IK3466 Просмотр технического описания (PDF) - IK Semicon Co., Ltd
Номер в каталоге
Компоненты Описание
производитель
IK3466
IK Semicon Co., Ltd
IK3466 Datasheet PDF : 10 Pages
| |||
IK3466
Operation Description
Unlike conventional PWM (Pulse width modulator) controllers, IK3466 uses a simple ON/OFF
control to regulate the output voltage. Figure 1 shows the electric block diagram.
The IK3466 consists of
132kHz oscillator ,
Enable circuit (sense and logic),
Voltage regulator 5.8 V
Under-voltage circuit
Leading edge circuit
Current limit circuit
Temperature protection circuit
Auto-restart counter
The oscillator frequency is internally set to 132 kHz. Two signals are generated from the
oscillator: the maximum duty cycle signal (DCMAX) and the Clock signal that indicates the start of
each cycle.
The oscillator contain built-in circuitry that introduces a small amount of frequency jitter, typically 8
kHz peak-to-peak, to minimize EMI emission. The modulation rate of the frequency jitter is set to
1 kHz to optimize EMI reduction for both average and quasi-peak emissions. The frequency jitter
should be measured with the oscilloscope synchronized at the falling edge of the waveform.
The enable input circuit at the EN/UV pin consists of a low impedance source follower
output set at 1.0 V. Under most operating conditions (except when close to noload), the low
impedance of the source follower keeps the voltage on the EN/UV pin from going much below 1.0
V in the disabled state. This improves the response time of the optocoupler
that is usually connected to this pin.
The 5.8 V regulator charges the bypass capacitor connected to the BYPASS pin to 5.8 V
by drawing a current from the voltage on the DRAIN pin, whenever the MOSFET is off. The
BYPASS pin is the internal supply voltage node for the IK3466. When the transistor VT5 is on, the
IK3466operates from the energy stored in the bypass capacitor. Extremely low power consumption
of the internal circuitry allows to operate continuously from current it takes from the DRAIN pin. A
bypass capacitor value of 0.1 F is sufficient for both high frequency decoupling and energy
storage.
In addition, there is a 6.3 V shunt regulator clamping the BYPASS pin at 6.3 V when
current is provided to the BYPASS pin through an external resistor.
The BYPASS pin under-voltage sensing circuit disables the transistor VT5 when the
BYPASS pin voltage drops below 4.8 V. Once the BYPASS pin voltage drops below 4.8 V, it must
rise back to 5.8 V to enable (turn-on) the transistor VT5.
The over temperature protection circuit disables the output power transistor VT5. To
prevent cyclic fault action the over temperature protection circuit has temperature hysteresis about
70oC. A large temperature hysteresis (~70oC) guarantees prevention of overheating of the PCB
under continuous fault condition.
The current limit circuit senses the current in the transistor VT5. When this current exceeds
the internal threshold (ILIMIT), the e transistor VT5 is turned off to the end of that cycle.
The current limit circuit reduces the current limit threshold under medium and light loads.
The leading edge blanking circuit inhibits the current limit comparator for a short time
(tLEB) after the transistor VT5 is
turned on. This leading edge blanking time has been set so that current spikes caused by
capacitance and secondary-side rectifier reverse recovery time will not cause untimely termination
of the switching pulse.
In the event of a fault condition such as output overload, output short circuit, or an open
loop condition, the IK3466enters into auto-restart mode.
If the EN/UV pin is not pulled low for 50 ms, the transistor VT5 switching is normally
disabled for 850 ms (except in the case of line under-voltage condition in which case it is disabled
until the condition is removed). The auto-restart alternately enables and disables the switching of
the transistor VT5 until the fault condition is removed.
2012, April Ver. 00
Share Link: