CDB5376 datasheet(29/78 Pages) CIRRUS

29 / 78 page

CDB5376

DS612DB2

2.3.6

RS-485 Telemetry

By default, CDB5376 communicates with the PC evaluation software through the microcontroller USB

port. Additional hardware is designed onto CDB5376 to use the microcontroller I2C port as a low-level

local telemetry, but it is provided for custom programming convenience only and is not directly supported

by the CDB5376 PC evaluation software or microcontroller firmware.

Telemetry signals enter CDB5376 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.

2.3.6.1

CLK, SYNC

Clock and synchronization telemetry signals into CDB5376 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.

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

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