MIC3002GML datasheet(30/65 Pages) MICREL

30 / 65 page

Micrel, Inc.

MIC3002

July 2007

M9999-073107-B

hbwhelp@micrel.com or (408) 955-1690

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 tCONV. This occurs at roughly 10Hz. To prevent

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 16xtCONV

intervals, or about 1.6 seconds. This can be expressed as

shown in Equation 10:

(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.

(11)

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.

Serial

Address

Byte

Addresses

Function

00h–3Fh

APC Look-up Table

40h–7Fh

IMOD Look-up Table

80h–BFh

IFLT Look-up Table

I2CADR+4h

C0h–FFh

Bias High Alarm Look-up

Table

90h–9Bh

APC Look-up Table (cont.)

A0h–ABh

IMOD Look-up Table

(cont.)

B0h–BBh

IFLT Look-up Table (cont.)

I2CADR+6h

C0h–CBh

Bias High Alarm Look-up

Table (cont.)

Table 16. Temperature Compensation Look-up Tables

MIC3002GML Datasheet(PDF) 30 Page - Micrel Semiconductor

MIC3002GML Datasheet(HTML) 30 Page - Micrel Semiconductor

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65

Datasheet Download

Link URL