A
20 Watt HP Triple Series DC/DC Converters
2401 Stanwell Drive Concord, California 94520 Ph: 925/687-4411 or 800/542-3355 Fax: 925/687-3333 www.calex.com Email: sales@calex.com
5
3/2001
Applying The Output
Figure 4 shows typical output connections for the HP Triple In
most applications no external output capacitance will be
necessary. Only your normal 1 to 10 F tantalum and 0.001
to 0.1 F ceramic bypass capacitors sprinkled around your
circuit as needed locally are required. Do not add extra output
capacitance and cost to your circuit “Just Because”.
If you feel you must add external output capacitance, do not
use the lowest ESR, biggest value capacitor that you can find!
This can only lead to reduced system performance or
oscillation. See our application note “Understanding Output
Impedance For Optimum Decoupling” for more information.
Figure 4.
The HP triple should be connected to your load as shown. All of the
ground return currents should be returned directly to CMN pin. If
desired, external transient protection diodes can be used.
Ultra Low Noise Output Circuit
The circuit shown in figure 5 can be used to reduce the output
noise to below 10 mV P-P over a 20 MHz bandwidth. Size
inductor L1 appropriately for the maximum expected load
current. All of the ground connections must be as short as
possible back to the CMN pin. The filter should be placed as
close to the HP triple as possible, even if your load is at some
distance from the converter.
Figure 5.
For very low output noise applications this circuit will reduce the
output noise to less than 10 mV P-P over a 0-20 MHz bandwidth. Be
sure to size L1 appropriately for the maximum expected load current
on the 5 volt output.
Operation With Very Light Loads
The HP Triple uses a technique called “Magnetically Coupled
Cross Regulation” to provide the best regulation available
with a single PWM regulator circuit. This scheme works very
well when all loads are operated within 25% to 100% of their
rated load range. When the loads become very unbalanced
(i.e. one or more outputs at no load and the others at full load)
the PWM can have difficulty trying to determine the best
output voltage. The best situation is to keep the minimum load
at 25% for each output and avoid operating any output
unloaded.
The regulation of the HP triple may be improved by using
dummy load resistors to keep the static output power above
about 2 watts (check the exact value required by your circuit).
The load may be balanced by adding a dummy load on the
most lightly loaded outputs, the exact value will depend on
your exact circuit requirements. This minimum load should
not be required to be greater than 25% of each outputs full
load value for quite good regulation.
Dynamic response of the HP triple will degrade when the
unit is operated with less than 25% of full rated power.
If large load excursions or operation with very large load
unbalances are required then a “Dual Loop” converter such as
the CALEX XC triple may provide better performance in your
circuit.
Thermal Overload Protection Option
The -FT option provides a thermal overload circuit that will
protect the converter against overtemperature faults. The
thermal overload circuit works by shutting the PWM circuit
OFF when the case temperature exceeds about 105° C.
When the case cools the converter will automatically restart.
The thermal overload circuit will prevent the converter from
being damaged under the following conditions,
Operation at abnormally high ambient temperatures.
Most long term short circuit conditions.
This option is useful in applications that require the utmost
reliability in unattended operation or where cooling system
failures must not cause permanent damage.
Grounding
The input and output sections are fully floating from each
other. They may be operated fully floating or with a common
ground. If the input and output sections are connected either
directly at the converter or at some remote location from the
converter it is suggested that a 3.3 to 10 F, 0.5 to 5 ohm ESR
capacitor bypass be used directly at the converters output
pins. These capacitors prevent any common mode switching
currents from showing up at the converters output as normal
mode output noise. See “Applying the Output” for more
information on selecting output capacitors.
Also see the CALEX application note “Dealing With
Common Mode Noise” for more information on using common
grounds.
C1 = 1F / 35V TANTALUM
C2 = 10F / 16V TANTALUM
C3 = 0.01F / 100V CERAMIC
FL1 = PANASONIC EXC-EMT103DT EMI FILTER
L1
= 5F / 2.5 AMP INDUCTOR