High Efficiency Single Synchronous Buck PWM Controller

Purpose

The RT8129A integrates a Constant-On-Time (COT) PWM controller and MOSFET driver so that the external circuit is easily designed and the components are reduced. The controller provides the PWM signal which relies on the FB voltage comparing with internal reference voltage. The synchronous 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 controller's input voltage and the output voltage to keep the frequency fairly constant over the input voltage and output voltage range. Another one-shot sets a minimum off-time.

Introduction

General Product Information

The RT8129A is a high efficiency singl phase synchronous buck controller with 5V/12V supply voltage. The RT8129A integrates a Constant-On-Time (COT) PWM controller and a MOSFET drivers with internal bootstrap diodes, which is specifically designed to improve converter efficiency at light load condition. At light load condition, it automaticallyoperates in the diode emulation mode to reduce switching frequency and improve conversion efficiency. Other features include power good indication, enable/disable control and internal soft-start function. The RT8129A also provide protection functions including Over Voltage Protection (OVP), Under Voltage Protection (UVP), current limit and thermal shutdown.

This device uses lossless low-side MOSFET R_DS(ON) current sense technique for current limit with adjustable threshold set by connecting a resistor between the LGATE/OCSET and GND.

With above functions, the RT8129A provides customers a cost-effective solution for high efficiency power conversion. The RT8129A is available in the WDFN-10L 3x3 package.

Product Feature

• Wide Input Voltage Range : 2.5V to 25V
• High Light Load Efficiency
• Integrated High Driving Capability N-MOSFET Gate
• Drivers and Embedded Switching Boot Diode
• Single IC Supply Voltage : 4.5V to 13.2V
• Power-Good Indicator
• Enable/Disable Control
• Internal Soft-Start
• Programmable Current Limit Threshold
• Under Voltage Protection
• Over Voltage Protection
• Thermal Shutdown

Key Performance Summary Table

Bench Test Setup Conditions

Headers Description and Placement

Please carefully inspect the EVB IC and external components, comparing them to the following Bill of Materials, to ensure that all components are installed and undamaged. If any components are missing or damaged during transportation, please contact the distributor or send e-mail to evb_service@richtek.com

Test Points

The EVB is provided with the test points and pin names listed in the table below.

Power-up & Measurement Procedure

1. Connect input power (2.5V < V_IN < 25V and 4.5V < V_CC < 13.2V).

2. Connect positive end and negative terminals of load to VOUT and GND test pins respectively.

3. EN pin is internal high, let JP1 open (JP1 short will turn off IC).

4. Verify the output voltage (VOUT approximately 1.5V, and FB approximately 0.8V) between VOUT to GND, and FB to GND.

5. Connect an external load up to 10A to the VOUT and GND terminals and verify the output voltage and current.

Output Voltage Setting

Set the output voltage with the resistive divider (R8, R10) between VOUT and GND with the midpoint connected to FB. The output is set by the following formula :

Schematic, Bill of Materials & Board Layout

EVB Schematic Diagram

Bill of Materials

PCB Layout

Top View (1^st layer)

PCB Layout—Inner Side (2^nd Layer)

PCB Layout—Inner Side (3^rd Layer)

Bottom View (4^th Layer)