**PERFORMANCE OF THE ANALOG DEVICES AD780BR VOLTAGE REFERENCE AT
CRYOGENIC TEMPERATURES**

Test Report

Richard Patterson

NASA Glenn Research Center

&

Ahmad Hammoud

QSS Group, Inc.

NASA Glenn Research Center

Cleveland, Ohio

March 22, 2002

[PERFORMANCE OF THE ANALOG DEVICES AD780BR]{.smallcaps}

[VOLTAGE REFERENCE AT CRYOGENIC TEMPERATURES]{.smallcaps}

# Background

The Analog Devices AD780 is an ultrahigh precision bandgap voltage
reference that can provide a pin-programmable output of 2.5 V or 3.0 V
from inputs between 4.0 V and 36 V. It can be used to improve the
performance of high-resolution analog-to-digital and digital-to-analog
converters due to its capacitive-load driving capability. The device is
specified for operation from --40 °C to +85 °C with low temperature
drift and low output noise \[1\]. A temperature output pin provided on
the AD780 allows the device to be configured as a temperature transducer
while providing a stable output reference voltage. The output of the
temperature transducer, which can be used to monitor changes in the
system ambient temperature, varies linearly with temperature. The
AD780BR device is capable of sourcing or sinking up to 10 mA and can be
used in series or shunt mode, thus allowing positive or negative output
voltages without external components. The performance of
plastic-packaged devices (in this case an SOIC 8 pin plastic package) at
low temperatures was investigated in this work.

# Test Setup

A circuit board, populated with the AD780BR and few passive components,
was designed and built for evaluation in the temperature range of +25 °C
to --180 °C. The device was characterized at test temperatures of 25, 0,
-40, -80, -100, -120, -140, -160 and ‑180 °C in a liquid nitrogen cooled
environmental chamber. At each test temperature, the device was allowed
to soak for 15 minutes before measurements were made. Limited thermal
cycle testing was also performed on the AD780BR. These tests consisted
of subjecting the device to a total of ten thermal cycles between +90 °C
and --125 °C at a temperature rate of 10 °C/min. Device characterization
was also performed at various temperatures after completion of the
thermal cycling activity.

The device performance was evaluated in terms of its 2.5 V output
voltage regulation and its temperature transducer output. These
characteristics were obtained using input voltages of 4, 18, and 36
volts and at three load levels. Differing resistive loads were selected
so that the load current ranged between 0 and 8.33 mA. The device is
specified to source or sink up to 10 mA.

## Results and Discussion

Figure 1 shows the deviation in the output voltage of the device with
respect to its room temperature value. The data, which is shown as a
function of temperature, is depicted for all input voltage and load
level combinations. It can be seen that the reference output voltage
remains within specifications (2.499 to 2.501 V) between temperatures of
25 °C to --40 °C. Beyond --40 °C, however, the output voltage begins to
decrease as the temperature is decreased. While this decrease in the
output voltage is very minimal down to temperatures of -120 °C, it
becomes more significant as the temperature is decreased further. In
addition, the device exhibits unstable operation at the two extreme low
temperatures; namely --160 °C and --180 °C. Instability was also
observed at the test temperature of -140 °C only when an input voltage
of 4 V is applied under no load condition. It is important to note that
if the output specifications were broadened to cover a range of 2.495 V
to 2.501 V, the device would be useful down to temperatures of --120 °C.
Table I lists all the data obtained under the various test conditions.
The operating points at which the output voltage went out of
specification limits and device instability occurred are shown as shaded
areas in Table I.

![](media/image1.emf)

Figure 1. Deviation in the output voltage versus temperature at
different test conditions.

The temperature sensor output of the AD780BR as a function of
temperature is shown in Figure 2 for three different test conditions. It
can be seen that for any selected input (supply) voltage, the transducer
output is nearly linear with temperature for most of the range between
25 °C and --180 °C. The non-linearity seen at the extreme temperatures
is due to the instability exhibited by the device, as was mentioned
earlier. Data of the temperature sensor output is listed also in Table
I.

![](media/image2.emf)

Figure 2. Temperature pin output versus temperature at different test
conditions.

Table I. Results of low temperature evaluation of Analog Devices AD780BR
voltage reference.

