When any iOS App is sent to the background it is required to stop executing after a fixed period of time so that it does not drain your device battery or consume CPU time when it is not in focus. As the time limit approaches, TTerm for iPad will be forced to stop executing and will be unable to maintain your host connection.
You can avoid disconnections by keeping TTerm for iPad as the App running in the foreground whilst it is connected to a host.
Several classes of application are exempt and permitted to run in the background by Apple. These include music playing apps, VoIP apps and Navigation Apps. Terminal emulators are not permitted to run in the background.