AK2571 Datasheet, PDF (11/52 Pages) Asahi Kasei Microsystems – Single-Chip Automatic Power/Temperature Control for WDM Laser Diodes

AKM Confidential
AK2571
3.6 Internal T_V converter
The internal temperature sensor’s output voltage function is shown in Figure 3-4. This offset is different for each device,
and is adjusted during factory test by AKM. If re-adjustment of the offset is necessary (for higher accuracy, etc.), it is
possible to rewrite the R(E)_TV_OFFSET. Table 3-10 diagrams the offset voltage and R_TV_OFFSET. The internal T_V
converter has a gain of –12.3mV / degree (typ) and the 8-bit ADC (full scale is 2.2V) is changed 0.7degree for each LSB.
Actually, only 5bits MSB of ADC is valid for feed forward APC, so the compensation data is renewed every 5.6 degrees.
The internal T_V converter monitors the surface temperature of the AK2571 and detects any difference between this
temperature, the ambient temperature and the temperature of external components. It is possible to increase the accuracy
of this function by “training” the device beforehand and writing the compensation data trained as described below.
1) Single-point temperature adjustment
Read R_TV at one ambient temperature, and using the T_V Conv. Gain (-0.7degree/LSB), calculates the 8-bit ADC value
and enter it into the look-up table address for Feed forward APC.
By performing this training, the offset error can be cancelled. Of course this training must be executed in conjunction with
an APC adjustment. Please refer to 5.3.1 APC/ATC adjustment.
2) Two-point temperature adjustment
Read R_TV at two ambient temperatures, calculate the T_V Conversion gain. From this gain, calculate the 8-bit ADC
value and enter it into the look-up table address for Feed forward APC.
By performing this training, the offset error and gain variation can be cancelled. Of course this training must be executed in
conjunction with an APC adjustment. Please refer to 5.3.1 APC/ATC adjustment.
Figure 3-4 Internal Temperature Sensor
InternalTem perature S ensor(T_V _C O N V ) (Typ characteristics)
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
-40
V = -0.0123t + 1.5709
S hifed by offset adjustm ent
0
40
80
120
Tem perature t [℃]
<Rev. 0.6E Preliminary>
-11-
2001/11