Datasheet

OUT _ OK OUT
V V 0.90 351 V= ´ »
E
Hysteresis 99 V
R 8.25M 3 2.74M
12 A 12 A
= = = W » ´ W
m m
F
OUT _ OK
E
2.5 V 2.5 V
R 82.25k
V 2.5 V 351V 2.5 V
12 A
12 A
8.22M
R
= = = W
- -
- m
- m
W
F
R 82.5k= W
( ) ( )
E F
OUT _ MIN
F
2.5 V R R 2.5 V 8.22M 82.5k
V 252 V
R 82.5k
+ W + W
= = »
W
( ) ( )
E F
OV _ FAILSAFE
F
4.87 V R R 4.87 V 8.22M 82.5k
V 490 V
R 82.5k
+ W + W
= = »
W
UCC28063
SLUSAO7 – SEPTEMBER 2011 www.ti.com
HVSENSE
The HVSENSE pin programs the PWMCNTL output of the UCC28063. The PWMCNTL open-drain output can be
used to disable a downstream converter while the PFC output capacitor is charging. PWMCNTL starts high
impedance and pulls to ground when HVSEN 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 25 to
Equation 30 show how to set the PWMCNTL pin to activate when the output voltage is within 90% of its nominal
value.
(25)
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 99 V of hysteresis, as shown in Equation 26. Three resistors in
series were used to meet voltage requirements.
(26)
Resistor R
F
is used to program the PWMCNTL active threshold, as shown in Equation 27.
(27)
Select a standard resistor value for R
F
.
(28)
This PWMCNTL output will remain active until a minimum output voltage (V
OUT_MIN
) is reached, as shown in
Equation 29.
(29)
According to these resistor values, the FailSafe OVP threshold will be set according to Equation 30
(30)
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Product Folder Link(s): UCC28063