MAX4554 Maxim, MAX4554 Datasheet - Page 17

• Manufacturer Part Number: MAX4554
• Description: The MAX4554/MAX4555/MAX4556 are CMOS analog ICs configured as force-sense switches for Kelvin sensing in automated test equipment (ATE)
• Manufacturer: Maxim

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.
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
Figure 3. 8-Wire Guarded Force-Sense Measurements
FORCE-SENSE AMPLIFIER
FORCE-SENSE AMPLIFIER
______________________________________________________________________________________
VOLTAGE SOURCE
V +
V+
V+
V+
V-
V-
V-
V-
12-Wire Measurements
V+
V-
GUARD AMPLIFIER
GUARD AMPLIFIER
CURRENT SENSE
CURRENT SENSE
V
V
8-WIRE PRECISION SOURCE-MONITOR
LEAKAGE CURRENT
LEAKAGE CURRENT
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.
Force-Sense Switches
-FORCE
-SENSE
+FORCE
-DRIVEN GUARD
+SENSE
+DRIVEN GUARD
TWINAX CABLE
TWINAX CABLE
LOAD
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