Datasheet

LC S1 CS D PA

K R R t N

´ ´ ´ ´

( )

OUT OCC

RUN

OCC

DD(on) DD(off )

C V

I 1 mA

V V 1 V

+ ´

- -

UCC28710, UCC28711

UCC28712, UCC28713

UCC28714, UCC28715

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SLUSB86 –NOVEMBER 2012

VDD Capacitance, C

The capacitance on VDD needs to supply the device operating current until the output of the converter reaches

the target minimum operating voltage in constant-current regulation. At this time the auxiliary winding can sustain

the voltage to the UCC28710 family. The total output current available to the load and to charge the output

capacitors is the constant-current regulation target. The equation below assumes the output current of the

flyback is available to charge the output capacitance until the minimum output voltage is achieved. There is an

estimated 1 mA of gate-drive current in the equation and 1 V of margin added to VDD.

(24)

VS Resistor Divider, Line Compensation, and Cable Compensation

The VS divider resistors determine the output voltage regulation point of the flyback converter, also the high-side

divider resistor (R

) determines the line voltage at which the controller enables continuous DRV operation. R

is initially determined based on transformer auxiliary to primary turns ratio and desired input voltage operating

threshold.

(25)

The low-side VS pin resistor is selected based on desired V

regulation voltage.

(26)

The UCC28710 family can maintain tight constant-current regulation over input line by utilizing the line

compensation feature. The line compensation resistor (R

) value is determined by current flowing in R

and

expected gate drive and MOSFET turn-off delay. Assume a 50-ns internal delay in the UCC28710 family.

(27)

On the UCC28710, UCC28714 and UCC28715 which has adjustable cable compensation, the resistance for the

desired compensation level at the output terminals can be determined using Equation 28.

(28)

Product Folder Links: UCC28710, UCC28711 UCC28712, UCC28713 UCC28714, UCC28715