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CP3923 User Guide
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6.1.3
Power Supply Units
Power supplies for the CP3923 must be specified with enough reserve for the remaining system consumption. In order to
guarantee a stable functionality of the system, it is recommended to provide more power than the system requires. An
industrial power supply unit should be able to provide at least twice as much power as the entire system requires. An ATX
power supply unit should be able to provide at least three times as much power as the entire system requires.
As the design of the CP3923 has been optimized for minimal power consumption, the power supply unit shall be stable even
without minimum load.
Where possible, power supplies which support voltage sensing should be used. Depending on the system configuration this
may require an appropriate backplane. The power supply should be sufficient to allow for backplane input line resistance
variations due to temperature changes, etc.
6.1.3.1
Start-up Requirement
Power supplies must comply with the following guidelines, in order to be used with the CP3923:
•
The input voltage shall rise at a rate of max. 1.5A per ms.
•
There must be a smooth and continuous ramp of each DC output voltage from 10% to 90% of the regulation band.
•
The slope of the turn-on waveform shall be a positive, almost linear voltage increase and have a value from 0 V to nom-
inal Vout.
6.1.3.2
Power-up Sequence
The +5 VDC output level must always be equal to or higher than the +3.3 VDC output during power-up and normal operation.
Both voltages must reach their minimum in-regulation level not later than 20 ms after the output power ramp start.
Note...
Non-industrial ATX PSUs require a greater minimum load than a single CP3923 is
capable of creating. When a PSU of this type is used, it will not power up correctly
and the CP3923 may hang up. The solution is to use an industrial PSU or to add
more load to the system.
