RT8105GS

RT8105 5V/12V Synchronous Buck PWM DC/DC Controller General Description Features The RT8105 is a high efficiency synchronous buck PWM controllers that generate logic-supply voltages in PC based systems. These high performance , single output devices include internal soft-start, frequency compensation networks and integrates all of the control, output adjustment, monitoring and protection functions into a single package. z Operating with 5V or 12V Supply Voltage z 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 Ratio Internal Soft-Start Adaptive Non-Overlapping Gate Driver Over-Current Fault Monitor on MOSFET, No Current Sense Resistor Required Full-Time Over Voltage Protection RoHS Compliant and Halogen Free The device operating at fixed 300kHz frequency provides an optimum compromise between efficiency, external component size, and cost. Adjustable over-current protection (OCP) monitors the voltage drop across the RDS(ON) of the lower MOSFET for synchronous buck PWM DC/DC controller. The overcurrent function cycles the soft-start in 4-times hiccup mode to provide fault protection, and in an always hiccup mode for under-voltage protection. z z z z z z z z Applications z z z Ordering Information RT8105 z z Package Type S : SOP-8 Graphic Card Motherboard, Desktop Servers IA Equipments Telecomm Equipments High Power DC/DC Regulators Pin Configurations (TOP VIEW) Lead Plating System G : Green (Halogen Free and Pb Free) Z : ECO (Ecological Element with Halogen Free and Pb free) BOOT Note : 8 PHASE UGATE 2 7 OPS GND 3 6 FB LGATE 4 5 VCC Richtek products are : ` ments of IPC/JEDEC J-STD-020. ` SOP-8 RoHS compliant and compatible with the current requireSuitable for use in SnPb or Pb-free soldering processes. Marking Information RT8105GS RT8105GS : Product Number RT8105 GSYMDNN YMDNN : Date Code RT8105ZS RT8105ZS : Product Number RT8105 ZSYMDNN DS8105-03 April 2011 YMDNN : Date Code www.richtek.com 1 RT8105 Typical Application Circuit +5V to +12V D1 BAT54 VIN +3.3V/+5V/+12V RBOOT 0 C2 0.1µF R1 10 1 5 C1 1µF 6 3 BOOT VCC UGATE PHASE RT8105 OPS FB GND LGATE Disable > R2 32 2 RUGATE 0 8 7 C3 1µF Q1 MU L1 3µH ROCSET Q2 ML 4 Q3 3904 C4 470µF R C C6 to C8 1000µFx3 R3 68 R4 200 to 1k VOUT VOUT = VREF × (1 + R3 ) R2 VREF : Internal reference voltage (0.8V ± 2%) C5 0.1 to 0.33µF Functional Pin Description BOOT (Pin 1) VCC (Pin 5) 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. Connect this pin to a well-decoupled 5V or 12V bias supply. It is also the positive supply for the lower gate driver, LGATE. FB (Pin 6) UGATE (Pin 2) Upper gate driver output. Connect to the gate of 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. 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. LGATE (Pin 4) Lower gate drive output. Connect to the gate of 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. www.richtek.com 2 Switcher feedback voltage. This pin is the inverting input of the error amplifier. FB senses the switcher output through an external resistor divider network. OPS (OCSET, POR and Shut-Down) (Pin 7) 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. PHASE (Pin 8) Connect this pin to the source of the upper MOSFET and the drain of the lower MOSFET. DS8105-03 April 2011 RT8105 Function Block Diagram VCC + EN PH_M - Reference 0.1V + Bias & Regulators (3V_Logic & 3VDD_Analog) Power On Reset 0.8VREF 1.5V 3V + 0.6V UV_S IOC Soft-Start & Fault Logic - OC + OVP 1V 1.3V 40uA OPS 0.4V + - VOC BOOT UGATE PHASE EO + + - - FB GM Gate Control Logic VCC LGATE Oscillator (300kHz) GND DS8105-03 April 2011 www.richtek.com 3 RT8105 Absolute Maximum Ratings z z z z z z z z z z z z (Note 1) Supply Voltage, VCC -------------------------------------------------------------------------------------- 16V BOOT to PHASE ------------------------------------------------------------------------------------------ 15V UGATE to PHASE DC ------------------------------------------------------------------------------------------------------------- −0.3V to (VBOOT-PHASE + 0.3V)