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NCP1654BD133R2G Datasheet(PDF) 19 Page - ON Semiconductor

Part No. NCP1654BD133R2G
Description  Power Factor Controller for Compact and Robust, Continuous Conduction Mode Pre-Converters
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Manufacturer  ONSEMI [ON Semiconductor]
Direct Link  http://www.onsemi.com
Logo ONSEMI - ON Semiconductor

NCP1654BD133R2G Datasheet(HTML) 19 Page - ON Semiconductor

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NCP1654
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19
Undervoltage Protection (UVP) for Open Loop
Protection or Shutdown
Figure 44. Undervoltage Protection
ISTDN
ICC2
Shutdown
Operating
8% VREF
12% VREF
Vfb
As shown in Figure 44, when Vfb is less than 8% of VREF,
the device is shut down and consumes less than 400
mA.
The device automatically starts operation when the output
voltage goes above 12% of VREF. In normal situation of
boost converter configuration, the output voltage Vout is
always greater than the input voltage Vin and the feedback
signal Vfb is always greater than 8% and 12% of VREF to
enable NCP1654 to operate.
This Undervoltage Protection function has 2 purposes.
Open Loop Protection − Protect the power stage from
damage at feedback loop abnormal, such as Vfb is
shorted to ground or the feedback resistor RfbU is
open.
Shutdown mode − Disables the PFC stage and forces a
low consumption mode. This feature helps to meet
stringent stand−by specifications. Power Factor being
not necessary in stand−by, the PFC stage is generally
inhibited to save the pre−converter losses. To further
improve the stand−by performance, the PFC controller
should consume minimum current in this mode.
Current Sense
The device senses the inductor current IL by the current
sense scheme in Figure 37. The device maintains the
voltage at CS pin to be zero voltage (i.e., Vcs ≈ 0 V) so that
(Equation 11),
Ics +
RSENSE
RCS
IL ,
can be formulated.
This scheme has the advantage of the minimum number
of components for current sensing. The sense current Ics
represents the inductor current IL and will be used in the
PFC duty modulation to generate the multiplier voltage
Vm, Over−Power Limitation (OPL), and Over−Current
Protection. (Equation 11) would insist in the fact that it
provides the flexibility in the RSENSE choice and that it
allows to detect in−rush currents.
Over−Current Protection (OCP)
Over−Current Protection is reached when Ics is larger
than IS(OCP) (200 mA typical). The offset voltage of the CS
pin is typical 10 mV and it is neglected in the calculation.
Hence, the maximum OCP inductor current threshold
IL(OCP) is obtained in (Equation 20).
(eq. 20)
IL(OCP) +
RCSIS(OCP)
RSENSE
+
RCS
RSENSE
@ 200 mA
When over−current protection threshold is reached, the
Drive Output of the device goes low. The device
automatically resumes operation when the inductor current
goes below the threshold.
Input Voltage Sense
The device senses the rms input voltage Vac by the
sensing scheme in Figure 45. Vbo senses the average
rectified input voltage Vin via the resistor divider. An
external capacitor CBO is to maintain the Vbo the average
value of Vin. Vbo is used for Brown−Out Protection, PFC
duty modulation and over−power limitation (OPL).
Brown−Out Protection
The device uses the Vbo signal to protect the PFC stage
from operating as the input voltage is lower than expected.
Re−formulate (Equation 9) to get (Equation 21). Refer to
Figure 45, Vin is different before and after the device
operating.
Before the device operates, Vin is equal to the peak
value of rms input voltage, Vac. Hence Vbo is as
described in (Equation 21).
(eq. 21)
Vbo +
RboL
RboL ) RboU
(Vin) +
RboL
RboL ) RboU
2 Vac
After device operates, Vin is the rectified sinusoidal
input voltage. Thanks to CBO, Vbo is the average of
rectified input voltage. Hence Vbo decays to 2/p of the
peak value of rms input voltage Vac as described in
(Equation 22).
(eq. 22)
Vbo +
RboL
RboL ) RboU
22
p Vac


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