DS1875T+ Maxim Integrated Products, DS1875T+ Datasheet - Page 24

• Manufacturer Part Number: DS1875T+
• Description: IC SFP CTRLR/TRIPLEXER 38-TQFN
• Manufacturer: Maxim Integrated Products

Specifications of DS1875T+

• Applications: Fiber Optics
• Interface: I²C
• Voltage - Supply: 2.85 V ~ 3.9 V
• Package / Case: *
• Mounting Type: Surface Mount
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

PON Triplexer and SFP Controller
Figure 10. RSSI Flowchart
Table 6. MON3 Configuration Registers
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CONFIG (RSSI_FC, RSSI_FF bits)
______________________________________________________________________________________
TIMESLICE RESULT IN A
COARSE CONVERSION?
CONVERSION RESULT
MODE CONVERSION
MODE CONVERSION
DID CURRENT FINE-
DID PRIOR MON3
(LAST RSSI = 1?)
PERFORM FINE-
LAST RSSI = 0
END OF MON3
REACH MAX?
REPORT FINE
TIMESLICE
TIMESLICE
MON3 FINE OFFSET
MON3 FINE SCALE
MON3
RIGHT SHIFT0/1
MON3 VALUE
N
N
REGISTER
Y
Y
N
CONVERSION RESULT
WAS CURRENT FINE-
MODE CONVERSION
MODE CONVERSION
PERFORM COARSE-
≥ 93.75% OF FS?
REPORT COARSE
LAST RSSI = 1
Y
A8h–A9h, Table 02h
98h–99h, Table 02h
8Eh–8Fh, Table 02h
FINE MODE
Dual-range functionality consists of two modes of opera-
tion: fine mode and coarse mode. Each mode is calibrat-
ed for a unique transfer function, hence the term, dual
range. Table 6 highlights the registers related to MON3.
Fine mode is equivalent to the other MON channels. Fine
mode is calibrated using the gain, offset, and right-shift-
ing registers at locations shown in Table 6 and is ideal
for relatively small analog input voltages. Coarse mode is
automatically switched to when the input exceeds the
threshold (to be discussed in a subsequent paragraph).
Coarse mode is calibrated using different gain and offset
registers, but lacks right-shifting (since coarse mode is
only used on large input signals). The gain and offset
registers for coarse mode are also shown in Table 6.
With the use of right-shifting, the fine mode full scale is
programmed to (1/2N)th the coarse mode full scale. The
DS1875 will now autorange to choose the range that
gives the best resolution for the measurement. To elimi-
nate chatter, 6.25% of hysteresis is applied when the
input resides at the boundary of the two ranges. See
Figure 10. Additional information for each of the registers
can be found in the Memory Map section.
Dual range operation is transparent to the end user. The
results of MON3 analog-to-digital conversions are still
stored/reported in the same memory locations (68–69h,
Lower Memory) regardless of whether the conversion
was performed in fine mode or coarse mode.
When the DS1875 is powered up, analog-to-digital con-
versions begin in a round-robin fashion. Every MON3
timeslice begins with a fine mode analog-to-digital con-
version (using fine mode’s gain, offset, and right-shift-
ing settings). See the flowchart in Figure 10. Then,
depending on whether the last MON3 timeslice resulted
in a coarse-mode conversion and also depending on
the value of the current fine conversion, decisions are
made whether to use the current fine-mode conversion
result or to make an additional conversion (within the
same MON3 timeslice), using coarse mode (using
coarse mode’s gain and offset settings, and no right-
shifting) and reporting the coarse-mode result. The
flowchart also illustrates how hysteresis is implement-
ed. The fine-mode conversion is compared to one of
68h–69h, Lower Memory
89h, Table 02h
ACh–ADh, Table 02h
9Ch–9Dh, Table 02h
COARSE MODE
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