UCC2891, UCC2892

UCC2893, UCC2894

SLUS542A − OCTOBER 2003 − REVISED JULY 2004

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APPLICATION INFORMATION: SETUP GUIDE

Step 5. Input Voltage Monitoring

The input voltage monitoring functions is governed by the following two expressions of the voltage at the

LINEUV terminal (pin 15):

V

R

IN2

R

at turn on, and

V

V

R

IN1

) I

HYST

R

I

2.5 V

R

DEL

0.05

expressions for the input voltage divider:

R

V

I

HYST

R

1.27 V

V

Similar methods can be used to define the divider components of the overvoltage protection input of the

UCC2892 and UCC2894 controllers.

Step 6. Current Sense and Slope Compensation

The UCC2891 family offers onboard, user programmable slope compensation. The programming of the right

of the filter design, it should be minimized to avoid filtering the slope compensation current exiting the CS pin.

The recommended range for the filter capacitance is between 50 pF and 270 pF. The value of the filter resistor

R

1

2

p

f

F

C

F

requirements of the inner peak current loop of the control algorithm and is measured by the number m. When

the slope of the applied compensation ramp equals the down slope of the output inductor current waveform

reflected across the primary side current sense resistor dV

to prevent current loop instability. Best current mode performance can be achieved around m=1. The further

increase of m moves the control closer to voltage mode control operation.

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