FXTH870xD
Sensors
Freescale Semiconductor, Inc.
9
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
.
Figure 6. Recommended Power Supply Connections
2.3.3
V
REG
Pin
The internal regulator for the analog circuits requires an external stabilization capacitor to AV
SS
.
2.3.4
RV
SS
Pin
Power in the RF output amplifier is returned to the supply through the RV
SS
pin. This conductor should be connected to the power
supply as shown in
Figure 6
using a “star” connection such that each metal trace does not share any load currents with other
supply pins.
2.3.5
RF Pin
The RF pin is the RF energy data supplied by the FXTH870xD to an external antenna.
2.3.6
XO, XI Pins
The XO and XI pins are for an external crystal to be used by the internal PLL for creating the carrier frequencies and data rates
for the RF pin.
2.3.7
LF[A:B] Pins
The LF[A:B] pins can be used by the LF receiver (LFR) as one differential input channel for sensing low level signals from an
external low frequency (LF) coil. The external LF coil should be connected between the LFA and the LFB pins.
Signaling into the LFR pins can place the FXTH870xD into various diagnostic or operational modes. The LFR is comprised of
the detector and the decoder.
Each LF[A:B] pin will always have an impedance of approximately 500 k
to V
SS
due to the LFR input circuitry. The LFA/LFB
pins are used by the LFR when the LFEN control bit is set and are not functional when the LFEN control bit is clear.
2.3.8
PTA[1:0] Pins
The PTA[1:0] pins are general purpose I/O pins. These two pins can be configured as normal bidirectional I/O pins with
programmable pullup or pulldown devices and/or wakeup interrupt capability; or one or both can be connected to the two input
channels of the A/D converter module. The pulldown devices can only be activated if the wakeup interrupt capability is enabled.
User software must configure the general purpose I/O pins so that they do not result in “floating” inputs as described in
. PTA[1:0] map to Keyboard Interrupt function bits [1:0].
0.1 µF
FXTH870xxx
V
DD
V
SS
to other
Battery
I
DD
I
LOAD
Bypass capacitors
closely coupled to
the package pins
FXTH870xxx and Other Load Currents
star connected to battery terminals
loads
0.1 µF
AV
DD
AV
SS
RV
SS
The decoupling devices, although
drawn here as 0.1
F capacitors,
may be any type of passive component(s)
sufficient to block or reduce unwanted
external radiated signals from corrupting
the power input protection circuits;
application tuning may be required.
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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