Datasheet

HVSENSE
V =V 0.90 351V´ »
OUT_OK OUT
(14)
R =
E
Hysteresis
36 Am
=
108V
36 Am
=3MW
(15)
R =
F
=
=31.185kW » W31.6k
2.5V
V 2.5V-
OUT_OK
R
E
- m36 A
2.5V
351V 2.5V-
3MW
- m36 A
(16)
V =
OUT_MIN
= » 240V
2.5V(R +R )
E F
R
F
2.5V(3M +31.6k )W W
31.6kW
(17)
V =
OV_FAILSAFE
= » 467V
4.87V(R +R )
E F
R
F
4.87V(3M +31.6k )W W
31.6kW
(18)
UCC28061
www.ti.com .............................................................................................................................................................. SLUS837A – JUNE 2008 – REVISED JULY 2009
The HVSENSE pin programs the PWMCNTL output of the UCC28061. The PWMCNTL open-drain output can be
used to disable a downstream converter while the PFC output capacitor is charging. PWMCNTL starts in high
impedance and pulls to ground when the HVSENSE increases above 2.5 V. Setting the point where PWMCNTL
becomes active requires a voltage divider from the boost voltage to the HVSEN pin to ground. Equation 14 to
Equation 18 show how to set the PWMCNTL pin to activate when the output voltage is within 90% of its nominal
value.
Resistor R
E
sets up the high side of the voltage divider and programs the hysteresis of the PWMCNTL signal.
For this example, R
E
was selected to provide 108 V of hysteresis, as shown in Equation 15 .
Resistor R
F
is used to program the PWMCNTL active threshold, as shown in Equation 16 .
This PWMCNTRL output remains active until a minimum output voltage (V
OUT_MIN
) is reached, as shown in
Equation 17 .
According to the resistor value, the FailSafe OVP threshold should be set according to Equation 18 :
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