ata5756-6dqy ATMEL Corporation, ata5756-6dqy Datasheet - Page 4

• Manufacturer Part Number: ata5756-6dqy
• Description: Ata5756 Uhf Ask/fsk Transmitter
• Manufacturer: ATMEL Corporation

3. General Description
4
ATA5756/ATA5757
Figure 2-2.
This fully integrated PLL transmitter allows the design of simple, low-cost RF miniature transmit-
ters for TPM and RKE applications. The VCO is locked to 24
ATA 5 7 5 6 / ATA 5 7 5 7 . T h u s , a 1 3 . 1 2 5 M H z / 1 3 . 5 6 M H z c r y s t a l i s n e e d e d f o r 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 con-
nected 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 transmission can start. This results in a signifi-
cantly 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.
Block Diagram
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
f
X T A L
/32
4702I–RKE–11/05
f
X T A L
for