RT8234AZQW

RT8234A Single Synchronous Buck PWM Controller with LDO Regulator General Description Features The RT8234A is a cost effective synchronous buck controller with an integrated 3A linear regulator. The PWM controller provides high efficiency, excellent transient response, and high DC output accuracy needed for stepping down high voltage batteries to generate low voltage supplies in notebook computers. z The constant on-time PWM control scheme handles wide input/output voltage ratios with ease and provides “instant-on” response to load transients while maintaining a relatively constant switching frequency. The Ultra Sonic Mode (USM) setting maintains the switching frequency above 30kHz, which eliminates noise in audio applications. The RT8234A is intended for CPU core, chipset, DRAM, or other low voltage supplies as low as 0.75V at a reduced cost without the need for a current sense resistor. The 3A LDO regulator maintains fast transient response, only requiring a 20μF ceramic output capacitor. In addition, the LDO supply input is provided by an external power source to significantly reduce the total power loss. The RT8234A is available in a WQFN-16L 3x3 package. PWM Controller Wide Input Voltage Range : 4.5V to 26V ` Adjustable Output Voltage Range : 0. 75V to 3.3V ` Resistor Programmable Current Limit ` Quick Load Step Response within 100ns ` 1% VOUT Accuracy Over Line and Load ` Resistor Programmable Frequency ` Over/Under Voltage Protection ` Linear Current Limit Soft-Start ` Drives Large Synchronous Rectifier FETs ` Power Good Indicator z LDO Regulator ` Output Current Up to 3A ` 1% Accuracy Over Line and Load ` Adjustable Output Voltage Down to 0.75V ` Independent Enable and Power Good Indicator z RoHS Compliant and 100% Halogen Free ` Applications z z z Notebook Computers CPU Core Supply Chipset/RAM Supply as Low as 0.75V Ordering Information Pin Configurations RT8234A Package Type QW : WQFN-16L 3x3 (W-Type) EN CS TON UGATE TOP VIEW Lead Plating System G : Green (Halogen Free and Pb Free) Z : ECO (Ecological Element with Halogen Free and Pb free) 16 15 14 13 FB PGOOD LVIN LOUT Note : 11 GND 3 10 17 4 6 7 9 PHASE BOOT VDD LGATE 8 LEN LFB LPOOGD PGND RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. ` 12 2 5 Richtek products are : ` 1 WQFN-16L 3x3 Suitable for use in SnPb or Pb-free soldering processes. Marking Information RT8234AGQW RT8234AZQW 07=: Product Code 07=YM DNN YMDNN : Date Code DS8234A-01 June 2011 07 : Product Code 07 YM DNN YMDNN : Date Code www.richtek.com 1 RT8234A Typical Application Circuit VIN RTON CIN RT8234A 14 TON 7 LPGOOD LPGOOD R4 10 VDD R5 PGOOD Mode Selection PWM Enable/Disable VDD C1 BOOT 11 UGATE 13 CBOOT VOUT Q1 LOUT R2* Q2 COUT R3* 16 5 15 ROCSET RUGATE PHASE 12 LGATE 9 C2* 2 PGOOD LDO Enable RBOOT 8 EN/MODE FB RFB1 1 LVIN 3 LEN C4* RFB2 * : Optional CLIN C3* CS PGND LOUT 4 LDO-VOUT RFB3 17 (Exposed Pad) GND R6* CLOUT C5* LFB 6 RFB4 www.richtek.com 2 DS8234A-01 June 2011 RT8234A Function Block Diagram TRIG On-time Compute 1-SHOT TON PHASE BOOT R Comp - + GM - + S PWM Q DRV PHASE Min. tOFF Q TRIG VREF UGATE 1-SHOT 125%VREF FB 70% VREF + - OV Latch S1 Q UV Latch S1 VDD + - DRV Q PGND C.C.M, D.E.M, U.S.M 90% VREF VDD UVLO LGATE SS RAMP + + GM + - + - Thermal Shutdown 10µA EN/MODE CS PGOOD PWM Controller LVIN LEN + - SS VREF = 0.75V SS Ramp + - LOUT LPGOOD - LFB 90% VREF + LDO Regulator DS8234A-01 June 2011 www.richtek.com 3 RT8234A Functional Pin Description Pin No. Pin Name Pin Function 1 FB VOUT Feedback Input. Connect FB to a resistor voltage divider from VOUT to GND to adjust the output from 0.75V to 3.3V. 2 PGOOD Power Good Indicator. It is an open drain output of the internal switch. This pin will be pulled high when the output voltage is within the target range. 3 LVIN Supply Input Pin for LDO. 4 LOUT Output Terminal of the LDO. 5 LEN Enable Input Pin for LDO with Internal Pull Low Resistor. LDO is enabled if LEN is greater than the ON level and disabled if LEN is less than the OFF level. 6 LFB LDO Feedback Input. Connect LFB to a resistive voltage divider from LOUT to GND to adjust the output voltage from 0.75V to 3V. 7 LPGOOD Power Good Indicator. It is an open drain output of LDO regulator. This pin will be pulled high when the output voltage is within the target range. 8 PGND Power Ground. 9 LGATE 10 VDD 11 BOOT 12 PHASE 13 UGATE 14 TON 15 CS 16 EN/MODE 17 (Exposed Pad) GND www.richtek.com 4 Low Side N-MOSFET Gate Drive Output for PWM. This pin swings between PGND and VDD. Supply Input Pin. Gate driver supply for external MOSFETS and analog supply for the device. Bypass to PGND with a 1μF ceramic capacitor. Bootstrap Power Pin. This pin powers the high side MOSFET driver. Connect a bootstrap capacitor between this pin and phase. Switch Node. This pin is not only the current sense input, but also the high side gate driver return. High Side N-MOSFET Gate Driver Output for PWM. This pin swings between PHASE and BOOT. On-Time Setting Pin. Connect to VIN through a resistor. TON is an input of the PWM controller. Over Current Set Input. Connect resistor from this pin to signal ground to set the current limit threshold. PWM enable, disable and mode selection input. Connect this pin to VDD for CCM mode, connect this pin to 3.3V for diode-emulation mode, connect this pin to 2V for ultra sonic mode and connect this pin to GND for shutdown mode. Ground. The exposed pad must be soldered to a large PCB and connected to GND for maximum power dissipation. DS8234A-01 June 2011 RT8234A Absolute Maximum Ratings (Note 1) Supply Input Voltage, TON to GND ------------------------------------------------------------------------------------- −0.3V to 32V z BOOT to PHASE ---------------------------------------------------------------------------------------------------------- −0.3V to 6V z PHASE to GND DC ----------------------------------------------------------------------------------------------------------------------------- −1V to 32V