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IK3401 Datasheet(PDF) 8 Page - IK Semicon Co., Ltd |
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IK3401 Datasheet(HTML) 8 Page - IK Semicon Co., Ltd |
8 / 11 page IK3401 Rev 00 OPERATION DESCRIPTION Start-Up Current The typical start-up current is only 14uA. This allows a high resistance, low-wattage start-up resistor to be used, to minimize power loss. A 1.5MOhm, 0.25W, start-up resistor and a 10uF/25V VDD hold-up capacitor would be sufficient for an AC/DC adapter with a universal input range. Operating Current The required operating current has been reduced to 4mA. This results in higher efficiency and reduces the VDD hold-up capacitance requirement. Green-Mode Operation. The proprietary green-mode function provides off-time modulation to continuously decrease the PWM frequency under light-load conditions. To avoid acoustic-noise problem, the minimum PWM frequency set above 22KHz. This green-mode function dramatically reduces power consumption under light-load and zero- load conditions. Power supplies using a IK3401 Controller can easily meet even the most restrictive international regulations regarding standby power consumption. Oscillator Operation A resistor connected from the RI pin to GND pin generates a constant current source for the IK3401 controller. This current is used to determinate the center PWM frequency. Using a 26KOhm resistor RI results in a corresponding 65KHz PWM frequency. The relationship between RI and switching frequency is: The range of the PWM oscillation frequency Is designed as 47KHz~109KHz. IK3401 also integrates frequency hopping function internally. The frequency variation ranges from around 62KHz to 68KHz for a center frequency 65KHz. The frequency hopping function helps reduce EMI emission of a power supply with minimum line filters. Leading Edge Blanking Each time the power MOSFET is switched on, a turn-on spike will inevitably occur at the sense-resistor. To avoid premature termination of the switching pulse, a leading-edge blanking time is build in. During this blanking period, the current-limit comparator is disabled, and it cannot switch off the gate drive. Under-Voltage Lockout (UVLO) The turn-on/turn-off thresholds are fixed internally at 16.5V/10.5V. To enable a IK3401 controller during start-up, the hold-up capacitor must first be charged to 16.5V through the start-up resistor. The hold-up capacitor will continue to supply VDD before energy can be delivered from the auxiliary winding of the main transformer. VDD must not drop below 1035V during this start-up process. This UVLO hysteresis window ensures that the hold-up capacitor can adequately supply VDD during start-up. Gate Output/Soft Driving The IK3401 BiCMOS output stage is a fast totem pole gate driver. Cross-conduction has been avoided to minimize heat dissipation, increase efficiency, and enhance reliability. The output driver is clamped by an internal 18V Zener diode in order to protect the power MOSFET transistors from any harmful over- voltage gate signals. A soft driving waveform is implemented to minimize EMI. Slope Compensation The sensed voltage across the current sense resistor is used for peak-current-mode control and cycle-by-cycle current limiting. The build-in slope compensation function improves power supply stability and prevents peak- current-mode control from causing sub- harmonic oscillations. Within every switching cycle, the IK3401 controller produces a positively sloped, synchronized ramp signal. |
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