RT6214AHGJ6F

RT6214A/B 3A, 18V, 500kHz, ACOTTM Step-Down Converter General Description Features The RT6214A/B is a high-efficiency, monolithic synchronous step-down DC/DC converter that can deliver up to 3A output current from a 4.5V to 18V input supply. The RT6214A/B adopts ACOT architecture to allow the transient response to be improved and keep in constant frequency. Cycle-by-cycle current limit provides protection against shorted outputs and soft-start eliminates input current surge during start-up. Fault conditions also include output under voltage  protection and thermal shutdown.  Ordering Information Applications RT6214A/B Package Type J6F : TSOT-23-6 (FC)        UVP Option H : Hiccup 0.8V  2% Voltage Reference Internal Start-Up from Pre-biased Output Voltage Compact Package: TSOT-23-6 pin High / Low Side Over-Current Protection and Hiccup Output Voltage Range : 0.8V to 6.5V  Set-Top Boxes  Portable TVs Access Point Routers  Lead Plating System G : Green (Halogen Free and Pb Free) Integrated 100m/50m MOSFETs 4.5V to 18V Supply Voltage Range 500kHz Switching Frequency ACOT Control   DSL Modems LCD TVs Marking Information RT6214AHGJ6F PSM/PWM A : PSM Mode B : PWM Mode 1G= : Product Code DNN : Date Code 1G=DNN Note : Richtek products are : RT6214BHGJ6F  RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020.  1F= : Product Code DNN : Date Code 1F=DNN Suitable for use in SnPb or Pb-free soldering processes. Simplified Application Circuit RT6214A/B BOOT VIN VIN CIN CBOOT L VOUT LX Enable EN R1 GND Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS6214A/B-01 November 2015 CFF COUT FB R2 is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT6214A/B Pin Configurations (TOP VIEW) BOOT EN 6 FB 5 4 2 3 GND LX VIN TSOT-23-6 (FC) Functional Pin Description Pin No. Pin Name Pin Function 1 GND System Ground. Provides the ground return path for the control circuitry and low-side power MOSFET. 2 LX Switch Node. LX is the switching node that supplies power to the output and connect the output LC filter from LX to the output load. 3 VIN Power Input. Supplies the power switches of the device. 4 FB Feedback Voltage Input. This pin is used to set the desired output voltage via an external resistive divider. The feedback voltage is 0.8V typically. 5 EN Enable Control Input. Floating this pin or connecting this pin to logic high can enable the device and connecting this pin to GND can disable the device. 6 BOOT Bootstrap Supply for High-Side Gate Driver. Connect a 100nF or greater capacitor from LX to BOOT to power the high-side switch. Function Block Diagram BOOT VIN VIN PVCC Reg Minoff PVCC VIBIAS VREF UGATE OC Control LX Driver LGATE UV GND GND LX PVCC Ripple Gen. EN + EN VIN + LX - Comparator On-Time LX FB Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS6214A/B-01 November 2015 RT6214A/B Operation The RT6214A/B is a synchronous step-down converter UVLO Protection with advanced constant on-time control mode. Using the ACOTTM control mode can reduce the output capacitance and provide fast transient response. It can minimize the component size without additional external compensation network. To protect the chip from operating at insufficient supply voltage, the UVLO is needed. When the input voltage of VIN is lower than the UVLO falling threshold voltage, the device will be lockout. Thermal Shutdown Current Protection The inductor current is monitored via the internal switches cycle-by-cycle. Once the output voltage drops under UV threshold, the RT6214A/B will enter hiccup mode. Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS6214A/B-01 November 2015 When the junction temperature exceeds the OTP threshold value, the IC will shut down the switching operation. Once the junction temperature cools down and is lower than the OTP lower threshold, the converter will autocratically resume switching. is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT6214A/B Absolute Maximum Ratings (Note 1)  Supply Input Voltage --------------------------------------------------------------------------------- 0.3V to 20V  Switch Node Voltage, LX ---------------------------------------------------------------------------- 0.3V to (VIN + 0.3V) < 10ns ---------------------------------------------------------------------------------------------------- 5V to 25V  BOOT Pin Voltage ------------------------------------------------------------------------------------ (VLX – 0.3V) to (VIN + 6.3V)  Other Pins ----------------------------------------------------------------------------------------------- 0.3V to 6V  Power Dissipation, PD @ TA = 25C TSOT-23-6 (FC) --------------------------------------------------------------------------------------- 1.667W  Package Thermal Resistance (Note 2) TSOT-23-6 (FC), JA --------------------------------------------------------------------------------- 60C/W TSOT-23-6 (FC), JC --------------------------------------------------------------------------------- 8C/W  Lead Temperature (Soldering, 10 sec.) ---------------------------------------------------------- 260C  Junction Temperature -------------------------------------------------------------------------------- 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 --------------------------------------------------------------------------------- 4.5V to 18V  Ambient Temperature Range----------------------------------------------------------------------- 40C to 85C  Junction Temperature Range ---------------------------------------------------------------------- 40C to 125C Electrical Characteristics (VIN = 12V, TA = 25C, unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max 4.5 -- 18 Unit Supply Voltage VIN Supply Input Operating Voltage VIN Under-Voltage Lockout Threshold VUVLO Under-Voltage Lockout Threshold Hysteresis VUVLO V 3.6 3.9 4.2 -- 340 -- mV Supply Current Supply Current (Shutdown) ISHDN VEN = 0V -- -- 5 µA Supply Current (Quiescent) IQ VEN = 2V, VFB = 0.85V -- 0.5 -- mA -- 1000 -- µS 1.38 1.5 1.62 -- 0.18 -- Soft-Start Soft-Start Time Enable Voltage Enable Voltage Threshold VEN Rising Enable Voltage Hysteresis Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 V is a registered trademark of Richtek Technology Corporation. DS6214A/B-01 November 2015 RT6214A/B Parameter Symbol Test Conditions Min Typ Max Unit 0.784 0.8 0.816 V -- 100 -- -- 50 -- 4 4.5 -- A fOSC -- 500 -- kHz Maximum Duty Cycle DMAX -- 90 -- % Minimum On Time tON(MIN) -- 60 -- Minimum Off Time tOFF(MIN) -- 240 -- UVP Detect 45 50 55 Hysteresis -- 10 -- Feedback Threshold Voltage VFB_TH 4.5V ≤ VIN ≤ 18V High-Side On-Resistance RDS(ON)_H VBOOT − VLX = 4.8V Low-Side On-Resistance RDS(ON)_L Feedback Threshold Voltage Internal MOSFET mΩ Current Limit Current Limit ILIM Valley Current Switching Frequency Switching Frequency On-Time Timer Control nS Output Under Voltage Protections UVP Trip Threshold % Thermal Shutdown Thermal Shutdown Threshold TSD -- 150 -- Thermal Shutdown Hysteresis TSD -- 20 -- °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. JA is measured at TA = 25C on a high effective thermal conductivity four-layer test board per JEDEC 51-7. The first layer of copper area is filled. 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. DS6214A/B-01 November 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT6214A/B Typical Application Circuit RT6214A/B 3 VIN CIN 22μF BOOT LX 5 Enable VIN 6 2 L 2.2μH EN GND 1 FB CBOOT 0.1μF VOUT R1 12k CFF Open COUT 44μF 4 Rt* 10k R2 24k * Note : When CFF is added, it is necessary to add Rt = 10k between feedback network and chip FB pin. Table 1. Suggested Component Values (VIN = 12V) VOUT (V) R1 (k) R2 (k) L (H) COUT (F) CFF (pF) 1.05 10 32.4 2.2 44 -- 1.2 20.5 41.2 2.2 44 -- 1.8 40.2 32.4 3.3 44 -- 2.5 40.2 19.1 3.3 44 22 to 68 3.3 40.2 13 4.7 44 22 to 68 5 40.2 7.68 4.7 44 22 to 68 Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 is a registered trademark of Richtek Technology Corporation. DS6214A/B-01 