T5753 ATMEL Corporation, T5753 Datasheet - Page 4

• Manufacturer Part Number: T5753
• Description: UHF ASK/FSK TRANSMITTER
• Manufacturer: ATMEL Corporation

Functional
Description
ASK Transmission
FSK Transmission
CLK Output
Clock Pulse Take-over
4
T5753
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.
Th e T 57 5 3 i s a c t i v at e d b y E NA B L E = H . P A _ E NA B L E m us t r e ma i n L f or
typically
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.
Th e T 57 5 3 i s a c t i v at e d b y E NA B L E = H . P A _ E NA B L E m us t r e ma i n L f or
typically
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 C
capacitances on each side of the crystal of C
capacitance of the crystal of C
FSK deviation of ±21.5 kHz typical with worst case tolerances of ±16.25 kHz to
±28.01 kHz results.
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.
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.
4
= 8.2 pF ± 5%, C
3 ms, then the CLK signal can be taken to clock the microcontroller and the
3 ms, then the CLK signal can be taken to clock the microcontroller and the
XTAL
V
S
~
5
= 10 pF ± 5%, a switch port with C
0
= 3.2 pF ± 10% and a crystal with C
C
Stray1
Crystal equivalent circuit
C
M
L
C
M
0
Stray1
R
S
= C
Stray2
C
Stray2
C
5
= 1 pF ± 10%, a parallel
Switch
C
Switch
C
4
= 3 pF ± 10%, stray
M
= 13 fF ± 10%, an
4510F–RKE–07/04