參數(shù)資料
型號: 88EM8081XX-SAG2C000-T
廠商: MARVELL SEMICONDUCTOR INC
元件分類: 穩(wěn)壓器
英文描述: 2 A POWER FACTOR CONTROLLER, 120 kHz SWITCHING FREQ-MAX, PDSO8
封裝: GREEN, SOIC-8
文件頁數(shù): 27/64頁
文件大?。?/td> 667K
代理商: 88EM8081XX-SAG2C000-T
Design and Applications Information
Input Voltage Resistor Divider on VIN Pin
Copyright 2010 Marvell
Doc. No. MV-S106340-01 Rev. B
August 6, 2010, Preliminary Information
Document Classification: Proprietary
Page 33
The values for the sensing resistors Ra, Rb, and Rc in Figure 16 are selected to get proper sinusoidal
AC voltage, under voltage lockout, and peak voltage detection. If the values are too small there will
be higher power loss and if they are too big there might be pickup noise on the VIN signal. The
recommended values are shown in the following equation:
Equation (1)
Where Ra + Rb is recommended to be 1.8M and Rc is selected as 18k. Knowing (Ra + Rb), Ra
and Rb can be designed.
For this input voltage resistor divider, the appropriate combination based on the voltage / power
rating of the resistors should also be considered.
Figure 17: Peak Detecting Signal for Predictive Sinusoidal AC Voltage
As can be seen in Figure 16, the internal peak detecting circuit generates peak detecting pulse
through the inside comparator which has a threshold voltage of 0.72V and external AC sensing
resistors of Ra, Rb and Rc. This pulse is processed in the DSP core to calculate the mid-point (peak
point) and the zero-crossing point of the sinusoidal waveform. The phase angle of
φ is calculated
using the widths (M and N) of the high and low signals.
Equation (2)
Equation (3)
Equation (4)
Peak value of the sinusoidal waveform is calculated by the following equation:
Equation (5)
5.2.1
Brown-out Protection
The signal that appears on the VIN pin is a half sinusoidal voltage waveform and its peak value has
to be higher than 0.72V for normal operation. Whenever the VIN voltage is less than 0.72V at the
peak value, it is considered as a Brown-out condition. During the brown-out condition, the IC
generates a low duty cycle of 6% to protect the system. For the design shown in equation (1) the
brown-out protection occurs at the AC input of 50V RMS (72V peak, VIN=0.72V). To adjust the
brown-out protection point, the resistance value of Ra, Rb and Rc can be changed.
R
a
R
b
+
R
c
------------------
100
1
---------
1.8M
Ω
18k
Ω
-----------------
==
V (
φ) = V
line_pk x sin φ
Half line cycle
N
MN
φ
Vline_pk
Half line cycle
Peak detecting Pulse
Vline_pk
VVIN_BR = 0.72V (Typ.)
φφ
φ
N
π 2
φ
()
=
M
π 2
φ
+
()
=
φ
MN
() 4
=
V
line_pk
V
φ
()
φ
sin
()
=
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