Design Note 100 Rev. 01 - Feb. 1999
• Safety and the low voltage directive
• Electromagnetic Compatibility Immunity
• Electromagnetic Compatibility Conducted and
Radiated Interference
• Telecom and Distributed Power Architecture Features
• System Protection Features
• Thermal Considerations
• Input Impedance Considerations
1. Safety and the Low Voltage Directive
The BXA15 and BXA30 series is intended to be supplied only from a
SELV (Safe Extra Low Voltage) circuit or a TNV (Telecommunications
Network Voltage) power source which are insulated from the AC
mains by reinforced insulation. Basic isolation, tested to 1,500VDC,
for EN60950 and UL1950, is provided.
DC Distributed Power of 12V, 24V or 48V
Central Office -48V
2. Electromagnetic Compatibility Immunity
Good design practice dictates that the electronic system be immune
to noise interference. This practice has now been encapsulated in
European law in the form of the EMC directive. It is imperative that
any system on sale in the European Union meets the terms of the
EMC directive and thus carries the CE mark. To simplify system
compliance to the EMC Directive, the BXA15 and BXA30 have been
designed to meet and comply with the necessary immunity standards.
Compliance Level
4kV Contact
8kV Discharge
Radiated Immunity
Fast Transients/Bursts
0.5KV (40 Ohm
Secondary surge
3. Electromagnetic Compatibility Conducted and
Radiated Interference
Radiated Interference:
The BXA15 and BXA30 series meet the harmonised standard
EN55022 level A and CISPR22 level A. The series almost meets the
requirements of level B. System performance to level B could be
assured with the appropriate enclosure.
Conducted Interference - Level A Internal Filter Option:
All three input voltage versions of the series, 12VDC, 24VDC and
48VDC, are available with an internal filter option which meets input
conducted noise per VDE0871/8-A or EN55022-A. To order a model
with the internal filter, add ‘-F’ after the model number eg. BXA1548S12-F.
Conducted Interference - Level B External Filter:
The addition of an external capacitor enables the BXA15 and
BXA30 products to meet VDE0871/8-B, EN55022-B and CISPR22-B
conducted noise limits. The test set-up is per VDE 0877 Part 1 fig.4
with the load < 10 cm's away from the test converter.
Input Voltage
48 Volt
24 Volt
12 Volt
Recommended External Cap.
Nippon Chemi-Con SXE series120uF, 100V
ITW PAKTRON Capstick series part number
405K100CS4, 4uF @ 100V
2 * ITW PAKTRON 405K100CS4
capacitors in close parallel.
For height critical applications, the ITW Paktron capacitor offers a
low profile of <7mm.
Note on the test set up and system grounding:
The products meet input conducted noise VDE0878-B, EN55022-B
and CISPR22-B 10kHz - 30MHz, if the load is not more than 10
cm's away. Tightly parallel tracks or twisted pair wiring to the load
should be used. Long leads to the load could radiate common
mode noise, typically above 20 MHz, back to the input power leads.
Conducted emissions should be checked at a system level.
If the unit fails level B at a frequency greater then 20MHz, because
of system wiring, an additional external ‘Y-capacitor’ could be connected between input ground and output common, to locally
decouple common-mode noise. This capacitor type is usually
intended for use in interference suppression between line and earth.
A recommended capacitor is EVOX-RIFA PME271Y422M or equivalent.
4. Telecom and Distributed Power Architecture
Input Undervoltage Protection:
Internally, the BXA15 and BXA30 series contain an undervoltage
lockout zener circuit. The converter should not be operated continuously at levels between the ‘maximum guaranteed-off-threshold’
and the ‘minimum guaranteed-on-threshold.’
Nominal Input
Maximum Off
Minimum On
Remote Sense:
The remote sense feature automatically adjusts the output voltage
of the dc/dc converter to compensate for line voltage drops to loads
which are distant form the output pins. Internally, 150R, 0.25Watt
resistors connect the sense circuitry to the output pins. In applications, the sense connections must be made. These can either be
made directly at the pins whereby compensation for voltage line
drops is not needed.
Design Note 100 Rev. 01
As an example, for the BXA15 and BXA30 with the baseplate
mounted vertically, in free natural convection:
Rth B.P - AMB. = 6.5°/Watt.
For a BXA15 and BXA30 with baseplate and heatsink mounted vertically, in free natural convection:
Or the connection can be made at the load or point of critical regulation. If the sense connections are not made the output voltage will
typically be up 7% on nominal and load regulation will be substantially degraded.
Rth (B.P.+H.S.) - AMB. = 5.2°/Watt.
For operation at output powers > 50% nominal max. and with input
voltages within 30% of nominal, the operating efficiency is approximately = the specified nominal efficiency:
Voltage Drops on the lines to the load may be compensated up to a
maximum value of 10%. This includes any voltage increase that
may result by use of the ‘TRIM’ function. If the output voltage is
raised above the nominal value +10%, the unit performance at low
input voltage may be degraded.
(Pdiss. MAX. * Rth B.P - AMB.) + T AMBIENT.MAX. ≤100°C.
