AP2181/ AP2191

Document number: DS31563 Rev. 7 - 2

10 of 17

www.diodes.com

March 2013

© Diodes Incorporated

AP2181/ AP2191

Under-Voltage Lockout (UVLO)

Under-voltage lockout function (UVLO) keeps the internal power switch from being turned on until the power supply has reached at least 1.9V, even

if the switch is enabled. Whenever the input voltage falls below approximately 1.9V, the power switch is 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.

Host/Self-Powered HUBs

Hosts and self-powered hubs (SPH) have a local power supply that powers the embedded functions and the downstream ports (see Figure 2). This

power supply must provide from 5.25V to 4.75V to the board side of the downstream connection under both full-load and no-load conditions. Hosts

and SPHs are required to have current-limit protection and must report over-current conditions to the USB controller. Typical SPHs are desktop

PCs, monitors, printers, and stand-alone hubs.

Figure 2 Typical One-Port USB Host / Self-Powered Hub

Generic Hot-Plug Applications

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 AP2181/AP2191, 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 AP2181/AP2191 also ensures that the switch is off

after the card has been removed, and that the switch is off during the next insertion.

By placing the AP2181/AP2191 between the VCC input and the rest of the circuitry, the input power reaches these devices first after insertion. The

typical rise time of the switch is approximately 1ms, providing a slow voltage ramp at the output of the device. This implementation controls system

surge current and provides a hot-plugging mechanism for any device.