Power Supply - Texas Instruments 2000 Series Reference Manual

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1.2.1 Power Supply

There are two separate 5V supplies to the Micro-reader, one for the output stage (VSP) and the other for
the logic (VSL). On power up VSL should rise faster than 0.1 V/ms to ensure a reliable operation. The
Micro-reader has an on-board reset circuit which will reset it should the supply fall below 4 V (± 0.2 V).
In order to avoid problems with noise conducted via the supply lines, we recommend that if a single supply
is used, separate connections from a common de-coupling capacitor are used to feed the Micro-reader.
Note: The RF Module must not be supplied by Switched Mode Power Supplies (SMPS). This is
because most SMPS operate at frequencies around 50 kHz. The harmonics of the
generated field can interfere with the TIRIS receiver. Therefore only use linear regulated
power supplies, or SMPS with a fundamental operating frequency of 200 kHz or higher.
1.2.2 Antenna
The Micro-reader has been designed for use with a 47 µH antenna with a Q of 10 to 20 to generate the
exciter frequency of 134.2 kHz. Because of the low Q the system does not need to be tuned.
CARE MUST BE TAKEN WHEN HANDLING THE MICRO-READER
AS HIGH VOLTAGES ACROSS THE ANTENNA PINS COULD BE
HARMFUL TO YOUR HEALTH.
1.2.3 Synchronization
There are two possible methods of wired synchronization:
1. Connect a pulse waveform to all RDEN- input pins of the Micro-readers to be synchronized. The pulse
would normally be at VSL, dropping to GND for 100 µs every 200 ms.
2. Connect all SYNC outputs to an 'Or' and then connect this as an input to RDEN- of each Micro-reader
to be synchronized.
Wireless synchronization of the Micro-reader is very effective at synchronizing to adjacent readers,
however problems may occur if the antennas are positioned such that a transponder can be within range
of two readers at the same time. In this situation one reader could synchronize with the transponder
instead of the other reader.
When the WLSC input is active the Micro-reader is in wireless synchronization mode. Wireless
synchronization can also be switched on/off by a corresponding command via the serial interface. During
execution of this command it has priority over the WLSC input. After the command execution the status of
the WLSC input will be considered again.
Note: It is not recommended to have both wired and wireless synchronization switched on as
synchronization could be unreliable.
We recommend the use of bus drivers for wired synchronization with other Micro-readers
and to prevent ESD damage.
Wired or wireless synchronization prolongs the cycle time by typically 20 ms.
SCBU027 – May 2000
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