Model 2651A High Power System SourceMeter® Instrument Reference Manual Section 2: General operation
2651A-901-01 Rev. A / March 2011 2-53
The figure below illustrates the connection scheme of two Model 2651A instruments connected in
parallel. Two Model 2651A can output up to 100 A at 36 V (see Combining SMU outputs
(on page 2-
48)). The current delivered to the DUT is the sum of currents output by SMU channels (I
T
). Combining
the two Model 2651A instrument's expands the power envelope. For further information, visit the
Keithley Instruments website
(http://www.keithley.com) for application notes on combining two Model
2651A instruments' channels.
Figure 18: Connecting channels in parallel for higher current
DUT
I
1
I
2
I
T
=
I
1
+
I
2
2651A
(2nd)
+
-
2651A
(1st)
+
-
HI
LO
HI
LO
I
1
Single SMU maximum pulse current: 50 A
I
2
Single SMU maximum pulse current: 50 A
I
T
Paralleled SMU channels maximum pulse current (as shown): 100 A
Guarding and shielding
Source-measure performance and safety are optimized with the effective use of guarding and
shielding (noise and safety shields).
Guarding
A driven guard is always enabled and provides a buffered voltage that is at the same level as the
input/output HI voltage. The purpose of guarding is to eliminate the effects of leakage current (and
capacitance) that can exist between input/output high and low. Without guarding, leakage and
capacitance in the external high-impedance test circuit could be high enough to adversely affect the
performance of the Model 2651A.
Guarding (shown below) should be used when test circuit impedance is >1 GΩ.
NOTE
See Guard (on page 4-17) for details on the principles of guarding.
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