www.ti.com

Overcurrent Protection

Overtemperature Protection (OTP)

Remote Sense

PTV08040W

SLTS257A – SEPTEMBER 2005 – REVISED JANUARY 2007

The output then progressively rises to the module’s setpoint voltage. Figure 12 shows the soft-start power-up

characteristic of the PTV08040W operating from a 12-V input bus and configured for a 3.3-V output. The

waveforms were measured with a 20-A constant current load and the Auto-Track feature disabled. The initial

rise in input current when the input voltage first starts to rise is the charge current drawn by the input capacitors.

Power-up is complete within 25 ms.

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, a

module periodically attempt 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.

Products with this feature incorporate one or two remote sense pins. Remote sensing improves the load

regulation performance of the module by allowing it to compensate for any IR voltage drop between its output

and the load. An IR drop is caused by the high output current flowing through the small amount of pin and trace

resistance.

To use this feature simply connect the Sense pins to the corresponding output voltage node, close to the load

circuit. If a sense pin is left open-circuit, an internal low-value resistor (15-

Ω or less) connected between the pin

and the output node, ensures the output remains in regulation.

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

should be limited to a maximum of 0.3 V.

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.

15

Submit Documentation Feedback