TOP242-249
also used to generate a temperature-compensated current
reference which is trimmed to accurately set the switching
frequency, MOSFET gate drive current, current limit, and the
lineOV/UVthresholds. TOPSwitch-GXhasimprovedcircuitry
to maintain all of the above critical parameters within very tight
absolute and temperature tolerances.
High-Voltage Bias Current Source
ThiscurrentsourcebiasesTOPSwitch-GXfromtheDRAINpin
and charges the CONTROL pin external capacitance during
start-up or hysteretic operation. Hysteretic operation occurs
duringauto-restart,remoteoffandover-temperatureshutdown.
In this mode of operation, the current source is switched on and
off with an effective duty cycle of approximately 35%. This
duty cycle is determined by the ratio of CONTROL pin charge
(IC) and discharge currents (ICD1 and ICD2). This current source
isturnedoffduringnormaloperationwhentheoutputMOSFET
is switching. The effect of the current source switching will be
seen on the DRAIN voltage waveform as small disturbances
and is normal.
E
7/01
August 8, 2000
10
POWERINT [ Power Integrations ]
