**EVALUATION OF LINEAR TECHNOLOGY LT1461 VOLTAGE REFERENCE AT LOW
TEMPERATURES**

# Test Report

Richard Patterson

NASA Glenn Research Center

&

Ahmad Hammoud

QSS Group, Inc.

NASA Glenn Research Center

Cleveland, Ohio

## April 25, 2002

EVALUATION OF LINEAR TECHNOLOGY LT1461 VOLTAGE REFERENCE AT LOW
TEMPERATURES

**Background**

The Linear Technology LT1461 is a low dropout micropower bandgap voltage
reference with low drift and very high accuracy. The device draws very
small current (35 μA) and is capable of providing an output drive
current of 50 mA \[1\]. The low supply current makes it ideal for low
power and portable applications, and its output current capability makes
suitable for high power requirements, such as power supplies,
analog-to-digital and digital-to-analog converters, and precision
regulators. The device has a shutdown feature that can be used to switch
full load currents and for system power down. It has excellent thermal
regulation and a built-in thermal shutdown protects against overload
conditions. The device provides a steady output of 2.5 V from inputs up
to 20 V, and is specified for operation from --40 °C to +125 °C \[1\].
The performance of plastic-packaged devices at low temperatures was
investigated in this work.

**Test Setup**

A circuit board, populated with an LT1461ACS8-2.5 voltage reference and
a 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 LT1461 voltage reference. 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 at the test temperatures. These characteristics were
obtained using input voltages between 3 and 20 volts and at three load
levels. Differing resistive loads were selected so that the load current
ranged between 0 and 20 mA. The LT1461ACS8-2.5 device is specified to
source or sink up to 50 mA with an output voltage between 2.499 and
2.501 volts.

**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 input voltages of 3, 12, and 20
volts at three different load levels. It can be seen that the reference
output voltage generally 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 fluctuate as the temperature is decreased.
While the output voltage undergoes a slight increase with decrease in
temperature for the no load condition, it exhibits a decrease when a
load is applied. The intensity of this drop in the output voltage seems
to depend on both the levels of the input voltage and the applied load.
For example, the decrease is most dramatic at the highest load level
with input voltages of 12 and 20 volts, as seen in Figure 1. In
addition, the beginning of this trend occurs at temperatures as low as
-- 80 °C, as compared to --120 °C for the case of other load/ input
voltage combinations. Furthermore, the device exhibits unstable
operation at the two extreme low temperatures; namely --160 °C and --180
°C. Instability was also observed at temperature as low as -80 °C only
when an input voltage of 3 V is applied under high load condition. It is
important to point out that at test temperature of --180 °C, the device
completely loses its voltage regulation and it tends to behave almost
like a unity-gain amplifier stage.

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.

Table I. Output voltage of Linear Technology LT1461 voltage reference at
various temperatures.

