AMIS-49200 Datasheet, PDF (21/22 Pages) AMI SEMICONDUCTOR – Fieldbus MAU Chip

AMIS-49200 Fieldbus MAU
Data Sheet
receive filter. It is unlikely that these would need to be changed. C8 is a noise filter for VMID. It is important that VMID have as little
noise as possible as it is used as a reference for many sub-circuits in the AMIS-49200.
There is one other minor difference in the recommended external circuitry between the µSAA22Q and the AMIS-49200. Figure 13
shows the startup circuits recommended for the µSAA22Q and the AMIS-49200. The circuit shown for the AMIS-49200 is different from
that shown for the µSAA22Q but either one will work. Both are current sources that turn on when power is applied to the H1 segment
terminals so that the AMIS-49200 can turn on without any turn-on transients on the network.
µ^{SAA 22Q}
Startup Circuit
Loop +
AMIS 49200
Startup Circuit
R5
100 k _R6
1k
Loop +
Q1
V Shunt
D3
5.1 V
V Shunt
Figure 13: Recommended Start-up Circuits
5.4 Active Components
Transistors Q1 – Q4 are ordinary small signal transistors. Diodes D1 and D2 are similarly ordinary small signal diodes. Users desiring
to replace a µSAA22Q with the AMIS-49200 in an existing design should be able to use whatever transistors and diodes were used with
the µSAA22Q. For new designs, the specified transistors can be used or other devices may be chosen.
5.5 Alternative Designs
Some users of the Yokogawa µSAA22Q did not use the exact recommended external circuit for the media interface circuit (see Figure
12). Using the AMIS-49200 that did not follow the Yokogawa recommended external circuit may result in some compatibility problems.
There are an almost infinite number of alternative designs and it is beyond the scope of this document to identify the possible designs
and their possible compatibility problems.
5.6 Verification
All designs using the AMIS-49200 should re-run the entire physical layer conformance test as defined in Fieldbus Foundation document
FF-830, FOUNDATION™ Specification 31.25 kbit/s Physical Layer Conformance Test. Board layout can alter the behavior of all circuit
implementations, even designs that follow the recommended implementation.
AMI Semiconductor – Jan. 07, M-20532-003
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