The channel-to-channel switching time is typically

180ns, with about 100ns of break-before-make delay.

This 100ns break-before-make delay prevents the

input-to-input short that would occur if two input chan-

nels were simultaneously connected to the output. In a

typical data acquisition system, the dominant delay is

not the switching time of the multiplexer, but is the set-

tling time of the amplifiers and S/H. Another limiting fac-

the signal source impedance multiplied by the load

capacitance on the output of the multiplexer. Even with

low signal source impedances, 100pF of capacitance

on the multiplexer output will approximately double the

settling time to 0.01% accuracy.

Operation with Supply Voltages

Other than ±15V

The main effect of supply voltages other than ±15V is

the reduction in output signal range. The MAX354 limits

the output voltage to about 1.5V below V+ and about

3V above V-. In other words, the output swing is limited

to +3.5V to -2V when operating from ±5V. The

Typical

power supplies. Maxim tests and guarantees the

MAX354/MAX355 for operation from ±4.5V to ±18V

supplies. The switching delays are increased by about

a factor of 2 at ±5V, but break-before-make action is

preserved.

The MAX354/MAX355 can operate with a single +4.5V

to +30V supply, as well as asymmetrical power sup-

plies such as +15V and -5V. The digital threshold

remains approximately 1.6V above the GND pin, and

mined by the total voltage difference between V+ and

V-. Connect V- to 0V when operating with a +4.5V to

+30V single supply.

The MAX354 digital threshold is relatively independent

of the power-supply voltages, going from 1.6V typical

when V+ is 15V to 1.5V typical when V+ is 5V. This

means that the MAX354/MAX355 operate with standard

TTL-logic levels, even with ±5V power supplies. In all

cases, the threshold of the enable (EN) pin is the same

as the other logic inputs.

Digital Interface Levels

The typical digital threshold of both the address lines

and the enable pin is 1.6V, with a temperature coeffi-

cient of about -3mV/°C. This ensures compatibility with

0.8V to 2.4V TTL-logic swings over the entire tempera-

ture range. The digital threshold is relatively indepen-

dent of the supply voltages, moving from 1.6V typical to

1.5V typical as the power supplies are reduced from

±15V to ±5V. In all cases, the digital threshold is refer-

enced to the GND pin.

The digital inputs can also be driven with CMOS-logic

levels swinging from either V+ to V- or from V+ to

ground. The digital input current is just a few nanoamps

of leakage at all input voltage levels, with a guaranteed

maximum of 1µA.

Operation as a Demultiplexer

The MAX354/MAX355 function as demultiplexers where

the input is applied to the output pin, and the input pins

are used as outputs. The MAX354/MAX355 provide

both break-before-make action and full fault protection

when operated as demultiplexers, unlike earlier genera-

tions of fault-protected muxes.

Channel-to-Channel Crosstalk,

Off-Isolation, and Digital Feedthrough

At DC and low frequencies the channel-to-channel

crosstalk is caused by variations in output leakage cur-

rents as the off-channel input voltages are varied. The

MAX354 output leakage varies only a few picoamps as

all seven off inputs are toggled from -10V to +10V. The

output voltage change depends on the impedance

signal source resistance in most cases, since the load

driven by the MAX354 is usually high impedance. For a

signal source impedance of 10k

Ω or lower, the DC

crosstalk exceeds 120dB.

Tables 2a and 2b show typical AC crosstalk and off-

isolation performance. Digital feedthrough is masked

by the analog charge injection when the output is

enabled. When the output is disabled, the digital

feedthrough is virtually unmeasureable, since the digi-

tal pins are physically isolated from the analog section

by the GND and V- pins. The ground plane formed by

these lines is continued onto the MAX354/MAX355 die

to provide over 100dB isolation between the digital and

analog sections.

Fault-Protected Analog Multiplexers

10

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