Overcurrent Protection

Overtemperature Protection (OTP)

Differential Output Voltage Remote Sense

PTH04T240F

For protection against load faults, all modules incorporate output overcurrent protection. Applying a load that

exceeds the regulator's overcurrent threshold causes the regulated output to shut down. Following shutdown, the

module periodically attempts to recover by initiating a soft-start power-up. This is described as a hiccup mode of

operation, whereby the module continues in a cycle of successive shutdown and power up until the load fault is

removed. During this period, the average current flowing into the fault is significantly reduced. Once the fault is

removed, the module automatically recovers and returns to normal operation.

A thermal shutdown mechanism protects the module’s internal circuitry against excessively high temperatures. A

rise in the internal temperature may be the result of a drop in airflow, or a high ambient temperature. If the

internal temperature exceeds the OTP threshold, the module’s Inhibit control is internally pulled low. This turns

the output off. The output voltage drops as the external output capacitors are discharged by the load circuit. The

recovery is automatic, and begins with a soft-start power up. It occurs when the sensed temperature decreases

by about 10°C below the trip point.

The overtemperature protection is a last resort mechanism to prevent thermal stress to the regulator.

Operation at or close to the thermal shutdown temperature is not recommended and reduces the long-term

reliability of the module. Always operate the regulator within the specified safe operating area (SOA) limits for

the worst-case conditions of ambient temperature and airflow.

Differential remote sense improves the load regulation performance of the module by allowing it to compensate

for any IR voltage drop between its output and the load in either the positive or return path. An IR drop is caused

by the output current flowing through the small amount of pin and trace resistance. With the sense pins

measured at the Sense pins, is the amount of IR drop being compensated by the regulator. This should be

limited to a maximum of 0.3V. Connecting the +Sense (pin 6) to the positive load terminal improves the load

regulation at the connection point. For optimal behavior the –Sense (pin 7) must be connected to GND (pin 4)

close to the module (within 10 cm).

pin to the module GND (pin 4).

The remote sense feature is not designed to compensate for the forward drop of nonlinear or frequency

dependent components that may be placed in series with the converter output. Examples include OR-ing

diodes, filter inductors, ferrite beads, and fuses. When these components are enclosed by the remote sense

connection they are effectively placed inside the regulation control loop, which can adversely affect the

stability of the regulator.

Copyright © 2008–2009, Texas Instruments Incorporated

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Product Folder Link(s): PTH04T240F