Sample Input Wiring
] 3.4.6 Outputs
The TTU’s outputs are designed to drive external relays. These outputs provide a high-
current, open-collector driver that can sink up to 150 mA each. These drivers may be
used to drive external relays that can then control vehicle functions such as door locks,
fuel shut-off valves, sirens and lights. If additional current is required to drive the relays,
external circuitry can be added to source the current. This diagram is a typical use of an
output to drive a relay.
Sample Relay Wiring
External vs Internal Power Switch
This output allows the TTU to switch between power sources when certain conditions are
met (e.g. low power on the currently selected supply). If this output is set then the TTU
will use its internal battery as its power supply. If this output is cleared, the TTU will use
the external power supply.
By default, this output is cleared so the TTU-2820™ will operate off external power.
Enable / Disable Battery Charging
This output allows the TTU to enable or disable the charging of its internal battery. If this
output is set then the TTU will stop charging the internal battery. If this output is cleared,
the TTU will charge the internal battery.
By default, this output is cleared (i.e. battery charging enabled)
