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# UCC28730-Q1: UCC28730-Q1 control

Part Number: UCC28730-Q1

Dear Team,

Customer has been analyzing the UCC28730-Q1 datasheet, and raised some queries regarding the control. Please, can you give us your feedback?

1. VCCR parameter

Datasheet: “The term VCCR is the product of the demagnetization constant, 0.432, and VCST(max)”

I don’t clearly understand why the RCS formula uses VCCR instead of VCST.

I thought that I should calculate the Rcs by the maximum current peak of magnetizing inductance of transformer (Ipp) and the Vcst (voltage across resistor). So, using this equation:

1. DMAGCC parameter

Datasheet: “DMAGCC is defined as the secondary diode conduction duty cycle during constant current, CC, operation. In the UCC28730-Q1, it is fixed internally at 0.432.”

→ For calculation, I should consider 0.432 as the maximum Duty of demagnetization time. Right?

So, in voltage mode, it will be always lower.

thanks

regards,

Juri

• Hi Juri,

Thank you for the query on UC28730.

Lets forget about the suare root of efficiency term at the moment.

Iout = (Ipp/2) x Nps x (tdm/tsw)

When the controller is at full load where it is at transition between CV and CC mode, the ratio of tdm/tsw approaches close to 0.432. This will be the point for which controller is dsigned.

Iout = (Vcst_max/2*Rcs) x Nps x 0.432; where Vcst_max =740mV

Rcs = (0.74x 0.432) x Nps/(2 x Iout)

Rcs = 0.319 x Nps/(2Iout)

So Rcs = Vccr x Nps/ (2 x Iout)

Hope this helps.

Regards,

Harish

• Hi Harish,

Additionally, there are two another questions related to UCC28730-Q1 coming from customer:

1) Which is its duty resolution?

2) Is there some strategy to perform a soft start up (HV). Like, adding some delay since it is detected the HV voltage threshold (30V).

thanks,

regards,

Juri

• Hi Juri,