+-------------+--------------+----------+---------------+-------------+
| **Input     | **Output**   | **Temp** | **Output**    | **Temp**    |
| Voltage**   |              |          |               |             |
|             | **Current**  | **(°C)** | **Voltage**   | **Voltage** |
| **(V)**     |              |          |               |             |
|             | **(mA)**     |          | **(V)**       | **(V)**     |
+-------------+--------------+----------+---------------+-------------+
| 4           | 0            | 25       | 2.5001        | .559        |
+-------------+--------------+----------+---------------+-------------+
| 18          | 0            | 25       | 2.5001        | .564        |
+-------------+--------------+----------+---------------+-------------+
| 36          | 0            | 25       | 2.5001        | .567        |
+-------------+--------------+----------+---------------+-------------+
| 4           | 1.78         | 25       | 2.5001        | .563        |
+-------------+--------------+----------+---------------+-------------+
| 18          | 1.78         | 25       | 2.5001        | .572        |
+-------------+--------------+----------+---------------+-------------+
| 36          | 1.78         | 25       | 2.5001        | .584        |
+-------------+--------------+----------+---------------+-------------+
| 4           | 8.33         | 25       | 2.4996        | .562        |
+-------------+--------------+----------+---------------+-------------+
| 18          | 8.33         | 25       | 2.4996        | .594        |
+-------------+--------------+----------+---------------+-------------+
| 36          | 8.33         | 25       | 2.4996        | .633        |
+-------------+--------------+----------+---------------+-------------+
|             |              |          |               |             |
+-------------+--------------+----------+---------------+-------------+
| 4           | 0            | 0        | 2.5001        | .510        |
+-------------+--------------+----------+---------------+-------------+
| 18          | 0            | 0        | 2.5001        | .514        |
+-------------+--------------+----------+---------------+-------------+
| 36          | 0            | 0        | 2.5001        | .517        |
+-------------+--------------+----------+---------------+-------------+
| 4           | 1.78         | 0        | 2.5001        | .513        |
+-------------+--------------+----------+---------------+-------------+
| 18          | 1.78         | 0        | 2.5001        | .519        |
+-------------+--------------+----------+---------------+-------------+
| 36          | 1.78         | 0        | 2.5001        | .529        |
+-------------+--------------+----------+---------------+-------------+
| 4           | 8.33         | 0        | 2.4999        | .516        |
+-------------+--------------+----------+---------------+-------------+
| 18          | 8.33         | 0        | 2.4999        | .541        |
+-------------+--------------+----------+---------------+-------------+
| 36          | 8.33         | 0        | 2.4999        | .575        |
+-------------+--------------+----------+---------------+-------------+
|             |              |          |               |             |
+-------------+--------------+----------+---------------+-------------+
| 4           | 0            | -40      | 2.4998        | .432        |
+-------------+--------------+----------+---------------+-------------+
| 18          | 0            | -40      | 2.4999        | .437        |
+-------------+--------------+----------+---------------+-------------+
| 36          | 0            | -40      | 2.4999        | .441        |
+-------------+--------------+----------+---------------+-------------+
| 4           | 1.78         | -40      | 2.4998        | .437        |
+-------------+--------------+----------+---------------+-------------+
| 18          | 1.78         | -40      | 2.4999        | .444        |
+-------------+--------------+----------+---------------+-------------+
| 36          | 1.78         | -40      | 2.5000        | .455        |
+-------------+--------------+----------+---------------+-------------+
| 4           | 8.33         | -40      | 2.4994        | .439        |
+-------------+--------------+----------+---------------+-------------+
| 18          | 8.33         | -40      | 2.4997        | .465        |
+-------------+--------------+----------+---------------+-------------+
| 36          | 8.33         | -40      | 2.5000        | .500        |
