Datasheet
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R
TR
IM(up)
+
R
O
V
R
ǒ
V
O
* V
SET
Ǔ
* R
P
(kW)
(1)
R
TR
IM(dwn)
+
R
O
ǒ
V
O
* V
R
Ǔ
ǒ
V
SET
* V
O
Ǔ
* R
P
(kW)
(2)
V
O
+
V
O
+
V
O
−
4
5
6
TRIM
4
5
6
TRIM
R
TR
IM
R
TRIM
C
O
C
O
V
O
+
V
O
−
V
O
−
V
O
+
V
O
−
(a) TRIM DOWN
(b) TRIM UP
ThermalConsiderations
On/OffEnableControls
PTMA403033
PTMA402050
PTMA401120
SLTS259B–FEBRUARY2006–REVISEDMAY2007
Forotheroutputvoltages,thevalueoftherequiredtrimresistormaybecalculatedusingEquation1toadjust
thevoltageuporEquation2toadjustthevoltagedown.
Table2givestherequiredR
TRIM
equationconstantsfortheconvertermodelselected.Tocalculatetherequired
valueofR
TRIM
,simplylocatetheapplicableconstantsandsubstitutetheseintotheformulaalongwiththe
desiredoutputvoltage.
Table2.TrimAdjustEquationConstants
ConstantsPTMA403033PTMA402050PTMA401120
V
R
(V)1.242.502.50
R
O
(Ω)205.1110
R
P
(Ω)1.02.055.11
V
SET
(V)3.35.012.0
V
O
(V)DesiredOutputVoltageDesiredOutputVoltageDesiredOutputVoltage
Figure14.OutputVoltageAdjustment
Airflowmaybenecessarytoensurethatthemodulecansupplythedesiredloadcurrentinenvironmentswith
elevatedambienttemperatures.Therequiredairflowrateisdeterminedfromthesafeoperatingarea(SOA).The
SOAistheareabeneaththeapplicableairflowratecurveonthegraphoftemperaturederatingvsoutput
current.(SeetheTypicalCharacteristics.)OperatingtheconverterwithintheSOAlimitsensuresthatallthe
internalcomponentsareatorbelowtheirstatedmaximumoperatingtemperatures.
On/Offenableoptionsincludepositivelogicornegativelogic.Apositivelogicdeviceenablesthemodule's
outputwhenalogichighvoltageispresentontheEnablepin(pin3)anddisablestheoutputwithalogiclow
voltage.AnegativelogicdevicedisablestheoutputwhenalogichighvoltageispresentontheEnablepinand
enablestheoutputduringalogiclowvoltage.SeetheElectricalCharacteristicstableforlogichighandlogiclow
limits.TheEnablepinisideallycontrolledwithanopen-collector(oropen-drain)discretetransistor.See
Figure15belowforatypicalOn/OffEnablecontrolcircuit.Forautomaticstart-up,theEnablepinshouldbeleft
openforapositivelogicmoduleandshouldbeshortedtoV
I
–(pin 2)foranegativelogicmodule.Bothinputsare
electricallyreferencedtoV
I
–ontheprimary(input)sideoftheconverter.Donotplaceanexternalpull-up
resistoronthisinputpin.
12
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