DS1873T+ Maxim Integrated Products, DS1873T+ Datasheet - Page 15

• Manufacturer Part Number: DS1873T+
• Description: IC CTLR SFP+ ANLG LDD 28-TQFN
• Manufacturer: Maxim Integrated Products
• Type: Laser Diode Controllerr

Specifications of DS1873T+

• 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
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 90-1873T+000

an update to the BIAS DAC, a settling time (as calculat-
ed below) is required to allow for the feedback on BMD
(MON2) to stabilize. This time is dependent on the time
constant of the filter pole used for the delta-to-sigma
BIAS output. During the timing of the settling rate, com-
parisons of APC comparisons of BMD are ignored until
32 sample periods (t
Monitoring functions on the DS1873 include five quick-
trip comparators and six ADC channels. This monitor-
ing combined with the alarm enables (Table 01h/05h)
determines when/if the DS1873 turns off the MOD and
BIAS DACs and triggers the TXF and TXDOUT outputs.
All the monitoring levels and interrupt masks are user
programmable.
Five quick-trip monitors are provided to detect potential
laser safety issues and LOS status. These monitor the
following:
1) High Bias Current (HBATH)
2) Low Transmit Power (LTXP)
3) High Transmit Power (HTXP)
4) Max Output Current (IBIASMAX)
5) Loss-of-Signal (LOS LO)
The high-transmit and low-transmit power quick-trip
registers (HTXP and LTXP) set the thresholds used to
compare against the MON2 voltage to determine if the
transmit power is within specification. The HBATH
quick trip compares the MON1 input (generally from the
laser driver’s bias monitor output) against its threshold
setting to determine if the present bias current is above
specification. The BIAS MAX quick trip determines if the
BIAS DAC is above specification (IBIASMAX). When the
new BIAS DAC value is calculated, it is compared
against the IBIASMAX register. The BIAS DAC is not
allowed to exceed the value set in the IBIASMAX regis-
ter. When the DS1873 detects that the bias is at the
limit, it sets the BIASMAX status bit and holds the BIAS
DAC setting at the IBIASMAX level. The bias and power
quick trips are routed to the TXF through interrupt
masks to allow combinations of these alarms to be
used to trigger these outputs. The user can program up
to eight different temperature-indexed threshold levels
for MON1 (Table 02h, Register D1h). The LOS LO quick
trip compares the MON3 input against its threshold set-
ting to determine if the present received power is below
SettlingTime = 51.2µs x (APC_SR[3:0] + 1)
SFP+ Controller with Analog LDD Interface
Five Quick-Trip Monitors and Alarms
Monitors and Fault Detection
______________________________________________________________________________________
REP
) have passed.
Monitors
the specification. The LOS LO quick trip can be used to
set the LOSOUT pin.
The ADC monitors six channels that measure tempera-
ture (internal temp sensor), V
using an analog multiplexer to measure them round
robin with a single ADC (see the ADC Timing section).
The five voltage channels have a customer-programma-
ble full-scale range and all channels have a customer-
programmable offset value that is factory programmed
to default value (see Table 2). Additionally,
MON1–MON4 can right-shift results by up to 7 bits
before the results are compared to alarm thresholds or
read over the I
fied ADC ranges to calibrate the ADC full scale to a fac-
tor of 1/2
signals. The DS1873 can then right-shift the results by n
bits to maintain the bit weight of their specification (see
the Right-Shifting ADC Result and Enhanced RSSI
Monitoring (Dual-Range Functionality) sections).
The ADC results (after right-shifting, if used) are com-
pared to the alarm and warning thresholds after each
conversion, and the corresponding alarms are set,
which can be used to trigger the TXF output. These
ADC thresholds are user programmable, as are the
masking registers that can be used to prevent the
alarms from triggering the TXF output.
There are six analog channels that are digitized in a
round-robin fashion in the order shown in Figure 4. The
total time required to convert all six channels is t
the Analog Voltage Monitoring Characteristics for
details).
If the weighting of the ADC digital reading must con-
form to a predetermined full-scale (PFS) value defined
by a standard’s specification (e.g., SFF-8472), then
right-shifting can be used to adjust the PFS analog
measurement range while maintaining the weighting of
Table 2. ADC Default Monitor Full-Scale
Ranges
Temperature (°C)
V
MON1–MON4 (V)
CC
(V)
SIGNAL
n
of their specified range to measure small
2
C bus. This allows customers with speci-
SIGNAL
127.996
6.5528
2.4997
+FS
Six ADC Monitors and Alarms
Right-Shifting ADC Result
7FFF
FFF8
FFF8
+FS
hex
CC
, and MON1–MON4
SIGNAL
-128
-FS
0
0
ADC Timing
RR
8000
0000
0000
hex
-FS
(see
15