CR6224S データシートの表示（PDF） - Unspecified

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CR6224S

Green-Power Current Mode PWM Power Switch

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CR622X

Green-Power Current Mode PWM Power Switch

OPERATION DESCRIPTION

The CR622X is a low power off-line SMPS

Switcher optimized for off-line flyback

converter applications in sub 24W power

range. The burst mode control greatly reduces

the standby power consumption and helps the

design easily to meet the international power

conservation requirements.

Startup Current and Start up Control

Startup current of CR622X is designed to be

very low so that VDD could be charged up

above UVLO threshold level and device starts

up quickly. A large value startup resistor can

therefore be used to minimize the power loss

yet achieve a reliable startup in application.

For AC/DC adaptor with universal input range

design, a 2 MΩ, 1/8 W startup resistor could

be used together with a VDD capacitor to

provide a fast startup and yet low power

dissipation design solution.

Operation current

The Operation current of CR622X is low at 2

mA. Good efficient is achieved with CR622X

low operating current together with the

‘Extended burst mode’ control features.

Soft Start

CR622X features an internal 4 ms soft start to

soften the electrical stress occurring in the

power supply during startup. It is activated

during the power on sequence. As soon as

VDD reaches UVLO(OFF), the peak current is

gradually increased from nearly zero to the

maximum level. Every restart up is followed by

a soft start.

Frequency shuffling for EMI improvement

The frequency shuffling (switching frequency

modulation) is implemented in CR622X. The

oscillation frequency is modulated so that the

tone energy is spread out. The spread

spectrum minimizes the conduction band EMI

and therefore eases the system design.

Extended Burst Mode Operation

At light load or zero load condition, most of the

power dissipation in a switching mode power

supply is from switching loss on the MOSFET,

the core loss of the transformer and the loss

on the snubber circuit. The magnitude of

power loss is in proportion to the switching

frequency. Lower switching frequency leads to

the reduction on the power loss and thus

conserves the energy.

The switching frequency is internally adjusted

at no load or light load condition. The switch

frequency reduces at light/no load condition to

improve the conversion efficiency. At light load

or no load condition, the FB input drops below

burst mode threshold level and device enters

Burst Mode control. The Gate drive output

switches only when VDD voltage drops below

a preset level and FB input is active to output

an on state to minimize the switching loss and

reduce the standby power consumption to the

greatest extend.

The switching frequency control also

eliminates the audio noise at any loading

conditions.

Oscillator Normal Operation

The normal switching frequency of CR622X is

internally fixed at 50 KHz. No external

frequency setting components are required for

PCB design simplification.

Current Sensing and Leading Edge

Blanking

Cycle-by-Cycle current limiting is offered in

CR622X current mode PWM control. The

switch current is detected by sense resistor

into the sense pin. An internal leading edge

blank circuit chops off the sensed voltage

Nov, 2009 V2.2

6/10

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