M02069 Datasheet, PDF (27/44 Pages) M/A-COM Technology Solutions, Inc. – 3.3 or 5 Volt VCSEL/FP Laser Driver IC for Applications to 4.3 Gbps

Functional Description
The modulation current amplitude is controlled by the MOD_SET input pin. The modulation current is temperature
compensated by the TC_SLOPE input.
If the temperature compensation at TC_SLOPE is disabled, the modulation output current is simply:
IOUT = 42 x (1.3V / R_MODSET) when CC_SEL is low
and
IOUT = 22 x (1.3V / R_MODSET) when CC_SEL is high and a 50Ω VCSEL is used.
Where R_MODSET is the resistance from pin MOD_SET to ground.
To temperature compensate the modulation current, choose R_TCSLOPE to meet the following relationship:
R_TCSLOPE = 19.5*(TC)^-1.5, where TC is the desired slope of the modulation current from 25°C to 85°C in%/°C and
R_TCSLOPE is in kΩ. If no temperature compensation is desired, leave R_TCSLOPE open.
In any case, R_TCSLOPE will have negligible effect at M02069 case temperatures below 10°C.
For example:
Given a common cathode VCSEL with a desired modulation current at low temperatures of 10 mA and a tempera-
ture coefficient of -0.5%/°C at high temperatures (which will require a laser driver temperature coefficient of
+0.5%).
Choose R_MODSET = 22 x (1.3V / 10mA) = 2.8kΩ.
Choose R_TCSLOPE =19.5*(0.5)^-1.5 kΩ = 55kΩ.
Figure 3-2. Selecting TC_SLOPE resistance in common anode configuration
60.00
50.00
40.00
30.00
20.00
10.00
0.00
-40
-20
0
20
40
60
80
-10.00
-20.00
-30.00
Ambient Temperature in degrees C
RTCslope:
22k
27k
33k
39k
47k
51k
62k
75k
82k
100k
120k
150k
220k
390k
750k
100^open
02069-DSH-001-D
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