Section 5: Source-measure considerations
2470 High Voltage SourceMeter Instrument Reference Manual
5-20
2470-901-01 Rev. A /
May
2019
Overtemperature protection
To prevent damaging heat build-up and ensure specified performance, make sure there is adequate
ventilation and air flow around the instrument to ensure proper cooling. Do not cover the ventilation
holes on the top, sides, or bottom of the instrument.
Even with proper ventilation, the instrument can overheat in the following situations:
•
If the ambient temperature is too high.
•
If you use the instrument as a power sink for long periods.
If the instrument overheats, the output is turned off and an event message is displayed.
If an overtemperature condition occurs, turn off the instrument and allow it to cool for
30 minutes. You cannot turn the output on until the instrument cools down. Verify that there
is adequate ventilation. When you return power to the instrument, verify that the cooling fan
is running. If not, contact Keithley Instruments. Leaving the instrument turned on with the
failure message displayed or with an inoperative cooling fan may result in damage to the
instrument.
Current breakdown protection
In some tests, the limited bandwidth of the SMU may cause current to exceed either the programmed
current or the limit current value. To prevent this from occurring, you can turn on the breakdown
protection function. This adds a 500
Ω resistor in series with the SMU force lead. This resistor limits,
at a wide bandwidth, the breakdown current to a maximum value of V
OUTPUT
/500.
When the breakdown protection is set for AUTO operation, the resistor is in place for the 200 V and
1000 V ranges and current ranges less than or equal to the 10 mA range. Above the 10 mA range or
on lower voltage ranges, the breakdown protection resistor is automatically taken out of series with
the SMU force lead.
An example of when breakdown protection is appropriate is when you are testing components to
specify the DUT breakdown voltage. One method is to test the component at the specified breakdown
voltage and determine if the leakage current has exceeded a threshold level. For example, if you are
testing a 1000 V rated MOSFET, you can short the gate to the source and apply 1050 V from the
drain to the source while measuring the actual drain current. Testing at 1050 V instead of 1000 V
provides some assurance that the component both meets and exceeds the breakdown requirement
by some user-specified margin. In this test, if the breakdown protection is off, you may find that at the
exact moment of component breakdown, the current may exceed the limit current value. With the
breakdown function on, the peak current is limited to V
OUTPUT
/500.