MC33814, replace pass transistor with buck

[SansTva]

I'm working with a design with where MC33814 is included.

I already have a buck controller for low voltage generation in the design.

Is it possible to remove the pass transistor drivven by VPPREF and connect the buck voltage (6,5V) to VPPSENS as VPP. And still be able to utilize the VCC and VCC-prot

Kind regards.

[SansTva]

I replaced the pass transistor with a separate low voltage generation. (buck) to feed VPPSENS.

The 5V generation at VCC and VPROT works as intended.
They both are contolled via KEYSW with default SPI setting

With a S23K144 in parallell with 24Ohm at VCC i was still able to boot the MCU.  ->Boot time 2,6mS, with some flickering and a  plateau at 2,7V at VCC

With only 24Ohm connected to VCC the-> boot time vas 1,4mS, no plateau on the VCC

With a S23K144 in parallell with 24Ohm at VCC, the VCC was fully working in the VPPSENS range from 5,2V - 7,5V

The only noticable was that i had 970mV back feed from VPPSENS if my buck was switched off.

So, as far i have measured this it works as inteded with replacing the pass transistor circutry with a buck feeding VPPSENS with 6,5V

[JozefKozon]

Dear Ludvig,

this is not recommended. Please refer to the section 5.4.1.2 in the MC33814 datasheet. 

Also there will be probably not enough current to drive the internal regulators, therefore there must be the transistor from VPWR.

With Best Regards,

Jozef