RT9218BPS

RT9218B 12V Synchronous Buck PWM DC-DC and Linear Power Controller General Description The RT9218B is a dual output with one synchronous buck PWM and one linear controller. The part is proposed to generate logic-supply voltages for PC based systems. The high-performance device includes internal soft-start, frequency-compensation networks, power good signaling with specific sequence, and it comes all of the logic control, output adjustment, power monitoring and protection functions into a small footprint package. The part is operated at fixed 300kHz frequeny providing an optimum compromise between efficiency, external component size, and cost. The linear controller is implemented to drive an external MOSFET for regulation and it's adjustable by setting external resistors. Moreover the specific internal PGOOD sequence and indicator is also implemented to conform to Intel® new platform requirement on FSB_VTT power plane. An adjustable over-current protection (OCP) is proposed to monitor the voltage drop across the RDS(ON) of the lower MOSFET for synchronous buck PWM DC-DC controller. Features Operating with 12V Supply Voltage Drives All Low Cost N-MOSFETs Voltage Mode PWM Control 300kHz Fixed Frequency Oscillator Fast Transient Response : High-Speed GM Amplifier Full 0 to 100% Duty Ration Internal Soft-Start Power Good Indicator Adaptive Non-Overlapping Gate Driver Over-Current Fault Monitor on MOSFET, No Current Sense Resistor Required Specific power good indicator for Intel® Grantsdale FSB_VTT power sequence RoHS Compliant and 100% Lead (Pb)-Free Applications Graphic Card Motherboard, Desktop Servers IA Equipments Telecomm Equipments High Power DC-DC Regulators Ordering Information RT9218B Package Type S : SOP-14 Operating Temperature Range P : Pb Free with Commercial Standard G : Green (Halogen Free with Commercial Standard) Pin Configurations (TOP VIEW) BOOT UGATE GND LGATE DRV NC NC 2 3 4 5 6 7 14 13 12 11 10 9 8 PHASE OPS FB VCC PGOOD FBL NC Note : RichTek Pb-free and Green products are : RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. Suitable for use in SnPb or Pb-free soldering processes. 100% matte tin (Sn) plating. SOP-14 DS9218B-09 March 2007 www.richtek.com 1 RT9218B Typical Application Circuit VIN 5 to 12V VCC 12V VCC 12V D1 1N4148 RBOOT 2.2 C8 0.1uF PHASE C1 to C2 1000uF x 2 SVOUT L1 2.2uH C3 to C4 1uF x 2 Q1 MU R Q2 ML C RUGATE C7 1uF RT9218B 1 BOOT 2 UGATE 3 4 GND LGATE PHASE OPS FB VCC 14 13 12 11 R3 10R ROCSET 2.2 PHASE Q4 C10 1uF 3904 Disable C5 to C6 1000uF x 2 Q3 R1 LVOUT 4k C9 470uF 5 DRV 6 NC 7 NC PGOOD 10 9 FBL 8 NC R2 8k R4 1k/NC R5 68R C11 0.1uF/NC R6 32R SVOUT = VREF × (1 + R5 ) R6 R1 ) LVOUT = VREF × (1 + R2 VREF : Internal reference voltage (0.8V ± 1%) www.richtek.com 2 DS9218B-09 March 2007 RT9218B Functional Pin Description UGATE (Pin 2) Upper gate driver output. Connect to gate of the high-side power N-MOSFET. This pin is monitored by the adaptive shoot-through protection circuitry to determine when the upper MOSFET has turned off. BOOT (Pin 1) Bootstrap supply pin for the upper gate driver. Connect the bootstrap capacitor between BOOT pin and the PHASE pin. The bootstrap capacitor provides the charge to turn on the upper MOSFET. PHASE (Pin 14) Connect this pin to the source of the upper MOSFET and the drain of the lower MOSFET. OPS (OCSET, POR and Shut-Down) (Pin 13) This pin provides multi-function of the over-current setting, UGATE turn-on POR sensing, and shut-down features. Connecting a resistor (ROCSET) between OPS and PHASE pins sets the over-current trip point. Pulling the pin to ground resets the device and all external MOSFETs are turned off allowing the output voltage power rails to float. This pin is also used to detect VIN in power on stage and issues an internal POR signal. LGATE (Pin 4) Lower gate drive output. Connect to gate of the low-side power N-MOSFET. This pin is monitored by the adaptive shoot-through protection circuitry to determine when the lower MOSFET has turned off. FB (Pin 12) Switcher feedback voltage. This pin is the inverting input of the error amplifier. FB senses the switcher output through an external resistor divider network. VCC (Pin 11) Connect this pin to a well-decoupled 12V bias supply. It is also the positive supply for the lower gate driver, LGATE. GND (Pin 3) Both signal and power ground for the IC. All voltage levels are measured with respect to this pin. Ties the pin directly to the low-side MOSFET source and ground plane with the lowest impedance. DRV (Pin 5) Connect this pin to the base/gate of an external transistor/ MOSFET. This pin provides the drive for the linear regulator's pass transistor/MOSFET. FBL (Pin 9) Linear regulator feedback voltage. This pin is the inverting input of the error amplifier and protection monitor. Connect this pin to the external resistor divider network of the linear regulator. PGOOD (Pin 10) PGOOD is an open-drain output used to indicate that the regulator is within normal operating voltage ranges and it's implemented with a specific sequence as following chart. NC (Pin 6,7,8) No internal connection. DS9218B-09 March 2007 www.richtek.com 3 RT9218B Function Block Diagram VCC EN + - 0.15V Bias & Regulators (3V_Logic & 3VDD_Analog) Reference 0.8VREF Power On Reset PH_M + - 1.5V 3V VCC DRV + - 0.6V + + - UV_S Soft-Start & Fault Logic 40uA OC OPS 0.6V UV_L + 0.4V FBL PGOOD + - BOOT UGATE + +GM EO PHASE + + Gate Control Logic VCC LGATE Oscillator (300k/600kHz) FB GND Timing Diagram Specific Power Sequence for LDO 90% 80% FSB_VTT (1.2V @ 5Amp) 1-10ms VTT_GD