Datasheet

DS1886
SFP and PON ONU Controller
with Digital LDD Interface
20Maxim Integrated
ADC Monitors and Alarms
The ADC monitors temperature (internal temp sen-
sor), V
CC
, laser bias (TXB), laser power (TXP), and
receive power (RSSIC for coarse, RSSIF for fine)
using an analog multiplexer to measure them using
a round-robin scheme with a single ADC (see the
ADC Timing section). The voltage channels have a
customer-programmable full-scale range and all chan-
nels have a customer-programmable offset value that
is factory programmed to a default value (Table 2).
Additionally, TXB, TXP, RSSIC, and RSSIF can right-shift
results as described in the Right-Shifting ADC Result
section. This allows customers with specified ADC
ranges to calibrate the ADC input gain by a factor of
2
n
to measure small signals (thereby reducing the full
scale by a factor of 2
n
). The DS1886 can then right-shift
the results by n bits (effectively multiplying by a factor
of 1/2
n
) to maintain the bit weight of their specification.
See the Right-Shifting ADC Result and Enhanced RSSI
Monitoring (Dual Range Functionality) sections for more
information.
Alarms and Warnings
The ADC results (after right-shifting, if used) are
compared to the alarm and warning thresholds after
each conversion, and the corresponding alarms and/
or warnings are set, which can be programmed to
create the internal signal TXFINT. The status of TXFINT
can be read in A2h Lower Memory, Register 71h. TXFINT
is one of the signals used to trigger TXFOUT. TXFOUT
can be programmed to cause TXDOUT outputs. These
ADC thresholds are user-programmable, as are the
masking registers that can be used to prevent the alarms
from triggering the TXFOUT and TXDOUT outputs.
ADC Timing
Five analog channels are digitized in a round-robin
fashion in the order as shown in Figure 2. RSSI is
measured twice to obtain coarse and fine measure-
ments (RSSIC and RSSIF, respectively). The total time
required to convert all channels is t
RR
(see the Analog
Voltage Monitoring Characteristics table for details). After
each TXMON conversion, a 3-wire communication is
initiated to toggle the MON_SEL bit (bit 6 in the
MAX3710’s TXCTRL2 register, programmed through A2h
Table 02h, Register E5h, bit 6). This causes the laser
driver to alternate sending laser bias (TXB) and laser
power (TXP) signals to the DS1886’s TXMON input.
The DS1886 has a burst mode option to allow internal
calculation of TXP using the MD0 and MD1 register
values read from the MAX3710 over the 3-wire inter-
face. In this option, the sampled TXP value is ignored.
The TXP value in this burst mode is calculated as
follows:
(MD0 REGH [7:0] + 8 x
MD1 REGH [7:0]) x 65536
TXP
TXP Scale
=
TXP is then right-shifted (Figure 1a).
RIGHT-SHIFT
1
is determined by KIMD[1:0],
TXCTRL3[4:3] as follows:
Table 2. ADC Default Monitor Full-Scale Ranges
SIGNAL (UNITS) +FS SIGNAL +FS HEX -FS SIGNAL -FS HEX
Temperature (°C) 127.996 7FFFh -128 8000h
V
CC
(V) 6.5528 FFF8h 0 0000h
TXB, TXP, RSSIC, RSSIF (V) 2.4997 FFF8h 0 0000h
KIMD[1:0]
TXCTRL3[4:3]
NO. OF RIGHT-SHIFTS
00 2
01 1
10 0
11 0