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THERMAL PROTECTION

UNDERVOLTAGE LOCKOUT (UVLO)

GENERIC HOT-PLUG APPLICATIONS (see Figure 36)

TPS2010A, TPS2011A

TPS2012A, TPS2013A

SLVS189C – DECEMBER 1998 – REVISED SEPTEMBER 2007

Where:

Compare the calculated junction temperature with the initial estimate. If they do not agree within a few degrees,

repeat the calculation, using the calculated value as the new estimate. Two or three iterations are generally

sufficient to get an acceptable answer.

Thermal protection prevents damage to the IC when heavy-overload or short-circuit faults are present for

extended periods of time. The faults force the TPS201xA into constant current mode, which causes the voltage

across the high-side switch to increase; under short-circuit conditions, the voltage across the switch is equal to

the input voltage. The increased dissipation causes the junction temperature to rise to high levels. The protection

circuit senses the junction temperature of the switch and shuts it off. Hysteresis is built into the thermal sense

circuit, and after the device has cooled approximately 20 degrees, the switch turns back on. The switch continues

to cycle in this manner until the load fault or input power is removed.

An undervoltage lockout ensures that the power switch is in the off state at power up. Whenever the input

voltage falls below approximately 2 V, the power switch will be quickly turned off. This facilitates the design of

hot-insertion systems where it is not possible to turn off the power switch before input power is removed. The

UVLO will also keep the switch from being turned on until the power supply has reached at least 2 V, even if the

switch is enabled. Upon reinsertion, the power switch will be turned on, with a controlled rise time to reduce EMI

and voltage overshoots.

In many applications it may be necessary to remove modules or p-c boards while the main unit is still operating.

These are considered hot-plug applications. Such implementations require the control of current surges seen by

the main power supply and the card being inserted. The most effective way to control these surges is to limit and

slowly ramp the current and voltage being applied to the card, similar to the way in which a power supply

normally turns on. Because of the controlled rise times and fall times of the TPS201xA series, these devices can

be used to provide a softer start-up to devices being hot-plugged into a powered system. The UVLO feature of

the TPS201xA also ensures the switch will be off after the card has been removed, and the switch will be off

during the next insertion. The UVLO feature guarantees a soft start with a controlled rise time for every insertion

of the card or module.

Figure 36. Typical Hot-Plug Implementation

device first after insertion. The typical rise time of the switch is approximately 9 ms, providing a slow voltage

ramp at the output of the device. This implementation controls system surge currents and provides a

hot-plugging mechanism for any device.

Copyright © 1998–2007, Texas Instruments Incorporated

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Product Folder Link(s): TPS2010A, TPS2011A TPS2012A, TPS2013A