Cirrus Logic CRD5378, Руководство пользователя

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CRD5378
DS639RD2 25
Telemetry signals enter CRD5378 through RS-485 transceivers, which are differential current mode
transceivers that can reliably drive long distance communication. Data passes through the RS-485 trans-
ceivers to the microcontroller I
2
C interface and the clock and synchronization inputs.
2.3.3.1 CLK, SYNC
Clock and synchronization telemetry signals into CRD5378 are received through RS-485 twisted pairs.
These signals are required to be distributed through the external system with minimal jitter and timing
skew, and so are normally driven through high-speed bus connections.
Synchronization of the measurement channel is critical to ensure simultaneous analog sampling across
a network. Several options are available for connecting a SYNC signal through the RS-485 telemetry to
the digital filter.
A direct connection is made when the SYNC_IO signal is received over the dedicated RS-485 twisted pair
and sent directly to the digital filter SYNC pin (with a 0
Ω
resistor installed at R71). The incoming SYNC_IO
signal must be synchronized to the network at the transmitter since no local timing adjustment is available.
A microcontroller hardware connection is made when the SYNC_IO signal is received over the dedicated
RS-485 twisted pair and detected by a microcontroller interrupt. The microcontroller can then use an in-
ternal counter to re-time the SYNC signal output to the digital filter SYNC input as required.
A microcontroller software connection is made when the SYNC signal output is created by the microcon-
troller on command from the system telemetry. The microcontroller can use an internal counter to re-time
the SYNC signal output to the digital filter SYNC input as required.
Specification Value
RS-485 Transceiver - Linear Tech LTC1480IS8
Surface Mount Package Type SOIC-8, 5mm x 6mm
Supply Voltage, Quiescent Current
3.3V, 600
µ
A
Maximum Data Rate 2.5 Mbps
Transmitter Delay, Receiver Delay 25 - 80 ns, 30 - 200 ns
Transmitter Current, Full Termination (60
Ω
)
25 mA
Transmitter Current, Half Termination (120
Ω
)
13 mA
Specification Value
Synchronous Inputs, 2 wires each CLK±, SYNC±
Specification Value
Distributed SYNC Signal Synchronization ± 240 ns
Distributed Clock Synchronization ± 240 ns
Analog Sampling Synchronization Accuracy ± 480 ns