DS1877T+T&R Maxim Integrated Products, DS1877T+T&R Datasheet - Page 16

• Manufacturer Part Number: DS1877T+T&R
• Description: IC CTLR/MON SFP 1-2CH 28TQFN
• Manufacturer: Maxim Integrated Products
• Type: SFP+ Controllerr

Specifications of DS1877T+T&R

• Input Type: Logic
• Output Type: Logic
• Interface: I²C
• Current - Supply: 2.5mA
• Mounting Type: Surface Mount
• Package / Case: 28-WFQFN exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 90-1877T+TRL

SFP Controller for Dual Rx Interface
Dual-range operation is transparent to the end user. The
results of RSSI1/RSSI2 ADCs are still stored/reported in
the same memory locations (68h−69h, Lower Memory)
regardless of whether the conversion was performed
in fine mode or coarse mode. The RSSIR bit indicates
whether a fine or coarse conversion generated the digital
result.
When the device is powered up, ADCs begin in a round-
robin fashion. Every RSSI1/RSSI2 time slice begins with
a fine mode ADC (using fine mode’s gain, offset, and
right-shifting settings). If the value is too large for a fine
conversion, a coarse conversion is performed and the
result is reported. The coarse-mode conversion is per-
formed using the coarse gain and offset settings. The
intersection between coarse and fine depends on the
crossover mode used.
The RSSIn_FC and RSSIn_FF 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 RSSIn_FC and RSSIn_FF
are factory programmed to 0 in EEPROM). Dual-range
functionality can be disabled by setting RSSIn_FC to 0
and RSSIn_FF to 1. These bits are also useful when cali-
brating RSSI1/RSSI2. See the register descriptions and
memory map for additional information.
For systems with a nonlinear relationship between the
ADC input and desired ADC result, the mode should be
set to crossover enabled (Figure 5). The RSSI measure-
ment of an APD receiver is one such application. Using
the crossover-enabled mode allows a piecewise linear
approximation of the nonlinear response of the APD’s
gain factor. The crossover point is the value where the
fine and coarse ranges intersect. The ADC result transi-
tions between the fine and coarse ranges as defined
by the XOVER registers. Right-shifting, slope adjust-
ment, and offset are configurable for both the fine and
coarse ranges. The XOVER1/XOVER2 FINE registers
determine the maximum results returned by the fine
ADC conversions before right-shifting. The XOVER1/
XOVER2 COARSE registers determine the minimum
results returned by coarse ADC conversions before
right-shifting.
The crossover-disabled mode is intended for systems
with a linear relationship between the RSSI1/RSSI2 input
and the desired ADC result. The ADC result transitions
16
Crossover Disabled
Crossover Enabled
between the fine and coarse ranges with hysteresis, as
shown in Figure 6.
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 automatically
ranges to choose the range that gives the best resolution
for the measurement. Table 4 shows the threshold values
for each possible number of right-shifts.
The device contains two power-on reset (POR) levels.
The lower level is a digital POR (POD) and the higher
level is an analog POR (POA). At startup, before the sup-
ply voltage rises above POA, the outputs are disabled,
all SRAM locations are set to their defaults, shadowed
EEPROM (SEE) locations are zero, and all analog cir-
cuitry is disabled. When V
recalled, and the analog circuitry is enabled. While V
remains above POA, the device is in its normal operating
state, and it responds based on its nonvolatile configu-
ration. If during operation V
still above POD, the SRAM retains the SEE settings from
the first SEE recall, but the device analog is shut down
and the outputs disabled. If the supply voltage recovers
back above POA, the device immediately resumes nor-
mal operation. If the supply voltage falls below POD, the
device SRAM is placed in its default state and another
SEE recall is required to reload the nonvolatile settings.
The EEPROM recall occurs the next time V
exceeds POA. Figure 7 shows the sequence of events
as the voltage varies.
Table 4. RSSI1/RSSI2 Hysteresis
Threshold Values
*This is the minimum reported coarse-mode conversion.
NO. OF RIGHT-
SHIFTS
0
1
2
3
4
5
6
7
FINE MODE
MAX (HEX)
7FFC
3FFE
FFF8
1FFF
0FFF
07FF
03FF
01FF
Low-Voltage Operation
CC
CC
reaches POA, the SEE is
falls below POA, but is
COARSE MODE
MIN* (HEX)
3C00
03C0
1E00
01E0
F000
7800
0F00
0780
n
CC
) of the
next
CC