EVA-7M - Hardware Integration Manual
UBX-12003235 - R05
Production Information
Design-in
Page 12 of 42
Function
I/O
Description
Remarks
ANT_DET
I
(pull-up)
Antenna detected
“high” = Antenna detected
“low” = Antenna not detected
Must be changed by
Low Level Configuration,
see section 2.3.3.
ANT_SHORT_N
I
(pull-up)
Antenna not shorted
“high” = antenna has no short
“low” = antenna has a short
Must be changed by
Low Level Configuration,
see section 2.3.3..
ANT_OFF
O
Control signal to turn on and off the antenna supply
“high” = turn off antenna supply
“low” = short to GND
Must be changed by
Low Level Configuration,
see section 2.3.3.
Table 4: 3-pin Antenna supervisor pins
The external circuitry, as shown in Appendix A.8, (see Figure 19) provides detection of an active antenna
connection status. If the active antenna is present, the DC supply current exceeds a preset threshold defined by
R4, R5, and R6. It will shut down the antenna via transistor T1 if a short circuit has been detected via U7 or if it
’
s
not required (e.g. in Power Save Mode).
The status of the active antenna can be checked by the UBX-MON-HW message. See the
u-blox 7 Receiver
Description including Protocol Specification
The open drain buffers U4, U7 and U8 (e.g. Fairchild NC7WZ07) are needed to shift the voltage levels. R3 is
required as a passive pull-up to control T1 because U4 has an open drain output. R4 serves as a current limiter in
the event of a short circuit.
2.3.4
Electromagnetic interference on I/O lines
Any I/O signal line (length > ~3 mm) may pick up high frequency signals and transfer this noise into the GNSS
receiver. This specifically applies to unshielded lines, lines where the corresponding GND layer is remote or
missing entirely, and lines close to the edges of the printed circuit board. If a GSM signal radiates into an
unshielded high-impedance line, noise in the order of volts can be generated and possibly not only distort
receiver operation but also damage it permanently.
In such case it is recommended to use feed-thru capacitors with good GND connection close to the GNSS
receiver in order to filter such high-frequency noise. See Appendix B.12 for component recommendations.
Alternatively, ferrite beads (see Appendix B.11) or resistors can be used. These work without GND connection
but may adversely affect signal rise time.
EMI protection measures are recommended when RF emitting devices are near the GNSS receiver. To minimize
the effect of EMI, a robust grounding concept is essential. To achieve electromagnetic robustness, follow the
standard EMI suppression techniques.
2.4
Real-Time Clock (RTC)
The use of the RTC is optional to maintain time in the event of power failure at
VCC_IO
. The RTC is required for
hot start, warm start, AssistNow Autonomous, AssistNow Offline and in some Power Save Mode operations.
The time information can either be generated by connecting an external RTC crystal to the EVA-7M, by deriving
the RTC from the internal crystal oscillator, by connecting an external 32.768 kHz signal to the RTC input, or by
time aiding of the GNSS receiver at every startup.
2.4.1
RTC using a crystal
The easiest way to provide time information to the receiver is to connect an RTC crystal to the corresponding
pins of the RTC oscillator,
RTC_I
and
RTC_O
. There is no need to add load capacitors to the crystal for frequency
tuning, because they are already integrated in the chip. Using an RTC crystal will provide the lowest current
consumption to
V_BCKP
in case of a power failure. On the other hand, it will increase the BOM costs and
requires space for the RTC crystal.
