Technical
Specification
IQ18-HPC Family
BASICꢀOPERATIONꢀANDꢀFEATURES
CONTROLꢀFEATURES
This converter series uses a two-stage power conversion
topology. The first stage is a buck-converter that keeps the
output voltage constant over variations in line, load, and
temperature. The second stage uses a transformer to provide
theꢀ functionsꢀ ofꢀ input/outputꢀ isolationꢀ andꢀ voltageꢀ step-upꢀ orꢀ
step-down to achieve the output voltage required.
RꢂMOꢁꢂ Oꢀ/OFF (Pin 2):ꢀTheꢀON/OFFꢀinput,ꢀPinꢀ2,ꢀpermitsꢀ
the user to control when the converter is on or off. This input
isꢀ referencedꢀ toꢀ theꢀ returnꢀ terminalꢀ ofꢀ theꢀ inputꢀ bus,ꢀ Vin(-).ꢀ
TheꢀON/OFFꢀsignalꢀisꢀactiveꢀlowꢀ(meaningꢀthatꢀaꢀlowꢀturnsꢀtheꢀ
converterꢀon).ꢀFigureꢀAꢀdetailsꢀfourꢀpossibleꢀcircuitsꢀforꢀdrivingꢀ
theꢀON/OFFꢀpin.ꢀFigureꢀBꢀisꢀaꢀdetailedꢀlookꢀofꢀtheꢀinternalꢀON/
OFFꢀcircuitry.
Both the first stage and the second stage switch at a fixed
frequencyꢀ forꢀ predictableꢀ EMIꢀ performance.ꢀ Rectificationꢀ ofꢀ
the transformer’s output is accomplished with synchronous
rectifiers.ꢀ Theseꢀ devices,ꢀ whichꢀ areꢀ MOSFETsꢀ withꢀ aꢀ veryꢀ lowꢀ
on-stateꢀ resistance,ꢀ dissipateꢀ farꢀ lessꢀ energyꢀ thanꢀ Schottkyꢀ
diodes. This is the primary reason that the converter has such
high efficiency, even at very low output voltages and very high
output currents.
RꢂMOꢁꢂ ꢃꢂꢀꢃꢂ(+) (Pins 7 and 5):ꢀ Theꢀ SENSE(+)ꢀ inputsꢀ
correct for voltage drops along the conductors that connect the
converter’s output pins to the load.
Pinꢀ 7ꢀ shouldꢀ beꢀ connectedꢀ toꢀ Vout(+)ꢀ andꢀ Pinꢀ 5ꢀ shouldꢀ beꢀ
connectedꢀtoꢀVout(-)ꢀatꢀtheꢀpointꢀonꢀtheꢀboardꢀwhereꢀregulationꢀ
isꢀ desired.ꢀ Aꢀ remoteꢀ connectionꢀ atꢀ theꢀ loadꢀ canꢀ adjustꢀ forꢀ aꢀ
voltage drop only as large as that specified in this datasheet,
that is
These converters are offered totally encased to withstand harsh
environmentsꢀandꢀthermallyꢀdemandingꢀapplications.ꢀDissipationꢀ
throughout the converter is so low that it does not require a
heatsinkꢀ forꢀ operationꢀ inꢀ manyꢀ applications;ꢀ however,ꢀ addingꢀ
a heatsink provides improved thermal derating performance in
extreme situations.
[Vout(+)ꢀ-ꢀVout(-)]ꢀ–ꢀ[Vsense(+)ꢀ-ꢀVsense(-)] <
SenseꢀRangeꢀ%ꢀxꢀVout
Pinsꢀ 7ꢀ andꢀ 5ꢀ mustꢀ beꢀ connectedꢀ forꢀ properꢀ regulationꢀ ofꢀ
the output voltage. If these connections are not made, the
converter will deliver an output voltage that is slightly higher
than its specified value.
This series of converters use the industry standard footprint and
pin-out configuration.
Note:ꢀ theꢀ outputꢀ over-voltageꢀ protectionꢀ circuitꢀ sensesꢀ theꢀ
voltageꢀ acrossꢀ theꢀ outputꢀ (pinsꢀ 8ꢀ andꢀ 4)ꢀ toꢀ determineꢀ whenꢀ
it should trigger, not the voltage across the converter’s sense
leadsꢀ(pinsꢀ7ꢀandꢀ5).ꢀꢀTherefore,ꢀtheꢀresistiveꢀdropꢀonꢀtheꢀboardꢀ
shouldꢀ beꢀ smallꢀ enoughꢀ soꢀ thatꢀ outputꢀ OVPꢀ doesꢀ notꢀ trigger,ꢀ
even during load transients.
ON/OFF
ON/OFF
5V
_
_
Vin( )
Vin( )
NegativeꢀLogic
(PermanentlyꢀEnabled)
RemoteꢀEnableꢀCircuit
50k
5V
ON/OFF
ON/OFF
50k
TTL
TTL/
CMOS
ON/OFF
100pF
_
Vin( )
_
_
Vin( )
Vin( )
OpenꢀCollectorꢀEnableꢀCircuit
DirectꢀLogicꢀDrive
Figure A: Various circuits for driving the ON/OFF pin.
Figure B: Internal ON/OFF pin circuitry
Product # IQ18xxxHPCxx
Phone 1-888-567-9596
www.synqor.com
Doc.# 005-005029 Rev. B
04/13/09
Page 24
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