FXTH870xD
Sensors
8
Freescale Semiconductor, Inc.
2.3
Signal Properties
The following sections describe the general function of each pin.
g
Figure 5. FXTH870xD Example Application
2.3.1
V
DD
and V
SS
Pins
The digital circuits operate from a single power supply connected to the FXTH870xD through the V
DD
and V
SS
pins. V
DD
is the
positive supply and V
SS
is the ground. The conductors to the power supply should be connected to the V
DD
and V
SS
pins and
locally decoupled as shown in
Figure 6
.
Care should be taken to reduce measurement signal noise by separating the V
DD
, V
SS
, AV
DD
, AV
SS
and RV
SS
pins using a “star”
connection such that each metal trace does not share any load currents with other external devices as shown in
Figure 6
.
2.3.2
AV
DD
and AV
SS
Pins
The analog circuits operate from a single power supply connected to the FXTH870xD through the AV
DD
and AV
SS
pins. AV
DD
is
the positive supply and AV
SS
is the ground. The conductors to the power supply should be connected to the AV
DD
and AV
SS
pins
and locally decoupled as shown in
Figure 6
.
FXTH870xxx
0.1 µF
V
DD
V
SS
3.0 V
BATTERY
LF
COIL
XTAL
RF
RV
SS
XI
XO
C1
ANT
L1
BKGD/PTA4
LFA
LFB
PTA1
RESET
GENERAL
PURPOSE I/O
PTA0
PTA2
AV
DD
AV
SS
V
REG
470 nF
0.1 µF
PTA3
MATCHING
NETWORK
C2
C3
C2, C3, C4
optimized
for crystal
C5
C4*
R2
R3
R2 and R3, <10 k
recommended for
highest EMC resistance
R1
PTB0
PTB1
L1 and matching network
optimized for specific PWB and
antenna layout. Recommend
0603 minimum size for L1 and
other matching network inductors
for maximum efficiency.
C1 and R1 optimized
for coil used, but
recommended
RC < 15.3
sec.
The device C
4
, although drawn here as a capacitor, may be any type of passive component(s) sufficient to block
or reduce unwanted external radiated signals from corrupting the crystal oscillator circuit: PCB traces for the LFA
/ LFB, AV
DD
/ V
DD
, and V
SS
/ AV
SS
pins and bypass capacitors
should be minimized to reduce unwanted external
radiated signals from corrupting the power input circuits.
Summary of Contents for FXTH870 D Series
Page 86: ...FXTH870xD Sensors 84 Freescale Semiconductor Inc Figure 57 Data Flow For Measurements...
Page 171: ...FXTH870xD Sensors Freescale Semiconductor Inc 169 Figure 128 QFN Case Outline...
Page 172: ...FXTH870xD Sensors 170 Freescale Semiconductor Inc Figure 129 QFN Case Outline...
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