ISO1212: why doesn't ISO12XX need to have 2 power supply even it has basic isolation?

Hi Takahashi-san,

Most digital isolators (like ISO77xx) require power supply on both sides of device, each side powering the die on that side and this requirement is independent of whether a device supports basic or reinforced isolation. Some devices (like ISOW78xx) have an integrated power supply which produces the isolated power supply on the other side that internally also powers the second die.

ISO121x is uniquely designed to require only one external power supply. Since field digital inputs are of voltages >>5V and since these inputs also support >2mA of current, the same digital input signal can also be used as power supply to keep the device powered as long as the input is signal is present. ISO121x exactly does that, its second die / field side die gets powered by the external digital input signal and operates normal. The second die / field side die is carefully designed to support this operation. The applications that ISO121x is targeted mostly requires only basic isolation and hence ISO121x is designed only to support basic isolation.

Let me know if you have any other question, thank you.

Regards,
Koteshwar Rao