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PDF US4651S Datasheet ( Hoja de datos )

Número de pieza US4651S
Descripción LOW COST POWER-SAVING MODE POWER-SWITCH
Fabricantes Unisonic Technologies 
Logotipo Unisonic Technologies Logotipo

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US4651S Hoja de datos, Descripción, Manual
UNISONIC TECHNOLOGIES CO., LTD
US4651S
LINEAR INTEGRATED CIRCUIT
LOW COST POWER-SAVING
MODE POWER-SWITCH FOR
FLYBACK CONVERTERS
DESCRIPTION
The UTC US4651S is a high performance current mode
power-switch ideally suited for low standby power. Drain start up
make the power reliable on startup design and lower standby
power. At no load condition, the IC operates in power-saving mode
for lower standby power, decreasing frequency for Higher
conversion efficiency at light load condition.
The UTC US4651S contains protection with automatic recovery
including OLP (over load protection), OTP (over temperature
protection), OVP (over voltage protection), UVLO (VDD over voltage
SOP-8
clamp and under voltage lockout).To protect the power MOSFET, Gate-drive output is fixed up to 16V max. The UTC
US4651S contains protection OCP (cycle-by-cycle current limiting).
The internal slope compensation improves system stability at high PWM duty cycle output. Leading-edge
blanking on current sense input removes the signal glitch, which offering minimal external component count in the
design. Excellent EMI performance is achieved with UTC proprietary frequency hopping technique
(ZL201020615247.1) together with soft driver control. Audio noise is eliminated due to switch frequency more than
20kHz during operation.
The UTC US4651S has such applications as: battery charger, power adaptor, set-top box power supplies, ink jet
printers, open-frame SMPS.
FEATURES
* UTC proprietary frequency hopping technology for Improved EMI
performance.
* Power-saving mode for high light-load and standby efficiency
* Soft Start
* Dynamic peak current limiting for constant output power
* Built-in synchronized slope compensation
* OLP,OVP,OTP and VDD clamp for higher security
* Drain start up for lower standby power
* Fixed switch frequency 65kHz
* Gate output voltage clamped at 15V
* Low start-up current
* Cycle-by-cycle Current Limiting
* Under voltage lockout (UVLO)
* Few external components required
ORDERING INFORMATION
Ordering Number
US4651SG-S08-R
Package
SOP-8
Packing
Tape Reel
US4651SG-S08-R
(1)Packing Type
(2)Package Type
(3)Green Package
(1) R: Tape Reel
(2) S08: SOP-8
(3) G: Halogen Free and Lead Free
www.unisonic.com.tw
Copyright © 2015 Unisonic Technologies Co., Ltd
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US4651S pdf
US4651S
LINEAR INTEGRATED CIRCUIT
OPERATION DESCRIPTION (Cont.)
Frequency Hopping For EMI Improvement
The Frequency hopping is implemented in the IC; there are two oscillators built-in the IC. The first oscillator is to
set the normal switching frequency; the switching frequency is modulated with a period signal generated by the 2nd
oscillator. The relation between the first oscillator and the 2nd oscillator as followed Fig.2. So the tone energy is
evenly spread out, the spread spectrum minimizes the conduction band EMI and therefore eases the system design
in meeting stringent EMI requirement.
Fig.2 Frequency Hopping
Built-in Slope Compensation
Built-in slope compensation circuit greatly improves the close loop stability at CCM and prevents the
sub-harmonic oscillation.
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 400ns 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.
Constant Output Power Limit
When the CS voltage, across the CS resistor RS, reaches the threshold voltage, around 0.8V, the output GATE
drive will be turned off after a small propagation delay tD. This propagation delay will introduce an additional current
proportional to tD×VIN/Lp. Since the propagation delay is nearly constant regardless of the input line voltage VIN.
Higher input line voltage will result in a larger additional current and hence the output power limit is also higher than
that under low input line voltage. To compensate this variation for wide AC input range, the threshold voltage is
adjusted by the VIN current. Since VIN pin is connected to the rectified input line voltage through a resistor RVIN, a
higher line voltage will generate higher VIN current into the VIN pin. The threshold voltage is decreased if the VIN
current is increased. Smaller threshold voltage, forces the output GATE drive to terminate earlier, thus reduce the
total PWM turn-on time and make the output power equal to that of low line input. This proprietary internal
compensation ensures a constant output power limit for wide AC input voltage from 90VAC to 264VAC.
Under Voltage Lockout (UVLO)
The turn-on and turn-off thresholds of the UTC US4651S are fixed internally at VTHD(ON)/VDD(MIN) During start-up,
the hold-up capacitor must be charged to VTHD(ON) through the start-up resistor, so that the UTC US4651S will be
enabled. The hold-up capacitor will continue to supply VDD until power can be delivered from the auxiliary winding of
the main transformer. VDD must not drop below VDD(MIN) during this start-up process. This UVLO hysteresis window
ensures that hold-up capacitor will be adequate to supply VDD during start-up.
Gate Output
The UTC US4651S output stage is a fast totem pole gate driver. Cross conduction has been avoided to minimize
heat dissipation, increase efficiency, and enhance reliability. A good tradeoff is achieved through dead time control.
The low idle loss and good EMI system design is easier to achieve with this dedicated control scheme. An internal
15V clamp is added for MOSFET gate protection at higher than expected VDD input.
UNISONIC TECHNOLOGIES CO., LTD
www.unisonic.com.tw
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