+----------------+------------------+------------+-------------------+
| **Input        | **Output**       | **Temp**   | **Output**        |
| Voltage**      |                  |            |                   |
|                | **Current**      | **(°C)**   | **Voltage**       |
| **(V)**        |                  |            |                   |
|                | **(mA)**         |            | **(V)**           |
+----------------+------------------+------------+-------------------+
| 3              | 0                | 25         | 2.4997            |
+----------------+------------------+------------+-------------------+
| 12             | 0                | 25         | 2.4997            |
+----------------+------------------+------------+-------------------+
| 20             | 0                | 25         | 2.4997            |
+----------------+------------------+------------+-------------------+
| 3              | 1.78             | 25         | 2.4996            |
+----------------+------------------+------------+-------------------+
| 12             | 1.78             | 25         | 2.4996            |
+----------------+------------------+------------+-------------------+
| 20             | 1.78             | 25         | 2.4996            |
+----------------+------------------+------------+-------------------+
| 3              | 18.79            | 25         | 2.4981            |
+----------------+------------------+------------+-------------------+
| 12             | 18.79            | 25         | 2.4981            |
+----------------+------------------+------------+-------------------+
| 20             | 18.79            | 25         | 2.4981            |
+----------------+------------------+------------+-------------------+
|                |                  |            |                   |
+----------------+------------------+------------+-------------------+
| 3              | 0                | 0          | 2.4997            |
+----------------+------------------+------------+-------------------+
| 12             | 0                | 0          | 2.4997            |
+----------------+------------------+------------+-------------------+
| 20             | 0                | 0          | 2.4997            |
+----------------+------------------+------------+-------------------+
| 3              | 1.78             | 0          | 2.4997            |
+----------------+------------------+------------+-------------------+
| 12             | 1.78             | 0          | 2.4997            |
+----------------+------------------+------------+-------------------+
| 20             | 1.78             | 0          | 2.4996            |
+----------------+------------------+------------+-------------------+
| 3              | 18.79            | 0          | 2.4983            |
+----------------+------------------+------------+-------------------+
| 12             | 18.79            | 0          | 2.4982            |
+----------------+------------------+------------+-------------------+
| 20             | 18.79            | 0          | 2.4982            |
+----------------+------------------+------------+-------------------+
|                |                  |            |                   |
+----------------+------------------+------------+-------------------+
| 3              | 0                | -40        | 2.5000            |
+----------------+------------------+------------+-------------------+
| 12             | 0                | -40        | 2.5000            |
+----------------+------------------+------------+-------------------+
| 20             | 0                | -40        | 2.5000            |
+----------------+------------------+------------+-------------------+
| 3              | 1.78             | -40        | 2.5000            |
+----------------+------------------+------------+-------------------+
| 12             | 1.78             | -40        | 2.5000            |
+----------------+------------------+------------+-------------------+
| 20             | 1.78             | -40        | 2.4999            |
+----------------+------------------+------------+-------------------+
| 3              | 18.79            | -40        | 2.4988            |
+----------------+------------------+------------+-------------------+
| 12             | 18.79            | -40        | 2.4986            |
+----------------+------------------+------------+-------------------+
| 20             | 18.79            | -40        | 2.4983            |
+----------------+------------------+------------+-------------------+
|                |                  |            |                   |
+----------------+------------------+------------+-------------------+
| 3              | 0                | -80        | 2.5011            |
+----------------+------------------+------------+-------------------+
| 12             | 0                | -80        | 2.5010            |
+----------------+------------------+------------+-------------------+
| 20             | 0                | -80        | 2.5009            |
+----------------+------------------+------------+-------------------+
| 3              | 1.78             | -80        | 2.5010            |
+----------------+------------------+------------+-------------------+
| 12             | 1.78             | -80        | 2.5007            |
+----------------+------------------+------------+-------------------+
| 20             | 1.78             | -80        | 2.5003            |
+----------------+------------------+------------+-------------------+
| 3              | 18.79            | -80        | 1.2001            |
+----------------+------------------+------------+-------------------+
| 12             | 18.79            | -80        | 2.4920            |
+----------------+------------------+------------+-------------------+
| 20             | 18.79            | -80        | 2.4728            |
+----------------+------------------+------------+-------------------+
|                |                  |            |                   |
+----------------+------------------+------------+-------------------+
| 3              | 0                | -100       | 2.5024            |
+----------------+------------------+------------+-------------------+
| 12             | 0                | -100       | 2.5019            |
+----------------+------------------+------------+-------------------+
| 20             | 0                | -100       | 2.5019            |
+----------------+------------------+------------+-------------------+
| 3              | 1.78             | -100       | 2.5024            |
+----------------+------------------+------------+-------------------+
| 12             | 1.78             | -100       | 2.5005            |
+----------------+------------------+------------+-------------------+
| 20             | 1.78             | -100       | 2.5000            |
+----------------+------------------+------------+-------------------+
| 3              | 18.79            | -100       | 1.2084            |
+----------------+------------------+------------+-------------------+
| **Input        | **Output**       | **Temp**   | **Output**        |
| Voltage**      |                  |            |                   |
|                | **Current**      | **(°C)**   | **Voltage**       |
| **(V)**        |                  |            |                   |
|                | **(mA)**         |            | **(V)**           |
+----------------+------------------+------------+-------------------+
| 12             | 18.79            | -100       | 2.4718            |
+----------------+------------------+------------+-------------------+
| 20             | 18.79            | -100       | 2.4311            |
+----------------+------------------+------------+-------------------+
|                |                  |            |                   |
+----------------+------------------+------------+-------------------+
| 3              | 0                | -120       | 2.5042            |
+----------------+------------------+------------+-------------------+
| 12             | 0                | -120       | 2.5037            |
+----------------+------------------+------------+-------------------+
| 20             | 0                | -120       | 2.5032            |
+----------------+------------------+------------+-------------------+
| 3              | 1.78             | -120       | 2.5042            |
+----------------+------------------+------------+-------------------+
| 12             | 1.78             | -120       | 2.4997            |
+----------------+------------------+------------+-------------------+
| 20             | 1.78             | -120       | 2.4987            |
+----------------+------------------+------------+-------------------+
| 3              | 18.79            | -120       |                   |
+----------------+------------------+------------+-------------------+
| 12             | 18.79            | -120       | 2.4527            |
+----------------+------------------+------------+-------------------+
| 20             | 18.79            | -120       | 2.3973            |
+----------------+------------------+------------+-------------------+
|                |                  |            |                   |
+----------------+------------------+------------+-------------------+
| 3              | 0                | -140       | 2.5049            |
+----------------+------------------+------------+-------------------+
| 12             | 0                | -140       | 2.5041            |
+----------------+------------------+------------+-------------------+
| 20             | 0                | -140       | 2.5035            |
+----------------+------------------+------------+-------------------+
| 3              | 1.78             | -140       | 2.5049            |
+----------------+------------------+------------+-------------------+
| 12             | 1.78             | -140       | 2.4960            |
+----------------+------------------+------------+-------------------+
| 20             | 1.78             | -140       | 2.4930            |
+----------------+------------------+------------+-------------------+
| 3              | 18.79            | -140       |                   |
+----------------+------------------+------------+-------------------+
| 12             | 18.79            | -140       | 2.4382            |
+----------------+------------------+------------+-------------------+
| 20             | 18.79            | -140       | 2.3741            |
+----------------+------------------+------------+-------------------+
|                |                  |            |                   |
+----------------+------------------+------------+-------------------+
| 3              | 0                | -160       | 2.5060            |
+----------------+------------------+------------+-------------------+
| 12             | 0                | -160       | 2.5042            |
+----------------+------------------+------------+-------------------+
| 20             | 0                | -160       | 2.5031            |
+----------------+------------------+------------+-------------------+
| 3              | 1.78             | -160       | 2.2760            |
+----------------+------------------+------------+-------------------+
| 12             | 1.78             | -160       | 2.4932            |
+----------------+------------------+------------+-------------------+
| 20             | 1.78             | -160       | 2.4836            |
+----------------+------------------+------------+-------------------+
| 3              | 18.79            | -160       |                   |
+----------------+------------------+------------+-------------------+
| 12             | 18.79            | -160       |                   |
+----------------+------------------+------------+-------------------+
| 20             | 18.79            | -160       |                   |
+----------------+------------------+------------+-------------------+
|                |                  |            |                   |
+----------------+------------------+------------+-------------------+
| 3              | 0                | -180       | 3.0010            |
+----------------+------------------+------------+-------------------+
| 6              | 0                | -180       | 5.9910            |
+----------------+------------------+------------+-------------------+
| 20             | 0                | -180       |                   |
+----------------+------------------+------------+-------------------+
| 3              | 1.78             | -180       |                   |
+----------------+------------------+------------+-------------------+
| 12             | 1.78             | -180       |                   |
+----------------+------------------+------------+-------------------+
| 20             | 1.78             | -180       |                   |
+----------------+------------------+------------+-------------------+
| 3              | 18.79            | -180       |                   |
+----------------+------------------+------------+-------------------+
| 12             | 18.79            | -180       |                   |
+----------------+------------------+------------+-------------------+
| 20             | 18.79            | -180       |                   |
+----------------+------------------+------------+-------------------+

