RT7280GQW Evaluation Board

Purpose

The RT7280 is a high-performance 700kHz 2A step down regulator with an internal power switch and synchronous rectifier. This document explains the function and use of the RT7280 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 RT7280 is a high-performance 700kHz 2A step down regulator with an internal power switch and synchronous rectifier. It features quick transient response using its Advanced Constant On-Time (ACOT^TM) control architecture that provides stable operation with small ceramic output capacitors and without complicated external compensation, among other benefits. The input voltage range is from 4.5V to 18V and the output is adjustable from 0.765V to 8V.

The proprietary ACOT^TM control improves upon other fast response constant on-time architectures, achieving nearly constant switching frequency over line, load, and output voltage ranges. Since there is no internal clock, response to transients is nearly instantaneous and inductor current can ramp quickly to maintain output regulation without large bulk output capacitance. The RT7280 is stable with and optimized for ceramic output capacitors.

With its internal 90mΩ switch and 60mΩ synchronous rectifier, the RT7280 displays excellent efficiency and good behavior across a range of applications, especially for low output voltages and low duty cycles. Cycle-by cycle current limit, input under-voltage lock-out, externally-adjustable soft-start, output under- and overvoltage protection, and thermal shutdown provide safe and smooth operation in all operating conditions.

The RT7280 evaluation board uses the RT7280GQW IC in a WDFN-10L3x3 package with an exposed thermal pad. The IC is also available in a PTSSOP-14 package with an exposed thermal pad.

Product Feature

• Fast Transient Response
• Steady 700kHz Switching Frequency at PWM
• 2A Output Current
• Advanced Constant On-Time (ACOT^TM) Control
• Optimized for Ceramic Output Capacitors
• 4.5V to 18V Input Voltage Range
• Internal 90mΩ Switch and 60mΩ Synchronous Rectifier
• 0.765V to 8V Adjustable Output Voltage
• Externally-adjustable, Pre-biased Compatible Soft-Start
• Cycle-by-Cycle Current Limit
• Output Over- and Under-voltage Shut-down

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 a jumper at JP1 terminals 1 and 2, connecting EN to GND, to disable operation.

2.Apply a 12V nominal input power supply (4.5V < V_IN < 18V) to the VIN and GND terminals.

3.Set the jumper at JP1 to connect terminals 2 and 3, connecting EN to VIN through resistor R30, to enable operation.

4.Verify the output voltage (approximately 1.05V) between VOUT and GND.

5.Connect an external load up to 2A to the VOUT and GND terminals and verify the output voltage and current.

Output Voltage Setting

Set the output voltage with the resistive divider (R23, R28) between VOUT and GND with the midpoint at FB. The output is set by the following formula:

The installed V_OUT capacitors (C11, C12) 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. Installing a small 5pF to 22pF capacitor at C30 (in parallel with R23) may be desirable to improve transient response for higher output voltages. See the RT7280 IC datasheet for more information.

Schematic, Bill of Materials and Board Layout

EVB Schematic Diagram

C7, C9: 10μF/50V/X5R, 1206, TDK C3216X5R1H106K

C11, C12: 22μF/16V/X5R, 1210, Murata GRM32ER61C226K

L1: 2.0μH TAIYO YUDEN NR8040T2R0N, DCR=9mΩ

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^th layer)