PKS606YSLASHF datasheet(3/24 Pages) FERYSTER

3 / 24 page

PKS603-607

Rev. I 02/07

Figure 4. Frequency Jitter.

PeakSwitch

Functional Description

PeakSwitch

integratesa700VpowerMOSFETswitchwitha

powersupplycontrolleronthesamedie.Unlikeconventional

pulsewidthmodulation(PWM)controllers,PeakSwitchusesa

simpleON/OFFcontroltoregulatetheoutputvoltage.

The controller consists of an oscillator, enable

circuit (sense and logic), current-limit state machine,

5.8 V regulator, BYPASS pin under-voltage circuit, over-

temperature protection, current limit circuit, and leading

edgeblanking.PeakSwitchincorporatesadditionalcircuitry

for adaptive current limit, line under-voltage sense,

programmable smart line sense, auto-restart, adaptive

switching cycle on-time extension, and frequency jitter.

Figure2isafunctionalblockdiagramofthedevice’smost

importantfeatures.

Oscillator

Thetypicaloscillatorfrequencyisinternallysettoanaverage

of277kHz.Twosignalsaregeneratedfromtheoscillator:the

maximumdutycycle(DC

MAX)signalandtheclocksignalthat

indicatesthebeginningofeachcycle.

Theoscillatorincorporatescircuitrythatintroducesasmall

amountoffrequencyjitter,typically16kHzpeak-to-peak,to

minimizeEMIemission.Themodulationrateofthefrequency

jitterissetto1.1kHztooptimizeEMIreductionforboth

averageandquasi-peakemissions.Thefrequencyjittershould

bemeasuredwiththeoscilloscopetriggeredatthefallingedge

oftheDRAINwaveform.ThewaveforminFigure4illustrates

thefrequencyjitter.

Enable Input and Current-Limit State Machine

TheenableinputcircuitattheEN/UVpinconsistsofalow

impedancesourcefolloweroutputsetat1.0V.Thecurrent

throughthesourcefollowerislimitedto240µA.Whenthe

current out of this pin exceeds 240µA, a low logic level

(disable)isgeneratedattheoutputoftheenablecircuit.This

enable circuit output is sampled at the beginning of each

cycleontherisingedgeoftheclocksignal.Ifhigh,thepower

MOSFETisturnedonforthatcycle(enabled).Iflow,thepower

MOSFETremainsoff(disabled).Sincethesamplingisdone

onlyatthebeginningofeachcycle,subsequentchangesinthe

EN/UVpinvoltageorcurrentduringtheremainderofthe

cycleareignored.

Thecurrent-limitstatemachinereducesthecurrentlimitby

discreteamountsatlightloadswhenPeakSwitchislikelyto

switchintheaudiblefrequencyrange.Thelowercurrentlimit

raisestheeffectiveswitchingfrequencyabovetheaudiorange

andreducesthetransformerfluxdensity,includingtheassociated

audible noise. The state machine monitors the sequence of

EN/UVpinvoltagelevelstodeterminetheloadconditionand

adjuststhecurrentlimitlevelaccordinglyindiscreteamounts.

Undermostoperatingconditions(exceptwhenclosetono-load),

thelowimpedanceofthesourcefollowerkeepsthevoltageon

theEN/UVpinfromgoingmuchbelow1.0Vinthedisabled

state.Thisimprovestheresponsetimeoftheoptocouplerthat

isusuallyconnectedtothispin.

5.8 V Regulator and 6.3 V Shunt Voltage Clamp

The5.8Vregulatorchargesthebypasscapacitorconnectedto

theBYPASSpinto5.8Vbydrawingacurrentfromthevoltage

ontheDRAINpinwhenevertheMOSFETisoff.TheBYPASS

pinistheinternalsupplyvoltagenode.WhentheMOSFET

ison,thePeakSwitch operatesfromtheenergystoredinthe

bypasscapacitor.ThevoltageontheDRAINpinpowersthe

bypassduringstart-up.

Thereisa6.3VshuntregulatorclampingtheBYPASSpinat

6.3Vwhencurrentisprovidedthroughanexternalresistor

from the bias winding in normal operation. Powering the

PeakSwitch

deviceinthiswayminimizesno-loadconsumption

toabout150mWat265VAC.Notethatabiaswindingmustbe

usedtopowerthedevice.SeeKeyApplicationConsiderations

sectionfordetails.

BYPASS Pin Under-Voltage

TheBYPASSpinunder-voltagecircuitrydisablesthepower

MOSFETwhentheBYPASSpinvoltagedropsbelow4.8V.

OncetheBYPASSpinvoltagedropsbelow4.8V,itmustrise

backto5.8Vtoenable(turnon)thepowerMOSFET.

Over Temperature Protection

Thethermalshutdowncircuitrysensesthedietemperature.

Thethresholdistypicallysetat142°Cwith75°Chysteresis.

When the die temperature rises above this threshold, the

powerMOSFETisdisabledandremainsdisableduntilthedie

temperaturefallsby75°C,atwhichpointitisre-enabled.Alarge

600

2.5

285 kHz

269 kHz

VDRAIN

Time (

µs)

500

400

300

200

100

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