Hi,
I am currently looking on laser driver MP5491. Nice to have 10 bit DAC to control dc current output. Worry about if the output current is regulated or open-loop? If open-loop, it seems not able to output constant current with accuracy?
Actually, it’s also better to have laser power feedback to monitor laser average power but I haven’t see that, too. Is there a work-round solution?
Thanks!
Looks like at half scale it is accurate to within 1.5% . So a setpoint of 100mA gives you a current of between 98.5 and 101.5.
The block “diagram” shows what could be a current sense resistor in the channel block.
You could wrap a power diode feedback around this via a TIA to A to D to micro processor to update setpoint via I2C quite a bit of bother.
The problem with power diode feedback is the coupling varies unit to unit so you have to calibrate each and every one. A straight current source is way easier in production although the intensity is ultimately more variable.
Hi,
Great thanks for your reply!
I got your point by calibrate by MCU and I2C of MP5491. I mean it would be quite slow to adjust which is not real time current control.
Or it seems the laser driver only does the job to set a 10bit accuracy constant current and is not able to do the fast modulation support Gb/s level data transceive? Am I understand right? But it seems the only chip connected to laser diode in the system…
Internet rando, but the bus is I2C which doesn’t seem compatible with Gb/s . I would guess that signal would be coupled in some other way. So this chip establishes some bias condition and then AC coupled signal gives you the wiggles you need? Sounds like you need serious apps support
Really appreciate your answer!
Do you know whether it is the right platform to ask question and apps would help answer?
Thanks!
well this is a block diagram off the internet of a TOSA module
Looks like this is the DC bias part
Thank you so much for the link!
Yes, jshannon is correct. The Laser Driver sets the DC bias current for light output of the TOSA. The optical transceiver provides high speed AC modulation (high speed data) of the TOSA.