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AP2181D

1.5A SINGLE CHANNEL CURRENT-LIMITED POWER SWITCH WITH OUTPUT DISCHARGE

Diodes Incorporated. 

AP2181D/AP2191D

1.5A SINGLE CHANNEL CURRENT-LIMITED POWER

SWITCH WITH OUTPUT DISCHARGE

Application Note

The AP2181D and AP2191D are integrated high-side power switches optimized for Universal Serial Bus (USB)

that requires protection functions. The power switches are equipped with a driver that controls the gate voltage

and incorporates slew-rate limitation. This, along with the various protection features and special functions, makes

these power switches ideal for hot-swap or hot-plug applications.

Protection Features:

Under-voltage Lockout (UVLO)

Under-voltage lockout function (UVLO) guarantees that the internal power switch is initially off during start-up. The

UVLO functions only when the switch is enabled. Even if the switch is enabled, the switch is not turned ON until

the power supply has reached at least 1.9V. Whenever the input voltage falls below approximately 1.9V, the

power switch is 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.

Over-current and Short Circuit Protection

An internal sensing FET is employed to check for over-current conditions. Unlike current-sense resistors, sense

FETs do not increase the series resistance of the current path. When an overcurrent condition is detected, the

device maintains a constant output current and reduces the output voltage accordingly. Complete shutdown

occurs only if the fault stays long enough to activate thermal limiting.

The different overload conditions and the corresponding response of the AP2181D/AP2191D are outlined below:

S. NO Conditions

1 Short circuit condition

at start-up

Explanation

Output is shorted before

input voltage is applied or

before the part is enabled

Behavior of the AP2181D/AP2191D

The IC senses the short circuit and immediately

clamps output current to a certain safe level

namely ILIMIT.

2 Short-circuit or

Short-Circuit or Overload • At the instance the overload occurs, higher

Overcurrent condition condition that occurs

current may flow for a very short period of

when the part is enabled. time before the current limit function can

react.

• After the current limit function has tripped

(reached the over-current trip threshold), the

device switches into current limiting mode

and the current is clamped at ILIMIT.

3 Gradual increase from Load increases gradually The current rises until ITRIG or thermal limit.

nominal operating

until the current-limit

Once the threshold has been reached, the

current to ILIMIT

threshold.(ITRIG)

device switches into its current limiting mode

and is set at ILIMIT.

Note that when the output has been shorted to GND at extremely low temperature (< -20oC), a minimum 120-μF

electrolytic capacitor on the output pin is recommended. A correct capacitor type with capacitor voltage rating and

temperature characteristics must be properly chosen so that capacitance value does not drop too low at the

extremely low temperature operation. A recommended capacitor should have temperature characteristics of less

than 10% variation of capacitance change when operated at extremely low temp. Our recommended aluminum

electrolytic capacitor type is Panasonic FC series.

AP2181D/2191D

Document number: DS32251 Rev. 1 - 2

9 of 18

www.diodes.com

June 2010

© Diodes Incorporated

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