+-------------+--------------+----------+---------------+-------------+
|             |              |          |               |             |
+-------------+--------------+----------+---------------+-------------+
| 4           | 0            | -80      | 2.4979        | .356        |
+-------------+--------------+----------+---------------+-------------+
| 18          | 0            | -80      | 2.4980        | .359        |
+-------------+--------------+----------+---------------+-------------+
| 36          | 0            | -80      | 2.4982        | .364        |
+-------------+--------------+----------+---------------+-------------+
| 4           | 1.78         | -80      | 2.4981        | .361        |
+-------------+--------------+----------+---------------+-------------+
| 18          | 1.78         | -80      | 2.4984        | .369        |
+-------------+--------------+----------+---------------+-------------+
| 36          | 1.78         | -80      | 2.4986        | .379        |
+-------------+--------------+----------+---------------+-------------+
| 4           | 8.33         | -80      | 2.4980        | .364        |
+-------------+--------------+----------+---------------+-------------+
| 18          | 8.33         | -80      | 2.4988        | .390        |
+-------------+--------------+----------+---------------+-------------+
| 36          | 8.33         | -80      | 2.4995        | .430        |
+-------------+--------------+----------+---------------+-------------+
|             |              |          |               |             |
+-------------+--------------+----------+---------------+-------------+
| 4           | 0            | -100     | 2.4973        | .321        |
+-------------+--------------+----------+---------------+-------------+
| 18          | 0            | -100     | 2.4974        | .342        |
+-------------+--------------+----------+---------------+-------------+
| 36          | 0            | -100     | 2.4976        | .330        |
+-------------+--------------+----------+---------------+-------------+
| 4           | 1.78         | -100     | 2.4978        | .324        |
+-------------+--------------+----------+---------------+-------------+
| 18          | 1.78         | -100     | 2.4976        | .331        |
+-------------+--------------+----------+---------------+-------------+
| 36          | 1.78         | -100     | 2.4980        | .343        |
+-------------+--------------+----------+---------------+-------------+
| 4           | 8.33         | -100     | 2.4971        | .327        |
+-------------+--------------+----------+---------------+-------------+
| **Input     | **Output**   | **Temp** | **Output**    | **Temp**    |
| Voltage**   |              |          |               |             |
|             | **Current**  | **(°C)** | **Voltage**   | **Voltage** |
| **(V)**     |              |          |               |             |
|             | **(mA)**     |          | **(V)**       | **(V)**     |
+-------------+--------------+----------+---------------+-------------+
| 18          | 8.33         | -100     | 2.4980        | .353        |
+-------------+--------------+----------+---------------+-------------+
| 36          | 8.33         | -100     | 2.4989        | .392        |
+-------------+--------------+----------+---------------+-------------+
|             |              |          |               |             |
+-------------+--------------+----------+---------------+-------------+
| 4           | 0            | -120     | 2.4955        | .285        |
+-------------+--------------+----------+---------------+-------------+
| 18          | 0            | -120     | 2.4958        | .289        |
+-------------+--------------+----------+---------------+-------------+
| 36          | 0            | -120     | 2.4960        | .292        |
+-------------+--------------+----------+---------------+-------------+
| 4           | 1.78         | -120     | 2.4955        | .286        |
+-------------+--------------+----------+---------------+-------------+
| 18          | 1.78         | -120     | 2.4961        | .295        |
+-------------+--------------+----------+---------------+-------------+
| 36          | 1.78         | -120     | 2.4967        | .306        |
+-------------+--------------+----------+---------------+-------------+
| 4           | 8.33         | -120     | 2.4955        | .290        |
+-------------+--------------+----------+---------------+-------------+
