CRE6354

Current Mode PWM Power Switch

Freq Shuffling

Product Specification

GENERAL DESCRIPTION

CRE6354 combines a dedicated current mode PWM controller with a high voltage power MOSFET. It is optimized for high performance, low standby power, and cost effective off-line flyback converter applications in sub 20W range.

CRE6354 offers complete protection coverage with automatic self-recovery feature including Cycle-by-Cycle current limiting (OCP), over load protection (OLP), VDD over voltage clamp and under voltage lockout (UVLO). Excellent EMI performance is achieved with Power- Source proprietary frequency shuffling technique together with soft switching control at the totem pole gate drive output.

The tone energy at below 20KHZ is minimized in the design and audio noise is eliminated during operation. CRE6354 is offered in SOP-8 & DIP8 package.

FEATURES

■Power on Soft Start Reducing MOSFET Vds Stress■Frequency shuffling for EMI

■Extended Burst Mode Control For Improved Efficiency and Minimum Standby Power Design■Audio Noise Free Operation■Fixed 50KHZ Switching Frequency■Internal Synchronized Slope Compensation

■Low VDD Startup Current and Low Operating Current■Leading Edge Blanking on Current Sense Input■Good Protection Coverage With Auto Self-Recovery

VDD Over Voltage Clamp and Under VoltageLockout with Hysteresis (UVLO)

On-Bright Proprietary Line Input CompensatedCycle-by-Cycle Over-current Threshold SettingFor Constant Output Power Limiting OverUniversal Input Voltage Range.Overload Protection (OLP).Over voltage Protection (OVP)

■Compatible with OB2353/OB2354/CR6224

APPLICATIONS

Offline AC/DC flyback converter for

■Pb-Free SOP-8L & DIP-8L

■Battery Charger ■PDA power supplies ■Digital Cameras and Camcorder Adaptor ■VCR, SVR, STB, DVD&DVCD Player SMPS ■Set-Top Box Power ■Auxiliary Power Supply for PC and Server ■Open-frame SMPS

TYPICAL APPLICATION

CRE6354

CRE Semiconductor Inc.

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CRE6354

Current Mode PWM Power Switch

Freq Shuffling

Product Specification

GENERAL INFORMATION

Pin Configuration

The CRE6354 is offered in SOP8 & DIP8 package as shown below.

Absolute Maximum Ratings

SOP8DIP8

TERMINAL ASSIGNMENTS

OUTPUT POWER TABLE

ProductCRE6354

230VAC±15%Open Frame

12W

85-2VACOpen Frame

8W

SOP8Package

Notes:

1. Maximum practical continuous power in an open frame design with sufficient drain pattern as a heat sink, at 50℃ambient.

CRE Semiconductor Inc.

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CRE6354

Current Mode PWM Power Switch

Freq Shuffling

Product Specification

BLOCK DIAGRAM

CRE Semiconductor Inc.

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CRE6354

Current Mode PWM Power Switch

Freq Shuffling

Product Specification

ELECTRICAL CHARACTERISTICS

(TA = 25C, VDD=VDDG=16V, if not otherwise noted)

Note:

CRE Semiconductor Inc.

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CRE6354

Current Mode PWM Power Switch

Freq Shuffling

Product Specification

CRE Semiconductor Inc.

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CRE6354

Current Mode PWM Power Switch

Freq Shuffling

Product Specification

CHARACTERIZATION PLOTS

(The characteristic graphs are normalized at Ta=25℃)

CRE Semiconductor Inc.

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CRE6354

Current Mode PWM Power Switch

Freq Shuffling

Product Specification

OPERATION DESCRIPTION

The CRE6354 is a low power off-line SMPS Switcher optimized for off-line flyback converter applications in sub 20W power range. The ‘Extended 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 CRE6354 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.

󰀀Operating Current

The Operating current of CRE6354 is low at 2mA.

Good efficiency is achieved with CRE6354 low operating current together with the ‘Extended burst mode’ control features.

󰀀Soft Start

CRE6354 features an internal 4ms 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 of 0.77V. Every restart up is followed by a soft start.Frequency shuffling for EMI improvementThe frequency Shuffling (switching frequency

modulation) is implemented in CRE6354. 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 ransformer 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 atno 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. Otherwise the gate drive remains at off state to minimize the switching loss and reduces the standby power consumption to the greatest extend.The switching frequency control also eliminates theaudio noise at any loading conditions.

Oscillator Operation

The switching frequency of CRE6354 is internally fixed at 50KHZ. 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 CRE6354 current mode PWM control. The switch current is detected by a sense resistor into the sense pin. An internal leading edge blanking circuit chops off the sensed voltage spike at initial internal power MOSFET on state due to snubber diode reverse recovery and surge gate current of internal power MOSFET so that the external RC filtering on sense input is no longer needed. The current limiting comparator is disabled and cannot turn off the internal power MOSFET during the blanking period. The PWM duty cycle is determined by the current sense input voltage and the FB input voltage.

Internal Synchronized Slope Compensation

Built-in slope compensation circuit adds voltage ramp onto the current sense input voltage for PWM generation. This greatly improves the close loop stability at CCM and prevents the sub-harmonic oscillation and thus reduces the output ripple voltage.

Drive

The internal power MOSFET in CRE6354 is driven by a dedicated gate driver for power switch control. Too weak the gate drive strength results in higher conduction and switch loss of MOSFET while too strong gate drive results the compromise of EMI.

CRE Semiconductor Inc.

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CRE6354

Current Mode PWM Power Switch

Freq Shuffling

Product Specification

OPERATION DESCRIPTION

A good tradeoff is achieved through the built-in totem pole gate design with right output strength and dead time control. The low idle loss and good EMI system design is easier to achieve with this dedicated control scheme.

In addition to the gate drive control scheme mentioned, the gate drive strength can also be adjusted externally by a resistor connected between VDD and VDDG, the falling edge of the Drain output can be well controlled. It provides great flexibility for system EMI design.

Protection Controls

Good power supply system reliability is achieved with its rich protection features including Cycle-by-Cycle current limiting (OCP), Over Load Protection (OLP) and over voltage clamp, Under Voltage Lockout on VDD (UVLO).With Power-Source Proprietary technology, the OCP is line voltage compensated to achieve constant output power limit over the universal input voltage range.At overload condition when FB input voltage exceeds power limit threshold value for more than TD_PL, control circuit reacts to shut down the switcher. Switcher restarts when VDD voltage drops below UVLO limit.VDD is supplied by transformer auxiliary winding output. It is clamped when VDD is higher than 30V. The output of CRE6354 is shut down when VDD drops below UVLO_ON limit and Switcher enters power on start-up sequence

CRE Semiconductor Inc.

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CRE6354

Current Mode PWM Power Switch

Freq Shuffling

Product Specification

PACKAGE MECHANICAL DATA

CRE Semiconductor Inc.

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CRE6354

Current Mode PWM Power Switch

Freq Shuffling

Product Specification

PACKAGE MECHANICAL DATA

8-Pin Plastic DIP

CRE Semiconductor Inc.

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