M02069 Datasheet, PDF (25/44 Pages) M/A-COM Technology Solutions, Inc. – 3.3 or 5 Volt VCSEL/FP Laser Driver IC for Applications to 4.3 Gbps

Functional Description
Table 3-2.
Pin Connection for Common Anode and Common Cathode Laser Modes
Pin Connection When:
Pin 18
SV_CC
IB_OUTCC
Pin 14
Pin 13
SGND
IB_OUTCA
I_PIN
Pin 22
PEAK_ADJ
Internal 50Ω pull-up resistors on
OUT+ and OUT-
Ratio of Bias current to BIAS_MON
current
Ratio of Modulation current to
MOD_MON current
Inactive
CC_SEL = High
Laser bias source current.
Ground for laser and all output load
components
Inactive
Monitor photodiode source current
Controls Negative going edge of OUT-
Active
13.5:1
30:1
CC_SEL = Low
Supply for laser and all output load
components.
Inactive
Inactive
Laser bias sink current.
Monitor photodiode sink current
Controls Negative going edge of OUT-, (do not
use)
Inactive
45.7:1
65:1
3.3.4
Bias Current Generator and Automatic Power Control
The M02069 can either source or sink bias current for the laser diode depending on whether it is in common anode
or common cathode mode. In common cathode mode (CC_SEL high) IB_OUTCC will source current. In common anode
mode (CC_SEL low) IB_OUTCA will sink current.
Regardless of whether the M02069 is configured for common anode or common cathode mode, the following infor-
mation applies.
To maintain constant average optical power, the M02069 incorporates a control loop to compensate for the
changes in laser threshold current over temperature and lifetime. The bias current will be determined by the value
of the external resistor R_APCSET and the transfer efficiency between the laser and monitor photodiode.
The photo current from the monitor photodiode mounted in the laser package is sunk or sourced at I_PIN. This photo
current is mirrored and an equivalent current is sourced from pins TxPwr_MON and APC_SET. The APC loop adjusts
the laser bias current (hence the monitor diode photo current) to maintain a voltage of 1.3V at APC_SET.
R_APCSET * I_PIN = 1.3 V
The APC loop has a time constant determined by C_APC, R_APCSET and the transfer efficiency between the laser and
monitor photodiode. The larger the C_APC capacitor the lower the bandwidth of the loop and the larger the R_APCSET
resistor the lower the bandwidth of the loop.
In general, it is recommended that at least 2.2 nF of external capacitance be added externally between C_APC and
V_CC3 to assure loop stability. With use of a 2.2 nF capacitor, the bias current can reach 90% of its final value within
1 millisecond.
02069-DSH-001-D
Mindspeed Technologies™
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