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PDF SD6835 Data sheet ( Hoja de datos )

Número de pieza SD6835
Descripción CURRENT MODE PWM+PFM CONTROLLER
Fabricantes SL 
Logotipo SL Logotipo



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Silan
Microelectronics
SD6835_Datasheet
CURRENT MODE PWM+PFM CONTROLLER WITH BUILT-IN HIGH
VOLTAGE MOSFET
DESCRIPTION
SD6835 is current mode PWM+PFM controller used for SMPS with
built-in high-voltage MOSFET and external sense resistor.
It features low standby power and low start current. In standby
mode, the circuit enters burst mode to reduce the standby power
dissipation.
The switch frequency is 25~67KHz decided by the load with jitter
frequency for low EMI.
Built-in peak current compensation circuit makes the limit peak
current stable even with different input AC voltage. Built-in limit
output power compensation circuit to balance the limit output power
under different AC voltage inputs. Built-in slope compensation
circuit to adapt to more transformer applications. Maximum peak
current compensation during power-on reduces pressure on
transformer to avoid saturation, the peak current compensation will
decrease for balance after power-on. Limit output current can be APPLICATIONS
adjusted through the resistor connected to CS.
It integrates various protections such as undervoltage lockout,
SMPS
overvoltage protection, overload protection, leading edge blanking
and thermal shutdown. The circuit will restart until normal if
protection occurs.
FEATURES
Energy Star 2.0 standard
Lower start-up current (4µA)
Various switching frequency following load for the high
efficiency
EMI Frequency jitter for low EMI
Overvoltage, overload and over temperature protections
External peak current sense resistor
* Limit output power compensation
Slope compensation
Undervoltage lockout
Built-in high voltage MOSFET
Auto restart mode
Peak current compensation
Maximum peak current compensation for initialization to
realize the soft start function.
Burst mode
Cycle by cycle current limit
HANGZHOU SILAN MICROELECTRONICS CO.,LTD
Http://www.silan.com.cn
REV: 0.4
2012.10.09
Page 1 of 9

1 page




SD6835 pdf
Silan
Microelectronics
SD6835_Datasheet
FUNCTION DESCRIPTION
SD6835 is designed for off-line SMPS, consisting of high voltage MOSFET, optimized gate driver and
current mode PWM+PFM controller which includes frequency oscillator and various protections such as
undervoltage lockout, overvoltage protection, overload protection, and over temperature protection.
Frequency jitter generated from oscillator is used to lower EMI. Peak current compensation reduces the
pressure on transformer during circuit starts and peak current limit can be adjusted by resistor through CS
pin. Burst mode is adopted during light load to lower standby power dissipation, and function of lead edge
blanking eliminates the MOSFET error shutdown caused by interference through minimizing MOSFET
turning on time. Few peripheral components are needed for higher efficiency and higher reliability and it is
suitable for flyback converter and forward converter.
1. Under Voltage Lockout and Self-Start
At the beginning, the capacitor connected to pin VCC is charged via start resistor by high voltage AC and the
circuit starts to work if voltage at VCC is 16V. The output and FB source current are shutdown if there is any
protection during normal operation and VCC is decreased because of powering of auxiliary winding. The
whole control circuit is shutdown if voltage at VCC is 8.5V below to lower current dissipation and the
capacitor is recharged for restarting.
VCC
VSTART
VSTOP
0
t
ICC
t
0
Powered by
start resistor
Powered by
assistant winding
Powered by start resistor
2. Frequency Jitter and reduced frequency mode
The oscillation frequency is kept changed for low EMI and decreasing radiation on one frequency. The
oscillation frequency changes within a very small range to simplify EMI design. The rule of frequency
changing (frequency center is 67KHz): ±2.5KHz change in 4ms, 63 frequency points in all.
For high efficiency, reduced frequency mode is adopted with two methods:
1. Frequency fis reduced according to current output from FB pin. If IFB is higher than I1, the frequency f
decreases from 67KHz and f is 25KHz when the IFB increases to I2 or higher. This is shown in left diagram
below.
2. IPK is changed according to IFB, shown in right diagram below.
HANGZHOU SILAN MICROELECTRONICS CO.,LTD
Http://www.silan.com.cn
REV: 0.4
2012.10.09
Page 5 of 9

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