ADL5317 Voltage Noise

Hello mcaputo, sorry about the delay answering these questions.

There is no ADL5317 specification for output voltage noise on the VAPD pin. If necessary, you might consider an LC filter between the VAPD pin and the APD cathode, to remove any troublesome high-frequency noise spectra. So far, we have never encountered this problem, and likewise we have never tested with such LC filter.

Regarding PSRR on the VPHV pin: We have no PSRR data. For development purpose, we recommend a low-noise, lab-grade power supply for VPHV. If noise later becomes a problem using an on-board supply, then either the HV on-board supply will need a fix, or consider the LC filter mentioned above. 

ADL5317 is in mass-production status. There are no plans at this time to obsolete. Thanks for pointing this out to us. We will bring this up with the distribution managers. Again, there is no plan to obsolete the ADL5317. 

Thanks very much for getting back to me.

I may explore the option of having output filtering on my design.

I notice that the VSET to VAPD response time is very quick, if I put more than 10 nF on the output, then I would theoretically get large inrush current. It seems like this device folds back the output current at around 18 mA, so it doesn't seem like it's meant for large inrush.

Two questions:

1. Is there a maximum capacitance on the VAPD output? (possibly due to inrush concerns?)

2. Alternatively, If I am to put an RC time constant on the VSET pin, is this an effective way of implementing "soft start" thus reducing inrush? For example, if I have a 1 ms time constant on the VSET pin, then I should be able to put 100 nF on the VAPD without exceeding 18 mA during a full 0 - 40 V VAPD step. Does this sound effective? Or should I just stay away from large filter capacitances?

Hi mcaputo,

1. I'm not aware of any max capacitance spec. for VAPD pin. 

2. An RC on the VSET should help reduce or eliminate the IAPD spikes. Another suggestion would be to carefully optimize the series-RC on the VAPD pin, depending on the application. A combination of these 2 methods sounds best. 

Hi mcaputo,

1. I'm not aware of any max capacitance spec. for VAPD pin. 

2. An RC on the VSET should help reduce or eliminate the IAPD spikes. Another suggestion would be to carefully optimize the series-RC on the VAPD pin, depending on the application. A combination of these 2 methods sounds best.