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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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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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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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
IN
10 uF
GND
OUT_F
VIN
OUT_SEN
10 uF 0.1 uF
VREF
0.1 uF
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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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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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Figure 4-4. Layout Bottom
Figure 4-5. Top Layer
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Figure 4-6. Bottom Layer
Figure 4-7. Top Solder Mask
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