| 18          | 8.33         | -120     | 2.4970        | .317        |
+-------------+--------------+----------+---------------+-------------+
| 36          | 8.33         | -120     | 2.4984        | .355        |
+-------------+--------------+----------+---------------+-------------+
|             |              |          |               |             |
+-------------+--------------+----------+---------------+-------------+
| 4           | 0            | -140     | 2.4981        | .252        |
+-------------+--------------+----------+---------------+-------------+
| 18          | 0            | -140     | 2.4982        | .254        |
+-------------+--------------+----------+---------------+-------------+
| 36          | 0            | -140     | 2.4981        | .258        |
+-------------+--------------+----------+---------------+-------------+
| 4           | 1.78         | -140     | 2.4973        | .251        |
+-------------+--------------+----------+---------------+-------------+
| 18          | 1.78         | -140     | 2.4976        | .260        |
+-------------+--------------+----------+---------------+-------------+
| 36          | 1.78         | -140     | 2.4976        | .272        |
+-------------+--------------+----------+---------------+-------------+
| 4           | 8.33         | -140     | 1.9386        | .037        |
+-------------+--------------+----------+---------------+-------------+
| 18          | 8.33         | -140     | 2.4966        | .283        |
+-------------+--------------+----------+---------------+-------------+
| 36          | 8.33         | -140     | 2.4976        | .321        |
+-------------+--------------+----------+---------------+-------------+
|             |              |          |               |             |
+-------------+--------------+----------+---------------+-------------+
| 4           | 0            | -160     | 2.4962        | .215        |
+-------------+--------------+----------+---------------+-------------+
| 18          | 0            | -160     | 2.4965        | .219        |
+-------------+--------------+----------+---------------+-------------+
| 36          | 0            | -160     | 2.4961        | .222        |
+-------------+--------------+----------+---------------+-------------+
| 4           | 1.78         | -160     | 2.4060        | .215        |
+-------------+--------------+----------+---------------+-------------+
| 18          | 1.78         | -160     | 2.4959        | .225        |
+-------------+--------------+----------+---------------+-------------+
| 36          | 1.78         | -160     | 2.4956        | .235        |
+-------------+--------------+----------+---------------+-------------+
| 4           | 8.33         | -160     |               |             |
+-------------+--------------+----------+---------------+-------------+
| 18          | 8.33         | -160     | 2.0040        | .040        |
+-------------+--------------+----------+---------------+-------------+
| 36          | 8.33         | -160     | 2.4967        | .286        |
+-------------+--------------+----------+---------------+-------------+
|             |              |          |               |             |
+-------------+--------------+----------+---------------+-------------+
| 4           | 0            | -180     | 2.4946        | .180        |
+-------------+--------------+----------+---------------+-------------+
| 18          | 0            | -180     | 2.6759        | .259        |
+-------------+--------------+----------+---------------+-------------+
| 36          | 0            | -180     | 2.6178        | .245        |
+-------------+--------------+----------+---------------+-------------+
| 4           | 1.78         | -180     | 1.5670        | 0           |
+-------------+--------------+----------+---------------+-------------+
| 18          | 1.78         | -180     | 2.5824        | .226        |
+-------------+--------------+----------+---------------+-------------+
| 36          | 1.78         | -180     | 2.5170        | .209        |
+-------------+--------------+----------+---------------+-------------+
| 4           | 8.33         | -180     |               |             |
+-------------+--------------+----------+---------------+-------------+
| 18          | 8.33         | -180     | 1.2795        | 0           |
+-------------+--------------+----------+---------------+-------------+
| 36          | 8.33         | -180     | 2.4951        | .252        |
+-------------+--------------+----------+---------------+-------------+

