RT6224DHGJ6F

® RT6224D 3A, 18V, 1.4MHz ACOTTM Synchronous Step-Down Converter General Description Features The RT6224D is a high-efficiency, monolithic synchronous step-down DC-DC converter that can deliver up to 3A output current from a 4.3V to 18V input supply. The RT6224D adopts ACOT TM architecture to allow the transient  Small Output Voltage at Light Load  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, output over-voltage protection, and thermal shutdown.  High-Side Over-Current Limit Ω/45mΩ Ω MOSFETs Integrated 90mΩ 4.3V to 18V Supply Voltage Range 1.4MHz Switching Frequency ACOTTM Control 0.6V ±1.5% Voltage Reference Monotonic Start-Up into Pre-Biased Outputs      Applications  Ordering Information  RT6224D  Package Type J6F : TSOT-23-6 (FC) Lead Plating System G : Green (Halogen Free and Pb Free)   Pin Configuration UVP Option H : Hiccup (TOP VIEW) PSM/PWM D : Force-PWM SW VIN EN 6 Note : Richtek products are :  RoHS compliant and compatible with the current require- 5 4 2 3 BOOT GND FB ments of IPC/JEDEC J-STD-020.  Set Top Box Portable TV Access Point Router DSL Modem LCD TV TSOT-23-6 (FC) Suitable for use in SnPb or Pb-free soldering processes. Simplified Application Circuit VIN VIN RT6224D BOOT SW Enable EN Copyright © 2016 Richtek Technology Corporation. All rights reserved. DS6224D-00 August 2016 GND VOUT FB is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT6224D Marking Information 1X= : Product Code 1X=DNN DNN : Date Code Functional Pin Description Pin No. Pin Name Pin Function 1 BOOT Bootstrap supply for high-side gate driver. Connect a 0.1F ceramic capacitor between the BOOT and SW pins. 2 GND Power ground. 3 FB Feedback voltage input. The pin is used to set the output voltage of the converter via a resistive divider. The converter regulates VFB to 0.6V. 4 EN Enable control input. Connect EN to a logic-high voltage to enable the IC or to a logic-low voltage to disable. Do not leave this high impedance input unconnected. 5 VIN Power input. The input voltage range is from 4.3V to 18V. Must bypass with a suitable large ceramic capacitor at this pin. 6 SW Switch node. Connected to external L-C filter. Functional Block Diagram BOOT VIN VIN Reg VCC VIBIAS VREF Min off VCC UGATE OC Control LGATE UV GND VCC SW Ripple Gen. + + Comparator FB Copyright © 2016 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 SW Driver GND SW VIN EN On-Time SW EN is a registered trademark of Richtek Technology Corporation. DS6224D-00 August 2016 RT6224D Operation The RT6224D is a synchronous step-down converter with advanced constant on-time control mode. Using the ACOT control mode can reduce the output capacitance and perform fast transient response. It can minimize the component size without additional external compensation network. Current Protection The inductor current is monitored via the internal switches cycle-by-cycle. Once the output voltage drops under UV threshold, the RT6224D will enter hiccup mode. UVLO Protection 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 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. Copyright © 2016 Richtek Technology Corporation. All rights reserved. DS6224D-00 August 2016 is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT6224D Absolute Maximum Ratings           (Note 1) VIN to GND ----------------------------------------------------------------------------------------------------SW to GND --------------------------------------------------------------------------------------------------- 3.3V) transient response is improved by adding a small “feedforward” capacitor (CFF) across the upper FB divider resistor (Figure 1), to increase the circuit's Q and reduce damping to speed up the transient response without affecting the steady-state stability of the circuit. Choose a suitable capacitor value that following below step. For automatic start-up the EN pin can be connected to VIN, through a 100kΩ resistor. Its large hysteresis band makes EN useful for simple delay and timing circuits. EN can be externally pulled to VIN by adding a resistorcapacitor delay (REN and CEN in Figure 2). Calculate the delay time using EN's internal threshold where switching operation begins (1.5V, typical).  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. BW 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 100kΩ pull-up resistor, REN, is connected between VIN and the EN pin. The 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 EN RT6224D CEN VOUT R1 REN GND CFF Figure 2. External Timing Control FB RT6224D R2 GND VIN Figure 1. CFF Capacitor Setting CFF can be calculated base on below equation : 1 CFF  2  3.1412  R1 BW  0.8 REN 100k EN Q1 Enable RT6224D GND  Figure 3. Digital Enable Control Circuit Internal Soft-Start (SS) The RT6224D soft-start uses an internal soft-start time 800μs. Following below equation to get the minimum capacitance range in order to avoid UV occur. COUT  VOUT  0.6  1.2 t (ILIM  Load Current)  0.8 t  800μs Copyright © 2016 Richtek Technology Corporation. All rights reserved. www.richtek.com 12 VIN REN1 REN2 EN RT6224D GND Figure 4. Resistor Divider for Lockout Threshold Setting is a registered trademark of Richtek Technology Corporation. DS6224D-00 August 2016 RT6224D Output Voltage Setting Set the desired output voltage using a resistive divider from the output to ground with the midpoint connected to FB. The output voltage is set according to the following equation : VOUT = 0.6 x (1 + R1 / R2) between BOOT and the external bootstrap capacitor. This will slow the high-side switch turn-on and VSW's rise. To remove the resistor from the capacitor charging path (avoiding poor enhancement due to undercharging the BOOT capacitor), use the external diode shown in Figure 6 to charge the BOOT capacitor and place the resistance between BOOT and the capacitor/diode connection. VOUT 5V R1 FB RT6224D BOOT R2 RT6224D GND Figure 5. Output Voltage Setting Place the FB resistors within 5mm of the FB pin. Choose R2 between 10kΩ and 100kΩ to minimize power consumption without excessive noise pick-up and calculate R1 as follows : R1  R2  (VOUT  0.6) 0.6 For output voltage accuracy, use divider resistors with 1% or better tolerance. External BOOT Bootstrap Diode When the input voltage is lower than 5.5V it is recommended to add an external bootstrap diode between VIN (or VINR) and the BOOT pin to improve enhancement of the internal MOSFET switch and improve efficiency. The bootstrap diode can be a low 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 VSW rises rapidly. During switch turn-off, SW is discharged relatively slowly by the inductor current during the deadtime 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 (