SNAU304A August   2024  – October 2024 REF80

 

  1.   1
  2.   Description
  3.   Get Started
  4.   Features
  5.   Applications
  6.   6
  7. 1Evaluation Module Overview
    1. 1.1 Introduction
    2. 1.2 Kit Contents
    3. 1.3 Specification
    4. 1.4 Device Information
  8. 2Hardware
    1. 2.1 Setup
    2. 2.2 EVM Connection
    3. 2.3 Jumper Information
    4. 2.4 Best Practices
  9. 3Implementation Results
    1. 3.1 Evaluation Setup
    2. 3.2 Performance Data and Results
  10. 4Hardware Design Files
    1. 4.1 Schematics
    2. 4.2 PCB Layouts
    3. 4.3 Bill of Materials (BOM)
  11. 5Compliance Information
    1. 5.1 Compliance and Certifications
  12. 6Additional Information
    1. 6.1 Trademarks
  13. 7Related Documentation
  14. 8Revision History

2.2 EVM Connection

There are multiple options to power up REF8EVM. There are onboard LDOs provided or users can bypass the LDOs to directly power REF80 with an external power supply. The TPS7A4901DRBR, a low noise LDO, and LM317AEMP/NOPB, a high output current LDO, can be used if a low noise, regulated input voltage is desired to further isolate the noise of REF80 from the noise generated by a bench power supply. These LDOs generate voltages at about 15V. REF8EVM has been validated to meet REF80 specifications with both options. The input voltage ranges of each device can be seen below in Table 2-1.

Table 2-1 Input Voltage Ranges for REF8EVM Setup
Input Setting

Device

EVM Minimum Input Voltage

EVM Maximum Input Voltage

VDD Bypass (J17)

REF80000B1NAJT (VDD Pin)

10V

16.5V

Heater Vin Bypass (J20)

 REF80000B1NAJT

(HEATP Pin)

10V

42V

VDD LDO (J17)

 TPS7A4901DRBR

16V

35V

Heater Vin LDO (J20)

 LM317AEMP/NOPB

18.5V

37V

Default EVM setup is shown in Figure 2-2. The output reference voltage can also be measured in many different ways. The output reference can be measured by connecting the VREF+ and VREF- directly to an 8.5 digit multimeter, by installing user provided binding posts J14 and J16 where J14 is VREF+ and J16 is VREF-, or by measuring the output voltage using SMA connector J4. For best temperature drift performance, use low thermal EMF banana plugs to measure VREF+ and VREF- rather than SMA cables to avoid unwanted offsets due to imbalanced thermal EMF effects.

REF8EVM REF8EVM Default Setup Figure 2-2 REF8EVM Default Setup
REF8EVM REF8EVM DMM Direct Connection Figure 2-3 REF8EVM DMM Direct Connection

Table 2-1 lists the detailed function of VIN and Heater VIN.

Table 2-2 REF8EVM Input Connection
TerminalPin ConnectionFunction
VINVDDConnect to power supply.

Connect jumper on J17 to select LDO power supply or bypass.

Heater VIN

HEATP

Connect to power supply. Ground connection for heater must be connected to the GND pin on J1.

Connect jumper on J20 to select LDO power supply or bypass.

There are also options to install a resistor R2 on the board to change the internal set temperature. Suggested values can seen below in Table 2-3.

Table 2-3 TSET Resistor Values
ResistanceInternal Heater Setpoint
0Default TSET
130kΩTSET - 10°C
360kΩTSET - 20°C
800kΩTSET - 30°C
OpenDefault TSET

Finally, footprints are included on the board to install precision film resistors on R4 and R5 to help aid in validation, if desired.

If users want to measure the output of REF8EVM using the SMA connector, then users can remove the banana plugs, thus allowing the board to rest on the standoffs installed in each corner of the board.

REF8EVM comes with a polycarbonate ULV94-V0 rated cover that is attached covering REF80 and the slots on the EVM. This is to restrict the air flow around REF80. This helps the temperature surrounding REF80 remain more constant, thus decreasing the amount of compensation and current that the internal heater must provide and improving the temperature drift.