AK2574 Datasheet, PDF (17/30 Pages) Asahi Kasei Microsystems – 156M Laser Diode Driver + APC for Burst Mode

ASAHI KASEI
[AK2574]
2.4 APC
AK2574 provides the APC (Auto Power Control) function for the burst mode application. APC is composed of a
programmable BIAS and MOD currents in response to the temperature (APC_FF), an on-chip temperature sensor,
and 2 current DACs (I-DAC1 and I-DAC2).
2.4.1 APC_FF
Fig 2-7 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 covers –40℃ to
+115℃ and EEPROM is prepared with 1.5℃ steps.
Fig 2-7 APC FF function
TEMPSENS
ADC
(7bit)
R_TEMP
EEPROM
R_DAC1
I-DAC1
MOD
Driver
MOD Current
LD
TEMPSENS
charatcteristics
Addressing with
R_TEMP
Address Data
R_DAC2
I-DAC2
BIAS
Driver
Memory for
I-DAC1
BIAS Current
Temperature
Memory for
I-DAC2
2.4.2 I-DAC
AK2574 has two current output 8 bit DACs; I-DAC1 and I-DAC2.
I-DAC1 is 85mA @ Full code sink type current DAC for MOD current and I-DAC2 is 54mA @ Full code sink type
current DAC for BIAS current.
Table 2-5 shows I-DAC1 characteristics and Table 2-6 shows I-DAC2 characteristics.
Table 2-5 I-DAC1 Characteristics
Item
Condition
min
Resolution
Output Current with IMOD = VDD – 1.8V 76
Full Code
1 LSB Current Step IMOD = VDD – 1.8V
DNL
IMOD = VDD – 1.8V -1
typ
max Unit Remark
8
bit
85
94
mA
0.333
mA
+1 LSB Code 20h to FFh
<MS0266-E-00>
-17-
2003/12