VNI8200XP - outputs switching sporadically at power-up and power-down

[ASomu.1]

Hello. I'm designing a new board where I use VNI8200XP to control some LEDs and relay loads.

In my case VNI is used in SPI mode (SEL2 pulled high to Vreg), internal DC/DC converter is disabled and Vreg is supplied from on-board +24V/+5V DC/DC Converter.

I'm observing following problem - when the board is powered up or down, some VNI outputs sporadically get high for a short duration (usually 200-400 microseconds).

I investigated the problem and probably found a reason:

• My system at power supplies +24V to Vcc and onboard +5V DC/DC Converter
• at about Vcc=10V VNI8200XP goes out of undervoltage protection into operational state.
• But my onboard +5V regulator is not yet fully operational at that moment because Vcc is still too low for it, Vreg is ramping up and is below 1V at that moment
• This causes VNI to sense SEL2=L and activate parallel mode instead of SPI mode
• As I have some pins tied to Vreg (SEL1 = H, OUT_EN=H, etc) which act as channel inputs in parallel mode, this activates appropriate outputs.
• As soon as Vreg goes above +2.2V the situation normalizes and outputs are switched off.

At power down, the situation is vice versa - as in my system +5V regulator can't handle as low voltage, as VNI, it shuts off, before VNI becomes inoperational.

I can't allow such sporadic outputs switching at power on/off, so how can I avoid it?

Best regards

Artyom