  -------------- --------------------------------------------------------
                 Voltage out of specifications

                 Unstable operation
  -------------- --------------------------------------------------------

# After this basic characterization with temperature, the device was subjected, as mentioned earlier, to ten thermal cycles between +90 °C and -- 125 °C. Measurements of the device parameters were then followed at various temperatures. The post-thermal cycling data is listed in Table II. The results obtained were in good agreement to those obtained prior to the thermal cycling. Hence, it can be concluded that this limited thermal cycling had no significant effect on the characteristics of the AD780BR voltage reference.

Table II. Post-thermal cycling results of Analog Devices AD780BR voltage
reference.

+-------------+--------------+----------+---------------+-------------+
| **Input     | **Output**   | **Temp** | **Output**    | **Temp**    |
| Voltage**   |              |          |               |             |
|             | **Current**  | **(°C)** | **Voltage**   | **Voltage** |
| **(V)**     |              |          |               |             |
|             | **(mA)**     |          | **(V)**       | **(V)**     |
+-------------+--------------+----------+---------------+-------------+
| 4           | 0            | 25       | 2.5006        | .558        |
+-------------+--------------+----------+---------------+-------------+
| 18          | 0            | 25       | 2.5007        | .561        |
+-------------+--------------+----------+---------------+-------------+
| 36          | 0            | 25       | 2.5006        | .574        |
+-------------+--------------+----------+---------------+-------------+
| 4           | 1.78         | 25       | 2.5005        | .559        |
+-------------+--------------+----------+---------------+-------------+
| 18          | 1.78         | 25       | 2.5005        | .567        |
+-------------+--------------+----------+---------------+-------------+
| 36          | 1.78         | 25       | 2.5005        | .603        |
+-------------+--------------+----------+---------------+-------------+
| 4           | 8.33         | 25       | 2.5000        | .562        |
+-------------+--------------+----------+---------------+-------------+
| 18          | 8.33         | 25       | 2.5000        | .594        |
+-------------+--------------+----------+---------------+-------------+
| 36          | 8.33         | 25       | 2.5002        | .651        |
+-------------+--------------+----------+---------------+-------------+
|             |              |          |               |             |
+-------------+--------------+----------+---------------+-------------+
| 4           | 0            | -40      | 2.4999        | .432        |
+-------------+--------------+----------+---------------+-------------+
| 18          | 0            | -40      | 2.5001        | .441        |
+-------------+--------------+----------+---------------+-------------+
| 36          | 0            | -40      | 2.5001        | .442        |
+-------------+--------------+----------+---------------+-------------+
| 4           | 1.78         | -40      | 2.4999        | .435        |
+-------------+--------------+----------+---------------+-------------+
| 18          | 1.78         | -40      | 2.5000        | .443        |
+-------------+--------------+----------+---------------+-------------+
| 36          | 1.78         | -40      | 2.5000        | .450        |
+-------------+--------------+----------+---------------+-------------+
| 4           | 8.33         | -40      | 2.4995        | .435        |
+-------------+--------------+----------+---------------+-------------+
| 18          | 8.33         | -40      | 2.4998        | .461        |
+-------------+--------------+----------+---------------+-------------+
| 36          | 8.33         | -40      | 2.5000        | .502        |
+-------------+--------------+----------+---------------+-------------+
|             |              |          |               |             |
+-------------+--------------+----------+---------------+-------------+
| 4           | 0            | -120     | 2.4945        | .285        |
+-------------+--------------+----------+---------------+-------------+
| 18          | 0            | -120     | 2.4948        | .288        |
+-------------+--------------+----------+---------------+-------------+
| 36          | 0            | -120     | 2.4952        | .294        |
+-------------+--------------+----------+---------------+-------------+
| 4           | 1.78         | -120     | 2.4945        | .285        |
+-------------+--------------+----------+---------------+-------------+
| 18          | 1.78         | -120     | 2.4950        | .292        |
+-------------+--------------+----------+---------------+-------------+
| 36          | 1.78         | -120     | 2.4958        | .305        |
+-------------+--------------+----------+---------------+-------------+
| 4           | 8.33         | -120     | 2.4944        | .289        |
+-------------+--------------+----------+---------------+-------------+
| 18          | 8.33         | -120     | 2.4962        | .318        |
+-------------+--------------+----------+---------------+-------------+
| 36          | 8.33         | -120     | 2.4980        | .357        |
+-------------+--------------+----------+---------------+-------------+

