IK3401
OPERATION DESCRIPTION
Start-Up Current
Leading Edge Blanking
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.
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.
Operating Current
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 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
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.
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.
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.
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:
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.
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.
Rev 00
IKSEMICON [ IK SEMICON CO., LTD ]
