About RC Time for external reset : CYT2B9

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WonjinHan
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Dears.

Now I’m checking out the RC time constant with RC circuit for use of  External reset (XRES) in CYT2B9

In datasheet, I understood the when asserting XRES from  logic ‘1” to logic “0”, XRES pin holding(Logic “0”) time is at least 265uS as the following. In other words,  Reset Holding time(Logic”0”) should be more than 265uS. . Is it correct ?

RC_TIME.jpg

Now I’m taking into account of use like that high side resistor 4.7KΩ and Low side Capacitor 0.1uF. So In this case, i can see the RC time is 470uS. 470uS is more than 264uS, finally I decided that this RC circuit for Reset, CYT2B9 is suitable. I would like you to review my understanding.

ResetRC.jpg

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Pranith
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Hello @WonjinHan ,

SID70 specifies the release to active transition (logic 0 to logic 1) time. It should not exceed 265us. 

As per the hardware design guide an internal pull up resistor and noise filter is made available. 

You can refer to section 5.1 in the latest design guide here: AN220270-hardware-design-guide-traveo-ii-family 

You could consider using a lower value resistor to meet the SID70 specification.

Regards,

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WonjinHan
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Hello Pranith.
Thank you for your feedback.

So you mean that high side resistor 4.7KΩ and Low side Capacitor 0.1uF are spec-out regarding of SID70 ?

Best Regards,
Kevin.

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Pranith
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Hi @WonjinHan 

The RC values here do not meet the SID70 spec.

 

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WonjinHan
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Hello Pranith.
Thank you for your answer.

The reason why i'm asking again about the suitability of "high side resistor 4.7KΩ and Low side Capacitor 0.1uF" is that this external RC reset circuit is already implemented in TVII-B-E-SK board which is one of the references I should believe.

Of course TVII-B-E-1M and TVII-B-E-2M have the same tXRES_ACT value.

ResetCircuit.jpg

 

 

 

 

 

 

 

 

 

I thought that is very unclear when making comparision between your explanation and actually applied circuit in TVII-B-E-SK board.


According to your explanation, this circuit in TVII-B-E-SK board is incorrect?

 

Br,
Kevin.

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WonjinHan
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Hello Pranith.

Could you give me your update ?

Thanks

Kevin.

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Pranith
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Hello Kevin,

Yes. The starter kit does not follow the reset specs mentioned in datasheet.

Generally we have higher timing for reset duration due to the power supply ramp-up during power on/off cycle.

It is recommended to use external reset controller that can sense the required rail. The Starter Kit board is designed for low cost so it does not have reset controller.

To meet the specs, C44 can be replaced with 20nF to 50nF capacitor.   

Regards,

Pranith