Datasheet
Input Brown-Out Protection (IBOP)
Input Brown-Out Protection (IBOP)
+
+
VIN
ENABLE_th
1.5V
S Q
QR
VIN
BROWNOUT_th
0.8V
C
VINS
Rectified AC Line
R
VINS1
R
VINS2
VINS
5V
20k
IBOPC
IN
2 1
2
ENABLE _ th
VINS VINS
ACturnon ENABLE _th
VINS
R R
V VINS
=
-
(1)
2
1 2
IN ( RMS )
VINS
VINS VINS
V
P
R R
=
+
(2)
UCC28019A
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.................................................................................................................................................. SLUS828B – DECEMBER 2008 – REVISED APRIL 2009
The sensed line-voltage input, VINS, provides a means for the designer to set the desired mains RMS voltage
level at which the PFC pre-regulator should start-up, V
ACturnon
, as well as the desired mains RMS level at which it
should shut down, V
ACturnoff
. This prevents unwanted sustained system operation at or below a brown-out
voltage, where excessive line current could overheat components. In addition, because VCC bias is not derived
directly from the line voltage, IBOP protects the circuit from low line conditions that may not trigger the VCC
UVLO turn-off.
Figure 21. Input Brown-Out Protection
Input line voltage is sensed directly from the rectified ac mains voltage through a resistor-divider filter network
providing a scaled and filtered value at the VINS input. IBOP will put the device into standby mode when VINS
falls (high to low) below 0.8 V, VINS
BROWNOUT_th
. The device comes out of standby when VINS rises (low to high)
above 1.5 V, VINS
ENABLE_th
. Bias current sourced from VINS, I
VINS_0V
, is less than 0.1 µ A. With a bias current this
low, there is little concern for any set-point error caused by this current flowing through the sensing network. The
highest praticable value resistance for this network should be chosen to minimize power dissipation, especially in
applications requiring low standby power. Be aware that higher resistance values are more susceptible to noise
pickup, but low-noise PCB layout techniques can help mitigate this. Also, depending on the resistor type used
and its voltage rating, R
VINS1
should be implemented with multiple resistors in series to reduce voltage stresses.
First, select R
VINS1
based on choosing the highest reasonable resistance value available for typical applications.
Then select R
VINS2
based on this value:
Power dissipated in the resistor network is:
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