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UNDERVOLTAGE LOCKOUT (UVLO)l

GENERIC HOT-PLUG APPLICATIONS (see Figure 26 )

TPS2080, TPS2081, TPS2082 DUAL

TPS2085, TPS2086, TPS2087 QUAD

SLVS202B – SEPTEMBER 2000 – REVISED OCTOBER 2007

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 pc 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. Due to the controlled rise times and fall times of the TPS208x, 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 TPS208x

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 insures a soft start with a controlled rise time for every insertion of the card or

module.

Figure 26. Typical Hot-Plug Implementation

By placing the TPS208x between the V

input and the rest of the circuitry, the input power will reach these

devices first after insertion. The typical rise time of the switch is approximately 2.5 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.

Product Folder Link(s): TPS2080, TPS2081, TPS2082 DUAL TPS2085, TPS2086, TPS2087 QUAD