Paralleling for Redundancy
The figure below shows how n + 1 redundancy can be achieved. The
diodes on the power module outputs allow a failed module to remove
itself from the shared group without pulling down the common output
bus. This configuration can be extended to additional numbers of
power modules and they can also be controlled individually or in
groups by means of signals to the primary RC inputs.
Output Ripple & Noise (VOac)
Output ripple is measured as the peak to peak voltage from 0 to
20MHz which includes the noise voltage and fundamental ripple.
Over Temperature Protection
The PKM 4000 DC/DC power modules are protected from thermal
overload by an internal over temperature shutdown circuit. When the
case temperature exceeds +110°C (+10, -5°C), the power module will
automatically shut down (latching). To restart the module the input
voltage must be cycled.
Input and Output Impedance
The impedance of both the power source and the load will interact
with the impedence of the DC/DC power module. It is most important
to have the ratio between L and C as low as possible, i.e. a low
characteristic impedance, both at the input and output, as the power
modules have a low energy storage capability. The PKM 4000 series of
DC/DC power modules has been designed to be completely stable
without the need for external capacitors on the input or output when
configured with low inductance input and output circuits. The
performance in some applications can be enhanced by the addition of
external capacitance as described below. If the distribution of the input
voltage source to the power module contains significant inductance,
the addition of a 220-470 µF capacitor across the input of the power
module will help insure stability. This capacitor is not required when
powering the module from a low impedance source with short, low
inductance, input power leads.
Output Capacitance
When powering loads with significant dynamic current requirements,
the voltage regulation at the load can be improved by the addition of
decoupling capacitance at the load. The most effective 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 capacitors
will handle the short duration high frequency components of the
dynamic current requirement. In addition, higher values of electrolytic
capacitors should be used to handle the mid-frequency components. It
is equally important to use good design practices when configuring the
DC distribution system.
27
Data Sheet AE/LZT 108 4913 R2 © Ericsson Inc., Microelectronics, May 2001
Low resistance and low inductance PCB (printed circuit board) layouts
and cabling should be used. Remember that when using remote
sensing, all the resistance, inductance and capacitance of the
distribution system is within the feedback loop of the power module.
This can have an effect on the modules compensation and the resulting
stability and dynamic response performance.
As a rule of thumb, 100 µF/A of output current can be used without
any additional analysis. For example, with a 20A (max PO100W)
power module, values of decoupling capacitance up to 2000 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 of 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 contact your local
Ericsson representative.
Quality
Reliability
The calculated MTBF of the PKM 4000 module family is greater than
(>) 2.8 million hours using Bellcore TR-332 methodology. The
calculation is valid for a 90ºC baseplate temperature. Demonstrated
MTBF has been in the range of 3.0 to 3.2 million hours.
Quality Statement
The power modules are designed and manufactured in an industrial
environment where quality systems and methods like ISO 9000, 6σ,
and SPC, are intensively in use to boost the continuous improvements
strategy. Infant mortality or early failures in the products are screened
out and they are subjected to an ATE-based final test.
Conservative design rules, design reviews and product qualifications,
plus the high competence of an engaged work force, contribute to the
high quality of our products.
Warranty
Ericsson Inc., Microelectronics warrants to the original purchaser or
end user that the products conform to this Data Sheet and are free
from material and workmanship defects for a period of five (5) years
from the date of manufacture, if the product is used within specified
conditions and not opened.
In case the product is discontinued, claims will be accepted up to three
(3) years from the date of the discontinuation. For additional details on
this limited warranty we refer to Ericsson’s “General Terms and
Conditions of Sales,” EKA 950701, or individual contract documents.
Limitation of Liability
Ericsson Inc., Microelectronics does not make any other warranties,
expressed or implied including any warranty of merchantability or
fitness for a particular purpose (including, but not limited to use in
life support applications, where malfunctions of product can cause
injury to a person’s health or life).