TRS3243E: Two device using the TPS3243 as Automatic Power Down can't communicate each other.

Hi,

When TRS3243E is in auto-powerdown mode and the device does not sense a valid RS-232 signal, the driver outputs will be disabled. In your setup, both transceivers are likely disabling their drivers and therefore do not see a valid signal and remain powered down. This would effectively put the system in a low-power mode. To regain communication, one of the devices would have to have FORCEON go high to re-enable drivers. Once the receiving device recognizes the valid input, it may also have FORCEON enabled to respond. 

1) Both devices are in low-power state. Drivers disabled 

FON=L; FOFF=H              FON=L; FOFF=H

 OP1(TPS3243) ============= OP2(TPS3243)

 Power = OFF                Power = OFF

2) Node 1 enables FORCEON to send message to Node 2

FON=*H*; FOFF=H            FON=L; FOFF=H

 OP1(TPS3243) ============= OP2(TPS3243) 

 Power = ON                Power = OFF

Send data  =>            => Receive data

3) Receiving Node 2 enables FORCEON to respond to Node 1

FON=H; FOFF=H              FON=*H*; FOFF=H

 OP1(TPS3243) ============= OP2(TPS3243)

 Power = ON                 Power = ON

                            <=Respond

I hope this is clear. Let me know if you have any more questions or would like further clarification.

Regards,

Eric