UCD3138: Front-end gain and Measurement Resolution issues for the UCD3138

zoujiangyilang

Part Number: UCD3138

Hello
I am learning the UCD3138 full-bridge hard switch development board firmware
I have some questions about void init_front_end0(void)

void init_front_end0(void)
{

FeCtrl0Regs.EADCCTRL.bit.AFE_GAIN = 3;

}

I know this sentence is to set the AFE's gain to 8 and the Measurement Resolution to 1mv,

but I'm not sure why the gain is set to 8, not 4, 2, and 1. Why is this? What factors determine the gain and Measurement Resolution.

over 6 years ago

0 Yitzhak Bolurian over 6 years ago

TI__Mastermind 18370 points

This is set by a trade off between the "best loop response" and "Noise sensitivity".
Gain og 8 offers the best input resolution, and therefore the best loop response. But it also may cause extra sensitivity to noise.
If you have a good layout and isolation of noise from output stage, gain of 8 should be the better choice.

0 zoujiangyilang over 6 years ago in reply to Yitzhak Bolurian

Genius 4560 points

Got it！Thank you！
ZJYL

0 zoujiangyilang over 6 years ago in reply to Yitzhak Bolurian

Genius 4560 points

I find
FeCtrl0Regs.EADCCTRL.bit.AFE_GAIN = 3;
FeCtrl1Regs.EADCCTRL.bit.AFE_GAIN = 3;
FeCtrl2Regs.EADCCTRL.bit.AFE_GAIN = 0;
Why do you set the gain to 8 for Vo and Io loops, and set the gain to 1 for Vin loops?
Is the Vin signal unstable compared to Vo and Io? Is Vin's interference signal more?

0 zoujiangyilang over 6 years ago in reply to zoujiangyilang

Genius 4560 points

There is also a difference in the setting of Vin compared to the setting of Vo, Io
FeCtrl0Regs.EADCCTRL.bit.SCFE_CLK_DIV_2 = 0 ;
FeCtrl1Regs.EADCCTRL.bit.SCFE_CLK_DIV_2 = 0 ;
FeCtrl2Regs.EADCCTRL.bit.SCFE_CLK_DIV_2 = 1 ;
Why Vo, Io is set to 128nsEADC conversion once, and Vin is set to 64ns conversion once.
What is the reason?

0 zoujiangyilang over 6 years ago in reply to Yitzhak Bolurian

Genius 4560 points

Similarly, Vo, Io have RAMP function, and Vin does not set RAMP function. What is the reason?

0 Yitzhak Bolurian over 6 years ago in reply to zoujiangyilang

TI__Mastermind 18370 points

We are not interested in detecting small changes in Vin. We actually want not to react to small changes and noise in Vin. So, high resolution is not desired.

0 Yitzhak Bolurian over 6 years ago in reply to zoujiangyilang

TI__Mastermind 18370 points

Why would you need ramp for Vin?
Vin is not controlled by us? We just want to measure it.
Vin measurement is for Vin feed-forward and not for regulating and closing a loop.

0 Yitzhak Bolurian over 6 years ago in reply to zoujiangyilang

TI__Mastermind 18370 points

Vin feed-forward needs to be very fast in order to be effective.
And we set the coeeficients to ignore small changes in Vin, so the noise does not matter and will not show up in Vout.
Please read the Input voltage feed forward section in User's Guid.

0 zoujiangyilang over 6 years ago in reply to Yitzhak Bolurian

Genius 4560 points

Thank you for your guidance. I understand it.

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UCD3138: Front-end gain and Measurement Resolution issues for the UCD3138