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ADN2830 Laser Diode Controller

Question asked by HStewart on Aug 7, 2012
Latest reply on Aug 8, 2012 by AndyR

I have spun a board for the ADN2830 to control a JDSU laser with internal photo detector. The good news is both the cathode and anode
are isolated from the case. I'm using two in master/slave as I need about 300ma Id. Currently I have a Si rectifier for the laser diode and a separate PD for the monitor (illuminated with a separate laser). Using lab supplies I know the actual PD has 1.0ma at the desired laser diode output with +5V on the PD's cathode. Pset resistor to ground is 1200 ohms from Rset = 1.23V/ Ipd = 1.23V/1ma = 1200 ohms. ALS is low and IMPD and IMPDMON are both tied to ground. I have 1.23V at Pset.


I have 550ma through my rectifier diode, if it was the actual laser it would now be a LED or ashes.... Except for ALS's ability to toggle the current on and off or completely disconnecting the PD nothing appears to change this current.

 

Questions:

  1. 1.) IBMON (pins 23, 24) are tied to ground through a 0.1 ohm resistor, is this too small?
  2. 2.) IMPD and IMPDMON are both tied to ground per data sheet figure 3, the eval board has a resistor on IMPDMON. Is it necessary?
  3. 3.) Per the data sheet "PAVCAP capacitor values greater than 22 nF are used to set the actual loop bandwidth." The data
    sheet fig 3 and the eval board use 1.0uF which was my choice. I would not expect this value to effect basic regulation, correct?
  4. 4.) Is there a key element* missing from figure 3 in the data sheet?

 

*I have +5V and bypass/decoupling caps right at the VCC1-5 and the thermal pad is well grounded (electrically and thermally). I built a second board, same result. It is a fairly simple board, I have run out of things to try. I'm sure I'm missing one simple but important thing.

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