AK2571 Datasheet, PDF (3/52 Pages) Asahi Kasei Microsystems – Single-Chip Automatic Power/Temperature Control for WDM Laser Diodes

AKM Confidential
AK2571
Circuit Description
1. Over view
The AK2571 has two primary functions. The first function is APC (Automatic Temperature Control) which supplies
adequate modulation /BIAS current to a Laser diode and the other is ATC (Automatic Temperature control) which
controls the TEC (Thermo Electric Cooler) to stabilize the temperature of the Laser diode.
1. 1 APC
There are three Digital to Analog Converters (I-DAC1, 2, 3) that output the current for modulation, BIAS and EA
(Electrical Absorption) Modulation.
Maximum output currents :
I-DAC1: 120mA (typ.),
I-DAC2 and I-DAC3: 20mA (typ.)
Each DAC has a current limit function whose value is stored in the internal EEPROM. This is especially important for
I-DAC1, which has the modulation function for dithering.
In WDM systems, there is no need for discrete laser diode temperature compensation. However the outer current
amplifier or LD drivers may be affected by ambient temperature changes. In order to compensate for these the AK2571
has a feed-forward APC that can supply adequate current corresponding to the ambient temperature change detected by
the internal T_V converter.
Please refer the part “3. APC” for details.
1.2 ATC
The AK2571 controls TEC to stabilize the input voltage from the temperature sensor of the LD module (Thermistor). The
control algorithm is PID (Proportion Integration Differential) which has user-programmable parameters that are stored in
EEPROM. There are two ways for driving TEC, one is PWM (more energy effective than DC drive), the other is DC
current drive through I-DAC, which has lower noise.
Please refer the part “4. ATC” for details.
1.3 Control Sequence
There are three functional modes in AK2571 below.
1) Self-operation mode: The AK2571 operates ATC and APC independently. When self-operating mode starts, , ATC Lock
(detects when the target temperature is reached), APC Count up (prevents jumps in BIAS and Modulation currents) and
Timer (counts the time from device start to beginning of operation) are available.
2) Register Access Mode: AK2571 permits writing registers through the digital interface. Customers can adjust any
parameters or tables in this mode.
3) EEPROM mode: AK2571 permits EEPROM writes. Customers can store the parameters or table data in EEPROM.
Please refer the part “5. Sequencer” for details.
<Rev. 0.6E Preliminary>
-3-
2001/11