RT6222AHGJ6F

® RT6222A/B 2.5A, 18V, 500kHz ACOTTM Synchronous Step-Down Converter General Description Features The RT6222A/B is a synchronous step-down converter with Advanced Constant On-Time (ACOTTM) control mode.  4.3V to 18V Input Voltage Range  The ACOTTM provides a very fast transient response with few external components. The low impedance internal MOSFET supports high efficiency operation with wide input voltage range from 4.3V to 18V. The proprietary circuit of the RT6222A/B enables to support all ceramic capacitors. The output voltage can be adjusted between 0.6V and 8V.  2.5A Output Current Advanced Constant On-Time Control Fast Transient Response Support All Ceramic Capacitors Up to 95% Efficiency 500kHz Switching Frequency Adjustable Output Voltage from 0.6V to 8V Cycle-by-Cycle Current Limit Input Under-Voltage Lockout Hiccup Mode Under-Voltage Protection Thermal Shutdown Power Saving Mode for High Efficiency at Light Load Low Output Voltage Ripple at Light Load High Side Over Current Limit RoHS Compliant and Halogen Free        Ordering Information  RT6222A/B  Package Type J6F : TSOT-23-6 (FC)  Lead Plating System G : Green (Halogen Free and Pb Free)   UVP Option H: Hiccup  PSM/PWM A : PSM/PWM B : Force-PWM Applications  Note :  Richtek products are :    RoHS compliant and compatible with the current require-  ments of IPC/JEDEC J-STD-020.  Suitable for use in SnPb or Pb-free soldering processes. Industrial and Commercial Low Power Systems Computer Peripherals LCD Monitors and TVs Green Electronics/Appliances Point of Load Regulation for High-Performance DSPs, FPGAs, and ASICs Simplified Application Circuit VIN RT6222A/B BOOT VIN SW Enable EN Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS6222A/B-00 October 2015 GND VOUT FB is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT6222A/B Marking Information Pin Configurations (TOP VIEW) RT6222AHGJ6F SW VIN EN 1K=DNN 6 5 4 2 3 1K= : Product Code DNN : Date Code RT6222BHGJ6F BOOT GND FB 1J= : Product Code 1J=DNN TSOT-23-6 (FC) 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. Connect to external L-C filter. Function Block Diagram BOOT VIN VIN Reg VCC VIBIAS VREF Min off VCC UGATE OC Control SW Driver LGATE UV GND VCC SW Ripple Gen. + + Comparator FB Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 GND SW VIN EN On-Time SW EN is a registered trademark of Richtek Technology Corporation. DS6222A/B-00 October 2015 RT6222A/B Operation The RT6222A/B 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 RT6222A/B 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 © 2015 Richtek Technology Corporation. All rights reserved. DS6222A/B-00 October 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT6222A/B 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. 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. 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 BW VIN REN EN RT6222A/B CEN GND VOUT Figure 2. External Timing Control R1 Cff FB RT6222A/B R2 GND VIN REN 100k EN Q1 Enable RT6222A/B GND Figure 1. Cff Capacitor Setting Cff can be calculated base on below equation : 1 Cff  2  3.1412  R1 BW  0.8  Figure 3. Digital Enable Control Circuit VIN REN1 REN2 EN RT6222A/B GND Figure 4. Resistor Divider for Lockout Threshold Setting Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 12 is a registered trademark of Richtek Technology Corporation. DS6222A/B-00 October 2015 RT6222A/B 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) VOUT can be slowed by placing a small (