Texas Instruments REF70EVM User manual

User’s Guide

REF70EVM User's Guide

ABSTRACT

The REF70EVM is a precision voltage reference evaluation module that demonstrates the REF70 ultra-low noise

integrated circuit from Texas Instruments (TI).

Table of Contents

Trademarks.................................................................................................................................................................................1

1 Overview..................................................................................................................................................................................2

1.1 REF70EVM Features......................................................................................................................................................... 2

1.2 REF70EVM Schematic...................................................................................................................................................... 3

1.3 REF70EVM Bill of Materials...............................................................................................................................................4

1.4 REF70EVM Board..............................................................................................................................................................5

2 Quick Setup Guide..................................................................................................................................................................6

2.1 Electrostatic Discharge Warning........................................................................................................................................ 6

2.2 Unpacking the EVM........................................................................................................................................................... 6

2.3 Power Supply Setup and Functional Test.......................................................................................................................... 6

3 EVM Theory and Operation....................................................................................................................................................7

3.1 VREF Output's OUTF and OUFS........................................................................................................................................ 7

3.2 Output Capacitor................................................................................................................................................................ 7

4 Layout and Component Placement.......................................................................................................................................8

Trademarks

All other trademarks are the property of their respective owners.

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REF70EVM User's Guide 1

1 Overview

The REF70EVM is an adjustable voltage reference evaluation module that demonstrates the REF70 integrated

circuit in its FKH ceramic package from Texas Instruments (TI).

The REF70 is a ultra-low noise voltage reference with 2 ppm/C temperature drift. The REF70 is used primarily

as a voltage reference for high accuracy data converters to allow for a larger noise free resolution.

The REF70 can be operated from VREF to 18 V, making this part optimal for a wide range of voltages for

applications such as precision data acquasition systems, industrial instrumentation, semiconductor test

equipment, and PLC analog I/O modules. In order for this device to operate as intended, it does require 6.5 mA

IQ(max) for proper operating across temperature. This device also comes with a enable pin that allows the

device to be set in shutdown mode. Under the shutdown condition, the REF70 only consumes 12 μA of current.

The REF70EVM is configured for a LCCC (FKH) ceramic package (U2) and includes a additional MSSOP (DGK)

landpattern for alternate packages (U1). The VIN header can be connected to an external power supply to

provide power. All of the REF70 input and output pins are accessible for external connection via test headers.

For users looking for a alternate packages to test the REF70, contact TI.

1.1 REF70EVM Features

• Includes: REF7025QFKH

• Footprints for resistors and capacitors

• Multiple outputs for voltage measurements

KEY PARAMETERS PARAMETER PARAMETER LIMITS

Supply Voltage: IN 0 V – 18V

Enable Pin EN 0V to IN

Fixed Output Voltage: VREF 2.5 V (REF7025)

Output Current: IOUT -10 mA to 10 mA

CAUTION

Applying voltages above the limitations given in this table may cause permanent damage to your

hardware.

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1.2 REF70EVM Schematic

The schematic for the REF70EVM is illustrated in Figure 1-1.

Figure 1-1. REF70EVM Schematic

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REF70EVM User's Guide 3

1.3 REF70EVM Bill of Materials

DESIGNATOR QUANTITY VALUE DESCRIPTION PACKAGE

REFERENCE

PART NUMBER MANUFACTURER

!PCB 1 Printed Circuit

Board

LP026 Any

C1, C3, C5, C7 4 10uF CAP, CERM, 10 uF,

35 V, +/- 10%, X7R,

1206

1206 GMK316AB7106KL Taiyo Yuden

C2, C6 2 0.1uF CAP, CERM, 0.1

uF, 50 V, +/- 10%,

X7R, AEC-Q200

Grade 1, 0603

0603 CGA3E2X7R1H104K0

80AA

TDK

C4, C8 2 0.1uF CAP, CERM, 0.1

uF, 16 V, +/- 10%,

X7R, 0603

0603 C0603X104K4RACTU Kemet

FID1, FID2, FID3 3 Fiducial mark.

There is nothing to

buy or mount.

