ATA5749-EK2 Atmel, ATA5749-EK2 Datasheet - Page 4

• Manufacturer Part Number: ATA5749-EK2
• Description: BOARD EVALUATION TPMS 433MHZ
• Manufacturer: Atmel
• Type: Transmitterr

Specifications of ATA5749-EK2

• Frequency: 433MHz
• For Use With/related Products: ATA5749
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

3. Functional Description
3.1
3.2
4
Fractional-N PLL
Selecting the RF Carrier Frequency
Atmel ATA5749
The Atmel
is determined by the contents of a 32-bit configuration register. The 15-bit value FREQ is used
with the 1-bit 434_N315 flag to determine the RF carrier frequency. This results in a user-select-
able frequency step size of 793Hz (with 13.000MHz crystal). With this level of resolution, it is
possible to compensate for crystal tolerance by adjusting the value of FREQ accordingly. This
enables the use of lower cost crystals without compromising final accuracy. In addition, software
programming of RF carrier frequency allows this device to be used in some multi-channel
applications.
Modulation type is selected with the 1-bit ASK_NFSK flag. FSK modulation is achieved by mod-
ifying the divider block in the feedback loop. The benefit to this approach is that performance-
reducing RF spurs (common in applications that create FSK by “pulling” the load capacitance in
the crystal oscillator circuit) are completely eliminated. The 8-bit value FSEP establishes the
FSK frequency deviation. It is possible to obtain FSK frequency deviations from ±396Hz to
±101kHz in steps of ±396Hz.
The PLL lock time is 1280/(external crystal frequency) and amounts to 98.46µs when using a
13.0000MHz crystal. When added to the crystal oscillator start-up time, a very fast time-to-trans-
mit is possible (typically 300µs). This feature extends battery life in applications like Tire
Pressure Monitoring Systems, where the message length is often shorter than 10ms and the
time “wasted” during start-up and settling time becomes more significant.
The fractional divider can be programmed to generate an RF output frequency f
the formulas shown in
down to the next integer value if FSEP is an odd number.
Table 3-1.
FSEP can take on the values of 1 to 255. Using a 13.000MHz crystal, the range of frequency
deviation f
ple, with FSEP = 100 the output frequency is FSK modulated with f
FREQ can take values in the range of values 2500 and 22000. Using a 13.0000MHz crystal, the
output frequency f
FSEP[0:7] = 100 and S434_N315 = 0. By setting FREQ[0:14] = 14342, FSEP[0:7] = 100 and
S434_N315 = 1, 433.92MHz can be realized.
RF Output Parameter
f
f
RF_FSK_HIGH
RF_FSK_LOW
f
DEV__FSK
f
RF ASK
®
DEV_FSK
ATA5749 block diagram is shown in
RF Output Parameter Formulas
is programmable from ±396Hz to ±101.16kHz in steps of ±396Hz. For exam-
RF
Table
(24 + (FREQ + FSEP/2 + 0.5)/16384)
can be programmed to 315MHz by setting FREQ[0:14] = 3730,
(24 + (FREQ + FSEP + 0.5)/16384)
(24 + (FREQ + 0.5)/16384)
3-1. Note that in the case of f
S434_N315 = LOW
FSEP/32768
f
f
XTO
XTO
f
XTO
Figure 1-1 on page
f
XTO
RF ASK
(32.5 + (FREQ + FSEP/2 + 0.5)/16384)
(32.5 + (FREQ + FSEP + 0.5)/16384)
(32.5 + (FREQ + 0.5)/16384)
, the FSEP/2 value is rounded
DEV_FSK
S434_N315 = HIGH
2. The operation of the PLL
FSEP/32768
= ±39.6kHz.
f
f
XTO
XTO
RF
9128G–RKE–03/11
f
XTO
according to
f
XTO