Download Final Documentation - University of Central Florida

considered as the primary source by the ICL7673. If the AC/DC adapter is
disconnected the ICL7673 switches to battery power, until the AC/DC adapter is
reconnected in. If the battery is fully depleted the system will shutoff. The
configuration of the ICL7673 is shown below. The LED shown in Figure 3233 will
let the user know that the unit is running on the primary source when it is lit.
Figure 32 – ICL7673 Automatic Backup Battery Switch Configuration
Power Switch
The power switch for the RDU is shown in Figure 2 above. It is an
OS102011MA1QS1 ON/ON slide switch used to turn the system on and off. This
switch is configured with the first pin connected to the battery voltage and the
second pin connected to the voltage in the DC/DC converter. The third pin is left
floating. This way if the switch is in the one-two position the system is on and
when the switch is in the two-three position the system is off.
DC/DC Conversion
The Enpirion EP5368QI is used for voltage regulation of the TSU. The
EP5368QI is a complete system on chip synchronous buck converter with
integrated inductor, PWM controller, MOSFETs, and compensation in a small
3mm x 3mm QFN package. This chip is ideal for noise sensitive RF as well as
area constrained applications like that of the TSU. The EP5368QI is powered by
the Li-Ion battery pack. The output voltage is set with the 3-pin VID selector and
the output voltage is 3.3V when connecting all three of the voltage select lines to
ground. The 4.7µF 0603 capacitor is required at the VIN by the system. Two
10µF 0805 capacitors are used at the VOUT pins to improve ripple performance.
A single 0.01µF 0603 capacitor is connected in parallel to the 10uF capacitors at
the output to improve transient suppression. The cost for this component is less
than $2. Figure 33 below is a diagram showing how the EP5368QI will be
configured in the TSU. Vsw is the voltage that comes from the On/Off switch,
which is +3.3V that is output from the buck converter for the system to use.
Power Line Filtering
The Analog and RF power lines for the CC430 are filtered to keep the digital
noise off them. This is accomplished with 1k, 250mA, 0402 ferrite chips, as
69