AK2572 Datasheet, PDF (27/50 Pages) Asahi Kasei Microsystems – APC for Burst Mode Applicable Direct Modulation Laser Diode

ASAHI KASEI
[AK2572]
6. Alarm Function
In Table 6-1, the outline of the AK2572 Alarm (ALM) functions such as TEMPALM, OPTALM, CURRALM,
EXTALM1 and EXTALM2, and TXFAULT output function where alarms to be selected by EEPROM/Register
setting are logically OR-ed, are listed.
Table 6-1 ALM Function Outlines
ALM Condition to output alarm
Detect time
[Typ.]
Note
TEMPALM
When detected temperature equivalent
exceeds ALM set value (E_TEMPALM)
value
64 ms
Temp. sense period=64ms
Set by RE_TEMPALM_SET
OPTALM
When monitor PD input voltage becomes lower
than ALM set value (RE_OPTALM)
5 μs [*]
Holding APC FB value
Set by RE_OPTALM_SET
CURRALM
When a current to be set to DAC exceeds ALM set
value (RE_CURRALM_BIAS / MOD)
125 μs
Set by RE_CURRALM_SET
EXTALM1 When same polarity ALM signal is input on
EXTALM2 EXTALM1/2-pin as set by RE_EXTALM1/2_POL
1 μs
Set by RE_EXTALM1_SET
Set by RE_EXTALM2_SET
TXFAULT
When any of the ALMs is detected as target alarms
available on TXFAULT-pin output which are set by
EEPROM / Register setting (Refer to note above in
this table)
Depend on
the detected
target alarm
Automatically shutdown
when any target alarm is
detected and RE_SFP_SET
＝”0”
[*] The detect time does not include the delay time caused by a time constant of external Rpd and Cpd.
6.1 TEMPALM
TEMPALM is generated when the following relation is established after digitally comparing the A-to-D
converted temperature sensor output value (R_TEMP [7:0]) with the ALM set value (R_TEMPALM) :
R_TEMP≧E_TEMPALM
6.2 OPTALM
1/3, 1/4, 1/6 or 1/7 value of the APC target value (apc_ref) can be set as OPTALM set value (optalm_ref) by
RE_OPTALM setting. OPTALM detect is done by an analog comparator and it is generated when the following
relation is established
vpd＜optalm_ref
6.3 CURRALM
CURRALM is generated when one of the following 3 conditions is met after digitally comparing DAC setting
value for Modulation current (R_DAC1 [I-DAC1 set value] or R_DAC3 [V-DAC3 set value]) or DAC setting value
for Bias current (R_DAC2 [I-DAC2 set value]) with the CURRALM setting value (R_CURRALM_BIAS,
R_CURRALM_MOD):
R_DAC2 (Upper 4 bits)＞R_CURRALM_BIAS
or R_DAC1(Upper 4 bits)＞R_CURRALM_MOD, or R_DAC3(Upper 4 bits)＞R_CURRALM_MOD
Alarm threshold values R_CURRALM_BIAS and R_CURRALM_MOD can be set in accordance with the LD
temperature characteristic (Set by approximately every 6 ℃ step with the data in E_CURRALM_BIAS_TC,
E_CURRALM_MOD_TC, Refer to Table 9-3).
CURRALM is also generated when either of R_DAC1 (R_DAC3) or R_DAC2 becomes its full code (FFh).
When a shutdown request is made, CURRALM is set to “Inactive“ polarity.
6.4 EXTALM1, EXTALM2
When the same polarity ALM signal is input on EXTALM1-pin as set by RE_EXTALM1_POL, EXTALM1
detection is made. On the other hand, when the same polarity ALM signal is input on EXTALM2 /
MOD_CTRL-pin as set by RE_EXTALM2_POL, EXTALM2 detection is made if RE_PWR_LVL1_SET＝”0” or
RE_SFP_SET＝”0” (EXTALM2 / MOD_CTRL -pin is set to EXTALM2-pin)
When RE_EXTALM1/2_POL＝"0", the ALM detect polarity of “H” at EXTALM1/2-pin is set.
When RE_EXTALM1/2_POL＝"1", the ALM detect polarity of “L” at EXTALM1/2-pin is set.
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< MS0290-E-01>
2004/8