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T5753 Datasheet(PDF) 4 Page - ATMEL Corporation

Part No. T5753
Description  UHF ASK/FSK TRANSMITTER
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Maker  ATMEL [ATMEL Corporation]
Homepage  http://www.atmel.com
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T5753 Datasheet(HTML) 4 Page - ATMEL Corporation

 
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4
T5753
4510F–RKE–07/04
Functional
Description
If ENABLE = L and the PA_ENABLE = L, the circuit is in standby mode consuming only
a very small amount of current so that a lithium cell used as power supply can work for
several years.
With ENABLE = H the XTO, PLL and the CLK driver are switched on. If PA_ENABLE
remains L only the PLL and the XTO is running and the CLK signal is delivered to the
microcontroller. The VCO locks to 32 times the XTO frequency.
With ENABLE = H and PA_ENABLE = H the PLL, XTO, CLK driver and the power
amplifier are on. With PA_ENABLE the power amplifier can be switched on and off,
which is used to perform the ASK modulation.
ASK Transmission
T he T 5 753 is activa ted by EN ABLE = H. PA_EN ABLE mu st r e m a in L fo r
typically
≥ 3 ms, then the CLK signal can be taken to clock the microcontroller and the
output power can be modulated by means of Pin PA_ENABLE. After transmission
PA_ENABLE is switched to L and the microcontroller switches back to internal clocking.
The T5753 is switched back to standby mode with ENABLE = L.
FSK Transmission
T he T 5 753 is activa ted by EN ABLE = H. PA_EN ABLE mu st r e m a in L fo r
typically
≥ 3 ms, then the CLK signal can be taken to clock the microcontroller and the
power amplifier is switched on with PA_ENABLE = H. The chip is then ready for FSK
modulation. The microcontroller starts to switch on and off the capacitor between the
XTAL load capacitor and GND with an open-drain output port, thus changing the refer-
ence frequency of the PLL. If the switch is closed, the output frequency is lower than if
the switch is open. After transmission PA_ENABLE is switched to L and the microcon-
troller switches back to internal clocking. The T5753 is switched back to standby mode
with ENABLE = L.
The accuracy of the frequency deviation with XTAL pulling method is about ±25% when
the following tolerances are considered.
Figure 4. Tolerances of Frequency Modulation
Using C4 = 8.2 pF ± 5%, C5 = 10 pF ± 5%, a switch port with CSwitch =3 pF ± 10%, stray
capacitances on each side of the crystal of CStray1 =CStray2 = 1 pF ± 10%, a parallel
capacitance of the crystal of C0 = 3.2 pF ± 10% and a crystal with CM = 13 fF ± 10%, an
FSK deviation of ±21.5 kHz typical with worst case tolerances of ±16.25 kHz to
±28.01 kHz results.
CLK Output
An output CLK signal is provided for a connected microcontroller, the delivered signal is
CMOS compatible if the load capacitance is lower than 10 pF.
Clock Pulse Take-over
The clock of the crystal oscillator can be used for clocking the microcontroller. Atmel’s
ATARx9x has the special feature of starting with an integrated RC-oscillator to switch on
the T5753 with ENABLE = H, and after 1 ms to assume the clock signal of the transmis-
sion IC, so that the message can be sent with crystal accuracy.
~
V
S
XTAL
C
Stray1
C
M
L
M
R
S
C
0
C
Stray2
C
4
C
5
Crystal equivalent circuit
C
Switch


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