Fault-Protected Analog Multiplexers

Maxim's Hl-508A and MAX358 are 8 channel single­-ended (1 of 8) multiplexers with fault protection. Maxim's Hl-509A and MAX359 are 4 channel differ­ential (2 of 8) multiplexers with fault protection. Using a series N-channel, P-channel, N-channel structure, these multiplexers provide significantly improved fault protection. If the power supplies to the Maxim fault-protected multiplexer are inadver­tently turned off while input voltages are still applied, a// channels in the multiplexer are turned off, and only a few nanoamperes of leakage current will flow into the inputs. This protects not only the multiplexer and the circuitry driven by the multiplexer, but also protects the sensors or signal sources which drive the multiplexer.

The Maxim series N-channel, P-channel, N-channel protection structure has two significant advantages over the simple current limiting protection scheme of the first generation fault protected multiplexers. First, the Maxim protection scheme limits fault currents to nanoamp leakage values rather than many milli­amperes. This prevents damage to sensors or other sensitive signal sources. Second, the Maxim fault-­protected multiplexers can withstand a continuous±35V overvoltage, unlike the first generation which has a continuous overvoltage limitation of about ±10V imposed by power dissipation considerations.

All digital inputs have logic thresholds of 0.8V and 2.4V, ensuring both TTL and CMOS compatibility without requiring pullup resistors. Break-before-­make operation is guaranteed. Power supply currents have been reduced and typical power dissipation is less than 2 milliwatts.

APPLICATIONS

* Data Acquisition Systems

* Industrial and Process Control Systems

* Avionics Test Equipment

* Signal Routing between Systems

* Improved 2nd Source (See "Maxim Advantage" on 3rd and 5th page)

* All Switches Off with Power Supplies Off

* On Channel Turns OFF If Overvoltage Occurs

* Only Nanoamperes of Input Current under All Fault Conditions