N/A N/A N/A

H1, H2, H3, H4 4 Bumpon,

Hemisphere, 0.44 X

0.20, Clear

Transparent

Bumpon

SJ-5303 (CLEAR) 3M

J1, J3, J5, J7 4 Header, 100mil,

3x1, Gold, TH

3x1 Header TSW-103-07-G-S Samtec

J2, J4, J6, J8 4 Header, 100mil,

2x1, Gold, TH

2x1 Header TSW-102-07-G-S Samtec

R1, R2 2 0 RES, 0, 5%, 0.063

W, 0402

0402 RC0402JR-070RL Yageo America

SH-J1, SH-J3, SH-

J5, SH-J7

4 1x2 Shunt, 100mil,

Flash Gold, Black

Closed Top

100mil Shunt

SPC02SYAN Sullins Connector

Solutions

U2 1 Ultra High-Precision

Voltage Reference

LCCC8 REF7025QFKH Texas Instruments

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1.4 REF70EVM Board

The PCB layout for the REF70EVM is illustrated in Figure 1-2 and Figure 1-3.

Figure 1-2. REF70EVM Board Top

Figure 1-3. REF70EVM Board Bottom

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REF70EVM User's Guide 5

2 Quick Setup Guide

This section describes the setup to quickly check the functionality of the REF70EVM.

2.1 Electrostatic Discharge Warning

Many of the components on the REF70EVM are susceptible to damage by electrostatic discharge (ESD).

Customers are advised to observe proper ESD handling precautions when unpacking and handling the EVM,

including the use of a grounded wrist strap at an approved ESD workstation.

CAUTION

Failure to observe ESD handling procedures may result in damage to EVM components.

2.2 Unpacking the EVM

After opening the REF70EVM package, ensure that the following is included:

1 pc. REF70EVM board using one REF7025QFKH

2.3 Power Supply Setup and Functional Test

Normal operation:

A 5-V power supply capable of 50 mA of current is required. The REF70 consumes 6.5 mA of current during

normal operationg and has a maximum 10 mA of output current for maintaining regulated voltage. During start-

up, the REF70 might consume ISC momentarily to charge the output capacitors.

Connect the positive power supply lead to the "VIN" on J6. Connect the negative power supply lead to "GND" on

J8.

Connect a voltmeter positive terminal to "OUTF" on J7. Connect the negative voltmeter terminal to "GND" on J8.

The output voltage of the REF7025QFKH will be 2.5V.

Shutdown mode:

The REF70 "EN" pin has an internal pull up which makes the REF70 be active when EN is floating. Use header

J5 to connect "EN" to "GND" to put the device in shutdown mode.

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3 EVM Theory and Operation

The following schematic is representative of the REF70EVM.

REF70xx

10 uF

GND

OUT_F

VIN

OUT_SEN

10 uF 0.1 uF

VREF

0.1 uF

Figure 3-1. REF7025 Schematic

The REF70EVM is designed to allow users to evaluate the configuration in Figure 3-1. With the provided

footprints, a user can change the passive components to better suit their application. As shown in Figure 1-2, the

EVM is designed to allow users to evaluate the REF70 in FKH. This EVM also has the land pattern for the

REF70 in DGK which allows users to test the device in their system with the provided pins.

3.1 VREF Output's OUTF and OUFS

The REF70 VREF is the output of the REF70 when the OUTF and OUTS are shorted together. OUTF and OUTS

refer to the force and sense configuration of the REF70 reference buffer. The benefit of having force and sense

connection is to reduce the IR loss from long trace wires at high currents. In the normal active configuration, the

OUTF and OUTS are shorted together. In the REF70EVM this is done by the R1 and R2 which are 0 Ohm

resistors. If R1 or R2 is removed, OUTF and OUTS must be connected in a loop by the headers J3/J7 or

externally for proper operation. If the OUTF and OUTS are not connected together in a loop then the device will

not operate the correct voltage.

EN Enable

Controller

Digital

Core

Bandgap

Core Reference

Buffer OUTF

Å

OUTS

VIN

GND

VIN

REN

Figure 3-2. REF70 Functional Block Diagram

3.2 Output Capacitor

The REF70 requires an output capacitor between 0.1 uF to 100uF for proper operation and stability. Larger

capacitors are able to help with load transcient respones.

A large capacitor can also help with lowering the broadband/white noise. It is necessary to understand output

capacitors when selecting the capacitor for the appliation.

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REF70EVM User's Guide 7

4 Layout and Component Placement

Figure 4 and Figure 5 show the top and bottom assemblies of the printed circuit board (PCB) to show the

component placement on the EVM.

Figure 6 and Figure 7 show the top and bottom layouts, Figure 8 and Figure 9 show the top and bottom layers,

and Figure 10 shows the top solder mask of the EVM.

Figure 4-1. Component Placement—Top Assembly

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Figure 4-2. Component Placement—Bottom Assembly

Figure 4-3. Layout Top

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REF70EVM User's Guide 9

Figure 4-4. Layout Bottom

Figure 4-5. Top Layer

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