Application information – Diodes AP2141/ AP2151 User Manual
Page 11
AP2141/ AP2151
Document number: DS31562 Rev. 7 - 2
11 of 17
March 2013
© Diodes Incorporated
AP2141/ AP2151
Application Information
(cont.)
Thermal Protection
Thermal protection prevents the IC from damage when heavy-overload or short-circuit faults are present for extended periods of time. The
AP2141/AP2151 implements a thermal sensing to monitor the operating junction temperature of the power distribution switch. Once the die
temperature rises to approximately 140°C due to excessive power dissipation in an over-current or short-circuit condition the internal thermal sense
circuitry turns the power switch off, thus preventing the power switch from damage. Hysteresis is built into the thermal sense circuit allowing the
device to cool down approximately 25°C before the switch turns back on. The switch continues to cycle in this manner until the load fault or input
power is removed. The FLG open-drain output is asserted when an over-temperature shutdown or over-current occurs with 7-ms deglitch.
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 AP2141/AP2151, 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 AP2141/AP2151 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 AP2141/AP2151 between the V
CC
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.