ATA5757 ATMEL Corporation, ATA5757 Datasheet - Page 4

• Manufacturer Part Number: ATA5757
• Description: (ATA5756 / ATA5757) UHF ASK/FSK TRANSMITTER
• Manufacturer: ATMEL Corporation

General Description
4
ATA5756/ATA5757
Figure 3. Block Diagram
This fully integrated PLL transmitter allows the design of simple, low-cost RF miniature
transmitters for TPM and RKE applications. The VCO is locked to 24 × f
for ATA5756/ATA5757. Thus, a 13.125 MHz/13.56 MHz crystal is needed for a
315 MHz/433.92 MHz transmitter. All other PLL and VCO peripheral elements are
integrated.
The XTO is a series resonance (current mode) oscillator. Only one capacitor and a
crystal connected in series to GND are needed as external elements in an ASK system.
The internal FSK switch, together with a second capacitor, can be used for FSK
modulation.
The crystal oscillator needs typically 0.6 ms until the CLK output is activated if a crystal
as defined in the electrical characteristics is used (e.g., TPM crystal). For most crystals
used in RKE systems, a shorter time will result.
The CLK output is switched on if the amplitude of the current flowing through the crystal
has reached 35% to 80% of its final value. This is synchronized with the 1.64/1.69 MHz
CLK output. As a result, the first period of the CLK output is always a full period. The
PLL is then locked <250 µs after CLK output activation. This means an additional wait
time of ≥250 µs is necessary before the PA can be switched on and the data transmis-
sion can start. This results in a significantly lower time of about 0.85 ms between
enabling the ATA5756/ATA5757 and the beginning of the data transmission which saves
battery power especially in tire pressure monitoring systems.
ANT2
ANT1
FSK
ASK
CLK
2
1
3
4
5
ATA5756 /
ATA5757
OR
f
8
PA
EN
EN
PLL
VCO
f
Power up/down
PFD
CP
LF
24/
32
XTO
Ampl. OK
10
ENABLE
GND
9
VS
8
7
6
XTO1
XTO2
XTAL
4702H–RKE–09/04
/32 × f
XTAL