SD4870TR Datasheet, PDF (4/8 Pages) Silan Microelectronics Joint-stock – CURRENT MODE PWM CONTROLLER

PIN CONFIGURATION
PIN DESCRIPTIONS
Pin No.
SD4870
SD4870A
SD4870C
1
8
2
7
3
5
4
4
5
2
6
1
3,6
Pin Name
GND
FB
RI
SENSE
VDD
GATE
NC
I/O
Description
-- Ground.
I
Feedback input pin.
Oscillator frequency setting pin.
I/O
A resistor connected between RI and GND.
I
Switch current sense input pin.
-- Power supply pin.
O Gate driver output pin.
-- Not connect
FUNCTION DESCRIPTIONS
SD4870 is a current mode PWM controller used in applications for offline flyback converter. The description of
functions is as follows.
Startup Control
Startup current of SD4870 is very low so that IC could start up quickly. A large value startup resistor can be used
in startup circuit to minimize standby power loss yet provides reliable startup in application.
A 2 MΩ, 1/8 W startup resistor is recommended in normal input range.
Frequency Shuffling Control
Frequency shuffling is used in SD4870 to improve EMI performance.
The oscillation frequency is modulated with a random sourse so that the tone energe is spread out. The spead
spectrum minmizes the conduction band EMI and the system design can be easier.
The entire application system design can become simpler.
HANGZHOU SILAN MICROELECTRONICS CO.,LTD
Http://www.silan.com.cn
REV:1.0 2009.09.22
Page 4 of 8