AK2572 Datasheet, PDF (29/50 Pages) Asahi Kasei Microsystems – APC for Burst Mode Applicable Direct Modulation Laser Diode

ASAHI KASEI
[AK2572]
7. Shutdown Control
7.1 Shutdown Operation
The AK2572 can be put into the shutdown condition by setting TXDIS-pin to “H”.
The condition for shutdown in Table 7-1, and operation during shutdown in Table 7-2 are shown.
Table 7-1 Shutdown Condition
TXDIS RE_SFP_SET TXFAULT
0
0
0
1
1
x
1
x
x
Operation
Normal operation
Shutdown
Normal operation
Shutdown
Note
Operation at TXFAULT detection for SFP support
Shutdown request via TXDIS-pin
Table 7-2 Operation during Shutdown
Function
Operation during Shutdown
Note
I-DAC1,2 output Hi-Z
[*]
V-DAC3 output 0.2 V [Max.]
[*]
APC
Feed Forward
Based on the detected temperature, temperature compensation data for I-DAC
and V-DAC are updated. But I-DAC output is in Hi-Z state and V-DAC output
voltage is 0.2 V [Max.]
APC
Feed Back
During shutdown requested via TXDIS, a value just before the shutdown is held.
During shutdown requested by TXFAULT (RE_SFP_SET＝“0”), a value just
before the shutdown is held and it is reset at shutdown release by TXDIS.
ALM
Normal operation (CURRALM is set to “ Disabled output“ state)
TXFAULT
At RE_SFP_SET =”0”, a value just before the shutdown is held.
At RE_SFP_SET =”1”, logical “OR” function of the selected ALMs is output.
[*] DAC output (I-DAC1 or V-DAC3), which is selected as EXTRA_DAC, is not shutdown.
7.2 Operation at Shutdown Release
Since the AK2572 continues its temperature detection and APC feed forward operation even during the
shutdown, current value that is set by Feed Forward function is temperature compensated even if any
temperature difference occurs before or after the shutdown.
On the other hand, whether a value just before the shutdown is held or an initial value is set as APC Feed Back
data (R_APC_FB) can be selected by RE_TEMP_DET setting. When to hold a value just before the shutdown, a
temperature at shutdown release (R_TEMP) and a temperature just before shutdown (to be retained at
R_TEMP_STDW) are compared. If the difference is larger than the set value (RE_TEMP_WIN), namely, when
the following relation is satisfied, ABS(R_TEMP–R_TEMP_STDW)＞RE_TEMP_WIN, a function to set
R_APC_FB to initial value is activated so that an excess power emission of LD and a turn-on delay of LD are
eliminated. As initialization of R_APC_FB is executed with being based on the detected temperature just before
shutdown release, a turn-on operation is accelerated if the initial setting function of APC_FB is selected
(RE_APC_INIT_SET＝“1”). In Table 7-3, R_APC_FB values at shutdown release are listed.
Table 7-3 R_APC_FB Values at Shutdown Release
RE_ TX- RE_
SFP_SET FAULT TEMP_DET
Temperature
difference
R_APC_FB
Note
0
x
Initial value
0
0
1
0
Held value ABS(TEMP–TEMP_STDW)＜TEMP_WIN
1
Initial value ABS(TEMP–TEMP_STDW)＞TEMP_WIN
1
x
x
Initial value
Shutdown released by TXDIS
0
x
Initial value
1
x
1
0
Held value ABS(TEMP–TEMP_STDW)＜TEMP_WIN
1
Initial value ABS(TEMP–TEMP_STDW)＞TEMP_WIN
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< MS0290-E-01>
2004/8