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5.2
Shorter Charge-Up (TX) Pulses for Speed Applications
(5-2)
Shorter Charge-Up (TX) Pulses for Speed Applications
This section is intended to provide information and examples regarding the two most important system
constraints (transponder charge-up level and field strength), so that if any of the parameters in your
system have to be changed, you can work it out using these examples as a basis.
The values in
are only valid in TX = 50 ms and RX = 40 ms. For countries with RMS and CISPR
regulations, the antenna voltage can be higher for shorter TX pulses. Use
to calculate the
maximum allowed antenna voltage (this level is the temperature limit of the antennas). With
you can calculate the antenna voltage for shorter TX pulses (only valid for countries with RMS FCC
regulations); this voltage must always be lower than that calculated with
:
There are two constraints:
1. V
cl
= 5 V
2. H
rms
= constant
Constraint 1:
For TX = 50 ms:
V
cl
= 5 = A
×
(1 – e
TX/RxC
)
where:
R = 302777
Ω
C = 120 nF
A = 6.689
For TX = TX
b
Where
b
= time chosen
A
b
= 5/(1 – e
TX/RxC
)
(5-1)
With a shorter TX pulse you get a higher coefficient 'Ab'. This means that the peak value of the magnetic
field strength must be Ab/A times higher than in the case of 50 ms charge-up time, to get the same
charge-up voltage.
A = the calculated value for 50 ms.
Constraint 2:
H
50ms,peak
is the magnetic field for 50 ms charge-up time:
For a different TX you have the magnetic field strength multiplication:
To find the correct charge-up time, TX must conform to
and
. Unfortunately this
is not possible. When you choose a shorter TX pulse, the magnetic field strength can become higher as
shown in
, but never high enough to charge the transponder to 5 V as in the case with 50 ms.
24
Speed Applications (Detecting Moving Transponders)
SCBU025 – November 1996
Summary of Contents for TIRIS SCBU025
Page 1: ...Antenna Reference Guide November 1996 SCBU025...
Page 2: ...Antenna Reference Guide Literature Number SCBU025 November 1996...
Page 6: ...www ti com 6 SCBU025 November 1996 Submit Documentation Feedback...
Page 20: ...www ti com Noise Characteristics 20 SCBU025 November 1996 Submit Documentation Feedback...
Page 30: ...www ti com Mechanical Characteristics 30 SCBU025 November 1996 Submit Documentation Feedback...
Page 34: ...www ti com Theory of Coupled Inductors 34 SCBU025 November 1996 Submit Documentation Feedback...