AP2181A/AP2191A

Document number: DS37618 Rev. 2 - 2

10 of 17

www.diodes.com

May 2018

© Diodes Incorporated

AP2181A/AP2191A

Application Information (Cont.)

Undervoltage Lockout (UVLO)

Undervoltage Lockout (UVLO) function 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.

IN

OUT

FLG

EN

GND

1

2,3

6,7

4

5

0.1

μF

USB Control

5V

3.3V

GND

D +

D -

Power Supply

Downstream

USB Ports

AP2181A

VBUS

0.1

μF

120

μF

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 and fall time of the AP2181A/AP2191A, 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 AP2181A/AP2191A 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 AP2181A/AP2191A 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.

Dual-Purpose Port Applications

AP2181A/AP2191A is suitable for use in dual-purpose port applications in which a single port is used for data communication between the host

and peripheral devices while simultaneously maintaining a charge to the battery of the peripheral device. An example of this is a shared

HDMI/MHL (Mobile High-Definition Link) port that allows streaming video between an HDTV or set-top box and a smartphone or tablet while

maintaining a charge to the smartphone or tablet battery. In such dual-purpose port applications, it is important to insure VIN of the

AP2181A/AP2191A is ramped to its operating voltage prior to enabling the output.