34 EN/LZT 146 051 R7A © Ericsson Power Modules, February 2007
PKM 4000E PI Datasheet
Operating Information
Over Temperature Protection (OTP)
The PKM 4000E Series DC/DC converters are protected
from thermal overload by an internal over temperature
shutdown circuit. When the PCB temperature adjacent to
the PWM control circuit exceeds 120 ºC the converter will
shut down immediately. The converter will make continuos
attempts to start up (non-latching mode) and resume normal
operation automatically when the temperature has dropped
>10ºC below the temperature threshold.
Input And Output Impedance
The impedance of both the power source and the load will
interact with the impedance of the DC/DC converter. It is
most important to have a ratio between L and C as low as
possible, i.e. a low characteristic impedance, both at the in-
put and output, as the converters have a low energy storage
capability. The PKM 4000E Series DC/DC converters have
been designed to be completely stable without the need
for external capacitors on the input or the output circuits.
The performance in some applications can be enhanced by
addition of external capacitance as described under maxi-
mum capacitive load. If the distribution of the input voltage
source to the converter contains significant inductance, the
addition of a 100µF capacitor across the input of the con-
verter will help insure stability. This capacitor is not required
when powering the DC/DC converter from a low impedance
source with short, low inductance, input power leads.
Parallel Operation
The PKM 4000E Series DC/DC converters can be paralleled
for redundancy if external o-ring diodes are used in series
with the outputs. It is not recommended to parallel the PKM
4000E Series DC/DC converters for increased power without
using external current sharing circuits.
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 load.
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 ESR. These ceramic ca-
pacitors will handle short duration high-frequency compo-
nents of dynamic load changes. In addition, higher values of
electrolytic capacitors should be used to handle the mid-fre-
quency components. It is equally important to use good de-
sign practise when configuring the DC distribution system.
Low resistance and low inductance PCB (printed circuit
board) layouts and cabling should be used. Remember that
when using remote sensing, all resistance, inductance and
capacitance of the distribution system is within the feed-
back loop of the converter. This can affect on the convert-
ers compensation and the resulting stability and dynamic
response performance. As a “rule of thumb”, 100µF/A of
output current can be used without any additional analysis.
For example with a 25A converter, values of decoupling
capacitance up to 2500 µF can be used without regard to
stability. With larger values of capacitance, the load transient
recovery time can exceed the specified value. As much of
the capacitance as possible should be outside the remote
sensing loop and close to the load. The absolute maximum
value of output capacitance is 10 000 µF. For values larger
than this, please contact your local Ericsson Power Modules
representative.
Current Limit Protection
The PKM 4000E Series DC/DC converters include current
limiting circuitry that allows them to withstand continuous
overloads or short circuit conditions on the output. The out-
put 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 overload. The load distribution system should be
designed to carry the maximum output short circuit current
specified.
Over Voltage Protection (OVP)
The PKM 4000E Series DC/DC converters have output over-
voltage protection. In the event of an overvoltage condition,
the converter will shut down immediately. The converter will
make continuous attempts to start up (non-latching mode)
and resume normal operation automatically.