ripple power supplies. Aluminum electrolytic current rating and long term reliability considerations. CIN and COUT Selection Ceramic The input capacitance, CIN, 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 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 This formula has a maximum at VIN = 2VOUT, where maximum junction temperature. The maximum power IRMS = IOUT / 2. This simple worst-case condition is dissipation depends on the thermal resistance of the IC commonly used for design because even significant package, PCB layout, rate of surrounding airflow, and deviations do not offer much relief. difference between junction and ambient temperature. Choose a capacitor rated at a higher temperature than The maximum power dissipation can be calculated by required. Several capacitors may also be paralleled to the following formula : meet size or height requirements in the design. The PD(MAX) = (TJ(MAX) TA) / θJA selection of COUT is determined by the required where TJ(MAX) is the maximum junction temperature, Effective Series Resistance (ESR) to minimize voltage TA is the ambient temperature, and θJA is the junction ripple. Moreover, the amount of bulk capacitance is to ambient thermal resistance. also a key for COUT selection to ensure that the control For recommended operating condition specifications, loop is stable. Loop stability can be checked by viewing the maximum junction temperature is 125°C. The the load transient response as described in a later junction to ambient thermal resistance, θJA, is layout section. The output ripple, VOUT, is determined by : dependent. For TSOT-23-8 (FC) package, the thermal   1 VOUT  IL   ESR   8fC OUT   resistance, θJA, is 70°C/W on a standard four-layer The output ripple will be highest at the maximum input TA = 25°C can be calculated by the following formula : Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS7296A-01 May 2015 thermal test board. The maximum power dissipation at is a registered trademark of Richtek Technology Corporation. www.richtek.com 11 RT7296A PD(MAX) = (125°C 25°C) / (70°C/W) = 1.428W for Layout Considerations TSOT-23-8 (FC) package For best performance of the RT7296A, the following The maximum power dissipation depends on the layout guidelines must be strictly followed. operating ambient temperature for fixed TJ(MAX) and  thermal resistance, θJA. The derating curve in Figure 4 possible. allows the designer to see the effect of rising ambient  temperature on the maximum power dissipation. SW should be connected to inductor by wide and short trace. Keep sensitive components away from this trace. 1.5 Maximum Power Dissipation (W)1 Input capacitor must be placed as close to the IC as Four-Layer PCB  1.2 Keep every trace connected to pin as wide as possible for improving thermal dissipation. 0.9 0.6 0.3 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 6 SW 2 PVCC 7 EN/SYNC GND VIN VOUT CIN COUT COUT TTH 8 BOOT 5 SW CIN R2 The feedback components must be connected as close to the device as possible. R4 R3 PVCC 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. www.richtek.com 12 is a registered trademark of Richtek Technology Corporation. DS7296A-01 May 2015 RT7296A 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. DS7296A-01 May 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 13