November 2015 RT6214A/B Typical Operating Characteristics Efficiency vs. Output Current Output Voltage vs. Output Current 100 1.40 90 1.35 Output Voltage (V) Efficiency (%) 80 70 VIN = 4.5V 60 VIN = 12V 50 VIN = 18V 40 30 1.30 VIN = 4.5V VIN = 12V 1.25 VIN = 18V 1.20 20 1.15 10 VOUT = 1.2V 0 0.001 VOUT = 1.2V 1.10 0.01 0.1 1 10 0 0.5 1 Output Current (A) 1.5 2 2.5 3 Output Current (A) Reference Voltage vs. Temperature EN Threshold vs. Temperature 0.820 1.60 Rising 1.50 0.810 EN Threshold (V) Reference Voltage (V) 0.815 0.805 0.800 0.795 0.790 1.40 1.30 Falling 1.20 0.785 VIN = 12V, IOUT = 1A 0.780 VOUT = 1.2V, IOUT = 0A 1.10 -50 -25 0 25 50 75 100 125 -50 Output Voltage vs. Temperature 0 25 50 75 100 125 Load Transient 1.220 1.210 Output Voltage (V) -25 Temperature (°C) Temperature (°C) VOUT (50mV/Div) 1.200 VIN = 12V, VOUT = 1.2V, IOUT = 0A to 3A , L = 2.2H VIN = 4.5V 1.190 VIN = 12V 1.180 VIN = 18V 1.170 VOUT = 1.2V, IOUT = 1A 1.160 -50 -25 0 25 50 75 100 Temperature (°C) Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS6214A/B-01 November 2015 125 IOUT (1A/Div) Time (100s/Div) is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT6214A/B Load Transient VOUT (50mV/Div) Output Ripple Voltage VSW (6V/Div) VIN = 12V, VOUT = 1.2V, IOUT = 3A , L = 2.2H IOUT (1A/Div) VOUT (20mV/Div) VIN = 12V, VOUT = 1.2V, IOUT = 1.5A to 3A , L = 2.2H Time (100s/Div) Time (1s/Div) Power On then Short Power On from EN VIN (5V/Div) VOUT (2V/Div) VIN = 12V, VOUT = 5V, IOUT = 3A VIN = 12V, VOUT = 5V VEN (2V/Div) VLX (10V/Div) VOUT (5V/Div) IOUT (2A/Div) IOUT (2A/Div) Time (4ms/Div) Time (1ms/Div) Power Off from EN Power On from VIN VIN (10V/Div) VOUT (2V/Div) VEN (5V/Div) VIN (10V/Div) VLX (2V/Div) VIN = 12V, VOUT = 5V, IOUT = 3A VEN (5V/Div) IOUT (2A/Div) IOUT (2A/Div) Time (20s/Div) Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 VIN = 12V, VOUT = 5V, IOUT = 3A Time (1ms/Div) is a registered trademark of Richtek Technology Corporation. DS6214A/B-01 November 2015 RT6214A/B Power Off from VIN VIN (10V/Div) VOUT (2V/Div) VIN = 12V, VOUT = 5V, IOUT = 3A VEN (5V/Div) IOUT (2A/Div) Time (20s/Div) Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS6214A/B-01 November 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT6214A/B Application Information Inductor Selection Selecting an inductor involves specifying its inductance and also its required peak current. The exact inductor value is generally flexible and is ultimately chosen to obtain the best mix of cost, physical size, and circuit efficiency. Lower inductor values benefit from reduced size and cost and they can improve the circuit's transient response, but they increase the inductor ripple current and output voltage ripple and reduce the efficiency due to the resulting higher peak currents. Conversely, higher inductor values increase efficiency, but the inductor will either be physically larger or have higher resistance since more turns of wire are required and transient response will be slower since more time is required to change current (up or down) in the inductor. A good compromise between size, efficiency, and transient response is to use a ripple current (IL) about 20% to 50% of the desired full output load current. Calculate the approximate inductor value by selecting the input and output voltages, the switching frequency (f SW ), the maximum output current (IOUT(MAX)) and estimating a IL as some percentage of that current. L= VOUT   VIN  VOUT  VIN  fSW  IL Once an inductor value is chosen, the ripple current (IL) is calculated to determine the required peak inductor current. IL = VOUT   VIN  VOUT  I and IL(PEAK) = IOUT(MAX)  L VIN  fSW  L 2 To guarantee the required output current, the inductor needs a saturation current rating and a thermal rating that exceeds IL(PEAK). These are minimum requirements. To maintain control of inductor current in overload and short circuit conditions, some applications may desire current ratings up to the current limit