RT2872 Step-Down Converter Evaluation Board

Purpose

The RT2872 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 RT2872 evaluation board (EVB) and provides information to enable operation and modification of the evaluation board and circuit to suit individual requirements.

Introduction

General Product Description

The RT2872 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 105mΩ 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 RT2872 provides complete protection functions such as input under voltage lockout, output under voltage protection, over current protection and thermal shutdown.

The RT2872 is available in the thermal enhanced SOP-8 (Exposed Pad) package.

Product Features

• 4.5V to 36V Input Voltage Range
• 3A Output Current
• Internal N-MOSFETs
• Current Mode Control
• Frequency Operation : 300kHz to 1MHz
• 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
• AEC-Q100 Grade 3 Certification

Application

• Point of Load Regulator in Distributed Power Systems
• Digital Set Top Boxes
• Broadband Communications
• Vehicle Electronics
• Automotive Audio, Navigation, and Information Systems
• Enterprise Datacom Platforms Point of Load (POL)
• Industrial Grade General Purpose Point of Load

Evaluation Board

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 RT2872 IC datasheet.

Specification

Schematic

BOM

PCB Layout

Top View (1^st layer)

Bottom View (4^th Layer)

Component Placement Guide—Component Side (1^st layer)

PCB Layout—Component Side (1^st Layer)

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^th layer)

Step-Down Converter Efficiency Test