TDA7210V_10 Datasheet, PDF (26/44 Pages) Infineon Technologies AG – ASK/FSK Single Conversion Receiver

TDA7210V
Applications
C18
R4+R5=600k
R4
R5
U_threshold
24
23
C13
R1
19
18
Uc>Us Uc<Us ^Iload
Uc
U2
+
0 / 240uA
20k
+3.1V
OTA
-
U2<2.4V : I=240uA
U2>2.4V : I=0
+2.4V
Data Filter ^{ASK/FSK Switch}
Us
Figure 14 Principle of the Precharge Circuit
This circuit charges the capacitor C13 with an inrush current Iload of typically 220 µA for a duration of T2 until the
voltage Uc appearing on the capacitor is equal to the voltage Us at the input of the data filter. This voltage is limited
to 2.5 V. As soon as these voltages are equal or the duration T2 is exceeded the precharge circuit is disabled.
t2 is the time constant of the charging process of C18 which can be calculated as:
τ ₂ = 20kΩ × C18
(15)
As the sum of R4 and R5 is sufficiently large and thus can be neglected. T2 can then be calculated according to
the following formula:
T_l
⎜⎛
=
τ
2
ln^⎜
⎜⎜⎝
1
−
1
2.4V
3V
⎟⎞
⎟
⎟⎟⎠
≈τ₂
×1.6
(16)
The voltage transient during the charging of C18 is shown in the following figure:
Data Sheet
26
Revision 1.1, 2010-06-18