Single-channel, 100-Mbps digital isolator

The ISO721, ISO721M, ISO722, and

ISO722M devices are digital isolators with a logic input and output buffer separated

by a silicon dioxide (SiO2) insulation barrier. This barrier provides

galvanic isolation of up to 4000VPK per VDE 0884-17. Used in conjunction

with isolated power supplies, these devices prevent noise currents on a data bus or

other circuits from entering the local ground, and interfering with or damaging

sensitive circuitry.

A binary input signal is conditioned,

translated to a balanced signal, then differentiated by the isolation barrier.

Across the isolation barrier, a differential comparator receives the logic

transition information, then sets or resets a flip-flop and the output circuit

accordingly. A periodic update pulse is sent across the barrier to provide the

proper dc level of the output.

If this dc-refresh pulse is not

received for more than 4µs, the input is assumed to be unpowered or not being

actively driven, and the failsafe circuit drives the output to a logic-high

state.

These devices require two supply

voltages of 3.3V, 5V, or any combination. All inputs are 5V tolerant when supplied

from a 3.3V supply and all outputs are 4mA CMOS.

The ISO722 and ISO722M devices include

an active-low output enable that when driven to a high logic level, places the

output in a high-impedance state and turns off internal bias circuitry to conserve

power.

The ISO721 and ISO722 devices have TTL

input thresholds and a noise filter at the input that prevent transient pulses of up

to 2ns in duration from being passed to the output of the device.

The ISO721M and ISO722M devices have

CMOS VCC / 2 input thresholds, but do not have the noise-filter and the

additional propagation delay. These features of the ISO721M device also provide for

reduced-jitter operation.

The ISO721, ISO721M, ISO722, and

ISO722M devices are characterized for operation over the ambient temperature range

of –40°C to +125°C.