Purpose

The RT7297C 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 18V. This document explains the function and use of the RT7297C 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 RT7297C is a high efficiency, monolithic synchronous step-down DC/DC converter that can deliver up to 3A output current from a 4.5V to 18V input supply. The RT7297C's current mode architecture and external compensation allow the transient response to be optimized over a wide range of loads and output capacitors. Cycle-by-cycle current limit provides protection against shorted outputs and soft-start eliminates input current surge during start-up. The RT7297C also provides output under voltage protection and thermal shutdown protection. The low current (<3μA) shutdown mode provides output disconnection, enabling easy power management in battery-powered systems. The RT7297C is available in an SOP-8 (Exposed Pad) package.

Product Feature

• ±1.5% High Accuracy Feedback Voltage
• 4.5V to 18V Input Voltage Range
• 3A Output Current
• Integrated N-MOSFET Switches
• Current Mode Control
• Fixed Frequency Operation : 800kHz
• Output Adjustable from 0.8V to 12V
• Up to 95% Efficiency
• Programmable Soft-Start
• Stable with Low-ESR Ceramic Output Capacitors
• Cycle-by-Cycle Over Current Protection
• Input Under Voltage Lockout
• Output Under Voltage Protection
• Thermal Shutdown Protection

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 < 18V) 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 (>2.7V) 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. The output is set by the following formula:

The installed VOUT 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 RT7297C 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: 3.6μH TAIYO YUDEN NR8040T3R6N, DCR=15mΩ

Bill of Materials

EVB Layout

Top View (1^stlayer)

Bottom View (2^nd Layer)

Component Placement Guide—Component Side (1^stlayer)

PCB Layout—Component Side (1^stLayer)

Component Placement Guide—Bottom Side (2^ndlayer)

PCB Layout—Bottom Side (2^ndlayer)