RT7272BGSP Evaluation Board

Purpose

The RT7272B is a high-efficiency current mode synchronous step-down regulator that can deliver up to 3A output current from a wide input voltage range of 4.5V to 36V. This document explains the function and use of the RT7272B evaluation board (EVB) and provides information to enable operation and modification of the evaluation board and circuit to suit individual requirements.

Introduction

General Product Information

The RT7272B is a high efficiency, current mode synchronous step-down DC/DC converter that can deliver up to 3A output current over a wide input voltage range from 4.5V to 36V. The device integrates a 150mΩ high side and an 80mΩ low side MOSFET to achieve high conversion efficiency up to 95%. The current mode control architecture supports fast transient response and uses a simple compensation circuit.

A cycle-by-cycle current limit function provides protection against a shorted output and an internal soft-start eliminates input surge current during start-up. The RT7272B provides complete protection functions such as input under voltage lockout, output under voltage protection, over current protection and thermal shutdown.

The RT7272B is available in the thermal enhanced SOP-8 (Exposed Pad) package.

Product Feature

• 4.5V to 36V Input Voltage Range
• 3A Output Current
• Internal N-MOSFETs
• Current Mode Control
• Fixed Frequency Operation : 500kHz
• Adjustable Output Voltage from 0.8V to 30V
• High Efficiency Up to 95%
• Stable with Low ESR Ceramic Output Capacitors
• Cycle-by-Cycle Current Limit
• Adjustable Current Limit

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.Apply a 12V nominal input power supply (4.5V < V_IN < 36V) to the VIN and GND terminals.

2.The EN voltage is pulled to logic high by R4 (100kΩ to VIN) to enable operation. Drive EN high (>2.0V) to enable operation or low (<0.4V) to disable operation.

3.Verify the output voltage (approximately 3.3V) between VOUT and GND.

4.Connect an external load up to 3A to the VOUT and GND terminals and verify the output voltage and current.

Output Voltage Setting

Set the output voltage with the resistive divider (R1, R2) between VOUT and GND with the midpoint connected to FB through RCAMP. The output is set by the following formula:

The installed V_OUT capacitors (C4, C5) are 22μF, 16V X5R ceramic types. Do not exceed their operating voltage range and consider their voltage coefficient (capacitance vs. bias voltage) and ensure that the capacitance is sufficient to maintain stability and provide sufficient transient response for your application. This can be verified by checking the output transient response as described in the RT7272B IC datasheet.

Schematic, Bill of Materials and Board Layout

EVB Schematic Diagram

C1, C2: 10μF/50V/X5R, 1206, TDK C3216X5R1H106K

C4, C5: 22μF/16V/X5R, 1210, Murata GRM32ER61C226K

L1: 4.7μH WE74437368047, DCR=15mΩ

Bill of Materials

EVB Layout

Top View (1^stlayer)

Bottom View (4^thLayer)

Component Placement Guide—Component Side (1^stlayer)

PCB Layout—Component Side (1^stLayer)

PCB Layout—Inner Side (2^nd Layer)

PCB Layout—Inner Side (3^rd Layer)

Component Placement Guide—Bottom Side (4^th Layer)

PCB Layout—Bottom Side (4^thlayer)