ZHCSH93 December 2017 TCAN4420
PRODUCTION DATA.
The VCC and VIO supply terminals have under voltage detection circuitry which places the device in a protected mode if an under voltage fault occurs. This protects the bus during an under voltage event on these terminals. If VIO is under voltage the RXD terminal is tri-stated (high impedance) and the device does not pass any signals from the bus. If VCC supply is lost, or has a brown out that triggers the UVLO, the device transitions to a protected mode. See Table 1.
If VIO drops below UVVIO under voltage detection, the transceiver switches off and disengage from the bus until VIO has recovered.
The device is designed to be an "ideal passive" or “no load” to the CAN bus if the device is unpowered. The bus terminals (CANH, CANL) have extremely low leakage currents when the device is unpowered, so they do not load the bus. This is critical if some nodes of the network are unpowered while the rest of the of network remains operational. Logic terminals also have low leakage currents when the device is unpowered, so they do not load other circuits which may remain powered.
| VCC | VIO | DEVICE STATE | BUS | RXD |
|---|---|---|---|---|
| > UVVCC | > UVVIO | Normal | Per TXD | Mirrors Bus |
| < UVVCC | > UVVIO | Protected | High Impedance | High (Recessive) |
| > UVVCC | < UVVIO | Protected | High Impedance | High Impedance |
| < UVVCC | < UVVIO | Protected | High Impedance | High Impedance |
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NOTE
Once an under voltage condition is cleared and the VCC supply has returned to valid level the device typically needs tMODE to transition to normal operation. The host processor should not attempt to send or receive messages until this transition time has expired.