need help to calculate the voltage and current if possible on a pin of max3766. Circu

Hello all senior ENGINEERS,

THANKS TO ALL THOSE DEXTERS AND INTELS IN ADVANCE.

I am not an electronics students, I dont know much of the electronics. I get help from this forum, whenever I need.

I want to calculate the voltage and or current from the op-amp max495 to the pin MD. Datasheet attached. Its very simple to calc, but I dont know how :-(

I have a laser driver circuit, which is finished and working properly for one laser diode which was shipped with the circuit. I tried replacing it with my laser diode. It works fine some times and fails some times.

The circuit is based on the MAX3766EEP, I have attached the circuit given in the official pdf.

The problem is that the LD I am using has a monitor diode which requires at-least 5 volts, I presume. Its NX5306EK form NEC. But the max3766 dont handle that voltage, I presume. And so some times when there is no enough current on the monitor pd, the FAIL on the max3766 is latched or starts and circuit wont work untill i restart. I tried reverse biasing the monitor diode which is the actual scenario used by all while connecting the PD but it failed and works when connected in BIAS.

So, I want to bypass that shutdown or fail by the max3766, as given in the max3766evkit. They connected the monitor diode pin directly to max495. So It drives some voltage and current to the MD pin, so there is no need to connect the monitor diode pin at all. Now the problem is solved. But As my circuit is already finished. I, Want to calc or know the voltage and or current from the max495 to that pin. So that I can add extra components lm358 or etc to drive that voltage to that md pin and solve the problem.

This is my solution, I hope you guys have more solutions.

Thanks again.

Page 9 of MAX3766.pdf :

If a monitor diode is not available, the APC feature can be disabled by connecting R_POWERSET to GND and leaving MD unconnected.

Click to expand...

HTH!

erikl said:

Page 9 of MAX3766.pdf :

HTH!

Click to expand...

Yes you are correct, but the problem is that the circuit is already designed. I don't want to change it. These things are high speed circuits and I believe that any small change will result in big noise.

SO I want to calc the voltage or current at pin 18



<a title="circuit.png" href="http://obrazki.elektroda.pl/9060708000_1383370604.png"><img src="http://obrazki.elektroda.pl/9060708000_1383370604_thumb.jpg" alt="circuit.png" /></a>

jeswanth123 said:

... I want to calc the voltage or current at pin 18

Click to expand...

You don't need to calc: the spec is given @ p. 3 of the data sheet:
As you don't use a monitor diode, there's no input current to MD. Typ. voltage at this pin is VCC-1.2V . No noise problem, as you block this input by C4 .

erikl said:

You don't need to calc: the spec is given @ p. 3 of the data sheet: View attachment 98021
As you don't use a monitor diode, there's no input current to MD. Typ. voltage at this pin is VCC-1.2V . No noise problem, as you block this input by C4 .

Click to expand...

O I see, Yes I think so, And thats why its working without pd attached. I have read it and also read that pd current programming will only reduce the current to the ld. So its better to remove that pd connection. And the ld can withhold 150ma.

Thanks a lot, for your generosity and taking time to read the pdfs.

By the way do you know any best pcb reverse engineering tools or software. I am reversing a 1x9 pcb. Hard to get all the photomask paint removed. Using NAOH solution to get rid of the soldermask paint.

Thanks a lot again Senior

jeswanth123 said:

... do you know any best pcb reverse engineering tools or software. I am reversing a 1x9 pcb. Hard to get all the photomask paint removed. Using NaOH solution to get rid of the soldermask paint.

Click to expand...

Sorry, not my field, actually. I'd try a CMP method: NaOH + rubbing. And mind your eyes!

May be you can get better advice from one of the dedicated hardware and PCB forums, e.g. from this one.