AKM Confidential
AK2571
3.2 Feed forward APC Function
The AK2571 compensates for ambient temperature variations caused by the current amplifier or driver chip located
outside of the LD module. If this function is not required, a fixed-current source for the LD can be used instead..
The Feed-forward process is described below:
1) The internal T_V converter (please refer to “3.6 Internal T-V converter”) senses the ambient temperature. The
integrated ADC converts the signal to a digital value.
2) 5-bit MSB data address for the EEPROM stores the temperature compensation data, which is sent to I-DACx.
3) Compensation current is output from I-DACx.
To execute feed forward APC, temperature compensation data must be stored in the internal EEPROM as a look-up table
that is programmed during the customer assembly process.
In Self-operation mode, all compensation operations (sensing T_V converter, access to EEPROM and compensation
current output through I-DACs) are automatically executed.
3.3 LD aging error compensation
Compensation current outputs are available for LD light power deterioration. APC_COMP compares the feedback voltage
from PDIN (vpd) with the output voltage of DACAPC (vapc_ref, R_APC_TRGT). Based on this result a compensation
current (R_APC_CMPNST) is added to the output current of I-DAC set by E_APC_FB_SET after averaging through a
digital filter.
LD Ageing error
compensation current
(R_APC_CMPNST)
PDGAIN
Monitor
PD
APC_
COMP
APC Target
(R_APC_TRGT)
PDIN
PDMON
RPD
CPD
DAC_APC
DIGITAL
FILTER
PD_MON Target
(R_PDMON_SET)
PD GAIN set
(R_PDGAIN)
LD Ageing compensation
Max value
(E_APC_FB_MAX)
PD voltage after
PDGAIN
(vpd)
vapc_ref
ADC*
PDMON Digital
(R_PDMOND)
*: Time shearing ADC
PDMON
set
3.3.1
PDMON / PDGAIN setting
Selects the output range from PDMON pin by R_PDMON_SET in the range from0.4 to 1.1V. Adjust the input signal level
using R_PD_GAIN (E_PD_GAIN) to make the initial input level equal the value of R_PDMON_SET. Table 3-2 indicates
the function of R_PDMON_SET and output voltages, Table 3-3 indicates the function of R_PDGAIN and Gain. After this
adjustment, the internal PD input voltage (vpd) is set at 1.8V(typ) in Self-operation mode.
<Rev. 0.6E Preliminary> -7-
2001/11
