Application Notes

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PT4660 & PT4680 Series

Operating Features & System Considerations for the

PT4660/PT4680 Dual-Output DC/DC Converters

Over-Current Protection

The dual-outputs of the PT4660 and PT4680 series of

DC/DC converters have independent output voltage

regulation and current limit control. Applying a load

current in excess of the current limit threshold at either

output will cause the respective output voltage to drop.

in regulation.

The current limit circuitry incorporates a limited amount

of foldback. The fault current flowing into an absolute

short circuit is therefore slightly less than the current

limit threshold. Recovery from a current limit fault is

automatic and the converter will not be damaged by a

continuous short circuit at either output.

Output Over-Voltage Protection

Each output is monitored for over voltage (OV). For fail

safe operation and redundancy, the OV fault detection

circuitry uses a separate reference to the voltage regulation

circuits. The OV threshold is fixed, and set nominally 25%

higher than the set-point output voltage. If either output

exceeds the threshold, the converter is shutdown and

must be actively reset. The OV protection circuit can be

reset by momentarily turning the converter off. This is

accomplished by either cycling one of the output enable

control pins (EN1 or EN2), or by removing the input

higher voltage, the margin between the respective steady-state

output voltage and its OV threshold is reduced. This can make

the module sensitive to OV fault detection, that may result

from random noise and load transients.

Over-Temperature Protection

The PT4660/80 DC/DC converters have an internal

temperature sensor, which monitors the temperature of

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

a nominal 115°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 further 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 PT4460/80 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.

Fuse Recommendations

If desired an input fuse may be added to protect against

the application of a reverse input voltage.