value. However, the IC's output under-voltage shutdown feature make this unnecessary for most applications. IL(PEAK) should not exceed the minimum value of IC's upper current limit level or the IC may not be able to Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 meet the desired output current. If needed, reduce the inductor ripple current (IL) to increase the average inductor current (and the output current) while ensuring that IL(PEAK) does not exceed the upper current limit level. For best efficiency, choose an inductor with a low DC resistance that meets the cost and size requirements. For low inductor core losses some type of ferrite core is usually best and a shielded core type, although possibly larger or more expensive, will probably give fewer EMI and other noise problems. Considering the Typical Operating Circuit for 1.2V output at 3A and an input voltage of 12V, using an inductor ripple of 0.9A (30%), the calculated inductance value is : L 1.2  12  1.2   2.4μH 12  500kHz  0.9A The ripple current was selected at 0.9A and, as long as we use the calculated 2.4H inductance, that should be the actual ripple current amount. The ripple current and required peak current as below : IL = 1.2  12  1.2  = 0.9A 12  500kHz  2.4μH and IL(PEAK) = 3A  0.9A = 3.45A 2 For the 2.4H value, the inductor's saturation and thermal rating should exceed 3.45A. Since the actual value used was 2.4H and the ripple current exactly 0.9A, the required peak current is 3.45A. Input Capacitor Selection The input filter capacitors are needed to smooth out the switched current drawn from the input power source and to reduce voltage ripple on the input. The actual capacitance value is less important than the RMS current rating (and voltage rating, of course). The RMS input ripple current (IRMS) is a function of the input voltage, output voltage, and load current : IRMS = IOUT(MAX)  VOUT VIN VIN 1 VOUT is a registered trademark of Richtek Technology Corporation. DS6214A/B-01 November 2015 RT6214A/B Ceramic capacitors are most often used because of their low cost, small size, high RMS current ratings, and robust surge current capabilities. However, take care For the Typical Operating Circuit for 1.2V output and an inductor ripple of 0.4A, with 2 x 22F output capacitance each with about 5m ESR including PCB when these capacitors are used at the input of circuits supplied by a wall adapter or other supply connected through long, thin wires. Current surges through the inductive wires can induce ringing at the RT6214A/B input which could potentially cause large, damaging voltage spikes at VIN. If this phenomenon is observed, some bulk input capacitance may be required. Ceramic capacitors (to meet the RMS current requirement) can be placed in parallel with other types such as tantalum, electrolytic, or polymer (to reduce ringing and overshoot). trace resistance, the output voltage ripple components are : Choose capacitors rated at higher temperatures than required. Several ceramic capacitors may be paralleled to meet the RMS current, size, and height requirements of the application. The typical operating circuit uses two 10F and one 0.1F low ESR ceramic capacitors on VRIPPLE(ESR) = 0.9A  5m = 4.5mV 0.9A = 5.11mV 8  44μF  500kHz VRIPPLE = 4.5mV  5.11mV = 9.61mV VRIPPLE(C) = Feed-forward Capacitor (Cff) The RT6214A/B are optimized for ceramic output capacitors and for low duty cycle applications. However for high-output voltages, with high feedback attenuation, the circuit's response becomes over-damped and transient response can be slowed. In high-output voltage circuits (VOUT > 3.3V) transient response is improved by adding a small “feed-forward” capacitor the input. (Cff) across the upper FB divider resistor (Figure 1), to increase the circuit's Q and reduce damping to speed Output Capacitor Selection up the transient response without affecting the steady-state stability of the circuit. Choose a suitable The RT6214A/B are optimized for ceramic output capacitors and best performance will be obtained using them. The total output capacitance value is usually determined by the desired output voltage ripple level and transient response requirements for sag (undershoot on positive load steps) and soar (overshoot on negative load steps). capacitor value that following below step.  