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.
- 1.) IBMON (pins 23, 24) are tied to ground through a 0.1 ohm resistor, is this too small?
- 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.) 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.) 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.