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

                 No readout/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 effect on the operational characteristics of the LT1461 voltage reference or its plastic-packaged assembly.

Table II. Post-thermal cycling results of Linear Technology LT1461
voltage reference.

+----------------+------------------+------------+-------------------+
| **Input        | **Output**       | **Temp**   | **Output**        |
| Voltage**      |                  |            |                   |
|                | **Current**      | **(°C)**   | **Voltage**       |
| **(V)**        |                  |            |                   |
|                | **(mA)**         |            | **(V)**           |
+----------------+------------------+------------+-------------------+
| 3              | 0                | 25         | 2.5004            |
+----------------+------------------+------------+-------------------+
| 12             | 0                | 25         | 2.5004            |
+----------------+------------------+------------+-------------------+
| 20             | 0                | 25         | 2.5003            |
+----------------+------------------+------------+-------------------+
| 3              | 1.78             | 25         | 2.5003            |
+----------------+------------------+------------+-------------------+
| 12             | 1.78             | 25         | 2.5002            |
+----------------+------------------+------------+-------------------+
| 20             | 1.78             | 25         | 2.5002            |
+----------------+------------------+------------+-------------------+
| 3              | 18.79            | 25         | 2.4988            |
+----------------+------------------+------------+-------------------+
| 12             | 18.79            | 25         | 2.4987            |
+----------------+------------------+------------+-------------------+
| 20             | 18.79            | 25         | 2.4986            |
+----------------+------------------+------------+-------------------+
|                |                  |            |                   |
+----------------+------------------+------------+-------------------+
| 3              | 0                | -40        | 2.5002            |
+----------------+------------------+------------+-------------------+
| 12             | 0                | -40        | 2.5002            |
+----------------+------------------+------------+-------------------+
| 20             | 0                | -40        | 2.5002            |
+----------------+------------------+------------+-------------------+
| 3              | 1.78             | -40        | 2.5000            |
+----------------+------------------+------------+-------------------+
| 12             | 1.78             | -40        | 2.5000            |
+----------------+------------------+------------+-------------------+
| 20             | 1.78             | -40        | 2.5000            |
+----------------+------------------+------------+-------------------+
| 3              | 18.79            | -40        | 2.4989            |
+----------------+------------------+------------+-------------------+
| 12             | 18.79            | -40        | 2.4985            |
+----------------+------------------+------------+-------------------+
| 20             | 18.79            | -40        | 2.4983            |
+----------------+------------------+------------+-------------------+
|                |                  |            |                   |
+----------------+------------------+------------+-------------------+
| 3              | 0                | -120       | 2.5042            |
+----------------+------------------+------------+-------------------+
| 12             | 0                | -120       | 2.5030            |
+----------------+------------------+------------+-------------------+
| 20             | 0                | -120       | 2.5030            |
+----------------+------------------+------------+-------------------+
| 3              | 1.78             | -120       | 2.5041            |
+----------------+------------------+------------+-------------------+
| 12             | 1.78             | -120       | 2.4997            |
+----------------+------------------+------------+-------------------+
| 20             | 1.78             | -120       | 2.4988            |
+----------------+------------------+------------+-------------------+
| 3              | 18.79            | -120       | 1.2680            |
+----------------+------------------+------------+-------------------+
| 12             | 18.79            | -120       | 2.4528            |
+----------------+------------------+------------+-------------------+
| 20             | 18.79            | -120       | 2.4042            |
+----------------+------------------+------------+-------------------+

