SVRTR2800D Series
6.2.2 Frequency Synchronization (SYNC)
The SVRTR2800D Series will free run at a switching frequency of approximately 525 kHz, which has been set for optimum converter
performance. Frequency synchronization is not necessary unless required by system constraints. The SVRTR2800D Series provides a
frequency synchronization input (SYNC) referenced to INCOM.
The SYNC pin can be driven by an external clock. The internal clock and internal power train will operate at the frequency applied to the
SYNC pin. The SYNC pin should be driven with a TTL type 5 V square wave signal. The duty cycle of the square wave should be
between 20% and 80%. The SYNC pin is internally capacitively-coupled and the internal load is equivalent to 220 pF. Proper layout
and circuit techniques are necessary to prevent noise from being injected into this pin. Synchronized converters should be physically
located close together and share a low impedance INCOM connection. The SYNC pin can be left open or connected to INCOM if not
used.
6.3 PROTECTION FEATURES
6.3.1 Input Undervoltage Lockout
The SVRTR2800D Series provides input undervoltage lockout protection. For input voltages below the turn-on voltage, the converter
will remain off, drawing minimal current from the source. When the input voltage exceeds the turn-on voltage, the converter will start.
The lockout circuit is designed to tolerate slow ramping input voltage waveforms. VPT’s proprietary magnetic feedback technology
provides bias voltage to all secondary control circuits and control amplifiers before the output starts, ensuring a well-controlled start up
sequence.
6.3.2 Output Soft Start
The SVRTR2800D Series utilizes an output soft-start function to ramp the output in a controlled manner, eliminating output voltage
overshoot and limiting inrush current at turn on. A voltage-mode soft-start ensures the output waveform remains consistent regardless
of changes in the load current. The output rise time is approximately 8 ms. The soft-start function is active whether the module is turned
on with an application of input voltage or from release of the inhibit pin. Under normal conditions, current drawn from the source during
turn on will not exceed the full load input current. The turn-on delay time is specified from the application of input voltage (or release of
the inhibit pin) until the output reaches 90% of its final value.
6.3.3 Output Overcurrent Protection
The SVRTR2800D Series provides output overcurrent and output short circuit protection. During a load fault condition, a constant
output current control circuit reduces the converter duty cycle to limit the total output current to approximately 125% its rated value. The
current limit protection circuit limits the sum of output currents in both +Vout and -Vout. It does not distinguish if the current is on the
positive or negative output. The converter will continue to provide constant current into any overload or short circuit condition. This
feature allows the converter to start into any capacitive load. Recovery is automatic and immediate upon removal of the fault condition.
Sustained short circuit or overload operation can cause excessive power dissipation. Care should be taken to control the operating
temperature of the converter in this condition.
6.4 THERMAL CONSIDERATIONS
The SVRTR2800D Series is rated for full power operation at 125 °C. Operation above 125 °C is allowed at reduced power. Specifically,
the output power should be derated linearly from full power at 125 °C to half power at 130 °C and to zero power at 135 °C. The
operating temperature of the converter is specified on the baseplate of the converter. The converter is designed to be conduction-
cooled, with the baseplate mounted to a heat sink, chassis, PCB or other thermal surface. The internal power dissipating components
are mounted to the baseplate of the converter and all heat flow is through the baseplate and mounting flanges. The lid of the converter
does not provide a good thermal path.
The hybrid DC-DC converter contains many semiconductor components. The maximum temperature rise from junction to case is
20 °C at full load.
Sales Information
Phone:(425) 353-3010
Fax: (425) 353-4030
SVRTR2800D - 9.0
Page 9
E-mail: vptsales@vptpower.com
Web: www.vptpower.com
VPT [ VPT, Inc. ]
