DS1864T+ Maxim Integrated Products, DS1864T+ Datasheet - Page 16

• Manufacturer Part Number: DS1864T+
• Description: IC LASER CTRLR 1CHAN 5.5V 28TQFN
• Manufacturer: Maxim Integrated Products
• Type: Laser Diode Controller (Fiber Optic)r

Specifications of DS1864T+

• Number Of Channels: 1
• Voltage - Supply: 2.97 V ~ 5.5 V
• Current - Supply: 3mA
• 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

SFP Laser Controller and
Diagnostic IC
The DS1864 manages all system monitoring functions
in a fiber-optic data transceiver module in accordance
with SFF-8472 MSA. The IC communicates with a host
system through a I
with a unique I
The IC offers temperature-controlled lookup tables for
its two current-sink DACs. Monitoring and calibration
functions for supply voltage, temperature and three
analog signals are available, as well as programmable
alarm and warning flags for these signals which can be
used to trigger interrupts based on user-specified limits.
The IC also possesses laser shutdown (eye safety) fea-
tures such as programmable fast-trip alarms and inter-
rupts, in addition to signals such as FETG for laser
safety disconnect.
The memory is protected by a customizable two-layer
password scheme. Furthermore, the memory layout
can be configured to be compatible with the
DS1852/DS1856 or the DS1859.
An overview of the DS1864’s functions is shown in the
block diagram in Figure 11. Additional DS1864 func-
tions are shown in Figures 12 and 13.
The DS1864 contains two current-sink DACs, DAC0 and
DAC1. Normally, each DAC is controlled by a tempera-
ture-indexed lookup table (LUT), which can change the
DAC settings based on the temperature measured by
the internal temperature sensor. However, each DAC
can also be manually programmed by the user.
The current-sink DACs are linear and have two user-
selectable ranges, 1.5mA and 0.5mA. The range is
selected by the DAC0R and DAC1R bits located in
address 88h in Table 04h (Table 01h in DS1859 config-
uration). The 1.5mA range is selected when the corre-
sponding bit is set to a 1, and the 0.5mA range is
selected when the corresponding bit is set to a 0. The
temperature-indexed LUT for each DAC determines the
value to be loaded in to the DAC0 and DAC1 registers
(bytes 82h and 83h respectively in Table 04h (Table 01h
in DS1859 configuration)). The DACs can be disabled
(placed in a high-impedance mode) by pulling the TX-D
pin high. The TXDC control bit (Lower Memory Register,
byte 6Eh, bit 6) can also be used to disable the DAC
outputs by placing them in a high-impedance state.
16
____________________________________________________________________
2
C address.
2
C bus, and can be programmed
Detailed Description
Control Features
DAC0 and DAC1
To determine the DAC position to produce a desired
current, the following equation can be used:
Update bits are provided to indicate when an A/D con-
version has completed for each monitored value. These
bits are located in Lower Memory, byte 77h.
The current-sink DAC settings are determined by tem-
perature-controlled Lookup Tables (LUTs). The LUTs
are located in Table 02h for DAC0 and Table 03h for
DAC1. The lookup tables are 72 bytes each and allow
the biasing to be adjusted every 2°C between -40°C
and +102°C. Temperatures less than -40°C or greater
than +102°C use the -40°C or +102°C values, respec-
tively. The values programmed into the LUTs are 8-bit
unsigned values that represent the desired DAC setting
for each 2°C temperature window. The LUTs have 1°C
hysteresis (see Figure 14) to prevent the DAC’s setting
from chattering in the event the temperature remains
near a LUT switching point. Table 1 shows which regis-
ter corresponds to which temperature in the LUTs.
Figure 14 shows how the LUT chooses which memory
location to use for the DACs depending on the temper-
ature read from the internal temperature sensor.
The Temperature Index Byte (address 81h, Table 04h
(Table 01h in DS1859 configuration)) is automatically
calculated following each temperature conversion and
points to the corresponding location in the LUTs for the
Figure 14. LUT Hysteresis
DESIRED POSITION
9Ah
99h
98h
97h
96h
95h
2
DAC Lookup Table (LUT) Operation
TEMPERATURE
DECREASING
=
4
⎛
⎜
⎝
TEMPERATURE (°C)
FULL SCALE CURRENT
DESIRED CURRENT
6
8
10
TEMPERATURE
INCREASING
12
⎞
⎟ × 255
⎠