RT8204BGQW

RT8204B Single Synchronous Buck with LDO Controller General Description Features The RT8204B PWM controller provides the high efficiency, excellent transient response, and high DC output accuracy needed for stepping down high voltage batteries to generate low voltage CPU core, I/O, and chipset RAM supplies in notebook computers. z A built-in LDO controller can drive an external N-MOSFET to provide a second output voltage from PWM output or other power source. The RT8204B can provide adjustable voltage down to 0.75V and maximum output voltage is depended on the selected MOSFET. The internal 0.75V reference voltage with ±1.5% accuracy provides tight regulation for the output voltage. The independent enable control, open drain power good indicator, under voltage protection and soft start make RT8204B to power the system friendly. The RT8204B is available in WQFN-16L 3x3 package. Ultra-High Efficiency ` Resistor Programmable Current Limit by Low Side RDS(ON) Sense (Lossless Limit) or Sense Resistor (High Accuracy) ` Quick Load Step Response within 100ns ` 1% VOUT Accuracy Over Line and Load ` Adjustable 0.75V to 3.3V Output Range ` 3V to 26V Battery Input Range ` Resistor Programmable Frequency ` Over/Under Voltage Protection ` 2 Steps Current Limit During Soft-Start ` Drives Large Synchronous-Rectifier FETs ` Power-Good Indicator LDO Controller ` 1.5% Accuracy Over Line and Load ` Adjustabe Output Voltage down to 0.75V ` Independent Enable and Power Good Indicator ` Drive N-MOSFETs within Rail to Rail Controller Voltage ` MLCC and POSCAP Stable RoHS Compliant and Halogen Free ` The constant-on-time PWM control scheme handles wide input/output voltage ratios with ease and provides 100ns “instant-on” response to load transients while maintaining a relatively constant switching frequency. The RT8204B achieves high efficiency at a reduced cost by eliminating the current sense resistor found in traditional current mode PWMs. Efficiency is further enhanced by its ability to drive very large synchronous rectifier MOSFETs. The buck conversion allows this device to directly step down high voltage batteries for the highest possible efficiency. The RT8204B is intended for CPU core, chipset, DRAM, or other low voltage supplies as low as 0.75V. PWM Controller z z Ordering Information RT8204B Package Type QW : WQFN-16L 3x3 (W-Type) Lead Plating System G : Green (Halogen Free and Pb Free) Note : Richtek products are : Applications z z z Notebook Computers CPU Core Supply Chipset/RAM Supply as Low as 0.75V ` RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. ` Suitable for use in SnPb or Pb-free soldering processes. Marking Information For marking information, contact our sales representative directly or through a Richtek distributor located in your area. DS8204B-04 April 2011 www.richtek.com 1 RT8204B Pin Configurations TON EN/DEM LEN BOOT (TOP VIEW) 16 15 14 13 VOUT VDD FB PGOOD 1 12 2 11 PHASE OC 9 VDDP GND 3 10 17 4 6 7 8 LPGOOD LFB LDRV LGATE 5 UGATE WQFN-16L 3x3 Typical Application Circuit D1 BAT254 VDDP 5V VIN 3V to 26V C1 4.7µF R2 100k R4 1M R1 10 RT8204B 16 BOOT 13 TON 9 VDDP UGATE 12 C2 1µF 2 VDD 4 PGOOD PGOOD 15 CCM/DEM 14 LDO Enable 5 LDO PGOOD EN/DEM PHASE R5 2.2 C3 0.1µF R6 0 11 LGATE 8 OC 10 Q2 AO4704 R7 10k VOUT1 1.2V Q1 AO4704 L1 2.4µH C9 220µF R8 C5 FB 3 R9 12k C6 C13 0.1µF R10 20k LEN LPGOOD VOUT 1 R3 100k LDRV 7 VDDP Exposed Pad(17) C4 10µF GND C7 33nF LFB 6 C12 Q3 AO4404 R11 C8 R12 12k C10 220µF C11 10µF VOUT2 1.05V R13 30k www.richtek.com 2 DS8204B-04 April 2011 RT8204B Functional Pin Description Pin No. Pin Name Pin Function VOUT Sense Input. Connect to the output of PWM converter. VOUT is an input of the PWM controller. 1 VOUT 2 VDD 3 FB 4 PGOOD 5 LPGOOD 6 LFB LDO Feedback Input. Connect LFB to a resistor voltage divider from VOUT to GND to adjust the output greater than 0.75V. 7 LDRV Drive Signal for the LDO’s path MOSFET. 8 LGATE 9 VDDP VDDP is the gate driver supply for the external MOSFETs. Bypass to GND with a 1μF ceramic capacitor. 10 OC PWM Current Limit Setting and sense. Connect a resistor between OC to PHASE for current limit setting. 11 PHASE Inductor Connection. This pin is not only the zero-current-sense input for the PWM converter, but also the UGATE high side gate driver return. 12 UGATE 13 BOOT Boost Capacitor Connection for PWM Converter. Connect an external ceramic capacitor to PHASE and an external diode to VDDP. 14 LEN LDO Enable Input 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. 15 EN/DEM Analog Supply Voltage Input for the internal analog integrated circuit. Bypass to GND with a 1μF ceramic capacitor. VOUT Feedback Input. Connect FB to a resistor voltage divider from VOUT to GND to adjust the output from 0.75V to 3.3V. Power Good Signal Open-Drain Output of PWM Converter. This pin will be pulled high when the output voltage is within the target range. Power Good signal Open-Drain Output of LDO Regulator. This pin will be pulled high when the output voltage is within the target range. Low side N-MOSFET Gate-Drive Output for PWM. This pin swings between GND and VDDP. High Side N-MOSFET Floating Gate-Driver Output for the PWM converter. This pin swings between PHASE and BOOT. PWM Enable and Operation Mode Selection Input. Connect to VDD for diode-emulation mode, connect to GND for shutdown mode and floating the pin for CCM mode. 16 TON 17 (Exposed Pad) GND DS8204B-04 April 2011 VIN Sense Input. Connect to VIN through a resistor. TON is an input of the PWM controller. Analog Ground and Power Ground. The exposed pad must be soldered to a large PCB and connected to GND for maximum power dissipation. www.richtek.com 3 RT8204B Function Block Diagram PWM Controller TRIG On-time Compute 1-SHOT VOUT TON SS (Internal) - + GM + - - R Comp S + BOOT Q DRV UGATE PHASE 0.75V VREF Q OV + 115% VREF Min. TOFF TRIG DRV - FB - 70% VREF UV + Latch S1 Q SS Timer LGATE PGND Diode Emulation - 90% VREF VDD VDDP 1-SHOT Latch S1 Q + 20µA Thermal Shutdown + OC - GND PGOOD EN/DEM LDO Controller SS LEN 0.75V VREF SS ramp LFB + - X1 LDRV LPGOOD - 90% VREF + - 50% VREF www.richtek.com 4 + DS8204B-04 April 2011 RT8204B Absolute Maximum Ratings z z z z z z z z z z z z z z (Note 1) Input Voltage, TON to GND ---------------------------------------------------------------------------------------------BOOT to GND -------------------------------------------------------------------------------------------------------------PHASE to BOOT ---------------------------------------------------------------------------------------------------------PHASE to GND DC ----------------------------------------------------------------------------------------------------------------------------