Get the BW the quickest method to do transient response form no load to full load. Confirm the damping frequency. The damping frequency is BW. Output Ripple Output ripple at the switching frequency is caused by the inductor current ripple and its effect on the output BW capacitor's ESR and stored charge. These two ripple components are called ESR ripple and capacitive ripple. Since ceramic capacitors have extremely low ESR and relatively little capacitance, both components are VOUT similar in amplitude and both should be considered if ripple is critical. VRIPPLE = VRIPPLE(ESR)  VRIPPLE(C) VRIPPLE(ESR) = IL  RESR VRIPPLE(C) = R1 FB RT6214A/B IL Cff R2 GND 8  COUT  fSW Figure 1. Cff Capacitor Setting Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS6214A/B-01 November 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 11 RT6214A/B  Cff can be calculated base on below equation : Cff  Output Voltage Setting Set the desired output voltage using a resistive divider 1 2  3.1412  R1 BW  0.8 from the output to ground with the midpoint connected to FB. The output voltage is set according to the following equation : Enable Operation (EN) For automatic start-up the high-voltage EN pin can be connected to VIN, through a 100k resistor. Its large hysteresis band makes EN useful for simple delay and VOUT = 0.8V x (1 + R1 / R2) VOUT timing circuits. EN can be externally pulled to VIN by adding a resistor-capacitor delay (REN and CEN in R1 FB Figure 2). Calculate the delay time using EN's internal threshold where switching operation begins. An external MOSFET can be added to implement digital control of EN when no system voltage above 2V is available (Figure 3). In this case, a 100k pull-up resistor, REN, is connected between VIN and the EN pin. MOSFET Q1 will be under logic control to pull down the EN pin. To prevent enabling circuit when VIN is smaller than the VOUT target value or some other desired voltage level, a resistive voltage divider can be placed between the input voltage and ground and connected to EN to create an additional input under voltage lockout threshold (Figure 4). EN VIN RT6214A/B R2 GND Figure 5. Output Voltage Setting Place the FB resistors within 5mm of the FB pin. Choose R2 between 10k and 100k to minimize power consumption without excessive noise pick-up and calculate R1 as follows : R1  R2  (VOUT  VREF ) VREF For output voltage accuracy, use divider resistors with 1% or better tolerance. External BOOT Bootstrap Diode REN EN RT6214A/B CEN When the input voltage is lower than 5.5V it is recommended to add an external bootstrap diode GND between VIN (or VINR) and the BOOT pin to improve Figure 2. External Timing Control VIN improve efficiency. The bootstrap diode can be a low REN 100k EN Q1 Enable RT6214A/B GND Figure 3. Digital Enable Control Circuit VIN REN1 EN REN2 RT6214A/B GND Figure 4. Resistor Divider for Lockout Threshold Setting Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 12 enhancement of the internal MOSFET switch and cost one such as 1N4148 or BAT54. External BOOT Capacitor Series Resistance The internal power MOSFET switch gate driver is optimized to turn the switch on fast enough for low power loss and good efficiency, but also slow enough to reduce EMI. Switch turn-on is when most EMI occurs since VLX rises rapidly. During switch turn-off, LX is discharged relatively slowly by the inductor current during the dead time between high-side and low-side switch on-times. In some cases it is desirable to reduce EMI further, at the expense of some additional power dissipation. The switch turn-on can be slowed by placing a small (