5 Robust Communication With the Built-in Hot-Swap Feature of the ISO164x

The ISO164x prevents loading an active I2C bus irrespective of whether a staggered connector is used or not. While Vcc2 is below the UVLO threshold, the ISO164x bus lines will avoid disrupting or corrupting an active I2C bus using internal circuitry, and if connected with a staggered connector, the SDA and SCL lines of the ISO164x are pre-charged to minimize inrush current required to charge the pin capacitance of the device, further reducing the effect of their addition to the bus as shown in Section 4.

In applications where staggered connectors are not used or are not possible to integrate, devices that are “power-on hot-swap” compliant only, requiring a staggered connector or hot-swap controller, have effects that can disrupt data communication when they are connected to systems like those shown in Section 4. TI’s ISO1640 and ISO1641, both “power-off hot-swap” devices, do not require staggered connectors, external hardware, or additional circuitry for hot swap. A specialized internal circuit that is agnostic to the presence or absence of a power supply ensures the open-drain output of the I2C pins remain in high-impedance mode and does not pull the data lines LOW during hot-swap or power-up transients. This ensures safe hot swap operation even while using standard connectors.

For conditions where generic connectors are used or Vcc2 levels on the I2C device are lower than on the bus, “power-off hot-swap” devices, including TI’s ISO164x devices, continue to help preserve signals on the bus as well. This saves users from having to power down a system to connect I2C nodes or cards since these devices do not corrupt the bus when connected whether they are powered on or powered off.