+----------------+------------------+------------+-------------------+
| **Input        | **Output**       | **Temp**   | **Output**        |
| Voltage**      |                  |            |                   |
|                | **Current**      | **(°C)**   | **Voltage**       |
| **(V)**        |                  |            |                   |
|                | **(mA)**         |            | **(V)**           |
+----------------+------------------+------------+-------------------+
| 3              | 0                | -140       | 2.5051            |
+----------------+------------------+------------+-------------------+
| 12             | 0                | -140       | 2.5036            |
+----------------+------------------+------------+-------------------+
| 20             | 0                | -140       | 2.5037            |
+----------------+------------------+------------+-------------------+
| 3              | 1.78             | -140       | 2.5050            |
+----------------+------------------+------------+-------------------+
| 12             | 1.78             | -140       | 2.4962            |
+----------------+------------------+------------+-------------------+
| 20             | 1.78             | -140       | 2.4941            |
+----------------+------------------+------------+-------------------+
| 3              | 18.79            | -140       | 0.8251            |
+----------------+------------------+------------+-------------------+
| 12             | 18.79            | -140       | 2.4381            |
+----------------+------------------+------------+-------------------+
| 20             | 18.79            | -140       | 2.3755            |
+----------------+------------------+------------+-------------------+
|                |                  |            |                   |
+----------------+------------------+------------+-------------------+
| 3              | 0                | -160       | 2.5058            |
+----------------+------------------+------------+-------------------+
| 12             | 0                | -160       | 2.5031            |
+----------------+------------------+------------+-------------------+
| 20             | 0                | -160       | 2.5031            |
+----------------+------------------+------------+-------------------+
| 3              | 1.78             | -160       | 2.2791            |
+----------------+------------------+------------+-------------------+
| 12             | 1.78             | -160       | 2.4930            |
+----------------+------------------+------------+-------------------+
| 20             | 1.78             | -160       | 2.4835            |
+----------------+------------------+------------+-------------------+
| 3              | 18.79            | -160       |                   |
+----------------+------------------+------------+-------------------+
| 12             | 18.79            | -160       | 2.4105            |
+----------------+------------------+------------+-------------------+
| 20             | 18.79            | -160       | 2.3485            |
+----------------+------------------+------------+-------------------+
|                |                  |            |                   |
+----------------+------------------+------------+-------------------+
| 3              | 0                | -180       | 2.9910            |
+----------------+------------------+------------+-------------------+
| 12             | 0                | -180       | 11.9732           |
+----------------+------------------+------------+-------------------+
| 20             | 0                | -180       | 19.9514           |
+----------------+------------------+------------+-------------------+
| 3              | 1.78             | -180       | 2.2325            |
+----------------+------------------+------------+-------------------+
| 12             | 1.78             | -180       | 7.3833            |
+----------------+------------------+------------+-------------------+
| 20             | 1.78             | -180       | 13.5450           |
+----------------+------------------+------------+-------------------+
| 3              | 18.79            | -180       | 0.6219            |
+----------------+------------------+------------+-------------------+
| 12             | 18.79            | -180       | 2.4632            |
+----------------+------------------+------------+-------------------+
| 20             | 18.79            | -180       | 2.2876            |
+----------------+------------------+------------+-------------------+

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

                 No readout/Unstable operation
  -------------- --------------------------------------------------------

**Conclusion**

The Linear Technology LT1461, which is a low dropout with very high
accuracy reference voltage device rated for --40 °C to +125 °C
operation, has been evaluated for potential use in low temperature
applications. The plastic-packaged device was characterized in terms of
its output voltage regulation in the temperature range of +20 °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
about --80 °C with little degradation in voltage regulation under heavy
load conditions. At temperatures beyond --80 °C, the device begins to
show appreciable loss in regulation at heavy loads and, in particular,
when an input voltage of 3 volts is used. At --180 °C, a complete loss
of voltage regulation takes place as the voltage reference integrated
circuit chip behaves as a unity gain amplifier. Subjecting the device to
limited thermal cycling between +90 °C and -125°C was found to produce
no effect on neither its operational characteristics nor its
plastic-encapsulated packaging.

**References**

1\. Linear Technology LT1461-2.5 Micropower Precision Low Dropout Series
Voltage Reference Data Sheet.

**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, EPAC Task "Effects of
Wide Temperature Exposure on Characteristics of Plastic Encapsulated
COTS Components for Space Applications" and EPAR Task "Electronics for
Extreme Environments".