SA7120A
TYPICAL APPLICATION
The chip powers up via the COIL1 and COIL2 pads,
deriving its energy from the rf carrier wave through the
resonating tank circuit made up by the external inductor,
LR, and internal capacitor, CR. An optional additional
external capacitor can be added for special requirements.
The data will automatically start modulating the rf signal
as soon as the chip has powered up to the power-on
reset level. The built in voltage protection and regulation
insures protection against high voltage from the tank
circuit.
TEST
8
VSS
TEST
6
TEST
5
TEST
4
VDD
3
7
CR
1
2
COIL1
COIL2
LR
The value of LR is determined by the following relationship.
fR = 1 / ( 2 p Ö LR * CR)
Where fR is the resonance frequency.
For a typical internal CR of 75 pf and for fR at 134.2 kHz,
LR = 18.75 mH
7/10
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