AK2573A Datasheet, PDF (16/38 Pages) Asahi Kasei Microsystems – 125M / 156M Laser Diode Driver + APC

ASAHI KASEI
[AK2573A]
4.2.1 PDGAIN
PD monitor current is converted to the average voltage with RPD and CPD and input to PDIN. PDIN voltage may be
gained at PDGAIN and monitored at PDMON. PDGAIN should be adjusted to PDMON = 1V typ. The gain range
of PDGAIN is –8.0dB to 23.5dB with 0.5dB steps (6-bits). PDGAIN is set via the I²C^TM interface. Table 4-1 shows
PDIN input range and Table 4-2 shows the relationship between PDGAIN and EEPROM setting.
Table 4-1 PDIN input range
Parameter
PDIN Input range
min
0.08V
max
Remark
2.5V
Table 4-2 PDGAIN
RE_PDGAIN_SET
000000 (0)
000001 (1)
:
111110 (62)
111111 (63)
Gain (typ) [dB]
23.5
23.0
:
-7.5
-8.0
Remark
0.5dB step
4.2.2 DACAPC
DACAPC generates the reference voltage of APC (vapc_ref). AK2573A supplies a programmed APC reference in
response to the temperature from an on-chip temperature sensor (every 6℃, APC reference data is stored in
E_APC_TRGT_TC, see Table 8-3 for more information). Write same data into E_APC_TRGT_TC for constant APC
reference. Table 4-3 shows the relationship between APC reference voltage (vapc_ref) and EEPROM setting.
Table 4-3 DACAPC
E_APC_TRGT_TC
(R_APC_TRGT)
00000(0)
:
01111 (15)
10000 (16)
10001 (17)
:
11111 (31)
DACAPC (vapc_ref) (typ) [V]
0.792
0.987
1.0
1.013
1.195
Remark
13mV step
4.2.3 Example of APC Setting
Table 4-4 shows the typical setting of APC function (APC_FF and APC_FB). The combination of APC is set by
RE_APC_FF and RE_APC_FB. Fig 4-5 shows the EEPROM area for MOD current (E_DAC1_TC) and BIAS
current (E_DAC2_TC). The data should be stored in E_DAC1_TC and E_DAC2_TC is determined by RE_APC_FF
and RE_APC_FB. Table 4-7 and 4-8 shows all combination of APC function.
RE_APC_FF is 2bit data to be assigned I-DAC for APC_FF operation. MSB is for I-DAC2 and LSB for I-DAC1.
RE_APC_FB is 2bit data to be assigned I-DAC for APC_FB operation. MSB is for I-DAC2 and LSB for I-DAC1.
In the case of RE_APC_FB=11(binary), AK2573A is in “Dual Feedback” (see Fig 4-9, 4-10 and Table 4-6).
<MS0189-E-01>
-16-
2004/5