Ensure the load power lines are never open circuit in a remote sense
application. Even transient open circuits in the power connections
could result in full load current flow through the sense leads, resulting in damage to the internal circuitry.
Pdiss. = Pout (100 - h) /h
h = Operating Efficiency %.
These formulae calculate deratings necessary at high operating temperatures. An optional heatsink is available to increase output power
at high ambient temperatures.
Minimum Operating Temperature:
All qualification and design testing were conducted with baseplates
ranging from -25°C to +100°C.
The usual rules for remote sensing apply:
a) The remote sense tracks should be parallel and close to each
other. Alternatively screened cable could be used. This minimises
inductive noise pick-up and reduces 2 pole roll-off effects in the
feedback loop.
b) Remote sensing provides DC regulation at the sense points but
AC regulation is degraded. To maintain best possible transient
response performance, a decoupling capacitor should be used at
point of sensing. A capacitance value >10uF/Amp is recommended.
Output Voltage Trim:
Output voltage trim enables the user to adjust the output voltage to
a pre-defined value within ±10% of the nominal output voltage.
5. System Protection Features
Overvoltage Protection:
Internally, a 400Watt/1ms semiconductor transient voltage suppressor has been inserted across each output voltage. This is designed
to protect both the BXA15/BXA30 and the customer’s load from
transient overvoltages induced or reflected by the load. This feature
is not intended to guarantee steady state overvoltage protection.
OVP Value
3.9V breakdown init.
6.7V breakdown init.
15.6V breakdown init.
18.9V breakdown init.
6. Thermal Considerations
Maximum Operating Temperatures:
The BXA15 and BXA30 baseplate must never be allowed to exceed
100°C. The maximum operating ambient temperature depends on
the ambient airflow, the ambient temperature, the unit mounting/orientation and the power dissipated by the unit. In application, the
worst case operating baseplate temperature should be measured.
Short Circuit Ratings:
The product is indefinitely short-circuit rated. The baseplate should
be maintained at less than 100°C. Under a short circuit, the typical
power dissipation is 7 Watts. This may be up to 10 Watts at maximum input voltage.
Short Circuit Protection on Multiple Output Units:
With the exception of the BXA15-48D05 and BXA30-48D05, all of
the multiple output units have short circuit protection as outlined
above. For details on the two exception models, please consult the
Cross Regulation Dual Output Models:
Internally the absolute value sum of the output voltages is regulated.
The total output on a 48D05 will be regulated to be 10 volts.
Regulation %
Load One
Load Other
These figures are typical for all dual models.
Remote ON/OFF:
Internally this is connected to a bipolar Vbe + 2 Si diodes in series.
The pin is connected to -Vin, via a 15K resistor. This provides noise
immunity. An open collector sink (maximum current 3mA) to a voltage <1Volt is required. The open circuit voltage will be 3 Volts.
Transient Response:
For best output voltage response to load transients; a minimum output load of 5% is recommended. On 12 Volt (input) models, the
input voltage should be maintained >9.5 Volts for optimum transient
Input Impedance Considerations:
Care needs to be taken to ensure the source impedance is sufficiently low to allow correct operation of the DC/DC over all operating conditions; particularly for power-ups and load transients.
Design Note 100 Rev. 01
It is imperative to account for both the resistive and reactive components of source impedance.
The input operating voltage range specified refers to the voltage
which must be maintained across the inputs pins, during all steady
state and transient conditions. Models without the internal filter
option will generally require a much lower reactive source impedance than for those with the internal filter installed. This is because
the input current will have large harmonics at the DC/DC converter
switching frequency.
The reactive source impedance can be effectively reduced by
adding local film or ceramic capacitors. A recommended film
capacitor is ITW Paktron 20µF, 50 Volts Capstick or equivalent.
(ITW Paktron Part Number: 206K050CS4).
Local Decoupling of High Frequency Input Ripple Current:
This is particularly important for 12Vin models. Non filter versions
have a maximum input current of 5 Amps DC with 0.7A ACrms
superimposed. The AC current is almost sinusoidal and at 350 400kHz. The source impedance must be able to supply this current
with negligible voltage ripple. Adding the recommended film capacitor across the input pins will allow the high frequency input current
requirement to be locally sourced. This will also dramatically reduce
both input conducted noise and radiated noise.
Start-up Surge Consideration:
Depending on lead inductance and source impedance a higher
value, parallel, ‘reservoir’ electrolytic may be required to ensure adequate input voltage is maintained during start-up and transients.
The start-up surge current is always well within ETSI limits but is still
significant and the source must be able to supply it with low
dropout. During this surge the input voltage should remain above
the minimum on threshold.
IR Steady State Voltage Drop Consideration:
Care must be taken with lead and connector resistances. The
source voltage should be a minimum of 9 Volts + R (total, leads +
Design Note Artesyn Technologies, 1999
The information and specifications contained in this design note are believed to be correct at time of publication. However, Artesyn
Technologies accepts no responsibility for consequences arising from printing errors or inaccuracies. Specifications are subject to change
without notice. No rights under any patent accompany the sale of any such product(s) or information contained herein.