Operating Information
Current Limit Protection
Maximum Capacitive Load
When powering loads with significant dynamic current requirements,
the voltage regulation at the load can be improved by addition of
decoupling capacitance at the loadꢀ The most affective technique
is to locate low ESR ceramic capacitors as close to the load as
possible, using several capacitors to lower the effective ESRꢀ
These ceramic capacitors will handle short duration high-frequency
components of dynamic load changesꢀ In addition, higher values of
electrolytic capacitors should be used to handle the mid-frequency
componentsꢀ It is equally important to use good design practise
when configuring the DC distribution systemꢀ
The PKB 4000 Series DC/DC converters include current limiting
circuitry that allows them to withstand continuous overloads or short
circuit conditions on the outputꢀ The output voltage will decrease
towards zero for output currents in excess of max output current
(Iomax)ꢀ
The converter will resume normal operation after removal of the
overloadꢀ The load distribution system should be designed to carry
the maximum output short circuit current specifiedꢀ
Low resistance and low inductance PCB layouts and cabling should
be usedꢀ Remember that when using remote sensing, all resistance,
inductance and capacitance of the distribution system is within the
feedback loop of the converterꢀ This can affect on the converters
compensation and the resulting stability and dynamic response
performanceꢀ As a “rule of thumb”, 100µF/A of output current can
be used without any additional analysisꢀ For example with a 25A
converter, values of decoupling capacitance up to 2500 µF can be
used without regard to stabilityꢀ With larger values of capacitance,
the load transient recovery time can exceed the specified valueꢀ As
much of the capacitance as possible should be outside the remote
sensing loop and close to the loadꢀ The absolute maximum value of
output capacitance is 10 000 µFꢀ For values larger than this, please
contact your local Ericsson Power Modules representativeꢀ
Over Voltage Protection (OVP)
The PKB 4000 Series DC/DC converters have output overvoltage
protectionꢀ In the event of an overvoltage condition, the converter
will shut down immediatelyꢀ The converter will make continuous at-
tempts to start up (non-latching mode) and resume normal operation
automaticallyꢀ
Over Temperature Protection (OTP)
The PKB 4000 Series DC/DC converters are protected from thermal
overload by an internal over temperature shutdown circuitꢀ When
the PCB temperature on the topside between the signal transformer
and output choke (position P1 as defined in Thermal consideration
section) exceeds 120 °C the converter will shut down immediatelyꢀ
The converter will make continuous attempts to start up (non-
latching mode) and resume normal operation automatically when the
temperature has dropped >10 ˚C below the temperature threshold.
Parallel Operation
The PKB 4000 Series DC/DC converters can be paralleled for redun-
dancy if external o-ring diodes are used in series with the outputsꢀ
It is not recommended to parallel the PKB 4000 Series DC/DC
converters for increased power without using external current shar-
ing circuitsꢀ
Input And Output Impedance
The impedance of both the power source and the load will interact
with the impedance of the DC/DC converterꢀ It is most important
to have a low characteristic impedance, both at the input and
output, as the converters have a low energy storage capabilityꢀ
The PKB 4000 Series DC/DC converters have been designed to be
completely stable without the need for external capacitors on the
input or the output circuitsꢀ The performance in some applications
can be enhanced by addition of external capacitance as described
under maximum capacitive loadꢀ If the distribution of the input
voltage source to the converter contains significant inductance, the
addition of a 100 µF capacitor across the input of the converter will
help insure stabilityꢀ This capacitor is not required when powering
the DC/DC converter from a low impedance source with short, low
inductance, input power leadsꢀ
EN/LZT 146 033 R9A ©Ericsson Power Modules, March 2007
39
PKB 4000 Datasheet
ERICSSON [ ERICSSON ]
