Fo rc e -S e n s e S w it c h e s
Increasing V- has no effect on the logic-level thresh-
olds, but it does increase the drive to the internal P-
c ha nne l s witc he s , re d uc ing the ove ra ll s witc h
on-resistance. V- also sets the negative limit of the ana-
log signal voltage.
nected to GND. All of the bipolar precautions must be
observed.
__________Ap p lic a t io n s In fo rm a t io n
S w it c h in g 4 -Wire
Fo rc e -S e n s e Circ u it s
Bipolar-Supply Operation
The MAX4554/MAX4555/MAX4556 operate with bipolar
supplies between ±4.5V and ±18V. However, since all
factory characterization is done with ±15V supplies
(and +20V, -10V for MAX4554), operation at other sup-
plies is not guaranteed. The V+ and V- supplies need
not be symmetrical, but their sum cannot exceed the
absolute maximum rating of 44V (see Absolute Max-
imum Ratings). VL must not exceed V+.
Figure 5 shows how to switch a single voltage or cur-
rent source between two loads using two MAX4555s. A
single CMOS inverter ensures that only one switch is on
at a time. On each MAX4555, switches 2 and 3 are the
high-current switches, so they should be used for force
circuits. By interchanging loads and sources, the circuit
can be reversed to switch two sources to a single load.
Additional MAX4555s and loads or sources can be
added to expand the circuit, but additional IN_ address
decoding must be incorporated.
Single-Supply Operation
The MAX4554/MAX4555/MAX4556 operate from a sin-
gle supply between +4.5V and +44V when V- is con-
V+
V-
VL
FORCE
SENSE
MAX4555
COM2
COM1
NC2
NC1
FEEDBACK
V
LOAD1
SENSE
FORCE
COM4
/MAX456
NC4
NC3
COM3
IN2
VOLTAGE/CURRENT SOURCE
IN1
GND
IN4
IN3
CMOS INVERTER
LOGIC
IN
0
LOAD
IN
2
1
V+
V-
VL
1
MAX4555
NC2
NC1
COM2
COM1
LOAD2
COM4
NC4
NC3
COM3
IN2
IN1
GND
IN4
IN3
Figure 5. Using the MAX4555 to Switch 4-Wire Force-Sense Circuits from One Source to Two Loads
20 ______________________________________________________________________________________
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
