AK2573A Datasheet, PDF (15/38 Pages) Asahi Kasei Microsystems – 125M / 156M Laser Diode Driver + APC

ASAHI KASEI
[AK2573A]
4.1 APC_FF Function
Fig 4-2 illustrates the APC FF functions. The operation is as follows:
(1) Analog to digital conversion of the voltage (7 bit) that reflects the temperature for every temperature detection
period (128ms typ).
(2) Read the 8 bit current data (address is indicated by the ADC data) from EEPROM and set this value to the
I-DACs.
If the current data over temperature is set to each EEPROM address, the compensated current is supplied to the LD
automatically.
To use this function, current data should be stored in EEPROM in advance. The temperature sensor is cover–40℃ to
115℃ and EEPROM is prepared with 1.5℃ steps.
Fig 4-2 APC FF function
TEMPSENS
ADC
(7bit)
R_TEMP
EEPROM
R_DAC1_FF
I-DAC1
Driver
MOD Current
LD
Addressing
with
TEMPSENS
R_TEMP
Address Data
charatcteristics
I-DAC2
R_DAC2_FF
BIAS Current
Memory for
I-DAC1
Temperature
Memory for
I-DAC2
4.2 APC_FB Function
Fig 4-3 shows APC_FB functions. It operates as follows:
(1) APC_COMP compares vpd and vapc_ref.
(2) The digital filter calculates the compensation current (R_APC_FB) to equalize vpd with vapc_ref to keep LD
power constant.
The vapc_ref (RE_APC_TRGT) can be changed over temperature automatically. Temperature compensation
procedure is as same as APC FF (data of DAC_APC is read out EEPROM in response to the temperature).
For the stable operation, the cut-off frequency of RPD and CPD should be 1kHz to 10kHz.
Fig 4-3 APC FB function
TEMPSENS
ADC
Monitor
PD
CPD
PDMON
RPD
PDIN
PDGAIN
vpd
Electrical volume for Monitor PD
R_TEMP
EEPROM
512kHz(typ)
APC_
COMP
comp_out
APC FF
may set initial valuein response to
the temperature at power-on
to accelerate power-up sequence
R_DACx
+
I-DAC
Digital Filter
1/N
1/s
R_APC_FB
RE_APC_TRGT
DAC_APC
vapc_ref
<MS0189-E-01>
-15-
2004/5