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PDF US3706 Datasheet ( Hoja de datos )

Número de pieza US3706
Descripción CURRENT MODE PWM POWER SWITCH
Fabricantes Unisonic Technologies 
Logotipo Unisonic Technologies Logotipo

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US3706 Hoja de datos, Descripción, Manual
UNISONIC TECHNOLOGIES CO., LTD
US3706
Preliminary
CURRENT MODE PWM POWER
SWITCH
CMOS IC
DESCRIPTION
The UTC US3706 combines a dedicated current mode PWM
controller with a high voltage power MOSFET. Low VDD startup
current make the power reliable on startup design and a large
value resistor could be used in the startup circuit to minimize the
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 US3706 offers complete protection coverage with
automatic self-recovery feature including Cycle-by-Cycle current
limiting (OCP), over load protection (OLP), over temperature
protection (OTP), over voltage protection and VDD under
voltage lockout (UVLO).
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 US3706 has such applications as: battery charger, power
adaptor, set-top box power supplies, ink jet printers, open-frame
SMPS.
1
FEATURES
* UTC proprietary frequency hopping technology for
* OLP,OVPand OTP for higher security
Improved EMI performance.
* Fixed switch frequency 65kHz
* Power-saving mode for high light-load and standby
* Low start-up current
efficiency
* Cycle-by-cycle Current Limiting
* Soft Start
* Under voltage lockout (UVLO)
* Dynamic peak current limiting for constant output power * Leading edge blanking on source input
* Built-in synchronized slope compensation
* Few external components required
TO-220F-6
ORDERING INFORMATION
Ordering Number
Lead Free
Halogen Free
US3706L-TF6-T
US3706G-TF6-T
Package
TO-220F-6
Packing
Tube
www.unisonic.com.tw
Copyright © 2015 Unisonic Technologies Co., Ltd
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US3706 pdf
US3706
Preliminary
CMOS IC
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 power MOSFET.
Under Voltage Lockout (UVLO)
The turn-on and turn-off thresholds of the US3706 are fixed internally at VDD(ON)/VDD(MIN) During start-up, the
hold-up capacitor must be charged to VDD(ON) through the start-up resistor, so that the US3706 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.
UNISONIC TECHNOLOGIES CO., LTD
www.unisonic.com.tw
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