CDB5378 datasheet(28/72 Pages) CIRRUS

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CDB5378

DS639DB3

Telemetry signals enter CDB5378 through RS-485 transceivers, which are differential current mode trans-

ceivers that can reliably drive long distance communication. Data passes through the RS-485 transceiv-

ers to the microcontroller I2C interface and the clock and synchronization inputs.

2.3.5.1

CLK, SYNC

Clock and synchronization telemetry signals into CDB5378 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 through jumper J56. 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_MC signal output to the digital filter SYNC input as required.

A microcontroller software connection is made when the SYNC_MC signal output is created by the micro-

controller on command from the system telemetry. The microcontroller can use an internal counter to re-

time the SYNC_MC 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

µA

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

CDB5378 Datasheet(PDF) 28 Page - Cirrus Logic

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