MAX328/MAX329
Ultra-Low Leakage Monolithic CMOS
Analog Multiplexers
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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.
