AMIS-492X0 Datasheet, PDF (19/22 Pages) ON Semiconductor – Fieldbus MAU

AMIS-492x0
5.3 External Circuitry
Figure 13 shows the external circuitry required to connect the AMIS-492x0 to an IEC 61158-2 conformant network. This schematic is
the circuit that was used to pass the FOUNDATION Fieldbus Physical Layer Conformance test as specified in FOUNDATION Fieldbus
specification FF830, Rev 1.5. This circuit is similar but not identical to the circuit recommended by Yokogawa for the μSAA22Q.
Figure 13: AMIS-492x0 Reference Circuit Implementation
Table 13 lists the four external component values that need to be changed with using the AMIS-492x0 in a circuit that previously used
the μSAA22Q.
Table 13: Passive External Component Value Differences Between the µSAA22Q and the AMIS-492x0
Component
μSAA22Q Value
AMIS-492x0 Value
C1
100pf
150pf
C3
100pf
47pf
C4
470pf
220pf
C8
10nf
1μf
C1 connects to signal CCD (Pin 32) and controls the carrier detect assert and drop-out timing. Particular implementations may require
that the value of C1 be changed to accommodate received signal level changes introduced by the addition of intrinsic safety
components added to the external circuitry. C3 and C4 are part of the receive filter and determine the band pass characteristics of the
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-492x0. C8 must be a large capacitor with maximum of
100nf. C8 recommended value is 1μf.
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