NCP1910A65DWR2G Datasheet, PDF (22/37 Pages) ON Semiconductor – High Performance Combo Controller for ATX Power

NCP1910
R_MI_CS^ǒV_LBO^{Ǔ 2}
ǒ Ǔ VM +
4 V_CTRL * V_{CTRLǒminǓ}
PFC Duty
Modulation
V_M
I_M
11
R_M ^CM
Figure 45. The Multiplier Voltage Pin Configuration
The multiplier voltage V_M is generated according to
Equation 8.
R_MI_CS^ǒV_LBO^{Ǔ 2}
ǒ Ǔ VM +
4 V_CTRL * V_CTRL(min)
(eq. 8)
Where:
♦ R_M is the external multiplier resistor connected to
V_M pin, which is constant.
♦ V_LBO is the input voltage signal appearing on the
LBO pin, which is proportional to the rms input
voltage,
♦ I_CS is the sense current proportional to the inductor
current I_L as described in Equation 13.
Line Brown−Out Protection
V_in
♦ V_CTRL is the control voltage signal, the output
voltage of Operational Trans−conductance Amplifier
(OTA), as described in Equation 17.
♦ V_CTRL(min) is not only the minimum operating
voltage of V_CTRL but also the offset voltage for the
PFC current modulation.
R_M directly limits the maximum input power capability.
Also, due to the V_in2 feed−forward feature, where the V_LBO
is squared, the transfer function and the power delivery is
independent from the ac line level. The relationship between
V_CTRL and power delivery will be depicted later on.
Ac line
EMI
Filter
C_in
R_LBOU
LBO
LBO comp.
V_LBOT
V_LBOcomp
PFC_BO
R_SENSE
C_LBO
R_LBOL
Vdd
I_LBOH
V_LBO(clamp)
S
LBO ^Q
R
reset
t_LBO(blank)
reset
t_LBO(window)
reset
Figure 46. The Line Brown−Out Configuration
As shown in Figure 46, the Line Brown−Out pin
(represented LBO pin) as receives a portion of the input
voltage (V_in). As V_in is a rectified sinusoid, a capacitor must
integrate the ac line ripple so that a voltage proportional to
the average value of V_in is applied to the brown−out pin.
The main function of the LBO block is to detect too low
input voltage conditions. A 7 mA current source lowers the
LBO pin voltage when a brown−out condition is detected.
This is for hysteresis purpose as required by this function.
In nominal operation, the voltage applied to LBO pin must
be above the internal reference voltage, V_LBOT (1 V
typically). In this case, the output of the LBO comparator
V_LBOcomp is low.
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