DS1878T+T&R Maxim Integrated Products, DS1878T+T&R Datasheet - Page 18

• Manufacturer Part Number: DS1878T+T&R
• Description: IC CTLR SFP W/DGTL LDD RX 28TQFN
• Manufacturer: Maxim Integrated Products
• Type: SFP+ Controllerr

Specifications of DS1878T+T&R

• Input Type: *
• Output Type: *
• Interface: *
• Current - Supply: *
• Mounting Type: Surface Mount
• Package / Case: 28-WFQFN exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

SFP+ Controller with Digital LDD Interface
The device offers a feature to improve the accuracy
and range of MON3, which is most commonly used for
monitoring RSSI. Using a traditional input, the accuracy
of the RSSI measurements is increased at the cost of
Table 4. MON3 Hysteresis Threshold Values
* This is the minimum reported coarse-mode conversion.
Table 5. MON3 Configuration Registers
Figure 8. RSSI with Crossover Enabled
18
RIGHT-SHIFT
(RSSI_FC and
RSSI_FF Bits)
MON3 VALUE
RIGHT-SHIFTS
REGISTER
(RSSIR Bit)
NUMBER OF
UPDATE
OFFSET
CNFGC
______________________________________________________________________________________
GAIN
0
1
2
3
4
5
6
7
0
Enhanced RSSI Monitoring (Dual-Range
A8h–A9h, Table 02h ACh–ADh, Table 02h
98h–99h, Table 02h 9Ch–9Dh, Table 02h
RSSI RESULT
8Fh, Table 02h
FINE MODE
FINE MODE
MAX (HEX)
68h–69h, Lower Memory
7FFC
FFF8
3FFE
1FFF
0FFF
07FF
03FF
01FF
6Fh, Lower Memory
8Bh, Table 02h
COARSE MODE
8Fh, Table 02h
COARSE MODE
Functionality)
MIN* (HEX)
3C00
03C0
F000
7800
1E00
0F00
0780
01E0
IDEAL RESPONSE
CROSSOVER POINT
reduced input signal swing. The device eliminates this
trade-off by offering “dual range” calibration on the
MON3 channel.
The dual-range calibration can operate in two modes:
crossover enabled and crossover disabled.
• Crossover Enabled: For systems with a nonlinear
• Crossover Disabled: The crossover disabled mode
relationship between the ADC input and desired ADC
result, the mode should be set to crossover enabled
(Figure 8). The RSSI measurement of an APD receiv-
er is one such application. Using the crossover
enabled mode allows a piecewise linear approxima-
tion of the nonlinear response of the APD’s gain fac-
tor. The crossover point is the point between fine and
coarse points. The ADC result transitions between the
fine and coarse ranges with no hysteresis. Right-shift-
ing, slope adjustment, and offset are configurable for
both the fine and coarse ranges. The XOVER FINE
register determines the maximum results returned by
fine ADC conversions, before right-shifting. The
XOVER COARSE register determines the minimum
results returned by coarse ADC conversions, before
right-shifting.
is intended for systems with a linear relationship
between the MON3 input and desired ADC result.
The ADC result transitions between the fine and
coarse ranges with hysteresis (Figure 9). In crossover
disabled mode, the thresholds between coarse and
fine mode are a function of the number of right-shifts
being used. With the use of right-shifting, the fine-
mode full scale is programmed to (1/2
coarse-mode full scale. The device now auto ranges
to choose the range that gives the best resolution for
the measurement. Table 4 shows the threshold val-
ues for each possible number of right-shifts.
MON3 INPUT
nth
) of the