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In OPT8241-CDK-EVM Illumination board. MosFET (seems Illumination driver) and Laser connected in parallel. I can't understand why. From my understands Illumination driver must be like below.
Hi Mr. Suzuka,
Both are possible ways of switching laser diode. In the parallel switch method as used in the EVM, laser turns on when the mosfet gate is low and turns off when the mosfet gate is high. The series method is preferred when we use voltage mode driver circuit. We have used current mode driving for the laser and hence preferred parallel switch. The driver circuitry used in the EVM helps to bring down the ringing in the optical waveform.
Thanks and regards
Nithin
Dear None,
TPS2559 is actually used as a current source. Actual design of TPS2559 is as a current limiting load switch. We use the current limiting feature of TPS2559, and make sure the voltage supply to TPS2559 is greater than the necessary voltage. Then, TPS2559 goes into current limiting and works like a current source with a limit on the higher voltage.
Regards,
Subhash
Hi Subhash,
Thanks for reply.
If you want to make TPS2559 work under the mode of what you said, it means to the load current should greater than the tps2559 current limit setting.
I check the OPT8241-CDK-EVM IB sch file,I foud tps2599 current limit to 2.4A. so the load current must be greater than 2.4A. but 22045498 Datasheet the laser
max operating current is 1.4A. So I still think it work on voltage mode. maybe there is something wrong.
thanks®ards
None
Dear None,
The laser peak power is 2.4W for 50% duty cycle. We operate the laser in that mode.
For a peak power of 2.4W, the current has to be of values greater than 1.4A. The 1.4A value is for continuous waveform operation.
Regards,
Subhash
Hi Subhash,
May be the datasheet about laser 22045498 I have is brief version.
because, for a peak of power of 2.4W,if want the current is greater than 1.4A,it should be the min operating voltage is V=2.4W/1.4A=1.71V.
may be operating in pluse mode this parameter is different. because there is something wrong.
thanks & regards
None
Hi Subhash,
From Laser Datasheet,it laser peak optical power is 2.4W(Max),it's test condition is at 50% duty cycle, so i think this is the pulse current.
but it slope efficiency is 1.1W/A, so we can get the max pulse current is 2.4/1.1=2.18A. according this, i think the laser driver circut is operating in voltage mode not current mode.
Thanks & Regards
None