MAX24001TL+ Maxim Integrated, MAX24001TL+ Datasheet - Page 19

• 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

Fast-Start Algorithm
[Control Register Address Range A4h: AAh to ACh]
Figure 11. Fast-Start Algorithm Timing
During fast-start, the MAX24001 is temporarily reconfigured. The modulation driver sinks a constant current of
I
monitoring circuit is reconfigured to supply a direct comparison between the received MPD current and the target
MPD current. The process of making a change to bias current and then a subsequent comparison of MPD current
and target current is referred to as iteration. An iteration has a fixed duration (nominally 62ns).
Initially, the bias current is stepped up on every iteration until the MPD current exceeds the threshold. The initial
bias current step size A is ideally ½ the modulation current, the rationale being that this is the largest step which
can be taken whilst ensuring that the P1 power level is not exceeded. More generally, the initial step size is
defined as A = (tx_fstart_initial/256) x I
When the target level is exceeded the step size then decays (C). Halving the step size every iteration amounts to a
binary search. In practice, incomplete settling of the loop can result in a small overshoot of the target current level.
It is therefore recommended that each step is slightly more than 0.5x the previous step. This is configurable using
the fstart_decay register. The fstart_decay register determines the multiplication factor applied to the step size on
each subsequent iteration of the fast start algorithm.
The direction of each current step depends on whether the measured MPD current is above or below the target
level. The number of iterations B is controlled by the fstart_duration register. The maximum number of iterations
which can be guaranteed to complete within 3 x 400ns bursts is 15.
Maxim Integrated
MOD
fstart_decay
/2 on TX_OUT to represent the contribution made by the signal current to the average power. The power
100000
100001
100010
100011
100100
100101
101110
101111
..
Target MPD current
A
STEP DECAY
MULTIPLIER
37/64 = 0.5785
33/64 = 0.516
34/64 = 0.531
35/64 = 0.547
36/64 = 0.563
46/64 = 0.719
47/64 = 0.734
32/64 = 0.5
..
MOD
.
B
C
D
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