ISO7221C-HT

The ISO7221 is a dual-channel digital isolator. To facilitate PCB layout, the channels are oriented in the opposite directions. This device has a logic input and output buffer separated by TI’s silicon-dioxide (SiO₂) isolation barrier, providing galvanic isolation of up to 4000 V. Used in conjunction with isolated power supplies, this device blocks high voltage, isolates grounds, and prevents 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 capacitive 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 ensure the proper dc level of the output. If this dc-refresh pulse is not received every 4 µs, the input is assumed to be unpowered or not being actively driven, and the failsafe circuit drives the output to a logic high state.

The small capacitance and resulting time constant provide fast operation with signaling rates available from 0 Mbps (dc) to 150 Mbps⁽³⁾. The A-, B- and C-option devices have TTL input thresholds and a noise filter at the input that prevents transient pulses from being passed to the output of the device. The M-option devices have CMOS V_CC/2 input thresholds and do not have the input noise-filter and the additional propagation delay.

This device requires two supply voltages of 3.3 V, 5 V, or any combination. All inputs are 5-V tolerant when supplied from a 3.3-V supply and all outputs are 4-mA CMOS.

The ISO7221 is characterized for operation over the ambient temperature range of –55°C to 175°C.