MAX4555CSE データシートの表示（PDF） - Maxim Integrated
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MAX4555CSE Datasheet PDF : 28 Pages
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Force-Sense Switches
8-WIRE PRECISION SOURCE-MONITOR
FORCE-SENSE AMPLIFIER
V+
CURRENT SENSE
V
V-
V+
+FORCE
+SENSE
+DRIVEN GUARD
TWINAX CABLE
GUARD AMPLIFIER
V-
V+
VOLTAGE SOURCE
V+ V-
LEAKAGE CURRENT
LEAKAGE CURRENT
LOAD
GUARD AMPLIFIER
V-
V
CURRENT SENSE
V-
FORCE-SENSE AMPLIFIER
-DRIVEN GUARD
-SENSE
-FORCE
TWINAX CABLE
Figure 3. 8-Wire Guarded Force-Sense Measurements
Note that although the positive and negative circuits are
identical, they are not redundant. Both are always used,
even when one side of the load is grounded, because
maintaining a precision output voltage requires losses in
the ground leads to be corrected by a force-sense
amplifier. If more than one power supply and load are
operated together, and they have a common connec-
tion, this requirement becomes even more critical.
Separate 8-wire connections prevent current changes in
one load from changing voltage in the other load.
12-Wire Measurements
Figure 4 shows a 12-wire circuit, which is an elabora-
tion of the 8-wire system using separate driven guards
for the force and sense wires. Four sets of triaxial
cables and connectors are used. The extra wires are
used for two reasons: 1) They provide better shielding
by having separate chassis grounds on each cable,
rather than separate ground wires external to the signal
cables; 2) In test equipment, where connection
changes are frequent, it is very convenient to use four
triax connectors or two quadrax (dual triax) connectors
for each load.
In addition, this method is slightly better for power sup-
plies or measurements that switch between constant
voltage and constant current, since separate driven
guards reduce circuit capacitance. Also, when trou-
bleshooting, it is convenient to be able to interchange
force and sense leads.
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