UPS25 21
RTD Embedded Technologies, Inc
The main 25W +5V step-down converter
The power supply circuitry is implemented with a switch-mode step down DC-DC
converter. The peak charge output power of this unit is 25W. This output power is
only available if adequate cooling is provided. The output current is internally
limited against over current and short circuit faults.
Connect a 10-40V DC source to the UPS25. A reverse voltage schottky diode will
withstand reverse voltages up to 40V DC. These devices are necessary to
protect the device in automotive and industrial installations.
This +5V converter output is not used to power any devices on the bus. This
+5V-supply is only used as a raw input to the battery charger step-up converter.
Current Limit
To protect against fault or short-circuit conditions the +5V DC/DC converter
module is equipped with a current limiting circuitry to provide continuous overload
protection. After reaching the current limit point (between 5.5 and 8.5Amps), the
voltage output will range between the rated output and zero depending on the
amount of overload. At this point the output current will be typically 25 to 30 % of
its maximum value. Once the short circuit condition is removed, the output will
return to the nominal value without restarting the unit.
Charger power converter
A 5V to +12V step up converter with 90% efficiency generates a n15V
for charging the battery pack. This architecture will permit the charging of the
battery pack at a higher voltage than the input of the UPS25. Charging will take
place while the input is over 10V, this trip level can be flexibly modified by
adjusting the trim pot controlling the UPS VIN trip voltage. This trim pot is
described later in this manual on Page 22. The +15V charge supply is limited to a
1,25A-peak current. If the battery being charged draws more current, the
converter will output a voltage less than the n15V output, typically during
fast charge the voltage is in the range of 11,5V to 12,5V depending on the
charge state of the battery.
