Design and Applications Information
Current Sensing and Over Current Protection
Figure 22: Output Voltage Resistor Divider
VOUT
RS1
FB
88EM8010/
8011
RS2
5.3
Current Sensing and Over Current Protection
5.3.1
Current Sensing through ISNS Pin
The voltage drop on the current sense resistor should be kept very small in order to reduce the
power consumption on the sense resistor (Rsen). The voltage drop (Vsen) across resistor (Rsen
represents the Boost current signal. As shown in Figure 23. Vsen is feedback to the ISNS pin
through a resistor RCS, which is around 200Ω. This resistor is necessary for the protection of the
ISNS pin during inrush and lightning surge condition.
)
The resistor (Rsen) should be designed and calculated such as the example in Table 6 where Rsen is
designed for a 64W Boost converter. The specification are: output power = 64W, input voltage range
= 85-264V, output voltage = 450V, 30% margin of over current on top of the normal current.
Figure 23: Current Sensing Circuit
L
DR2
iL
Load
Q1
CO2
Rsen
Vsen
Rcs
Using Kelvin sensing connection for
current sensing signal and SGND
with separate trace from PGND
SW
ISNS
SGND
VIN
VDD
88EM8010/
8011
PGND
FB
Copyright © 2009 Marvell
September 30, 2009, 2.00
Doc. No. MV-S104861-01 Rev. –
Page 31
Document Classification: Proprietary
MARVELL [ MARVELL TECHNOLOGY GROUP LTD. ]
