inverting converter, EMI concern

[sdouble]

Dear All,
i'm back to you about some concern about an inverting regulator that i'm designing currently.
That pretty much far from my usual business.
Basically the idea is to generate a 120 to 200 V (adjustable) negative voltage from a 9 V source. I need to pipe out only 1 to 5 uA.. so basically nothing.
I ended up with the following design.

I have a major concern about EMI. The circuit should be really quiet.
I reduced drastically  the current driven by the regulator (about 80mA only) but the voltage tripler leads to a long return path for the current.
every comment or advice are very much welcome.
J.

[sdouble]

no idea ? 

[dmills]

If you have a 100Meg ohm load, then a few RC filter stages with high value resistors will not drop much voltage, just be careful of microphonics if using MLCCs in the output filter.

A couple of poles of the 1M/100nF sort feels appropriate, this kind of thing is commonplace in capacitor microphones.

Regards, Dan.

[sdouble]

agreed, but my concern was more related to radiated noise.

[T3sl4co1l]

Radiation depends upon how the device is built; you've shown us nothing to comment on, as far as how much it will radiate.

That leaves general advice: build it on ground plane, and place the CW stack, in particular C12 (is that what it is? I can't tell, the labels are such a mess) near U2, R7 and C1.

More importantly though, the LTC3863 control loop is not compatible with a capacitive load inverter.  Note that, when the transistor turns on, there is a direct, instantaneous path (through diodes and capacitors) to the output, capable of ~unlimited peak current flow.

You need very little average power, so it's probably not noticeable anyway (it'll always be in burst mode, except during startup which will be much slower than expected), but it's not good practice.  The direct consequence of this is low efficiency.

Preferred method is a tapped inductor.  Coilcraft for example have coupled inductors in modest ratios, like 1:3 and 1:10, in the LPR and other series.

Tim