Datasheet

MAX328/MAX329
Ultra-Low Leakage Monolithic CMOS
Analog Multiplexers
8 _______________________________________________________________________________________
Applications Information
Figure 4 is a typical circuit for converting the
MAX328/MAX329 into a fault-tolerant mux. In this
application, the internal diodes limit the voltage at the
MAX328 input to ±15.7V (±15V supplies). No external
diodes need to be added with the MAX328/MAX329,
unlike conventional multiplexers requiring external
diodes.
The resistors, R, need to be 39kΩ or higher to limit the
power dissipation in the resistor when a 120V AC fault
occurs (i.e., power dissipation is (120-16)
2
/39kΩ or
0.28W. This is why a 1/2/W resistor is needed). The circuit
withstands an indefinite fault to a 120V AC line with no
damage to any component.
In addition to allowing fault-protection, the guaranteed
low leakage of the MAX328/MAX329 also reduces signal
errors. The circuit in Figure 4 produces an error voltage of
10pA (max leakage) x 39kΩ or 0.39µV at room tempera-
ture and 39µV at +125°C. Therefore, for 10V signals, the
MAX328/MAX329 allows 17-bit resolution (38µV = 1LSB)
over the full temperature range.
16
15
14
13
12
11
10
9
1
2
3
4
5
6
7
8
A0
A1
A2
MAX328
EN
D
S4
S3
S2
S1
1µF
-15V
R
R
R
R
R
R
R
R
S5
S6
S7
S8
1µF
+15V
R = 39kΩ 1/2W
Figure 4. Fault-Tolerant Mux (indefinitely withstands 120V AC
fault voltages)
16 EN 15 A0 14 A1 13 A2
10 S5
11 V+
12 GND
9S6
2S1
1V-
3S2
4S3
5S4 6D 7
S8
8S7
MAX328
LOGIC
16 EN 15 A0 14 A1 13 GND
10 S2B
11 S1B
12 V+
9 S3B
2S1A
1V-
3S2A
4S3A
5S4A 6DA 7
DB
8S4B
MAX329
LOGIC
TOP VIEW
Functional Diagrams