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Operating Features of the PT3400 Series

of Isolated DC/DC Converters

Under-Voltage Lockout

An Under-Voltage Lock-Out (UVLO) inhibits the opera-

tion of the converter until the input voltage is above the

UVLO threshold (see the data sheet specification). Below

this voltage, the module’s output is held off, irrespective

of the state of either the EN1 & EN2 enable controls.

The UVLO allows the module to produce a clean transi-

tion during both power-up and power-down, even when

the input voltage is rising or falling slowly. It also reduces

the high start-up current during normal power-up of the

converter, and minimizes the current drain from the

input source during low-input voltage conditions. The

UVLO threshold includes about 1V of hysteresis.

is left open, the module will automatically power up when

the input voltage rises above the UVLO threshold (see

data sheet ‘Standard Application’ schematic). Once

operational, the converter will conform to its operating

specifications when the minimum specified input voltage

is reached.

Over-Current Protection

To protect against load faults, the PT3400 series incor-

porates output over-current protection. Applying a load

that exceeds the converter’s over-current threshold (see

applicable specification) will cause the regulated output

to shut down. Following shutdown the module will peri-

odically attempt to automatically recover by initiating a

soft-start power-up. This is often described as a “hiccup”

mode of operation, whereby the module continues in the

cycle of succesive shutdown and power up until the load

fault is removed. Once the fault is removed, the converter

then automatically recovers and returns to normal op-

eration.

Primary-Secondary Isolation

Electrical isolation is provided between the input termi-

nals (primary) and the output terminals (secondary). All

converters are production tested to a primary-secondary

withstand voltage of 1500VDC. This specification com-

plies with UL60950 and EN60950 and the requirements

for operational isolation. Operational isolation allows these

converters to be configured for either a positive or negative

input voltage source. The data sheet ‘Pin-Out Information’

uses shading to indicate which pins are associated with the

primary. They include pins 1 through 4, inclusive.

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 5A, is

recommended. Active current limiting can be imple-

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

Thermal Considerations

Airflow may be necessary to ensure that the module can

supply the desired load current in environments with

elevated ambient temperatures. The required airflow

rate may be determined from the Safe Operating Area

(SOA) thermal derating chart (see converter specifica-

tions). The recommended direction for airflow is into the

longest side of the module’s metal case. See Figure 1-1.

Figure 1-1

PT3400 Series

Recommended direction for airflow is

into (perpendicular to) the longest side

Application Notes