DS1874T+ Maxim Integrated Products, DS1874T+ Datasheet - Page 18

• Manufacturer Part Number: DS1874T+
• Description: IC CTLR SFP+ ANLG LDD 28-TQFN
• Manufacturer: Maxim Integrated Products
• Type: Laser Diode Controllerr

Specifications of DS1874T+

• Number Of Channels: 1
• Voltage - Supply: 2.85 V ~ 3.9 V
• Current - Supply: 2.5mA
• Operating Temperature: -40°C ~ 95°C
• Package / Case: 28-WFQFN Exposed Pad
• Mounting Type: Surface Mount
• Number Of Outputs: 5
• Duty Cycle (max): 50 %
• Output Voltage: 0 V to 3.9 V
• Mounting Style: SMD/SMT
• Switching Frequency: 0 KHz to 400 KHz
• Operating Supply Voltage: 2.85 V to 3.9 V
• Supply Current: 2.5 mA to 10 mA
• Maximum Operating Temperature: + 95 C
• Fall Time: 300 ns
• Minimum Operating Temperature: - 40 C
• Rise Time: 300 ns
• Synchronous Pin: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 90-1874T+000

SFP+ Controller with Digital LDD Interface
Figure 7. RSSI Flowchart
Then, depending on whether the last MON3 timeslice
resulted in a coarse-mode conversion and also depend-
ing on the value of the current fine conversion, decisions
are made whether to use the current fine-mode conver-
sion 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 flow-
chart in Figure 7 also illustrates how hysteresis is
18
______________________________________________________________________________________
TIMESLICE RESULT IN A
COARSE CONVERSION?
CONVERSION RESULT
MODE CONVERSION
MODE CONVERSION
DID CURRENT FINE-
(LAST RSSIR = 1?)
DID PRIOR MON3
PERFORM FINE-
LAST RSSI = 0
END OF MON3
REACH MAX?
REPORT FINE
TIMESLICE
TIMESLICE
MON3
N
N
Y
Y
N
CONVERSION RESULT
WAS CURRENT FINE-
MODE CONVERSION
MODE CONVERSION
PERFORM COARSE-
≥ 93.75% OF FS?
REPORT COARSE
LAST RSSIR = 1
Y
implemented. The fine-mode conversion is compared to
one of two thresholds. The actual threshold values are a
function of the number of right-shifts being used. With
the use of right-shifting, the fine mode full-scale is pro-
grammed to (1/2
DS1874 now auto ranges to choose the range that gives
the best resolution for the measurement. Hysteresis is
applied to eliminate chatter when the input resides at
the boundary of the two ranges. See Figure 7 for details.
Table 4 shows the threshold values for each possible
number of right-shifts.
The RSSI_FF and RSSI_FC bits are used to force fine-
mode or coarse-mode conversions, or to disable the
dual-range functionality. Dual-range functionality is
enabled by default (both RSSI_FC and RSSI_FF are
factory programmed to 0 in EEPROM). It can be dis-
abled by setting RSSI_FC to 0 and RSSI_FF to 1. These
bits are also useful when calibrating MON3. For addi-
tional information, see Figure 19.
Table 4. MON3 Hysteresis Threshold
Values
* This is the minimum reported coarse-mode conversion.
Table 5. MON3 Configuration Registers
RIGHT-SHIFT
MON3 VALUE
RIGHT-SHIFTS
(RSSIR BIT)
REGISTER
NUMBER OF
UPDATE
OFFSET
CNFGC
GAIN
0
1
2
3
4
5
6
7
0
A8h–A9h, Table 02h ACh–ADh, Table 02h
98h–99h, Table 02h 9Ch–9Dh, Table 02h
n
th) of the coarse mode full-scale. The
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
COARSE MODE
MIN* (hex)
3C00
03C0
F000
7800
1E00
0F00
0780
01E0
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