RT8237EZQW

® RT8237E High Efficiency Single Synchronous Buck PWM Controller General Description Features The RT8237E PWM controller provides 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.  Wide Input Voltage Range : 2.7V to 26V  Output Voltage Range : 0.7V to 3.3V Built-In 0.5% 0.7V Reference Voltage Quick Load-Step Response within 100ns 4700ppm/°°C Current Source for Current Limit RDS(ON) Adjustable Current Limit with Low-Side MOSFET 4 Selectable Frequency Setting Soft-Start Control Drives Large Synchronous-Rectifier FETs Integrated Boot Switch Built-In OVP/OCP/UVP Thermal Shutdown Power Good Indicator 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 RT8237E 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 and enter diode emulation mode at light load condition. The Buck conversion allows this device to directly step down high voltage batteries at the highest possible efficiency. The pre-set frequency selections minimize design effort required for new designs. The RT8237E is intended for CPU core, chipset, DRAM, or other low voltage supplies as low as 0.7V. The RT8237E is available in the WDFN-10L 3x3 package.      Applications     Notebook Computers CPU Core Supply Chipset/RAM Supply as Low as 0.7V Generic DC-DC Power Regulator Simplified Application Circuit RT8237E VCC VCC BOOT PGOOD VIN UGATE EN RF CS PHASE LGATE GND Copyright © 2020 Richtek Technology Corporation. All rights reserved. DS8237E-02 October 2020 VOUT FB is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT8237E Ordering Information (2) (TOP VIEW) Pin 1 Orientation (2) : Quadrant 2, Follow EIA-481-D PGOOD CS EN FB RF Package Type QW : WDFN-10L 3x3 (W-Type) Lead Plating System Z : ECO (Ecological Element with Halogen Free and Pb free) Note : 1 2 3 4 5 GND RT8237E Pin Configuration 11 10 9 8 7 6 BOOT UGATE PHASE VCC LGATE WDFN-10L 3x3 Marking Information Richtek products are : 88 : Product Code  RoHS compliant and compatible with the current require-  Suitable for use in SnPb or Pb-free soldering processes. ments of IPC/JEDEC J-STD-020. 88 DF A26 DFA26 : Date Code Functional Pin Description Pin No. Pin Name 1 PGOOD 2 CS 3 EN 4 FB 5 RF 6 LGATE 7 VCC 8 PHASE 9 UGATE 10 BOOT 11 GND (Exposed Pad) Pin Function Open drain power good indicator. High impedance indicates power is good. Current limit threshold setting input. Connect a setting resistor to GND and the current limit threshold is equal to 1/8 of the voltage at this pin. Enable control input. Pull low to GND to disable the PWM. VOUT feedback input. Connect FB to a resistor voltage divider from VOUT to GND to adjust the output from 0.7V to 3.3V Switching frequency selection. Connect a resistance to select switching frequency as shown in Electrical Characteristics. The switching frequency is detected and latched after startup. This pin also controls diode emulation mode or forced CCM selection. Pull down to GND with resistor: Diode Emulation Mode. Connect to PGOOD with resistor: forced CCM after PGOOD becomes high. Gate drive output for low-side external MOSFET. Supply voltage input. This pin provides the power for the buck controller, the lowside driver and the bootstrap circuit for high-side driver. Bypass to GND with a 1F ceramic capacitor. External inductor connection pin for PWM converter. It behaves as the current sense comparator input for low-side MOSFET RDS(ON) sensing and reference voltage for on time generation. Gate drive output for high-side external MOSFET. Bootstrap supply for high-side gate driver. Connect through a capacitor to the floating node (PHASE). Ground. The exposed pad must be soldered to a large PCB and connected to GND for maximum power dissipation. Copyright © 2020 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS8237E-02 October 2020 RT8237E Functional Block Diagram TRIG On-time Compute RF BOOT PHASE R - COMP S + FB 70% VREF + PWM DRV UGATE PHASE VREF 125% VREF Q OV Latch S1 Q UV Latch S1 Q Min. tOFF Q TRIG VCC + DRV LGATE GND - DEM/FCCM 125% VREF - PGOOD + VCC POR SS Timer EN - 90% VREF + Thermal Shutdown + X(1/8) + 10µA X(-1/8) CS Copyright © 2020 Richtek Technology Corporation. All rights reserved. DS8237E-02 October 2020 is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT8237E Operation The RT8237E integrates a Constant-On-Time (COT) PWM controller, and the controller provides the PWM signal which relies on the output ripple voltage comparing with internal reference voltage. The UGATE driver is turned on at the beginning of each cycle. After the internal one-shot timer expires, the UGATE driver will be turned off. The pulse width of this one-shot is determined by the converter's input voltage and the output voltage to keep the frequency fairly constant over the input voltage and output voltage range. Power On Reset, UVLO Power On Reset (POR) occurs when VCC rises above to approximately 4.1V (typical), the RT8237E will reset the fault latch and prepare the PWM for operation. When the input voltage below 3.7V(min), the Under Voltage Lockout (UVLO) circuitry inhibits switching by keeping UGATE and LGATE low. Soft-Start The output voltage will track the internal ramp voltage during soft-start interval to prevent large inrush current and output voltage overshoot while the converter is being powered up. Copyright © 2020 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 Mode Selection The RT8237E supports mode selection through the RF by connecting a resistor from the RF pin to either GND or PGOOD. When the resistor is connected to GND, the controller operates in diode emulation mode. When the resistor is connected to PGOOD, the controller operates in CCM mode. Current Limit Setting The RT8237E has a cycle-by-cycle current limit control. The current limit circuit employs a unique “valley” current sensing algorithm. If the magnitude of the sensing signal at PHASE is above the current limit threshold, the PWM is not allowed to initiate a new cycle. Over Voltage Protection The output voltage can be continuously monitored for over voltage condition. When the output voltage exceeds 25% of its set voltage threshold, the UGATE goes low and the LGATE is forced high. Under Voltage Protection The output voltage can be continuously monitored for under voltage condition. When the output voltage is less than 70% of its set voltage, under voltage protection is triggered and then both UGATE and LGATE gate drivers are forced low. is a registered trademark of Richtek Technology Corporation. DS8237E-02 October 2020 RT8237E Absolute Maximum Ratings (Note 1) VCC, FB, PGOOD, EN, CS, RF to GND ----------------------------------------------------------------------------BOOT to GND DC -----------------------------------------------------------------------------------------------------------------------------