+-------------+--------------+----------+---------------+-------------+
| **Input     | **Output**   | **Temp** | **Output**    | **Temp**    |
| Voltage**   |              |          |               |             |
|             | **Current**  | **(°C)** | **Voltage**   | **Voltage** |
| **(V)**     |              |          |               |             |
|             | **(mA)**     |          | **(V)**       | **(V)**     |
+-------------+--------------+----------+---------------+-------------+
| 4           | 0            | -140     | 2.4937        | .249        |
+-------------+--------------+----------+---------------+-------------+
| 18          | 0            | -140     | 2.4938        | .255        |
+-------------+--------------+----------+---------------+-------------+
| 36          | 0            | -140     | 2.4938        | .259        |
+-------------+--------------+----------+---------------+-------------+
| 4           | 1.78         | -140     | 2.4936        | .254        |
+-------------+--------------+----------+---------------+-------------+
| 18          | 1.78         | -140     | 2.4939        | .262        |
+-------------+--------------+----------+---------------+-------------+
| 36          | 1.78         | -140     | 2.4942        | .274        |
+-------------+--------------+----------+---------------+-------------+
| 4           | 8.33         | -140     | 1.9758        | .060        |
+-------------+--------------+----------+---------------+-------------+
| 18          | 8.33         | -140     | 2.4944        | .283        |
+-------------+--------------+----------+---------------+-------------+
| 36          | 8.33         | -140     | 2.4965        | .322        |
+-------------+--------------+----------+---------------+-------------+
|             |              |          |               |             |
+-------------+--------------+----------+---------------+-------------+
| 4           | 0            | -160     | 2.4944        | .217        |
+-------------+--------------+----------+---------------+-------------+
| 18          | 0            | -160     | 2.4945        | .220        |
+-------------+--------------+----------+---------------+-------------+
| 36          | 0            | -160     | 2.4942        | .225        |
+-------------+--------------+----------+---------------+-------------+
| 4           | 1.78         | -160     | 2.4941        | .218        |
+-------------+--------------+----------+---------------+-------------+
| 18          | 1.78         | -160     | 2.4940        | .226        |
+-------------+--------------+----------+---------------+-------------+
| 36          | 1.78         | -160     | 2.4939        | .238        |
+-------------+--------------+----------+---------------+-------------+
| 4           | 8.33         | -160     | 1.4200        | .000        |
+-------------+--------------+----------+---------------+-------------+
| 18          | 8.33         | -160     | 1.9000        | .064        |
+-------------+--------------+----------+---------------+-------------+
| 36          | 8.33         | -160     | 2.4948        | .286        |
+-------------+--------------+----------+---------------+-------------+
|             |              |          |               |             |
+-------------+--------------+----------+---------------+-------------+
| 4           | 0            | -180     | 2.4963        | .18         |
+-------------+--------------+----------+---------------+-------------+
| 18          | 0            | -180     | 2.6200        | .244        |
+-------------+--------------+----------+---------------+-------------+
| 36          | 0            | -180     | 2.5700        | .229        |
+-------------+--------------+----------+---------------+-------------+
| 4           | 1.78         | -180     | 2.1200        | .049        |
+-------------+--------------+----------+---------------+-------------+
| 18          | 1.78         | -180     | 2.5433        | .217        |
+-------------+--------------+----------+---------------+-------------+
| 36          | 1.78         | -180     | 2.5040        | .209        |
+-------------+--------------+----------+---------------+-------------+
| 4           | 8.33         | -180     | 0.6170        | 0           |
+-------------+--------------+----------+---------------+-------------+
| 18          | 8.33         | -180     | 1.3000        | 0           |
+-------------+--------------+----------+---------------+-------------+
| 36          | 8.33         | -180     | 2.4939        | .251        |
+-------------+--------------+----------+---------------+-------------+

  -------------- --------------------------------------------------------
                 Voltage out of specifications

                 Unstable operation
  -------------- --------------------------------------------------------

# Conclusion

The Analog Devices AD780BR is a commercial-grade, ultrahigh precision
voltage reference device rated for --40 °C to +85 °C operation. The SOIC
8 pin plastic package device was evaluated for potential use in low
temperature applications down to --180 °C with a 2.5 V output reference
voltage. The device was characterized in terms of its output regulation
and temperature sensing output in the temperature range of +25 °C to
‑180 °C. While the device performed well with respect to output voltage
regulation with temperature down to --40 °C, the manufacturer's
specified low temperature rating, it does have potential use down to
--120 °C if the acceptable output is broadened to cover the range of
2.495 V to 2.501 V. With an input voltage level of 36 V, the acceptable
output just mentioned can be obtained down to --160 °C. The output of
the built-in temperature sensor worked well and was linear with
temperature for most of the test range between 25 °C and --180 °C. No
effect was observed in the operational characteristics of the device due
to the applied limited thermal cycling. Further testing and long-term
cycling are needed, however, to fully characterize the performance of
the device and to determine its reliability for operation in low
temperature environments.

# References

1\. Analog Devices AD780 High Precision Reference Data Sheet, Rev. B.

# Acknowledgments

This work was performed under the NASA Glenn Research Center GESS
Contract \# NAS3-00145. Support was also provided from the NASA
Electronic Parts and Packaging (NEPP) Program, EPAR Task "Electronics
for Extreme Environments".