BackgroundI am working on a test setup to lifetime test high voltage insulation products. The HV source
https://www.matsusada.com/product/electrostatic-chuck-power-supplies/rack-mount/ec/ can supply +/-10kV at 20mA constant current. The output capacitance, including DUT and cabling, is a couple hundred pF.
There are three primary functions for the test cards:
- Measure output voltage at 25kHz per channel with minimal loading
- Provide switching for 8 channels
- 1Hz measurement of leakage current
There is a controller board with an isolated UART interface. The controller interfaces with the A/D converters through SPI over LVDS and, physically, shielded CAT5 cabling is used. The shield is connected to the isolated ground.
The power supplies are not isolated - their return has to connect to the transimpedance amplifier ground. The output of the voltage amplifiers is routed through the middle of the board, between the relays for creepage/clearance reasons. It's between two ground pours that have via stitching on the edges. The LVDS and A/D section will be shielded and the shield connected to the local ground.
Question:Anecdotally, when using off-the-shelf picoamp meters
https://rbdinstruments.com/products/picoammeter.html (isolated), the USB communication is interrupted when there are discharge events. In this product, the transimpedance amplifier and A/D converter are digitally isolated so the unit can float to 5kV.
How can I improve the design in this regard? Is the current approach susceptible to conducted noise from discharge events?
Attached are the relevant schematic and layout/stackup pictures.