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PSoC 4 MCU

YuMa_1534086
Contributor

Hello Cypress.

I have questions about power supply for PSoC4S CSX component block.

Please confirm and answer below questions.

Q1)

What is PSoC4S CSX component block’s power supply source?

Where does CSX block get power supply from?

Is it VDDA? Or VDDD?

And is the voltage applied directly from power supply source?

Or is the voltage dropped internally?

Is there internal LDO for CSX block?

Q2)

Will VDDA and VDDD affect CSX SNR?

Below is my understanding.

Is below correct?

================================

VDDA does not affect CSX SNR.

But VDDD(or VDDIO) affects CSX SNR.

Because VDDD(or VDDIO) is equal to Vtx.

And CSX SNR becomes higher also if VDDD(Vtx) becomes higher.

================================

Best Regards.

Yutaka Matsubara

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1 Solution
RyanZhao
Moderator
Moderator

Hello Matsubara-san,

A1)

IDAC and Vref of CSX are sourced from VDDA and Vtx is sourced from VDDD.

Yes. The voltage is applied directly from power supply source. There is no LDO for CSX block.

A2)

In this case, as you can see, both VDDA and VDDD will be used in CSX block. Therefore, both VDDA and VDDD will affect CSX SNR.

Best Regards,

Ryan Zhao

View solution in original post

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6 Replies
RyanZhao
Moderator
Moderator

Hello Matsubara-san,

A1)

IDAC and Vref of CSX are sourced from VDDA and Vtx is sourced from VDDD.

Yes. The voltage is applied directly from power supply source. There is no LDO for CSX block.

A2)

In this case, as you can see, both VDDA and VDDD will be used in CSX block. Therefore, both VDDA and VDDD will affect CSX SNR.

Best Regards,

Ryan Zhao

View solution in original post

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YuMa_1534086
Contributor

Ryan-san.

Thank you for your support.

Q1)

Below is CSX block diagram.

CSX block has some function blocks(IDAC, comparator, FB LOGIC, FF, Counter etc).

These function blocks other than Vtx are sourced from VDDA directly(No LDO).

Is my understanding correct?

pastedImage_0.png

Q2)

Is power source of CSX Vref(1.2V) VDDA?

And is there LDO between Vref and this power source for voltage drop?

Q3)

Below is CSX RawCount calculation formula.

This formula does not contain VDDA parameter.

So I think that VDDA does not affect CSX SNR.

Why does VDDA affect CSX SNR?

Could you please let us know mechanism that VDDA affects CSX SNR?

It is difficult to understand that VDDA affects CSX SNR because there is no VDDA in the formula...

pastedImage_1.png

Best Regards.

Yutaka Matsubara

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RyanZhao
Moderator
Moderator

Matsubara-san,

A1)

Yes. You're correct. Especially for Vref and IDAC.

A2)

Vref(1.2V) is not exact description. 1.2V is one of the choice. But by default, for CSDv2, Vref value has relationship with VDDA settings and actual VDDA value.

pastedImage_3.png

A3)

Yes. There is no VDDA appeared in the equation.

But if VDDA is noisy, IDAC or Vref will be noisy. Raw count will be noisy. SNR will be lower.

Hope this can help you out.

Best Regards,

Ryan

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YuMa_1534086
Contributor

Ryan-san.

Thank you for your response.

I think that CSX Vref is fixed value(1.2V).

Is my understanding correct?

Please confirm below figure.

pastedImage_0.png

Is below Vref(1.2V) generated by internal LDO from VDDA?

pastedImage_1.png

Best Regards.

Yutaka Matsubara

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RyanZhao
Moderator
Moderator

Matsubara-san,

Thank you for your correction. I think you are right. Vref of CSX is 1.2V as you described. I mixed it with self-capsense scan. Sorry for that!

And the 1.2V is not from LDO, it is internal bangap reference voltage.

Bangap voltage is hard to be effected by VDDA. In this case, if VDDA is noisy, IDAC will be noisy. Raw count will be noisy. SNR will be lower.

Best Regards,

Ryan

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YuMa_1534086
Contributor

Ryan-san.

Thank you for your response.

I understand.

Best Regards.

Yutaka Matsubara

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