Datasheet

Remote Sense
Overcurrent Protection
Overtemperature Protection (OTP)
PTH12020W/L
SLTS208I – MAY 2003 – REVISED MARCH 2009 ............................................................................................................................................................. www.ti.com
Products with this feature incorporate an output voltage sense pin, V
O
Sense. A 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. 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 V
O
Sense pin to the V
O
node, close to the load circuit (see data sheet
standard application 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.
With the sense pin connected, the difference between the voltage measured directly between the V
O
and GND
pins, and that measured from V
O
Sense to GND, is the amount of IR drop being compensated by the regulator.
This should be limited to a maximum of 0.3 V.
Note: 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.
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 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.
The PTH12020, PTV12020, and PTH12030 products have overtemperature protection. These products have an
on-board temperature sensor that 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.
Note: 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 will reduce 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.
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