Application Notes

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PT4840 Series

Operating Features of the PT4840 Triple-Output

DC/DC Converters

Over-Current Protection

The current limit function of the PT4840 series of

triple-output DC/DC converters is divided into two

Each protection zone incorporates a latch-off time-out

period of approximately 200ms. A transient or momentary

fault lasting less than this period will allow the prompt

recovery of all affected outputs. Faults applied for longer

than this period will cause the affected zone to latch off.

from a latched shutdown condition requires the removal

and corresponding re-application of input power to the

converter.

Over-Temperature Protection

The PT4840 DC/DC converter series have an internal

temperature sensor, which monitors the temperature of

the module’s metal case. If the case temperature exceeds

a nominal 110°C the converter will shut down. The

converter will automatically restart when the sensed

temperature returns to about 100°C. The analog voltage

generated by the sensor is also made available at the

‘TEMP’ output (pin 5), and can be monitored by the host

system for diagnostic purposes. Consult the ‘Pin Descrip-

tions’ section of the data sheet for more information on

this feature.

Under-Voltage Lock-Out

The Under-Voltage Lock-Out (UVLO) circuit prevents

operation of the converter whenever the input voltage to

the module is insufficient to maintain output regulation.

The UVLO has approximately 2V of hysterisis. This is

to prevent oscillation with a slowly changing input voltage.

Below the UVLO threshold the module is off and the

enable control inputs, EN1 and EN2 are inoperative.

Primary-Secondary Isolation

The PT4840 series of DC/DC converters incorporate

electrical isolation between the input terminals (primary)

and the output terminals (secondary). All converters are

production tested to a withstand voltage of 1500VDC.

The isolation complies with UL60950 and EN60950,

and the requirements for operational isolation. This

allows the converter to be configured for either a positive

or negative input voltage source.

The regulation control circuitry for these modules is

located on the secondary (output) side of the isolation

barrier. Control signals are passed between the primary

and secondary sides of the converter via a proprietory

magnetic coupling scheme. This eliminates the use of

opto-couplers. The data sheet ‘Pin Descriptions’ and

‘Pin-Out Information’ provides guidance as to which

reference (primary or secondary) that must be used for

each of the external control signals.

Input Current Limiting

The converter is not internally fused. For safety and

overall system protection, the maximum input current to

the converter must be limited. Active or passive current

limiting can be used. Passive current limiting can be a

fast acting fuse. A 125-V fuse, rated no more than 10A,

is recommended. Active current limiting can be imple-

mented with a current limited “Hot-Swap” controller.