mic3002 Micrel Semiconductor, mic3002 Datasheet - Page 30

• Manufacturer Part Number: mic3002
• Description: Mic3002 Fom Management Ic With Internal Calibration
• Manufacturer: Micrel Semiconductor

Micrel, Inc.
July 2007
MIC3002 provides a facility for temperature compensation
of the A.P.C. loop set-point, laser modulation current, bias
current fault comparator threshold, and bias current high
alarm flag threshold. Temperature compensation is
performed using a look-up table (LUT) that stores values
corresponding to each measured temperature over a
150°C span. Four identical tables reside at serial address
A4h and A6h as summarized in Table 16. Each table
entry is a signed twos complement number that is used
as an offset to the parameter being compensated. The
default value of all table entries is zero, giving a flat
response.
The A/D converter reports a new temperature sample
each t
temperature oscillation due to thermal or electrical noise,
sixteen successive temperature samples are averaged
together and used to index the L.U.T.s. Temperature
compensation results are therefore. updated at 16xt
intervals, or about 1.6 seconds. This can be expressed as
shown in Equation 10:
Each time an updated average value is acquired, a new
offset value for the APC setpoint is read from the
corresponding look-up table (see Table 17) and
transferred to the APC circuitry. This is illustrated in
Equation 11. In a same way, new offset values are taken
from similar look-up tables (see Table 18 and Table 19),
added to the nominal values and transferred into the
modulation and fault comparator DACs. The bias current
high alarm threshold is compensated using a fourth look-
up table (see Table 20). This compensation happens
internally and does not affect any host-accessible
registers.
CONV
. This occurs at roughly 10Hz. To prevent
(10)
CONV
If the measured temperature is greater than the maximum
table value, the highest value in each table is used. If the
measured temperature is less than the minimum, the
minimum value is used. Hysteresis is employed to further
enhance noise immunity and prevent oscillation about a
table threshold. Each table entry spans two degrees C. The
table index will not change unless the new temperature
average results in a table index beyond the midpoint of the
next entry in either direction. There is therefore 2 to 3°C of
hysteresis on temperature compensation changes. The
table index will never oscillate due to quantization noise as
the hysteresis is much larger than ±1⁄2 LSB.
30
Serial
Address
I2CADR+4h
I2CADR+6h
Table 16. Temperature Compensation Look-up Tables
Byte
Addresses
00h–3Fh
40h–7Fh
80h–BFh
C0h–FFh
90h–9Bh
A0h–ABh
B0h–BBh
C0h–CBh
[e-mail]
Function
APC Look-up Table
I MOD Look-up Table
IFLT Look-up Table
Bias High Alarm Look-up
Table
APC Look-up Table (cont.)
I MOD Look-up Table
(cont.)
IFLT Look-up Table (cont.)
Bias High Alarm Look-up
Table (cont.)
or [phone]
M9999-073107-B
(11)
MIC3002