tda5251f1 Infineon Technologies Corporation, tda5251f1 Datasheet - Page 54

• Manufacturer Part Number: tda5251f1
• Description: Ask/fsk 315mhz Wireless Transceiver
• Manufacturer: Infineon Technologies Corporation

Confidential
3.2.4
1. Determination of necessary crystal frequency using formula [3-19].
2. Determine corresponding C
3. Necessary C
1. When the necessary C
To compensate frequency errors due to crystal and component tolerance C
be varied. To enable this correction, half of the necessary capacitance variation has to be realized
with the internal C-banks.
If no finetuning is intended it is recommended to leave XIN (Pin 21) open. So the parasitic
capacitance of Pin 21 has no effect.
Note: Please keep in mind also to include the Pad parasitics of the circuit board.
In the suitable range for the serial capacitor, either capacitors with a tolerance of 0.1pF or 1% are
available.
A spreadsheet, which can be used to predict the total frequency error by simply entering the crystal
specification, may be obtained from Infineon.
3.2.5
The FSK-switch can be used either in a bipolar or in a FET mode. The mode of this switch is
controlled by bit D0 of the XTAL_CONFIG register (subaddress 0EH).
In the bipolar mode the FSK-switch can be controlled by a ramp function. This ramp function is set
by the bits D1 and D2 of the XTAL_CONFIG register (subadress 0EH). With these modes of the
FSK-switch the bandwidth of the FSK spectrum can be influenced.
When working in the FET mode the power consumption can be reduced by about 200 mA.
Preliminary Specification
FSK_RX:
-FSK:
+FSK:
FSK-receive) are known the external capacitors and the internal tuning caps can be calculated
using the following formulas:
e.g.
e.g. f
e.g. C
FSK-
Calculation of the external capacitors
FSK-switch modes
L FSK
C
C
V
C
C
= f
v1
v2
V
using formula [3-17].
v3
- = C
-
COSC LOW
+
+
=
+
C
C
C
C
L ±
tune1
tune2
L
tune2
,
1
FSK
v
for the 3 frequencies (C
-
+
=
=
Load
=
(
2
C
(
--------------------------------------------------------------------- - C
(
p
(
------------------------------------------------------------------------ - C
C
(
C
1
v-
C
applying formula [3-18].
f
C
v1
FSK
v1
v1
v1
–
+
-
+
C
+
+
)
2
C
21
C
C
*
C
tune1
tune1
tune1
L
tune1
OSC
)
54
) C
)
)
–
×
–
(
×
(
v-
C
(
(
C
for FSK LOW, C
C
v+
v+
vm
vm
–
–
–
C
–
C
C
21
21
C
21
21
)
)
–
)
)
–
20
v+
20
for FSK HIGH and C
–
C
v1
v2
, C
–
v2
C
TDA5251 F1
and C
22
Version 1.0
Application
2003-02-18
v3
[3 – 28]
[3 – 29]
[3 – 27]
have to
vm
for