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| UPSR104G-AG6-R Datasheet, PDF (5/8 Pages) Unisonic Technologies – CMOS IC | |||
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UPSR104
Preliminary
ï® OPERATION DESCRIPTION (Cont.)
Adjustable Output Power By Changing Rcs
Vout
Large
Rcs
Small
Rcs
CMOS IC
Iout
Secondary Current Waveform
Is
Ipks
Iout
Tdemag
t
Tsw
In CC operation, the CC loop control function of UTC UPSR104 will keep a fixed proportion between secondary
inductance de-magnetization time (Tdemag) and switching cycle time (Tsw). The fixed proportion is
Tdemag
Tsw
=
1
2
(2)
Thus the output current is given by:
Iout
=
1
2
Ã
NP
NS
ÃIpk Ã
Tdemag
Tsw
=
1
4
Ã
NP
NS
ÃIpk
(3)
Programmable Cable Drop Compensation
UTC UPSR104 has a built-in cable voltage drop compensation to achieve good load regulation. An offset voltage
is generated at INV pin by an internal current flowing into the resistor divider. The current is inversely proportional to
the voltage of COMP pin. As a result, it is inversely proportional to the output load current. The voltage drop across
the cable is compensated by this offset voltage at INV pin. It can also be programmed by adjusting the resistance of
the divider to compensate the drop for various cable lines used.
Current Sensing and Leading Edge Blanking
Cycle-by-cycle current limiting is offered in UTC UPSR104. The switch current is detected by a sense resistor into
the CS pin. When the power switch is turned on, a turn-on spike will occur on this resistor. A 600ns leading-edge
blanking is built in to avoid false-termination of the switching pulse so that the external RC filtering is no longer
needed.
UNISONIC TECHNOLOGIES CO., LTD
www.unisonic.com.tw
5 of 8
QW-R103-113.a
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