MAX24001TL+ Maxim Integrated, MAX24001TL+ Datasheet - Page 18

• Manufacturer Part Number: MAX24001TL+
• Description: Laser Drivers 2.5G Burst Mode Laser Xcvr
• Manufacturer: Maxim Integrated
• Type: Laser Driverr

Specifications of MAX24001TL+

• Rohs: yes
• Data Rate: 2.5 Gbps
• Operating Supply Voltage: 3 V to 3.6 V
• Supply Current: 136 mA
• Maximum Operating Temperature: + 95 C
• Package / Case: TQFN-40
• Maximum Power Dissipation: 2857.1 mW
• Minimum Operating Temperature: - 40 C
• Mounting Style: SMD/SMT
• Part # Aliases: 90-Y24001+XS1

Closed-Loop Operation
Set the apc_enable register for closed-loop operation.
The automatic power control (APC) loop compares a value of laser output power produced by the power monitoring
circuits with a target level set by tx_apc_target. This proportional error value is scaled using the apc_loop_gain
and is then used to adjust the value of tx_biasdac (which has a number of internal precision extension bits). The
apc_loop_gain register thus controls the bandwidth of the APC loop.
Since the bandwidth of the loop is not very high, it is desirable to set the tx_biasdac register to a point as close as
possible to the target laser power level before the APC loop takes over. This is achieved by preloading the
tx_biasdac register with a value from the bias LUT and/or running a search algorithm (referred to as fast-start).
These actions are both triggered by the bias_lut_enable and faststart_enable bits. When these bits are set, then
a table lookup or fast-start will occur at the next available opportunity. Once the lookup or fast-start has occurred
then these bits are cleared. The host may therefore re-trigger fast/lut start by resetting bias_lut_enable and
faststart_enable at any time. The bits are also set automatically as follows:
On power-up:
During SLEEP:
During TX_DISABLE: The value in faststart_after_txdisable is transferred to faststart_enable
Thus, the required loop behavior when the laser is enabled can be independently configured for reset, sleep mode
and tx disable. This is further illustrated in the figure below:
Figure 10. Behavior of the tx_biasmode Register in Closed-Loop Mode
Maxim Integrated
faststart_enable
bias_lut_enable
apc_enable
0
0
0
1
1
1
The value in bias_lut_after_sleep is transferred to bias_lut_enable
The value in bias_lut_after_txdisable is transferred to bias_lut_enable
The value in faststart_after_sleep is transferred to faststart_enable
tx_biasmode is configured from EEPROM
initialising
1
1
0
bias_lut_after_sleep
faststart_after_sleep
1
0
0
normal operation
1
1
bias_lut_after_tx_disable
faststart_after_tx_disable
1
1
1
sleep
1
1
0
1
0
0
normal operation
1
0
1
1
0
disabled
1
0
0
normal operation
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