UCC28070-Q1 - Rdmax

Dice-K

Mastermind 6330 points

Other Parts Discussed in Thread: UCC28070-Q1, UCC28070

Hello,

I have a question about UCC28070-Q1.

About a design of Rdmax (in the case of the external clock synchronization)

When Dsync is 50%, does Dmax of PFC fall down to around 50% equally, too?

(Is a circuit narrowing Duty necessary because now SYNC component is Duty=50%?)

Regards,

Daisuke

over 8 years ago

0 John Griffin1 over 8 years ago

TI__Mastermind 34465 points

Equation 10 of the UCC28070 data sheet (page 18) shows how to calculate RDM resistor.

In your case you wish to use a 50% sync pulse duty cycle so for equation 10 to be valid

2(D_MAX) > 1.5

D_MAX> 0.75

So to use an external sync pulse with a 50% duty cycle you will need to have the greater than 0.75

D_MAX is set by equation 4

Regards,

John Griffin

0 Dice-K over 8 years ago in reply to John Griffin1

Mastermind 6330 points

Hello John,

Thank you for your reply.

Please teach me the reason of this equation.

2(D_MAX) > 1.5

Is the reason that equation 10 is not minus?

2 * D_MAX - 1 - Dsync > 0

2 * D_MAX - 1 - 0.5 > 0

Best regards,

Daisuke

0 John Griffin1 over 8 years ago in reply to Dice-K

TI__Mastermind 34465 points

Hi Daisuke,
Yes you are correct.
Equation 10 needs to be a positive number
Regards,
John

0 Dice-K over 8 years ago in reply to John Griffin1

Mastermind 6330 points

Hello John,
Thank you for your reply.

I want to use as 4-phase application(Figure 18).
But I cannot operate 4-phase using equation(10).

Can I use Rdmx larger than equation(10)?
When I use equation(4), I can operate 4-phase.
Gate wave is below.

TEK0005.TIF

Best regards,
Daisuke

0 Dice-K over 8 years ago in reply to Dice-K

Mastermind 6330 points

Hello John,
I add a postscript to follows in the contribution mentioned above.
I read the data-sheet "SLUSA71A".
I use as 4-phase application(Figure-18 of Page-19).

When I use Rdmx calculated by equation(10), the Gate wave is below.

PFC_Gate_NG.TIF

But when I use Rdmx calculated by equation(4), the Gate wave is below.

PFC_Gate_OK.TIF

1ch:phase-A(1st-IC), 2ch:phase-B(1st-IC), 3ch:phase-A(2nd-IC), 4ch:phase-B(2nd-IC)

Please teach me the reason.

The conditions are follows.
fpwm = 65kHz
fsync = 130kHz
Dmax = 0.935
Dsync = 0.5

Best regards,
Daisuke

0 John Griffin1 over 8 years ago in reply to Dice-K

TI__Mastermind 34465 points

Hi Daisuke,

My understanding of the data sheet is that you should use Equation 4 to calculate RDMX.

And when you do this the system is working correctly.

Equation 10 is not used to calculate RDMX.

It is used to calculate DMAX.

It is confusing because of the way Equation 10 is written but you should use Equation 10 to calculate DMAX and Equation 4 to calculate RDMX

Regards,

John

0 Dice-K over 8 years ago in reply to John Griffin1

Mastermind 6330 points

Hello John,
Thank you for your reply.

Does "you should use Equation 10 to calculate DMAX " mean that I satisfy "2 * D_MAX - 1 - Dsync > 0"?

Best regards,
Daisuke

0 John Griffin1 over 8 years ago in reply to Dice-K

TI__Mastermind 34465 points

Hi Daisuke,

In order to use Equation 10, you will find that

2 * D_MAX - 1 - Dsync > 0

Regards,

John

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UCC28070-Q1 - Rdmax