AP2161D データシートの表示（PDF） - Diodes Incorporated.

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AP2161D

1A SINGLE CHANNEL CURRENT-LIMITED POWER SWITCH WITH OUTPUT DISCHARGE

Diodes Incorporated. 

AP2161D/AP2171D

Application Note

The AP2161D and AP2171D are integrated high-side power switches optimized for Universal Serial Bus (USB) that require 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 over-current 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 AP2161D/2171D are outlined below:

S.NO

Conditions

1

Short circuit condition at

start-up

2

Short-circuit or over-current

condition

Gradual increase from

3 nominal operating current to

ILIMIT

Explanation

Output is shorted before input

voltage is applied or before the

part is enabled

Short-Circuit or Overload

condition that occurs when the

part is enabled.

Load increases gradually until

the current-limit threshold.(ITRIG)

Behavior of the AP2161D/2171D

The IC senses the short circuit and immediately clamps output

current to a certain safe level namely ILIMIT.

 At the instance the overload occurs, higher current may flow

for a very short period of 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.

The current rises until ITRIG or thermal limit. Once the threshold

has been reached, the 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 (< -30°C), 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.

Thermal Protection

Thermal protection prevents the IC from damage when the die temperature exceeds safe margins. This mainly occurs when heavy-overload or

short-circuit faults are present for extended periods of time. The AP2161D/AP2171D implements thermal sensing to monitor the operating junction

temperature of the power distribution switch. Once the die temperature rises to approximately +140°C, the Thermal protection feature gets

activated as follows: The internal thermal sense circuitry turns the power switch off and the FLG output is asserted thus preventing the power

switch from damage. Hysteresis in the thermal sense circuit allows the device to cool down to approximately +25°C before the output is turned

back on. The built-in thermal hysteresis feature avoids undesirable oscillations of the thermal protection circuit. The switch continues to cycle in

this manner until the load fault is removed, resulting in a pulsed output. The FLG open-drain output is asserted when an over-current occurs with

7-ms deglitch.

Reverse Current Protection

In a normal MOSFET switch, current can flow in reverse direction (from the output side to the input side) when the output side voltage is higher

than the input side, even when the switch is turned off. A reverse-current blocking feature is implemented in the AP21x1 series to prevent such

back currents. This circuit is activated by the difference between the output voltage and the input voltage. When the switch is disabled, this feature

blocks reverse current flow from the output back to the input.

AP2161D/AP2171D

Document number: DS32250 Rev. 5 - 2

10 of 19

www.diodes.com

March 2013

© Diodes Incorporated

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