AK2571 Datasheet, PDF (15/52 Pages) Asahi Kasei Microsystems – Single-Chip Automatic Power/Temperature Control for WDM Laser Diodes

AKM Confidential
AK2571
4.1 ATC Block Explanation
Table 4-1 indicates the functions of the ATC block
Block
Function
Remarks
Regulator
Gain & Offset
ADC
Supplies voltage to thermister included in the LD module. REFOUT=2.3V (typ). Thermister output
voltage (TEMPIN) error tracks the varying voltage supply temperature characteristics of REFOUT and
automatically calculates and cancels this in the AK2571.
AK2571 amplifies (x13 typically) the input signal to enable higher resolution from the 8-bit ADC. The input
signal should be set to the midpoint of its full scale to meet the target temperature of the offset setting
function. For example, when thermister R0=10kohm.@25 degree, B=3900, load resistance 6.8kohm., its
sensitivity is about 0.03degree/LSB.
8b-it A-to-D converter. Reference voltage is 2.2V (typ). Temperature signal from Gain & OFFSET is
converted to digital and transferred to PID calculator.
PID
TEC_CTRL
Executes a PID (Proportion, Integration and differential) calculation to meet the temperature signal
(R_TMPRT_CRNT) at the target temperature (R_TMPRT_TRGT). Output data (R_PID_VALABS) is
composed of 13-bits absolute value and a positive/negative bit. Each PID parameter can be set in the
EEPROM. The cycle time for this calculation is 8mS (typ) and is set by the internal oscillator.
Using the PID data (R_PID_VALABS), the TEC (Thermo Electric Cooler) is controlled by PWM or
Analog control. When PWM control is selected, the FET switch is controlled through the PWM division set
register (R_TEC_PWM_SET).
I-DAC4H
I-DAC4C
10b-it current D-to-A converter. When analog control for TEC is selected, the IDAC outputs current
following 10bits MSB data from PID. Its full-scale output current is 50mA (typ). When Analog-1 is selected
(Control the current direction by FET: refer to figure 4-4), it is possible for I-DAC4H to output both cooling
and heating current, depending on current direction. On the other hand, when Analog-2 is selected,
heating current is output through I-DAC4H (I-DAC4C output is GND) and cooling current is output
through I-DAC4C (I-DAC4H output is GND).
ATC_FB
Change the target temperature according to LD aging error from PD monitor voltage. Its value
(R_ATC_CMPNST) is calculated from the parameter (E_ATC_FB_SET). This function assumes that
there is first order function between the LD aging error and moving the wavelength to the longer, can
compensate wavelength shift cause from aging. When use this function, please note this assumption
carefully.
ATC_LOCK
Detect the stabilization of LD temperature from start or reset of AK2571. The stabilization judge range
(E_LK_TMPRT_WIN) and its decision term (E_LK_CNT_SET) are set in EEPROM. If the LD
temperature data (R_TMPRT_CRNT) stays within the stabilization judge range for a period that is longer
than the decision term, the AK2571 moves to the next operation.
TEMPALMCOMP ^{If the difference between LD temperature data (R_TMPRT_CRNT) and target temperature}
(R_TMPRT_TRGT) exceeds the temperature alarm threshold (E_TEMPALM_WIN), TEMPALM is
triggered. RegisterI R_ALM_POL sets the polarity of this signal.
PIDALMCOMP
When the PID control value (R_PID_VALUE) exceeds the PID alarm threshold (E_PIDALM_SET), PID
alarm is triggered. RegisterI R_ALM_POL sets the polarity of this signal
WLALMCOMP
When the aging target temperature aging (R_ATC_CMPNST) is exceeds the threshold of the wavelength
aging error alarm (E_WLALM_SET), WLALM is output. Its polarity is selectable by the R_ALM_POL
register.
<Rev. 0.6E Preliminary>
-15-
2001/11