PKB 4713 PINB
Circuit Configuration for Output Voltage
Adjustment (Trim)
Input and Output Impedence
The impedence of both the power source and the load will
interact with the impedence of the DC/DC converter. It is
most important to have the ratio between L and C as low as
possible, i.e. a low characteristic impedence, both at the
input and output, as the conveters have a low energy
storage capability. 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 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 converter contains significant inductance, the
addition of a 100uF capacitor across the input of the
converter will help insure stability. This capacitor is not
required when powering the converter from a low
impedence source with a short, low inductance, input
power lead.
+VOUT
+VOUT
+SENSE
D
+SENSE
D
Load
R
TRIM-DOWN
Load
TRIM
-SENSE
-VOUT
TRIM
-SENSE
-VOUT
RTRIM-UP
TRIM DOWN
TRIM UP
Output Ripple & Noise (VOac
)
Output ripple is measured as the peak to peak voltage
from 0 to 20MHz which includes the noise voltage and
the fundamental ripple.
Over Temperature Protection (OTP)
The PKB 4000 series DC/DC converters are protected
from thermal overload by an internal over temperature
shutdown circuit. When the Pcb temperature adjacent to
the primary mosfet exceeds +120oC (+5oC, -5oC), the
power module will automatically shut down. It will restart
when the temperature drops to +100oC (+5oC, -5oC).
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 short duration high
frequency components of dynamic load changes. 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.
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 converter. This can have
an affect on the converter's compensation and the
resulting stability and dynamic response performance.
As a "rule of thumb", 100uF/A of output current can
be used without any additional analysis. For example,
with a 20A converter, values of decoupling capacitance
up to 2000uF 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 10,000uF.
For values larger than this, please contact your local
Ericsson Power Modules representative.
Paralleling for Redundancy
The figure below illustrates how n + 1 redundancy can be
achieved. The customer provided diodes on the converter
outputs allow a failed converter to remove itself from the
shared group without pulling down the common output
bus. This configuration can be extended to additional
numbers of converters. Based on the desired circuit, the
converters can be controlled individually or in groups by
means of signals to the primary Remote On/Off inputs.
EN/LZT 108 6071 P1D ©Ericsson Inc., Power Modules , February 2003
7
ERICSSON [ ERICSSON ]
