88EM8010/88EM8011
Datasheet
Figure 21: Input Voltage Resistor Divider Layout Guidelines
Ra
SW
ISNS
VIN
PGND
SGND
88EM8010/
8011
Rb
Rc Cc
VDD
FB
Keep layout of Rb, Rc and Cc as
close as possible to Vin pin to
have high noise immunity
5.2
Voltage Loop & Output Voltage Feedback on FB Pin
The 88EM8010/88EM8011 IC integrates the voltage loop into digital DSP core. This internal voltage
loop has the lower corner frequency for the PFC requirement. The FB pin is the internal voltage loop
feedback signal input. The voltage reference of the IC is 2.5V for the rated output voltage.
It is well known that the front-end PFC with Boost topology has to maintain low enough bandwidth
(less than 20Hz) in order to achieve a good sinusoidal current waveform and power factor under a
wide input voltage and load condition. In order to achieve a good sinusoidal current waveform and
power factor, the voltage loop regulation coefficient should also be designed properly corresponding
to the different input voltages. The adaptive voltage loop coefficient is designed inside the IC to
select different voltage regulation parameters corresponding to the different input voltage. This
achieves a much better power factor and sinusoidal current waveform compared to any of PFC
power system on the market now.
The design of RS1and RS2, as shown in Figure 22, is based on the rated output voltage and the
power loss of the resistor divider. In order to keep low power consumption on the resistor divider and
good signal to noise immunity, a total resistance of several MΩ is recommended for the pair of
resistors RS1 and RS2. Because there is a 200kΩ resistor inside of the IC between the FB pin to the
SGND, the value of RS1 and RS2 is designed based on Equation (6) as:
Vref Vref
-------- --------
V
out – Vref
-------------------------
+
=
Equation (6)
Rs2 R0
Rs1
Where Vref is 2.5V and R0 is 200kΩ.
Doc. No. MV-S104861-01 Rev. –
Page 30
Copyright © 2009 Marvell
September 30, 2009, 2.00
Document Classification: Proprietary
MARVELL [ MARVELL TECHNOLOGY GROUP LTD. ]
