ATA6286 ATMEL Corporation, ATA6286 Datasheet - Page 15

• Manufacturer Part Number: ATA6286
• Description: (ATA6285 / ATA6286) TPMS Control and Transmitter IC
• Manufacturer: ATMEL Corporation

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4.5.3
4.5.4
4.5.5
4958AS–AUTO–09/06
4
Accuracy of Frequency Deviation
Accuracy of the Center Frequency
CLK Output
The accuracy of the frequency deviation using the XTAL pulling method is about ±20% if the fol-
lowing tolerances are considered. One important aspect is that the values of C
typical crystals are strongly correlated which reduces the tolerance of the frequency deviation.
Figure 4-6.
Using a crystal with a motional capacitance of C
of CL
C
internal FSK switch with C
the resulting C
deviation of ±19.3 kHz with worst case tolerances of ±15.8 kHz to ±23.2 kHz.
The imaginary part of the impedance in large signal steady state oscillation IM
pin 7 (XTO1), causes some additional frequency tolerances, due to pulling of the XTO oscillation
frequency. These tolerances have to be added to the tolerances of the crystal itself (adjustment
tolerance, temperature stability and ageing) and the influence to the center frequency due to tol-
erances of C
should be absorbed into the C
choosing C
quency deviation is as expected. Then, from the nominal value, the IM
using the pulling formula P = –IM
additional frequency tolerance of P = ±16.86 ppm results. If using crystals with other C
additional frequency tolerance can be calculated in the same way. For example, a lower
C
increases the tolerance to 21.07 ppm.
An output CLK signal of 1.64 MHz (ATA6285 operating at 315 MHz) and 1.69 MHz (ATA6286
operating at 433.92 MHz) is provided for a connected microcontroller. The delivered signal is
CMOS-compatible with a High and Low time of >125 ns if the load capacitance is lower than
20 pF. The CLK output is Low in power-down mode due to an internal pull-down resistor. After
enabling the PLL and XTO the signal stays Low until the amplitude of the crystal oscillator has
reached 35% to 80% of its amplitude. Then, the CLK output is activated synchronously with its
output signal so that the first period of the CLK output signal is a full period.
0
M
= 297
= 3.1 fF will reduce the frequency tolerance to 11.87 ppm, where a higher C
NOM
= 18 pF and a parallel capacitance of C
4
C
and C
M
4
4
, C
Tolerances of Frequency Modulation
(the correlation has a tolerance of 10%, so C
and C
5
XTAL
, C
5
, so that the XTO center frequency equals the crystal frequency, and the fre-
V
S
Switch
5
values are C
Switch
and C
= 0.9 pF ±20% and estimated parasitics of C
4
XTO
and C
Stray
ATA6285/ATA6286 [Preliminary]
Crystal equivalent circuit
4
C
= 10 pF ±1% and C
. The nominal value of IM
M
C
5
M
values by using a crystal with known frequency and
L
C
M
0
Pi
M
R
f
XTO
= 4.37 fF ±15%, a nominal load capacitance
S
0
with f
= 1.30 pF correlated with C
5
= 15 pF ±1% for a nominal frequency
XTO
0
C
= 267 to 326
Stray
= 13.56 MHz and C
C
XTO
5
C
= 110 , C
Switch
C
XTO
4
has ±90 tolerances,
Stray
XTO
C
Switch
= 0.7 pF ±10%,
M
, seen into the
). If using the
M
0
M
= 4.4 fF an
and C
and C
M
results in
= 5.5 fF
M
M
Stray
the
15
of