Trouble understanding VREF for VTT generation.

[thanibee]

I am having a MSI g41 motherboard. The VTT voltage for north bridge should be around 1.2V. But it is generating only 0.9V. The 1.2V VRef is coming from SIO chip. See the attachments for reference. Any help appreciated. Thanks

[mon2]

Re: Trouble understanding VREF for VTT generation.

No. The pins you are showing are also connected to the same ref 1v2 voltage rail. The source of this power rail is somewhere else in the schematic. Check your power supply area or search the exact text to locate the true voltage source.

[thanibee]

Re: Trouble understanding VREF for VTT generation.

No. The pins you are showing are also connected to the same ref 1v2 voltage rail. The source of this power rail is somewhere else in the schematic. Check your power supply area or search the exact text to locate the true voltage source.

I am having trouble finding the source of this VREF.
I have attached the pdf (password is 254422)of the schematic here. Please help finding it.

[mon2]

Re: Trouble understanding VREF for VTT generation.

Check U6 on top-right of sheet 30. What is the voltage on Vout?

Voltage on pin 5,6,7,8 of U6?

[piernov]

Re: Trouble understanding VREF for VTT generation.

The voltage references come from the SIO. According to its datasheet, they are 0.9V by default.
So 1_2VREF = 0.9V (feeding U14A non-inverting input), and V_FSB_VTT = 1.2V (since U14A inverting input stabilizes at 0.9V thanks to the voltage divider R296/R297).

[thanibee]

Re: Trouble understanding VREF for VTT generation.

The voltage references come from the SIO. According to its datasheet, they are 0.9V by default.
So 1_2VREF = 0.9V (feeding U14A non-inverting input), and V_FSB_VTT = 1.2V (since U14A inverting input stabilizes at 0.9V thanks to the voltage divider R296/R297).

Makes sense. Thank you.