EM4095 Просмотр технического описания (PDF) - EM Microelectronic - MARIN SA
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EM4095 Datasheet PDF : 10 Pages
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EM4095
Appendix
Equations
Antenna resonant frequency f0:
f0 = 2π
1
LAC0
(1)
Where C0 is resonant capacitor composed of CRES, CDV1
and CDV2:
C0
=
CRES
+
CDV 1∗CDV 2
CDV 1 + CDV 2
(2)
Usually antenna coil is specified by its inductance (LA) and
Q factor (QA). Serial resistance of antenna is defined by
following equation:
R ANT
=
2πf 0 LA
QA
(3)
The equations which follow are valid for bridge
configuration as defined on Figures 1, 2 and 3. For figures
1 and 2 RSER has to be considered 0.
The AC current amplitude at resonant frequency is
defined as follows:
Peak to peak voltage on antenna is defined by following
equation:
V ANTpp
=
I ANT
πf 0 C 0
(6)
To ensure correct operation of the AM demodulation
chain, the AC peak to peak voltage on DEMOD_IN pin
(VDMOD_INpp) has to be inside common mode range. Once
peak to peak voltage on antenna is known the capacitor
divider division factor can be calculated:
VDMOD _ INpp
= VANTpp
C DV1
CDV1 + CDV 2
(7)
Power dissipation is composed of power dissipated on
ANT drivers and internal power consumption:
( ) P = 2 ⋅ I RMS 2 ⋅ RAD + I DDon VDD − VSS (7)
Temperature increase of die due to power dissipation is:
∆T = P ⋅ RTh
(8)
Where RTh is Package thermal resistor.
I ANT
=
4
π
R ANT
Vdd − Vss
+ RSER + 2RAD
(4)
RMS antenna current (important for power dissipation
calculation):
I RMS
=
I ANT
2
(5)
EM Microelectronic-Marin SA cannot assume responsibility for use of any circuitry described other than circuitry
entirely embodied in an EM Microelectronic-Marin SA product. EM Microelectronic-Marin SA reserves the right to
change the circuitry and specifications without notice at any time. You are strongly urged to ensure that the
information given has not been superseded by a more up-to-date version.
© EM Microelectronic-Marin SA, 07/02, Rev. Ê/490
Copyright 2002, EM Microelectronic-Marin SA
10
www.emmicroelectronic.com
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