DS1864 Maxim Integrated Products, DS1864 Datasheet - Page 18

• Manufacturer Part Number: DS1864
• Description: SFP Laser Controller and Diagnostic IC
• Manufacturer: Maxim Integrated Products

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SFP Laser Controller and
Diagnostic IC
Internal calibration applies to measured values acquired
by the ADC, and does not apply to the fast alarms. If inter-
nal calibration is desired, each analog channel requires
that registers 8Eh through AFh in Table 04h (Table 01h in
DS1859 configuration) are loaded with the appropriate val-
ues to calibrate for gain and offset. Every gain and offset
register is 2-bytes wide. Both gain and offset calibration
are independently capable of converting input variables
into a digital output range spanning 0000h to FFFFh.
The last adjustment is made by using right-shifting.
Right-shifting registers are located in registers A2h
through ABh and AEh to AFh, and store a 3-bit value
used to shift each MON value from 0 to 7 spaces to the
right. The effect of this is to make better use of the ADC
range and increase the accuracy of the readings. Right-
shifting is the last function performed on the MON sig-
nal before the digital value is sent to the MON register.
The internal temperature monitor values are stored in
16-bit 2’s complement format, and located in memory
addresses 60h and 61h of the Lower Memory. The tem-
perature conversions are updated every t
do not occur during an active read or write to memory.
The factory default calibration values for the tempera-
ture monitor are shown in Table 2.
Table 2. Internal Temperature Monitor
Factory Default Calibration
To convert the 2s complement register value to the tem-
perature it represents, first convert the 2-byte hexadeci-
mal value to a decimal value as if it is an unsigned value,
then divide the result by 256. Finally, subtract 256 if the
result of the division is greater than or equal to +128.
Example converted values are shown in Table 3 below.
18
Table 3. Temperature Conversion Values
Temperature
SIGNAL
01000000
01000000
01011111
11110110
11011000
____________________________________________________________________
MSB
(bin)
+127.96875°C
SIGNAL
00000000
00001111
00000000
00000000
00000000
+FS
(bin)
LSB
Temperature Monitor Operation
(hex)
7FF8
+FS
TEMPERATURE
-128.00°C
SIGNAL
64.059
-FS
(°C)
-10
-40
64
95
FRAME
(hex)
8000
, and
-FS
The offset of the temperature sensor can be adjusted
using the internal calibration registers to account for
differences between the ambient temperature at the
location of the DS1864 and the temperature of the
device it is biasing. When offsets are applied to the
temperature measurement, the value converted is off-
set by a fixed value from the DS1864’s ambient temper-
ature. For more information, see the following
Temperature Monitor Offset Calibration section.
The DS1864’s temperature sensor comes precalibrated
and requires no further adjustment by the customer for
proper operation. However, it is possible to characterize
a system and add a fixed offset to the DS1864’s temper-
ature reading so it is representative of another location’s
temperature. This is not required for biasing because
the temperature offset can be accounted for by adjust-
ing the data’s location in the LUTs, but this feature is
available for customers that see application benefits.
To change the temperature sensor’s offset: write the
temperature offset register to 0000h, measure the
source reference temperature (T
temperature from the DS1864 (T
following formula can be used to calculate the value for
the temperature offset register.
Once the value is calculated, write it to the temperature
offset register.
In addition to monitoring temperature, the DS1864 mon-
itors V
fashion using its 13-bit A/D converter. The converted
values are stored in memory addresses 62h to 69h as
16-bit unsigned numbers with the ADC results left justi-
fied in the register. The round-robin update time is
specified by t
characteristics.
The default factory-calibrated values for the voltage
monitors are shown in Table 4.
By using the internal gain and offset calibration regis-
ters the +FS and -FS signal values shown in Table 4
can be modified to meet customer needs. For more
information on calibration, see the following Voltage
Monitor Calibration section.
Note: ±FS voltages shown in Table 4 were calculated
assuming factory-programmed gain and offset values
in addition to right shifting set to 0.
TEMP OFFSET
CC
and the three MON inputs in a round-robin
Temperature Monitor Offset Calibration
FRAME
=
XOR
(
64
in the analog voltage monitoring
× −
BITWISE
(
Voltage Monitor Operation
275
+
REF
DS1864
BB h
T
REF
40
, °C), and read the
−
, °C). Then, the
T
DS
1864
)
)