MC7773N6 Datasheet, PDF (7/11 Pages) Cystech Electonics Corp. – Current Mode PWM Controller

CYStech Electronics Corp.
Spec. No. : C151N6
Issued Date : 2012.11.08
Revised Date :
Page No. : 7/11
Built-in Slope Compensation and Frequency Shuffling
While MC7773N6 works in CCM mode, slope compensation and frequency shuffling is activated. The
sensed voltage across the sense resistor is used for pwm control, and pulse by pulse current limit, Built-in
slope compensation circuit adds a voltage ramp onto the current sense input voltage. This greatly improves
the close loop stability and prevents the sub-harmonic oscillation of peak current mode pwm control
scheme.
To improve the EMI performance, the frequency of CCM mode is shuffling to 65kHz ± 4%.
Line Slope Compensation
Adjusting the RSENSE can set the Max output power of the power supple mode. The current flowing by the
power MOSFET has an extra value due to the system delay T that the current detected from the sense pin to
power MOSFET cut off in the MC7773N6. To guarantee the output power is a constant for universal input
AC voltage, there is a positive ramp signal to compensate the system delay T and the line input. At lower
line-input voltage the higher OCP threshold will bring constant power OCP as below.
Leading Edge Blanking
Each time when the power MOSFET is switched on, a turn-on spike will inevitably occur on the
sense-resistor. To avoid premature termination of the switching pulse, a 300 nsec leading-edge blanking
time is built in. Conventional RC filtering can therefore be omitted. During this blanking period, the
current-limit comparator is disabled and it cannot switch off the gate driver.
Gate Driver
The output stage of MC7773N6 is a fast totem pole gate driver. Cross conduction has been avoided to
minimize heat dissipation, increases efficiency and enhances reliability. The output driver is clamped by an
internal 18V Zener diode in order to protect power MOSFET transistors against undesirable gate over
voltage. A soft driving waveform is implemented to minimize EMI.
MC7773N6
CYStek Product Specification